Astronomers Studying The Oumuamua ‘Alien Spaceship’ Identify Its Interstellar Origins

Astronomers Studying The Oumuamua ‘Alien Spaceship’ Identify Its Interstellar Origins

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The huge, strange, cigar-shaped object known as ‘Oumuamua’ originated beyond our solar system and “is consistent with a natural origin” and “probably not" an alien controlled interstellar spaceship, according to a team of scientists.

When looking for the catalytic writers who interpret rocks as space ships you would expect the author to be, maybe, the star of History Channel’s hit television series ‘Ancient Aliens’ and director of Erich von Däniken's center for ancient alien astronaut research, Giorgio A. Tsoukalos. Most of us would never expect the creator of such a theory to be a Harvard astrophysicist, in this case Avi Loeb ; who last year published a scientific paper suggesting the rock might be “an alien probe”. According to a Science Alert article at the time “It was like a spark to dry tinder, honestly, and other scientists have been running around with buckets ever since.”

The ‘Oumuamua’ Debate

When this paper came out last year I covered it for Ancient Origins , finding it unusual that a scientist would talk about “leakage from planet-sized alien transmitters powering giant spaceships with light sails bouncing radio beams off a huge reflective sheet to provide thrust.”

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In that article I concluded “So long as the world’s leading scientists endorse theoretical thinking about advanced alien technologies, of course a majority of Americans will continue to believe, and want for, extraterrestrials .” And I suggested the “community would be out to get him”. Well, look at what’s happened now…

SETI telescope at night. (sdecoret / Adobe Stock)

Where Did She Come From Where Did She Go?

A new research paper written by an international team of 'Oumuamua scientists and published in Nature Astronomy ; says it “can't tell for sure without closely examining the thing” and “it's really a mystery still” but Matthew Knight, an astronomer at University of Maryland regards the conclusion of their findings as a “fire hose” on Avi Loeb's speculations that the rock is a powered spaceship. While the “alien spacecraft hypothesis is a fun idea” this new analysis proposes a “whole host of natural phenomena that could explain it,” wrote Knight.

With a deep dark reddish coloration caused by the metallic chunks’ radiation-baked composition, Oumuamua was identified in our solar system in October 2017, having spent hundreds of millions of years piercing the vast silence of deep space . Measuring 400 meters (0.25 miles) in length, all scientists agree that Oumuamua is “strange” and performs “weirdly” and it “is somehow like both a comet and an asteroid,” according to a recent Science Alert article about the scientist paper.

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The researchers claim that even when the “weirdness” and complexities are considered “it doesn't hold that Oumuamua is a spaceship”, and Knight added “This thing is weird and admittedly hard to explain, but that doesn't exclude other natural phenomena that could explain it.”

The paper suggests the most likely explanation is that the object started as a planetesimal fragment (a planet still in the process of forming in a star system far away) “that got ejected into space” and the reason we don't spot them much is because they're usually below our threshold of detection.

Oumuamua has passed now, but astronomers will soon be tracking it using future planned telescopes such as, for example, the 2022 US National Science Foundation's Large Synoptic Survey Telescope (LSST), with which Knight said “That's when we'll start to know whether 'Oumuamua is weird, or common” and whether the team will have to “reexamine our explanations.”

In this tiny space left by Knight, that the team might have to “reexamine our explanations“, we will sure to be seeing more stories about the spaceship that passed without saying “hi”.

Was The Interstellar Object Known As “Oumuamua” An Extraterrestrial Ship? One Harvard Scientist Thinks So

In November 2017, an object passed by our planet that was unlike anything astronomers had ever seen. Spotted by a telescope in Hawaii, this strange thing was dubbed ‘Oumuamua. It moved too fast for it to have come from our solar system, its orbit was unusual, and it didn’t have any of the traditional markings of an asteroid or comet. All this led Dr. Avi Loeb to hypothesize that ‘Oumuamua was artificially made, perhaps a piece of technology or some debris from a faraway alien civilization. Before you discount Loeb, you should know that he isn’t the average UFO-spotting kook you might see on a rerun of Unsolved Mysteries. He’s an astrophysicist who has been teaching astronomy at Harvard since 1993, and chaired its astronomy department for nine years. In his new book, Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, which comes out on January 26, Loeb makes a persuasive scientific argument about ‘Oumuamua’s otherworldly origins, and delves into why his peers have been so hostile to the idea of life outside of Earth.

“Overall, about a quarter of our galaxy’s 200 billion stars are orbited by planets that are habitable the way Earth is, with surface conditions that allow liquid water and the chemistry of life as we know it,” he writes. “Given so many worlds … with similar life-friendly conditions, it’s very likely that intelligent organisms have evolved elsewhere.” The opposition to even the mere concept of extraterrestrial life, Loeb contends, “boils down to conservatism, which many scientists adopt in order to minimize the number of mistakes they make during their careers.”

The object was discovered by the Pan-STARRS [Panoramic Survey Telescope and Rapid Response System] telescope in Hawaii and was given the name ‘Oumuamua, which means a scout or a messenger from far away in the Hawaiian language. It was the very first object spotted near the earth that came from outside our solar system. It moved too fast to be bound to the sun. It was clearly coming from interstellar space. When this object was analyzed, it looked like there was an extra push on it, in addition to the force of gravity from the sun. Usually with comets, you get this extra push from the cometary tail, the rocket effect. When gases evaporate, and go in one direction, they push the object in the opposite direction, just like a jet plane. The only problem is this extra push was not accompanied by a cometary tail. So what gave it this push remains a mystery.

In September 2020, there was another object that exhibited an extra push without the cometary tail. It was found that the object is actually a rocket booster from a launch of a lunar lander in 1966. Here is an object that we can identify as artificially made, that we produced it, and it behaves in a similar way to ‘Oumuamua.

Oumuamua was tumbling and spinning, and the brightness varied by a factor of ten as it was tumbling every eight hours. That means that it has an extreme geometry that is at least ten times longer than it is wide, because as it’s spinning around, you’re seeing the area that reflects sunlight changing by a factor of ten. The best fit for the light curve we saw was a flat object, pancake-like.

These are the facts: A pancake-like object the size of a football field seems to be pushed by a force that is not related to a cometary tail. So we suggested that it’s a light sail, like the sail on a boat that is being pushed by wind. It is a very thin surface that is pushed by reflecting sunlight. We are actually developing light-sail technology for space exploration because it offers the advantage of not needing to carry fuel with the spacecraft. It’s just being pushed by light.

So it seems that ‘Oumuamua is shaped like a disc, which is the stereotypical shape that we associate with UFOs. Is that a coincidence?
It could be a coincidence. It could be just the surface layer of a spaceship or something else that was torn apart. It could be something like a sort of space junk. It’s just like walking on the beach. Most of the time you see rocks or seashells, but every now and then you see a plastic bottle that is artificially made. This could be junk like that. Even if it’s not functional, the significance of ‘Oumuamua is that it implies, perhaps, that we are not alone, that it was not naturally produced, that it was produced by a technological civilization.

It’s a very different type of evidence than in the past. We searched for radio signals. This is very different. It’s like a message in a bottle, a physical object that we trace that is artificially produced. The moral of the story is that even though we didn’t get enough evidence on this object to get an image of it, or be sure that it’s artificial, it is sufficiently intriguing. We should continue to search the sky for similar objects.

The first known interstellar object to visit our solar system, 1I/2017 U1 &lsquoOumuamua, was discovered Oct. 19, 2017 by the University of Hawaii&rsquos Pan-STARRS1 telescope, funded by NASA&rsquos Near-Earth Object Observations (NEOO) Program, which finds and tracks asteroids and comets in Earth&rsquos neighborhood. While originally classified as a comet, observations revealed no signs of cometary activity after it slingshotted past the Sun on Sept. 9, 2017 at a blistering speed of 196,000 miles per hour (87.3 kilometers per second). It was briefly classified as an asteroid until new measurements found it was accelerating slightly, a sign it behaves more like a comet.

The first confirmed object from another star to visit our solar system, this interstellar interloper appears to be a rocky, cigar-shaped object with a somewhat reddish hue. The object, named &lsquoOumuamua by its discoverers, is up to one-quarter mile (400 meters) long and highly-elongated&mdashperhaps 10 times as long as it is wide. That aspect ratio is greater than that of any asteroid or comet observed in our solar system to date. While its elongated shape is quite surprising, and unlike objects seen in our solar system, it may provide new clues into how other solar systems formed.

The observations suggest this unusual object had been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with our star system.

&ldquoFor decades we&rsquove theorized that such interstellar objects are out there, and now ― for the first time ― we have direct evidence they exist,&rdquo said Thomas Zurbuchen, associate administrator for NASA&rsquos Science Mission Directorate in Washington, in November 2017.

Immediately after its discovery, telescopes around the world, including ESO&rsquos Very Large Telescope in Chile, were called into action to measure the object&rsquos orbit, brightness and color. Urgency for viewing from ground-based telescopes was vital to get the best data.

Combining the images from the FORS instrument on the ESO telescope using four different filters with those of other large telescopes, a team of astronomers led by Karen Meech of the Institute for Astronomy in Hawaii found that &lsquoOumuamua varies in brightness by a factor of 10 as it spins on its axis every 7.3 hours. No known asteroid or comet from our solar system varies so widely in brightness, with such a large ratio between length and width. The most elongated objects we have seen to date are no more than three times longer than they are wide.

&ldquoThis unusually big variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape,&rdquo said Meech. &ldquoWe also found that it had a reddish color, similar to objects in the outer solar system, and confirmed that it is completely inert, without the faintest hint of dust around it.&rdquo

These properties suggest that &lsquoOumuamua is dense, composed of rock and possibly metals, has no water or ice, and that its surface was reddened due to the effects of irradiation from cosmic rays over hundreds of millions of years.

A few large ground-based telescopes continued to track the fading object as it receded from our planet. Two of NASA&rsquos space telescopes ( Hubble and Spitzer ) tracked the object traveling about 85,700 miles per hour (38.3 kilometers per second) relative to the Sun. Its outbound path is about 20 degrees above the plane of planets that orbit the Sun. The object passed Mars&rsquos orbit around Nov. 1 and will pass Jupiter&rsquos orbit in May of 2018. It will travel beyond Saturn&rsquos orbit in January 2019 as it leaves our solar system, &lsquoOumuamua will head for the constellation Pegasus.

Preliminary orbital calculations suggest that the object came from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, it took so long for the interstellar object to make the journey ― even at the speed of about 59,000 miles per hour (26.4 kilometers per second) ― that Vega was not near that position when the &lsquoOumuamua was there about 300,000 years ago.

Astronomers estimate that an interstellar object similar to &lsquoOumuamua passes through the inner solar system about once per year, but they are faint and hard to spot and have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS1, are powerful enough to have a chance to discover them.

&ldquoWhat a fascinating discovery this is!&rdquo said Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA&rsquos Jet Propulsion Laboratory, Pasadena, California. &ldquoIt&rsquos a strange visitor from a faraway star system, shaped like nothing we&rsquove ever seen in our own solar system neighborhood.&rdquo

How Oumuamua Got its Name

The object was officially named 1I/2017 U1 by the International Astronomical Union (IAU), which is responsible for granting official names to bodies in the solar system and beyond. In addition to the technical name, the Pan-STARRS team dubbed it &lsquoOumuamua (pronounced oh MOO-uh MOO-uh), which is Hawaiian for &ldquoa messenger from afar arriving first.&rdquo

6 Strange Facts about the Interstellar Visitor 'Oumuamua

On October 19, 2017, the first interstellar object, &lsquoOumuamua, was discovered by the Pan-STARRS survey. The experience was similar to having a surprise guest for dinner show up from another country. By examining this guest, we can learn about the culture of that country without the need to travel there&mdasha good thing in this case, given that it would take us a hundred thousand years to visit even the nearest star using conventional chemical rockets.

Surprisingly, our first interstellar guest appeared to be weird and unlike anything we have seen before. By the time we realized it, the guest was already out the door with its image fading into the dark street, so we did not have a chance to get a second look at its mysterious qualities. Below is a list of six peculiarities exhibited by &lsquoOumuamua:

  1. Assuming that other planetary systems resemble the solar system, Pan-STARRS should not have discovered this or any other interstellar rock in the first place. In a paper published a decade ago, we predicted an abundance of interstellar asteroids that is smaller by many (two to eight) orders of magnitude than needed to explain the discovery of &lsquoOumuamua, assuming it&rsquos a member of a random population of objects. Put another way, &lsquoOumuamua implies that the population of interstellar objects is far greater than expected. Each star in the Milky Way needs to eject 10 15 such objects during its lifetime to account for a population as large as &lsquoOumuamua implies. Thus, the nurseries of &lsquoOumuamua-like objects must be different from what we know based on our own solar system.
  2. &lsquoOumuamua originated from a very special frame of reference, the so-called local standard of rest (LSR), which is defined by averaging the random motions of all the stars in the vicinity of the sun. Only one star in 500 is moving as slowly as &lsquoOumuamua in that frame. The LSR is the ideal frame for camouflage, namely for hiding the origins of an object and avoiding its association with any particular star. The relative motion between &lsquoOumuamua and the sun reflects the motion of the sun relative to the LSR. &lsquoOumuamua is like a buoy sitting at rest on the surface of the ocean, with the solar system running into it like a fast ship. Could there be an array of buoys that serves as a network of relay stations or road posts, defining the average galactic frame of reference in interstellar space?
  3. Most interstellar asteroids are expected to be ripped away from their parent star when they lie in the outskirts of their birth planetary system (such as our solar system&rsquos Oort cloud, which extends to 100,000 times the Earth-sun separation), where they are most loosely bound to the star&rsquos gravity. At these outskirts, they can be removed with a small velocity nudge of less than a kilometer per second, in which case they will maintain the speed of their host star relative to the LSR. If &lsquoOumuamua came from a typical star, it must have been ejected with an unusually large velocity kick. To make things more unusual, its kick should have been equal and opposite to the velocity of its parent star relative to the LSR, which is about 20 kilometers per second for a typical star like the sun. The dynamical origin of &lsquoOumuamua is extremely rare no matter how you look at it. This is surprising, since the first foreign guest to a dinner party should be statistically common (especially given the larger than usual population inferred in the first point above).
  4. We do not have a photo of &lsquoOumuamua, but its brightness owing to reflected sunlight varied by a factor of 10 as it rotated periodically every eight hours. This implies that &lsquoOumuamua has an extreme elongated shape with its length at least five to 10 times larger than its projected width. Moreover, an analysis of its tumbling motion concluded that it would be at the highest excitation state expected from its tumultuous journey, if it has a pancake-like geometry. The inferred shape is more extreme than for all asteroids previously seen in the solar system, which have an length-to-width ratio of at most three.
  5. The Spitzer Space Telescope did not detect any heat in the form of infrared radiation from &lsquoOumuamua. Given the surface temperature dictated by &lsquoOumuamua&rsquos trajectory near the sun, this sets an upper limit on its size of hundreds of meters. Based on this size limit, &lsquoOumuamua must be unusually shiny, with a reflectance that is at least 10 times higher than exhibited by solar system asteroids.
  6. The trajectory of &lsquoOumuamua deviated from that expected based on the sun&rsquos gravity alone. The deviation is small (a tenth of a percent) but highly statistically significant. Comets exhibit such a behavior when ices on their surface heat up from solar illumination and evaporate, generating thrust through the rocket effect. The extra push for &lsquoOumuamua could have originated by cometary outgassing if at least a tenth of its mass evaporated. But such massive evaporation would have naturally led to the appearance of a cometary tail, and none was seen. The Spitzer telescope observations also place tight limits on any carbon-based molecules or dust around &lsquoOumuamua and rule out the possibility that normal cometary outgassing is at play (unless it is composed of pure water). Moreover, cometary outgassing would have changed the rotation period of &lsquoOumuamua, and no such change was observed. Altogether, &lsquoOumuamua does not appear to be a typical comet nor a typical asteroid, even as it represents a population that is far more abundant than expected.

The extra push exhibited by &lsquoOumuamua&rsquos orbit could not have originated from a breakup into pieces because such an event would have provided a single, impulsive kick, unlike the continuous push that was observed. If cometary outgassing is ruled out and the inferred excess force is real, only one possibility remains: an extra push due to radiation pressure from the sun. In order for this push to be effective, &lsquoOumuamua needs to be less than a millimeter thick but with a size of at least 20 meters (for a perfect reflector), resembling a lightsail of artificial origin. In this case &lsquoOumuamua would resemble the solar sail demonstrated by the Japanese mission IKAROS or the lightsail contemplated for the Starshot initiative. An artificial origin offers the startling possibility that we discovered &ldquoa message in a bottle&rdquo following years of failed searches for radio signals from alien civilizations. Reassuringly, such a lightsail would survive collisions with interstellar atoms and dust as it travels throughout the galaxy.

In contemplating the possibility of an artificial origin, we should keep in mind what Sherlock Holmes said: &ldquowhen you have excluded the impossible, whatever remains, however improbable, must be the truth.&rdquo The Kepler satellite revealed that about a quarter of all the stars in the Milky Way have a habitable planet of the size of the Earth, with the potential to have liquid water on its surface and the chemistry of life as we know it. It is therefore conceivable that interstellar space is full of artificially made debris, either in the form of devices that serve a purpose on a reconnaissance mission or in the form of defunct equipment. However, to validate an exotic artificial origin for &lsquoOumuamua, we need more data. As Carl Sagan said, &ldquoextraordinary claims require extraordinary evidence.&rdquo

In fact, the possibility of a targeted mission adds some explanatory power. It is unlikely that 10 15 solar sails are launched per star to make up a random population of &lsquoOumuamua-like objects. This would require the unreasonable rate of a launch every five minutes from a planetary system even if all civilizations live as long as the full lifetime of the Milky Way galaxy. Instead, the required numbers could be reduced dramatically if &lsquoOumuamua-like objects do not sample all possible orbits randomly but rather follow special orbits that dive into the innermost, habitable regions of planetary systems like our solar system.

&lsquoOumuamua moves too fast for our chemical rockets to catch up with it now without a gravitational assist from planets. But since it would take &lsquoOumuamua thousands of years to leave the solar system entirely, getting a closer look of it through a flyby remains a possibility if we were to develop new technologies for faster space travel within a decade or two. Interestingly, some interstellar objects that pass close to Jupiter can lose energy and get captured by the solar system. These are dinner guests who bumped into a wall on their way out and stayed around after dinner. The Sun-Jupiter system acts as a fishing net. If we can identify trapped interstellar objects through their unusual bound orbits with unusually high inclinations relative to the solar system plane, we could design missions to visit them and learn more about their nature.

Alternatively, we can wait for the next interstellar guest to show up. Within a few years, the Large Synoptic Survey Telescope (LSST) will become operational and be far more sensitive to the detection of &lsquoOumuamua-like objects. It should therefore discover many such objects within its first year of operation. If it does not find any, we will know that &lsquoOumuamua was special and that we must chase this guest down the street in order to figure out its origin.

Studying interstellar objects resembles my favorite activity when walking along the beach with my daughters. We enjoy picking up seashells that were swept ashore and learning about their different origins. Every now and then, we find a plastic bottle that indicates an artificial origin. Similarly, astronomers should examine any object that enters the solar system and study its properties. There is no doubt that the six peculiar features of &lsquoOumuamua have the potential to usher in a dramatic new era in space science.

The views expressed are those of the author(s) and are not necessarily those of Scientific American.

Have Aliens Found Us? A Harvard Astronomer on the Mysterious Interstellar Object ‘Oumuamua

Avi Loeb, the chair of Harvard’s astronomy department, believes that the peculiar nature of the interstellar object called ‘Oumuamua raises questions about its possible origins. Courtesy ESA/Hubble, NASA, ESO, M. Kornmesser

On October 19, 2017, astronomers at the University of Hawaii spotted a strange object travelling through our solar system, which they later described as “a red and extremely elongated asteroid.” It was the first interstellar object to be detected within our solar system the scientists named it ‘Oumuamua, the Hawaiian word for a scout or messenger. The following October, Avi Loeb, the chair of Harvard’s astronomy department, co-wrote a paper (with a Harvard postdoctoral fellow, Shmuel Bialy) that examined ‘Oumuamua’s “peculiar acceleration” and suggested that the object “may be a fully operational probe sent intentionally to Earth’s vicinity by an alien civilization.” Loeb has long been interested in the search for extraterrestrial life, and he recently made further headlines by suggesting that we might communicate with the civilization that sent the probe. “If these beings are peaceful, we could learn a lot from them,” he told Der Spiegel.

I recently spoke by phone with Loeb, who was frustrated that scientists saw ‘Oumuamua too late in its journey to photograph the object. “My motivation for writing the paper is to alert the community to pay a lot more attention to the next visitor,” he told me. During our conversation, which has been edited and condensed for clarity, we discussed why Loeb thinks we need to consider the possibility that ‘Oumuamua was sent by aliens, the dangers of unscientific speculation, and what belief in an advanced extraterrestrial civilization has in common with faith in God.

Your explanation of why ‘Oumuamua might be an interstellar probe may be hard for laypeople to understand. Why might this be the case, beyond the fact that lots of things are possible?

There is a Scientific American article I wrote where I summarized six strange facts about ‘Oumuamua. The first one is that we didn’t expect this object to exist in the first place. We see the solar system and we can calculate at what rate it ejected rocks during its history. And if we assume all planetary systems around other stars are doing the same thing, we can figure out what the population of interstellar objects should be. That calculation results in a lot of possibilities, but the range is much less than needed to explain the discovery of ‘Oumuamua.

There is another peculiar fact about this object. When you look at all the stars in the vicinity of the sun, they move relative to the sun, the sun moves relative to them, but only one in five hundred stars in that frame is moving as slow as ‘Oumuamua. You would expect that most rocks would move roughly at the speed of the star they came from. If this object came from another star, that star would have to be very special.

What are some of the other strange facts?

When it was discovered, we realized it spins every eight hours, and its brightness changed by at least a factor of ten. The fact that its brightness varies by a factor of ten as it spins means that it is at least ten times longer than it is wide. We don’t have a photo, but, in all the artists’ illustrations that you have seen on the Web, it looks like a cigar. That’s one possibility. But it’s also possible that it’s a pancake-like geometry, and, in fact, that is favored.

What would be the meaning of a pancake-like geometry—

Wait. The most unusual fact about it is that it deviates from an orbit that is shaped purely by the gravitational force of the sun. Usually, in the case of comets, such a deviation is caused by the evaporation of ice on the surface of the comet, creating gases that push the comet, like the rocket effect. That’s what comets show: a cometary tail of evaporated gas. We don’t see a cometary tail here, but, nevertheless, we see a deviation from the expected orbit. And that is the thing that triggered the paper. Once I realized that the object is moving differently than expected, then the question is what gives it the extra push. And, by the way, after our paper appeared, another paper came out with analysis that showed very tight limits on any carbon-based molecules in the vicinity of this object.

What is the significance of that?

It means that there is no evidence of gas that relates to the evaporation of ice. We don’t see the telltale signatures of cometary tail. Moreover, if it was cometary activity, then we would expect the spin period of this object to change, and we don’t see that. All of these things are indicative of the fact that it is nothing like a comet that we have seen before in the solar system. And it is also nothing like an asteroid. Its brightness varies by a factor of ten, and the maximum you typically observe is a factor of three. It has a much more extreme geometry, and there is some other force pushing it. The question is, what’s providing this force, and that was the trigger for our paper.

The only thing that came to my mind is that maybe the light from the sun, as it bounces off its surface, gives it an extra push. It’s just like a wind bouncing off a sail on a sailboat. So we checked that and found that you need the thickness of the object to be less than a millimetre in order for that to work. If it is indeed less than a millimetre thick, if it is pushed by the sunlight, then it is maybe a light sail, and I could not think of any natural process that would make a light sail. It is much more likely that it is being made by artificial means, by a technological civilization.

I should say, just as background, I do not view the possibility of a technological civilization as speculative, for two reasons. The first is that we exist. And the second is that at least a quarter of the stars in the Milky Way galaxy have a planet like Earth, with surface conditions that are very similar to Earth, and the chemistry of life as we know it could develop. If you roll the dice so many times, and there are tens of billions of stars in the Milky Way, it is quite likely we are not alone.

So this civilization would be out of the solar system and in the galaxy?

In the galaxy. It may be dead by now, because we don’t take good care of our planet. Imagine another history, in which the Nazis have a nuclear weapon and the Second World War ends differently. You can imagine a civilization that develops technology like that, which would lead to its own destruction.

It’s possible that the civilization is not alive anymore, but it did send out a spacecraft. We ourselves sent out Voyager I and Voyager II. There could be a lot of equipment out there. The point is that this is the very first object we found from outside the solar system. It is very similar to when I walk on the beach with my daughter and look at the seashells that are swept ashore. Every now and then we find an object of artificial origin. And this could be a message in a bottle, and we should be open-minded. So we put this sentence in the paper.

It’s different, of course, but the way you said that reminded me of an argument I have heard for creationism, which is that if you find a watch on the beach, you know it must be man-made, and, since our eyes are as complex as a watch, we must also be designed by a creator.

An advanced technological civilization is a good approximation to God. Suppose you took a cell phone and showed it to a caveperson. The caveperson would say it was a nice rock. The caveperson is used to rocks. So now imagine this object—‘Oumuamua—being the iPhone and us being the cave people. We look at it and say it’s a rock. It’s just an unusual rock. The point of this analogy is that, for a caveperson, the technologies we have today would have been magic. They would have been God-given.

The Uncensored Guide To ‘Oumuamua, Aliens, And That Harvard Astronomer

This very deep combined image shows the interstellar object ‘Oumuamua at the centre of the picture. … [+] It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving interloper. This image was created by combining multiple images from ESO’s Very Large Telescope as well as the Gemini South Telescope. The object is marked with a blue circle and appears to be a point source, with no surrounding dust.

In 2017, an astronomical event occurred that was unlike any other: for the first time, we observed an object that we are certain originated from beyond our Solar System. Initially, its origin was a hot topic of contention. Was it a comet, albeit one with an unusual orbit? Was it an asteroid, on account of the fact that it didn’t develop a notable tail? Or was it something entirely unique: a visitor from elsewhere in the galaxy, and the first example of an entirely new class of object? Named ‘Oumuamua — Hawaiian for “messenger from the distant past” — it became a spectacular discovery, and a window into what objects exist throughout interstellar space.

But one scientist, enamored with his own hypothesis and ignoring the large amounts of research done by other professionals who specialize in this particular field, has embarked on a public crusade to convince the world of the most far-fetched explanation for this natural phenomenon: aliens. For the better part of the past four years, Harvard astronomer Avi Loeb has appeared all over the media to gather public support for an idea that absolutely defies the scientific evidence. Contrary to the narratives you’ll find elsewhere, including in Loeb’s new book, Extraterrestrial: The First Sign of Life Beyond Earth, this is not a possibility worth taking seriously as a scientist. A straightforward look at the evidence shows us why.

The orbits of the planets and comets, among other celestial objects, are governed by the laws of … [+] universal gravitation. The objects that are gravitationally bound to our Sun all have an eccentricity of less than 1, while those that become unbound will have their eccentricities cross over to be greater than 1. An eccentricity over 1.06 or so indicates an origin from beyond our Solar System.

Kay Gibson, Ball Aerospace & Technologies Corp

According to the law of gravity, every object that’s gravitationally influenced by the Sun will take one of four orbital paths:

  • circular, with an eccentricity of 0,
  • elliptical, with an eccentricity greater than 0 but less than 1,
  • parabolic, with an eccentricity exactly equal to 1,
  • or hyperbolic, with an eccentricity greater than 1.

Before 2017, we had seen a few objects with eccentricities that were 1 or greater, but only by a tiny amount: values like 1.0001 or so. Even with a kick from Jupiter, the fastest-moving Solar System object ever seen only reached an eccentricity of 1.06. This corresponds to an object escaping the Sun’s gravity, but only by a tiny amount. By the time an object like this makes it to interstellar space, it will only have a speed of

But for ‘Oumuamua, it was an entirely different story. It immediately became clear that this object was something special, as its eccentricity was about 1.2, corresponding to an escape speed that was more like 26 km/s. It was the fastest-moving naturally occurring object to leave the Solar System with such a speed, a phenomenon that would be impossible from even an ideal gravitational interaction with a planet like Jupiter or Neptune, which weren’t in the path of ‘Oumuamua at any point. Clearly, it must have originated from outside of our neighborhood.

The Pan-STARRS1 Observatory atop Haleakala Maui at sunset. By scanning the entire visible sky to … [+] shallow depth but frequently, Pan-STARRS can automatically find any moving object within our Solar System above a specific apparent brightness. The discovery of ‘Oumuamua was made in exactly that fashion, by tracking its motion relative to the background of fixed stars.

Theoretically, this lines up with a population of objects we’ve long expected to be there, but hadn’t found until now: the analogue of asteroids, comets, Kuiper belt objects, and Oort cloud objects from other solar systems. We’ve long known that objects like this routinely get ejected from our own cosmic backyard, and likely have for billions of years, dating all the way back to the formation of the Sun and the planets. We’ve witnessed other solar systems forming similarly, and we’ve fully anticipated that there ought to be millions or even billions of these objects for every star in our galaxy.

According to simulations and calculations, many of these objects should pass through our Solar System on an annual basis, but we wouldn’t be able to identify them unless we started taking regular, almost nightly pictures of the entire sky to great sensitivity, over and over again. That’s exactly what the Pan-STARRS telescope (above) — the precursor to the Vera Rubin Observatory — has been doing for years now, and it was that very telescope that discovered ‘Oumuamua. It marks the first detection of an interstellar interloper, and that’s the designation that scientists eventually settled on when it came to classifying this object.

An animation showing the path of the interstellar interloper now known as ʻOumuamua. The combination … [+] of speed, angle, trajectory, and physical properties all add up to the conclusion that this came from beyond our Solar System, but we were unable to discover it until it was already past Earth and on its way out of the Solar System.

Of course, the only reason we found this one is that it managed to get so close to the Sun, a rare occurrence for objects such as this. It actually passed interior to Mercury’s orbit: where our telescopes rarely scan, because you never want to run the risk of accidentally pointing your telescope at the Sun. We didn’t actually discover it until it had crossed over to the other side of Earth’s orbit, when it was on its way out of the Solar System. We found it when it was near its closest to Earth: 23,000,000 kilometers away.

When it made its closest approach to the Sun, it was moving incredibly fast: up to 88 km/s, or three times the speed that Earth orbits the Sun. But we were lucky to image it at all. It was small (only about 100 meters long), faint, and very red in color, similar to the Trojan asteroids we see in orbit around Jupiter. Its color is different from the icy bodies we know of, failing to match up with comets, Kuiper belt objects, or even centaurs, and follow-up observations revealed a certain amount of boring-ness to ‘Oumuamua, as it displayed no molecular or atomic absorption or emission features. In fact, if it weren’t for two odd features about this object, there would have been very little to note about it, other than the fact that it exists and has the trajectory we observed.

Because of the brightness variations seen in interstellar object 1I/’Oumuamua, where it varies by a … [+] factor of 15 from its brightest to its faintest, astronomers have modeled that it is very likely an elongated, tumbling object. The size ratio of its long axis to its short axis may be approximately 8-to-1, similar to weathered, elongated rocks found at the bottom of rivers.

nagualdesign / Wikimedia Commons

The first odd feature about ‘Oumuamua was noticed in October of 2017, shortly following its discovery. Because it was relatively close to Earth but also moving away very quickly, we only had a short window of time to do follow-up observations, and a series of telescopes set their sites on this interstellar oddity. Over a timescale of about 3.6 hours — but not periodically like clockwork — the object varied in brightness by about a factor of 15. Objects like comets or asteroids might vary by a few percent, or even a factor of 2, but a factor of 15 is unheard of. The leading explanation from models of this object is that it must be both elongated and tumbling, which would explain its regular, severe brightness variations.

The reason this is such a good explanation is that unless there’s some mechanism for obscuring the light from this object on one side, like an interstellar analogue of Saturn’s two-toned moon Iapetus, or perhaps dust or outgassing, a change in the object’s apparent size could explain the large brightness variations. It’s not a surprise that this object would be tumbling, but seeing an object so thoroughly elongated, like a rock that’s spent a very long time being weathered in a river or ocean, makes this object all the more interesting.

The nominal trajectory of interstellar asteroid ʻOumuamua, as computed based on the observations of … [+] October 19, 2017 and thereafter. The observed trajectory deviated by an acceleration that corresponds to an extremely small

5 microns-per-second^2 over what was predicted, but that’s significant enough to demand an explanation.


The second odd feature came when we tracked ‘Oumuamua’s path out of the solar system. What we expected, perhaps naïvely, is that it would follow a hyperbolic orbit, as though the only force acting on it would be gravitational. What we found, however, was that a normal, perfectly hyperbolic orbit didn’t quite fit what we observed. It was as though there was an additional acceleration, as though something unobserved were pushing it, in addition to the influence of gravity.

There are many reasons, of course, that an additional acceleration could occur. We’ve seen spacecrafts accelerate in exactly this fashion when they heat unevenly, and an asymmetric, rotating body fits that profile very well. Additionally, there could have been some form of outgassing coming from ‘Oumuamua the only feature we could even test for was a coma, which it lacked, but that only rules out an icy nature. Given its small size and great distance, we concluded it didn’t have a halo of gas around it, but could say nothing about whether it had a diffuse jet of ejecta coming off of it: an eminent possibility.

Even most asteroids in our Solar System contain substantial amounts of volatile compounds, and can … [+] often develop tails when they approach near the Sun. Even though ʻOumuamua may not have had an identifiable tail or coma, there is very likely an astrophysical explanation for its behavior that is related to outgassing, and has absolutely nothing at all to do with aliens.

Since the discovery of ‘Oumuamua, there have been many papers written about it by the astrophysics community, bringing together the lessons we learned from it, synthesizing our pre-existing theories with the new observations to create a holistic picture of what might be lurking in interstellar space. An individual object like ‘Oumuamua will only pass so close to a star in the Milky Way once every

100 trillion (10 14 ) years, or about 10,000 times the present age of the Universe.

How did we get so lucky, then, as to see it?

It’s because of the sheer number of them. There may be, according to some estimates, as many as

10 25 objects like this — interstellar interlopers — that are flying through our galaxy. Every so often, given the incredible number of these objects out there, they’ll pass through our Solar System, up to a few times per year. If we have the right tools, scanning the sky often enough, comprehensively enough, pollution-free enough, and to faint enough magnitudes, we’ll get to observe them. Many speculated that ‘Oumuamua would be a one-off as astronomer Gregory Laughlin quipped, “this was the time of ‘Oumuamua’s life.” But just two years later, we found a second interstellar interloper: the very comet-like object, Borisov.

This time-lapse series of Hubble Space Telescope observations of interstellar object 2I/Borisov … [+] spans seven hours, and was taken with Borisov at a distance of 260 million miles. A blue, comet-like coma can clearly be seen as the object streaks past the background stars. At an extraordinary speed of more than 110,000 miles per hour, it is the fastest natural object to be detected in our Solar System thus far.

NASA, ESA and J. DePasquale (STScI)

Borisov, in August of 2019, became the second example of a significant object whose origin is beyond our Solar System, but it was very different from ‘Oumuamua. Comparing the two, we find that Borisov was:

  • extremely eccentric, with an eccentricity of 3.35, nearly triple any other object,
  • very large, with a diameter of about 6 kilometers, versus 0.1-0.3 km for ‘Oumuamua,
  • and distinctly comet-like, with a clear coma and a long tail, rich in cynaide and diatomic carbon gases.

Borisov, unlike ‘Oumuamua, has an appearance that was familiar to us. So why, then, were these two objects so different from one another?

We have to recognize that there could be many answers to that question. Perhaps they’re not that different, but ‘Oumuamua was too small to measure in detail with the instruments we had in 2017. We discovered Borisov when it was on its way into the Solar System, giving us plenty of time to study it, but only saw ‘Oumuamua when it was already on its way out. Perhaps they are different, because there are many populations of these objects out there: some are planetesimals, others are rocky and ice-free, some have been weathered by a journey of billions of years in interstellar space, etc. The way to answer a question like this is to build better instruments, collect more and superior data, increase our sample size, and actually begin studying these interstellar objects in detail whenever they happen to pass close enough to be observed.

Compared with a number of other known objects with Solar System origins, the interstellar objects … [+] 1I/’Oumuamua and 2I/Borisov appear very different from one another. Borisov fits in extremely well with comet-like objects, while ‘Oumuamua appears completely depleted of volatiles. Discovering why is a task that still awaits humanity.

Casey M. Lisse, presentation slides (2019), private communication

As you can see, there’s a rich scientific tapestry that the astronomical community is weaving about these new classes of objects. We expect the interstellar medium to be filled with remnants and ejecta from the hundreds of billions of solar systems throughout the Milky Way, and owing to the recent advances in our technology, we’ve finally started to detect them. We only have two such objects so far, but the coming years — assuming that mega-constellations of satellites don’t ruin our view — should help us better understand and classify these objects.

That is, unless we decide to take the fundamentally unscientific approach of Avi Loeb, and insist on considering an alien origin for the first of these objects.

Loeb, who’s been intimately involved with the Breakthrough Starshot project, has written papers with his postdocs and students insisting that ‘Oumuamua is just as likely to be an alien spacecraft (that looks suspiciously like a light-sail) as it is to be one of the expected

10 25 naturally occurring objects in our own galaxy. Despite the fact that the spectral signatures of the object — its color, reflectivity, size, etc. — are consistent with a natural origin, Loeb offers only loud, immodest speculation about aliens and diatribes about community groupthink. Coupled with inadequate data, which is the only data we have, he’s impossible to prove wrong.

Normally, structures like IKAROS, shown here, are viewed as potential sails in space. By taking … [+] advantage of the solar radiation pressure, an object like this could propel itself through space with a significant acceleration that departs from what gravity, alone, predicts. However, speculating that an asteroid-like object is an alien spacecraft is not worthy of serious scientific consideration.

Wikimedia Commons user Andrzej Mirecki

What is a responsible scientist to do in this situation? There are literally hundreds of astronomers who work in this field, and Loeb continues to ignore all of them — their work, their data, their conclusions, and the full suite of evidence at hand — instead focusing on his own idea which has no convincing data to back it up. He claims that he didn’t court this public attention, but my own inbox shows that to be a lie. Prior to 2017, I had received 0 emails from Avi Loeb since 2018, I have received 74 from him and even more from his students. All of them have been unsolicited nearly all of them advertise his viewpoints about extraterrestrials, including the bizarre claim that astronomers are somehow resistant to considering the possibility of aliens. Given that planetary scientists are looking for life elsewhere in our Solar System, astronomers are searching for biosignatures on exoplanets and in interstellar materials, and that SETI continues to seek technosignatures, it’s a claim that’s countered by an enormous suite of evidence.

Loeb was a once-respected scientist who made important contributions to astrophysics and cosmology, particularly when it came to black holes and the first stars. But his work on extraterrestrial signatures continues to be largely unappreciated by the community — a position as justifiable as ignoring the comparable idea of Russell’s teapot — and rather than address their scientific objections, he’s stopped listening to other astronomers entirely, instead choosing to try his scientific case in the most unscientific place imaginable: the court of public opinion. Loeb, like everyone, has the freedom to choose which hill his career and reputation will die on. While the possibility of aliens will certainly attract a large amount of public attention, these extraordinary claims that lack even modest supporting evidence will continue, deservedly so, to remain far out of the scientific mainstream.

Mystery of Interstellar Visitor &lsquoOumuamua Gets Trickier

Aliens? Or a chunk of solid hydrogen? Which idea makes less sense?

'Oumuamua&mdasha mysterious, interstellar object that crashed through our solar system two years ago&mdashmight in fact be alien technology. That&rsquos because an alternative, non-alien explanation might be fatally flawed, as a new study argues.

But most scientists think the idea that we spotted alien technology in our solar system is a long shot.

In 2018, our solar system ran into an object lost in interstellar space. The object, dubbed 'Oumuamua, seemed to be long and thin&mdashcigar-shaped&mdashand tumbling end over end. Then, close observations showed it was accelerating, as if something were pushing on it. Scientists still aren't sure why.

One explanation? The object was propelled by an alien machine, such as a lightsail&mdasha wide, millimeter-thin machine that accelerates as it's pushed by solar radiation. The main proponent of this argument was Avi Loeb, a Harvard University astrophysicist.

Most scientists, however, think 'Oumuamua's wonky acceleration was likely due to a natural phenomenon. In June, a research team proposed that solid hydrogen was blasting invisibly off the interstellar object's surface and causing it to speed up.

Now, in a new paper published Monday (Aug. 17) in The Astrophysical Journal Letters, Loeb and Thiem Hoang, an astrophysicist at the Korea Astronomy and Space Science Institute, argue that the hydrogen hypothesis couldn't work in the real world&mdashwhich would mean that there is still hope that our neck of space was once visited by advanced aliens&mdashand that we actually spotted their presence at the time.

Here's the problem with 'Oumuamua: It moved like a comet, but didn't have the classic coma, or tail, of a comet, said astrophysicist Darryl Seligman, an author of the solid hydrogen hypothesis, who is starting a postdoctoral fellowship in astrophysics at the University of Chicago.

'Oumuamua was the first object ever seen flying into our solar system and back out again. That's opposed to most solar system objects that turn circles around the sun, never leaving the celestial neighborhood. Its journey and the fact that it was accelerating suggested 'Oumuamua, which is estimated to be about 1,300 to 2,600 feet (400 to 800 meters) long, was a comet. And yet, "there was no 'coma' or outgassing detected coming from the object," Seligman said. Normally, comets come from regions more distant from the sun than asteroids, and ice on their surface turns straight into gas as they approach the sun, leaving behind a trail of gas, or what we see as a beautiful comet tail, Seligman said.

That outgassing changes how the comet moves through space, he said. It's a bit like a very slow rocket engine: The sun strikes the comet, the warmest part of the comet bursts with gas, and that gas flowing away from the comet sends it tumbling faster and faster away from the sun.

In a paper published June 9 in The Astrophysical Journal Letters, Seligman and Yale astrophysicist Gregory Laughlin proposed that the object was a comet made up partly or entirely of molecular hydrogen&mdashlightweight molecules composed of two hydrogen atoms (H2).

H2 gas freezes into a puffy, low-density solid only when it's very cold&mdashminus 434.45 degrees Fahrenheit (minus 259.14 degrees Celsius, or just 14.01 degrees above absolute zero) in Earth's atmosphere. Researchers had already proposed the existence of "hydrogen icebergs" out in the very cold reaches of space, Laughlin and Seligman wrote in the study. And outgassing hydrogen wouldn't be visible from Earth&mdashmeaning it wouldn't leave behind a visible comet tail.

The numbers worked out neatly while a few other substances (like solid neon) could potentially explain the coma-free acceleration, hydrogen was the best match for the data.

But in their new paper, Hoang and Loeb respond to this idea and argue that the hydrogen iceberg explanation has a basic problem: Comets form when icy grains of dust bump into each other in space and form clumps, and then those clumps attract more dust and other clumps. And comets are like snowmen: they survive only as long as they don't melt.

The stickiness that helps form comets is similar to the stickiness of ice cubes coming straight out of a cold freezer. Leave an ice cube on the counter for a minute or two, let its surface warm up a bit, and it won't feel sticky anymore. A thin film of liquid water on its surface makes it slippery.

Hoang and Loeb argued that even starlight in the coldest parts of space would warm up small chunks of solid hydrogen before they could clump together and form a comet of 'Oumuamua's large scale. And more importantly, the trek from the nearest "giant molecular cloud"&mdasha dusty, gassy region of space where hydrogen icebergs are thought to form&mdashis far too long. A hydrogen iceberg travelling hundreds of millions of years through interstellar space would have fallen apart, cooked by starlight.

Seligman said that Loeb's analysis was correct that no hydrogen comet would survive such a long trip."Hydrogen icebergs don't live that long in the galaxy.," he said. "And you definitely don't have time to get all the way from [the nearest] giant molecular cloud."

The theory only works if 'Oumuamua is just 40 million years old, he said. Over that time frame, outgassing could have molded the comet's oblong shape without destroying it entirely.

He pointed to a paper published in April in The Astronomical Journal, which proposed a number of nearby origin points for 'Oumuamua.

The paper's authors didn't nail down the comet's home entirely, which would be impossible, they said. 'Oumuamua was hardly moving when it arrived in our sun's gravity well, which makes tracking the comet through space tricky. But the researchers looked at what else passed through the Milky Way neighborhood that our sun is now passing through in recent cosmic history. They landed on two groups of young stars, the Carina and Columba moving groups, said Tim Hallatt, a graduate student and astrophysicist at McGill University in Montreal, and lead author of the paper published in April.

They all formed around 30 million to 45 million years ago in a cloud of gas that then dispersed. That small, dissipated cloud of molecular gas, with just a few young stars, is one where hydrogen icebergs might form, Hallatt said

"There are many processes that can eject 'Oumuamua-type objects from young stars in moving groups&mdashlike gravitational nudges between stars in the group, planet formation, or as Seligman and Laughlin 2020 argue, the molecular clouds that create the stars in the first place," Hallatt told Live Science.

All three papers fit neatly together if you assume 'Oumuamua was a hydrogen iceberg that originated in Carina or Columba, Hallatt added.

"Seligman & Laughlin's idea could work here because H2 objects should have a short lifetime in the galaxy (as Loeb correctly concludes), and an origin in Carina or Columba would make it young enough to survive its journey," he said.

"Shortening the distance that that H2 iceberg needs to travel does not solve the problems we outline in our paper, because the H2 iceberg would have formed when its parent planetary system formed, billions of years ago,&rdquo and in those eons, the iceberg would have evaporated, he told Live Science in an email.

Loeb also said that hydrogen icebergs are expected to come from giant molecular clouds, not parts of space like Carina or Columba. And he reiterated that no hydrogen iceberg could survive the trek from the nearest giant molecular cloud.

Asked if there is a clear leading candidate explanation for 'Oumuamua's acceleration, Loeb referred Live Science to a not-yet-released book he authored called "Extraterrestrial: The First Sign of Intelligent Life Beyond Earth," due for publication in January.


As the first known object of its type, ʻOumuamua presented a unique case for the International Astronomical Union, which assigns designations for astronomical objects. Originally classified as comet C/2017 U1, it was later reclassified as asteroid A/2017 U1 due to the absence of a coma. Once it was unambiguously identified as coming from outside the Solar System, a new designation was created: I, for Interstellar object. As the first object so identified, ʻOumuamua was designated 1I, with rules for the eligibility of objects for I-numbers and the names to be assigned to these interstellar objects yet to be codified. The object may be called 1I 1I/2017 U1 1I/ʻOumuamua or 1I/2017 U1 (ʻOumuamua). [4]

The name comes from Hawaiian ʻoumuamua 'scout' [33] (from ʻou 'reach out for', and mua , reduplicated for emphasis 'first, in advance of' [4] ), and reflects the way the object is like a scout or messenger sent from the distant past to reach out to humanity. It roughly translates to 'first distant messenger'. [4] [34] The first character is a Hawaiian ʻokina, not an apostrophe, and is pronounced as a glottal stop the Pan-STARRS team chose the name [35] in consultation with Kaʻiu Kimura and Larry Kimura of the University of Hawaiʻi at Hilo. [36]

Before the official name was decided, Rama was suggested, the name given to an alien spacecraft discovered under similar circumstances in the 1973 science fiction novel Rendezvous with Rama by Arthur C. Clarke. [37]

Observations and conclusions concerning the trajectory of ʻOumuamua were primarily obtained with data from the Pan-STARRS1 Telescope, part of the Spaceguard Survey, [38] and the Canada–France–Hawaii Telescope (CFHT), and its composition and shape from the Very Large Telescope and the Gemini South telescope in Chile, [39] as well as the Keck II telescope in Hawaii. These were collected by Karen J. Meech, Robert Weryk and their colleagues and published in Nature on 20 November 2017. [40] [41] After the announcement, the space-based telescopes Hubble and Spitzer joined in the observations. [42]

ʻOumuamua is small and not very luminous. It was not seen in STEREO HI-1A observations near its perihelion on 9 September 2017, limiting its brightness to approximately 13.5 mag. [18] By the end of October, ʻOumuamua had already faded to about apparent magnitude 23, [43] and in mid-December 2017, it was too faint and fast moving to be studied by even the largest ground-based telescopes. [39]

ʻOumuamua was compared to the fictional alien spacecraft Rama due to its interstellar origin. Adding to the coincidence, both the real and the fictional objects are unusually elongated. [44] ʻOumuamua has a reddish hue and unsteady brightness, which are typical of asteroids. [45] [46] [47]

The SETI Institute's radio telescope, the Allen Telescope Array, examined ʻOumuamua, but detected no unusual radio emissions. [48] More detailed observations, using the Breakthrough Listen hardware and the Green Bank Telescope, were performed [44] [48] [49] the data were searched for narrowband signals and none were found. Given the close proximity to this interstellar object, limits were placed to putative transmitters with the extremely low effective isotropically radiated power of 0.08 watts. [50]

Trajectory Edit

ʻOumuamua appears to have come from roughly the direction of Vega in the constellation Lyra. [45] [46] [51] [52] The incoming direction of motion of ʻOumuamua is 6° from the solar apex (the direction of the Sun's movement relative to local stars), which is the most likely direction, from where objects coming from outside the Solar System should approach. [51] [53] On 26 October, two precovery observations from the Catalina Sky Survey were found dated 14 and 17 October. [54] [43] A two-week observation arc had verified a strongly hyperbolic trajectory. [7] [40] It has a hyperbolic excess velocity (velocity at infinity, v ∞ !> ) of 26.33 km/s (94,800 km/h 58,900 mph), its speed relative to the Sun when in interstellar space. [d]

ʻOumuamua speed relative to the Sun [55]
Distance Date Velocity
2300 AU 1605 26.34
1000 AU 1839 26.35
100 AU 2000 26.67
10 AU 2016 29.50
1 AU 9 August 2017 49.67
Perihelion 9 September 2017 87.71 [10]
1 AU 10 October 2017 49.67 [e]
10 AU 2019 29.51
100 AU 2034 26.65
1000 AU 2196 26.36
2300 AU 2430 26.32

By mid-November, astronomers were certain that it was an interstellar object. [56] Based on observations spanning 80 days, ʻOumuamua's orbital eccentricity is 1.20, the highest ever observed [57] [10] until 2I/Borisov was discovered in August 2019. An eccentricity exceeding 1.0 means an object exceeds the Sun's escape velocity, is not bound to the Solar System and may escape to interstellar space. While an eccentricity slightly above 1.0 can be obtained by encounters with planets, as happened with the previous record holder, C/1980 E1, [57] [58] [f] ʻOumuamua's eccentricity is so high that it could not have been obtained through an encounter with any of the planets in the Solar System. Even undiscovered planets in the Solar System, if any should exist, could not account for ʻOumuamua's trajectory nor boost its speed to the observed value. For these reasons, ʻOumuamua can only be of interstellar origin. [59] [60]

Inbound velocity at 200 AU from the Sun
compared to Oort cloud objects [55]
Object Velocity
# of observations
and obs arc [g]
90377 Sedna 1.99 196 in 9240 days
C/1980 E1 (Bowell) 2.96 179 in 2514 days
C/1997 P2 (Spacewatch) 2.96 94 in 49 days
C/2010 X1 (Elenin) 2.96 2222 in 235 days
C/2012 S1 (ISON) 2.99 6514 in 784 days
C/2008 J4 (McNaught) 4.88 22 in 15 days [h]
1I/2017 U1 (ʻOumuamua) 26.5 207 in 80 days

ʻOumuamua entered the Solar System from north of the plane of the ecliptic. The pull of the Sun's gravity caused it to speed up until it reached its maximum speed of 87.71 km/s (315,800 km/h 196,200 mph) as it passed south of the ecliptic on 6 September and made a sharp turn northward at its closest approach to the Sun (perihelion) on 9 September at a distance of 0.255 AU (38,100,000 km 23,700,000 mi) from the Sun, i.e., about 17% closer than Mercury's closest approach to the Sun. [61] [10] [i] The object is now heading away from the Sun towards Pegasus towards a vanishing point 66° from the direction of its approach. [j]

On the outward leg of its journey through the Solar System, ʻOumuamua passed beyond the orbit of Earth on 14 October while being at a distance of approximately 0.1618 AU (24,200,000 km 15,040,000 mi) from Earth. On 16 October it moved back north of the ecliptic plane and passed beyond the orbit of Mars on 1 November. [61] [51] [7] ʻOumuamua passed beyond Jupiter's orbit in May 2018, beyond Saturn's orbit in January 2019, and will pass beyond Neptune's orbit in 2022. [61] As it leaves the Solar System it will be approximately right ascension 23'51" and declination +24°45', in Pegasus. [10] It will continue to slow down until it reaches a speed of 26.33 kilometres per second (94,800 km/h 58,900 mph) relative to the Sun, the same speed it had before its approach to the Solar System. [10]

Non-gravitational acceleration Edit

On 27 June 2018, astronomers reported a non-gravitational acceleration to ʻOumuamua's trajectory, potentially consistent with a push from solar radiation pressure. [63] [64] Initial speculation as to the cause of this acceleration pointed to the comet-like outgassing, [22] whereby volatile substances inside the object evaporate as the Sun heats its surface. Although no such tail of gases was ever observed following the object, researchers estimated that enough outgassing may have increased the object's speed without the gases being detectable. [65] A critical re-assessment of the comet hypothesis found that, instead of the observed stability of ʻOumuamua's spin, outgassing would have caused its spin to rapidly change due to its elongated shape, resulting in the object tearing apart. [8]

Indications of origin Edit

Accounting for Vega's proper motion, it would have taken ʻOumuamua 600,000 years to reach the Solar System from Vega. [40] But as a nearby star, Vega was not in the same part of the sky at that time. [51] Astronomers calculate that one hundred years ago the object was 83.9 ± 0.090 billion km 52.1 ± 0.056 billion mi (561 ± 0.6 AU) from the Sun and traveling at 26.33 km/s with respect to the Sun. [10] This interstellar speed is very close to the mean motion of material in the Milky Way in the neighborhood of the Sun, also known as the local standard of rest (LSR), and especially close to the mean motion of a relatively close group of red dwarf stars. This velocity profile also indicates an extrasolar origin, but appears to rule out the closest dozen stars. [66] In fact, the closeness of ʻOumuamua's velocity to the local standard of rest might mean that it has circulated the Milky Way several times and thus may have originated from an entirely different part of the galaxy. [40]

It is unknown how long the object has been traveling among the stars. [61] The Solar System is likely the first planetary system that ʻOumuamua has closely encountered since being ejected from its birth star system, potentially several billion years ago. [67] [40] It has been speculated that the object may have been ejected from a stellar system in one of the local kinematic associations of young stars (specifically, Carina or Columba) within a range of about 100 parsecs, [68] some 45 million years ago. [69] The Carina and Columba associations are now very far in the sky from the Lyra constellation, the direction from which ʻOumuamua came when it entered the Solar System. Others have speculated that it was ejected from a white dwarf system and that its volatiles were lost when its parent star became a red giant. [70] About 1.3 million years ago the object may have passed within a distance of 0.16 parsecs (0.52 light-years) to the nearby star TYC 4742-1027-1, but its velocity is too high to have originated from that star system, and it probably just passed through the system's Oort cloud at a relative speed of about 15 km/s (34,000 mph 54,000 km/h). [71] [k] A more recent study (August 2018) using Gaia Data Release 2 has updated the possible past close encounters and has identified four stars [ which? ] that ʻOumuamua passed relatively close to and at moderately low velocities in the past few million years. [72] This study also identifies future close encounters of ʻOumuamua on its outgoing trajectory from the Sun. [73]

In April 2020, astronomers presented a new possible scenario for the object's origin. [74] [75] According to one hypothesis, ʻOumuamua could be a fragment from a tidally disrupted planet. [76] [l] If true, this would make ʻOumuamua a rare object, of a type much less abundant than most extrasolar "dusty-snowball" comets or asteroids. However, this scenario leads to cigar-shaped objects whereas ʻOumuamua's lightcurve favors a disc-like shape. [77]

In May 2020, it was proposed that the object was the first observed member of a class of small H2-ice-rich bodies that form at temperatures near 3 K in the cores of giant molecular clouds. The non-gravitational acceleration and high aspect ratio shape of ʻOumuamua might be explainable on this basis. [78] However, it was later calculated that hydrogen icebergs cannot survive their journey through interstellar space. [79]

Classification Edit

Initially, ʻOumuamua was announced as comet C/2017 U1 (PANSTARRS) based on a strongly hyperbolic trajectory. [3] In an attempt to confirm any cometary activity, very deep stacked images were taken at the Very Large Telescope later the same day, but the object showed no presence of a coma. [m] Accordingly, the object was renamed A/2017 U1, becoming the first comet ever to be re-designated as an asteroid. [5] Once it was identified as an interstellar object, it was designated 1I/2017 U1, the first member of a new class of objects. [4] The lack of a coma limits the amount of surface ice to a few square meters, and any volatiles (if they exist) must lie below a crust at least 0.5 m (1.6 ft) thick. [14] It also indicates that the object must have formed within the frost line of its parent stellar system or have been in the inner region of that stellar system long enough for all near-surface ice to sublimate, as may be the case with damocloids. [ citation needed ] It is difficult to say which scenario is more likely due to the chaotic nature of small body dynamics, [ citation needed ] although if it formed in a similar manner to Solar System objects, its spectrum indicates that the latter scenario is true. Any meteoric activity from ʻOumuamua would have been expected to occur on 18 October 2017 coming from the constellation Sextans, but no activity was detected by the Canadian Meteor Orbit Radar. [67]

On 27 June 2018, astronomers reported that ʻOumuamua was thought to be a mildly active comet, and not an asteroid, as previously thought. This was determined by measuring a non-gravitational boost to ʻOumuamua's acceleration, consistent with comet outgassing. [22] [80] [65] [81] However, studies submitted in October 2018 suggest that the object is neither an asteroid nor a comet, [8] [9] although the object could be a remnant of a disintegrated interstellar comet (or exocomet), as suggested by astronomer Zdenek Sekanina. [23] [24]

Appearance, shape and composition Edit

Spectra from the Hale Telescope on 25 October showed red color resembling comet nuclei or Trojans. [67] Higher signal to noise spectra recorded by the 4.2 m (14 ft) William Herschel Telescope later that day showed that the object was featureless, and colored red like Kuiper belt objects. [82] Spectra obtained with the 8.2 m (27 ft) Very Large Telescope the following night showed that behaviour continued into near-infrared wavelengths. [83] Its spectrum is similar to that of D-type asteroids. [14]

ʻOumuamua is not rotating around its principal axis, and its motion may be a form of tumbling. [16] [84] This accounts for the various rotation periods reported, such as 8.10 hours (±0.42 hours [18] or ±0.02 hours [17] ) by Bannister et al. and Bolin et al. with a lightcurve amplitude of 1.5–2.1 magnitudes , [17] whereas Meech et al. reported a rotation period of 7.3 hours and a lightcurve amplitude of 2.5 magnitudes. [85] [n] Most likely, ʻOumuamua was set tumbling by a collision in its system of origin, and remains tumbling since the time scale for dissipation of this motion is very long, at least a billion years. [16] [86]

The large variations on the light curves indicate that ʻOumuamua may be anything from a highly elongated cigar-like object, comparable to or greater than the most elongated Solar System objects, [18] [17] to an extremely flat object, a pancake or oblate spheroid. [87] However, the size and shape have not been directly observed as ʻOumuamua appears as nothing more than a point source of light even in the most powerful telescopes. Neither its albedo nor its triaxial ellipsoid shape is known. If cigar-shaped, the longest-to-shortest axis ratio could be 5:1 or greater. [16] Assuming an albedo of 10% (slightly higher than typical for D-type asteroids [88] ) and a 6:1 ratio, ʻOumuamua has dimensions of approximately 100 m–1,000 m × 35 m–167 m × 35 m–167 m (328 ft–3,281 ft × 115 ft–548 ft × 115 ft–548 ft) [11] [12] [13] [14] [15] with an average diameter of about 110 m (360 ft). [14] [15] According to astronomer David Jewitt, the object is physically unremarkable except for its highly elongated shape. [15] Bannister et al. have suggested that it could also be a contact binary, [18] although this may not be compatible with its rapid rotation. [41] One speculation regarding its shape is that it is a result of a violent event (such as a collision or stellar explosion) that caused its ejection from its system of origin. [41] JPL News reported that ʻOumuamua "is up to one-quarter mile, 400 m (1,300 ft), long and highly-elongated-perhaps 10 times as long as it is wide". [42] [89]

A 2019 paper finds the best models as either a cigar-shape, 1:8 aspect ratio, or disc-shape, 1:6 aspect ratio, with the disc more likely since its rotation does not require a specific orientation to see the range of brightnesses observed. [90] Monte Carlo simulations based on the available orbit determination suggest that the equatorial obliquity of ʻOumuamua could be about 93 degrees, if it has a very prolate or cigar-like shape, or close to 16 degrees, if it is very oblate or disk-like. [91]

Light curve observations suggest the object may be composed of dense metal-rich rock that has been reddened by millions of years of exposure to cosmic rays. [41] [92] [93] It is thought that its surface contains tholins, which are irradiated organic compounds that are more common in objects in the outer Solar System and can help determine the age of the surface. [94] [95] This possibility is inferred from spectroscopic characterization and its reddish color, [94] [83] and from the expected effects of interstellar radiation. [83] Despite the lack of any cometary coma when it approached the Sun, it may still contain internal ice, hidden by "an insulating mantle produced by long-term cosmic ray exposure". [83]

In November 2019, some astronomers have noted that ʻOumuamua may be a "cosmic dust bunny", due to its "very lightweight and 'fluffy' conglomerate of dust and ice grains". [96] [97] [98]

In August 2020, astronomers reported that ʻOumuamua is not likely to have been composed of frozen hydrogen which had been proposed earlier the compositional nature of the object continues to be unknown. [99] [100]

Additional measurements Edit

In December 2017, astronomer Avi Loeb of Harvard University, an adviser to the Breakthrough Listen Project, cited ʻOumuamua's unusually elongated shape as one of the reasons why the Green Bank Telescope in West Virginia would listen for radio emissions from it to see if there were any unexpected signs that it might be of artificial origin, [89] although earlier limited observations by other radio telescopes such as the SETI Institute's Allen Telescope Array had produced no such results. [48] On 13 December 2017, the Green Bank Telescope observed the object for six hours across four bands of radio frequency. No radio signals from ʻOumuamua were detected in this very limited scanning range, but observations are ongoing. [101] [102]

In September 2018, astronomers described several possible home star systems from which ʻOumuamua may have originated. [103] [104]

Nitrogen ice theory Edit

Outgassing of nitrogen ice (N2) could explain why no outgassing was detected. Nitrogen ice the size of 'Oumuamua could survive for 500 million years in the interstellar medium and would reflect two-thirds of the Sun's light. [105] This explanation has been further supported in March 2021 when scientists presented a theory based on nitrogen ice, and further concluded that ʻOumuamua may likely be a piece of an exoplanet similar to the dwarf planet Pluto, an exo-Pluto as noted, from beyond our solar system. [29] [30] [31] [32]

Hydrogen ice theory Edit

It has been proposed that ʻOumuamua contains a significant amount of hydrogen ice. [106] [107] This would point to it originating from the core of an interstellar molecular cloud, where conditions for the formation of this material might exist. [108] The Sun's heat would cause the hydrogen to sublimate, which would in turn propel the body. The hydrogen coma formed by this process would be difficult to detect from Earth-based telescopes, as the atmosphere blocks those wavelengths. [109] Regular water-ice comets undergo this as well, however to a much lesser extent and with a visible coma. This may explain the significant non-gravitational acceleration that ʻOumuamua underwent without showing signs of coma formation. Significant mass loss caused by the sublimation would also explain the unusual cigar-like shape, comparable to how a bar of soap becomes more elongated as it is used up.

However, it was later shown that hydrogen icebergs cannot form out of small grains and that irrespective of their origin, they would quickly evaporate during their journey in interstellar space. [110]

Hypothetical space missions Edit

The Initiative for Interstellar Studies (i4is) launched Project Lyra to assess the feasibility of a mission to ʻOumuamua. [111] Several options for sending a spacecraft to ʻOumuamua within a time-frame of 5 to 25 years were suggested. [112] [113] Different mission durations and their velocity requirements were explored with respect to the launch date, assuming direct impulsive transfer to the intercept trajectory. [ citation needed ]

The Space Launch System (also being looked at for "interstellar precursor missions") would be even more capable. [114] [115] Such an interstellar precursor could easily pass by ʻOumuamua on its way out of the Solar System, at speeds of 63 km/s (39 mi/s). [116] [117]

More advanced options of using solar, laser electric, and laser sail propulsion, based on Breakthrough Starshot technology, have also been considered. The challenge is to get to the interstellar object in a reasonable amount of time (and so at a reasonable distance from Earth), and yet be able to gain useful scientific information. To do this, decelerating the spacecraft at ʻOumuamua would be "highly desirable, due to the minimal science return from a hyper-velocity encounter". [53] If the investigative craft goes too fast, it would not be able to get into orbit or land on the object and would fly past it. The authors conclude that, although challenging, an encounter mission would be feasible using near-term technology. [53] [111] Seligman and Laughlin adopt a complementary approach to the Lyra study but also conclude that such missions, though challenging to mount, are both feasible and scientifically attractive. [118]

Alien object hypothesis Edit

On 26 October 2018, theoretical physicist Avi Loeb and his postdoc Shmuel Bialy submitted a paper exploring the possibility of ʻOumuamua being an artificial thin solar sail [119] [120] accelerated by solar radiation pressure, in an effort to help explain the object's comet-like non-gravitational acceleration. [63] [64] [121] Other scientists have stated that the available evidence is insufficient to consider such a premise, [122] [123] [124] and that a tumbling solar sail would not be able to accelerate. [125] In response, Loeb wrote an article detailing six anomalous properties [ which? ] of ʻOumuamua that make it unusual, unlike any comets or asteroids seen before. [126] [127] A subsequent report on observations by the Spitzer Space Telescope set a tight limit on cometary outgassing of any carbon-based molecules and indicated that ʻOumuamua is at least ten times more shiny than a typical comet. [128] The alien object hypothesis is considered unlikely by many experts. [129] [130]

Other interstellar objects Edit

2I/Borisov was discovered on 30 August 2019, and was soon confirmed to be an interstellar comet. Arriving from the direction of Cassiopeia, the object arrived at perihelion (closest point to the Sun) on 8 December 2019.