Don’t current categories of interstellar bodies limit the discovery of “new” categories of interstellar bodies?

“Interstellar objects passing through our solar system” is a discrete category that is clearly defined. Basically any object that is *not* gravitationally bound to our solar system is “interstellar.”

How was the name ‘Oumuamua selected? What does it mean?

We decided that as this was discovered in Hawai’i and was the first of its kind, it should have a Hawaiian name. We asked the CFHT director, Doug Simons, to get in touch with Hawaiian language experts, and he contacted Larry Kimura and Ka’iu Kimura and gave them two days to come up with a name. They suggested ‘visitor from the past reaching out to us from the distant past.’

How big is ‘Oumuamua?

It is probably somewhere between 100 and 200 meters in diameter. Think one or two football fields.

How far away is ‘Oumuamua from Earth now?

About half the distance between the orbits of Uranus and Neptune – so a little farther away than Uranus. In astronomical units, it is about 24 astronomical units away. An astronomical unit is the average distance from Earth to Sun.

Might the albedo vary substantially on ‘Oumuamua (similar to lapetus around Saturn)?

It may, but we can’t and won’t know for sure. It is always difficult to tell the difference between changes in shape and changes in albedo, even for objects that we can see over long periods of time in our own solar system.

What does ‘Oumuamua seem to be made of?

It looks like organic-rich comet or asteroid surfaces.

What do we know about its shape — is it long and slender, or could it be shaped like a frisbee?

We cannot easily distinguish between the cigar shape and the frisbee. If we had a longer time sequence of observations, perhaps we could distinguish. However, it became faint quickly, and the moon became bright.

What are the arguments for it being either a natural formation or a product of intelligent design?

Its size, surface color, and rotation look similar to solar system comets and asteroids. Its acceleration is typical of what we see in comets from uneven release of gas. So a natural explanation is that it is a comet. What was unusual was the elongated shape, and the non-detection of dust.

Can you comment about the relative motion of ‘Oumuamua with respect to the local standard of rest? Is this unexpected?

The implication of the velocity being low is that it came from nearby and thus was recently ejected from its home system. This is what gave scientists the hope that we could trace its path back to the home system.

Can we quantify the acceleration (or relate it to acceleration that we may experience in our everyday world)?

‘Oumuamua’s acceleration is about one millionth the acceleration of objects falling to the surface of Earth.

Could the object have been ejected from a supernova? As if it was orbiting a star that went supernova and was far enough away in its orbit that it survived the event and got kicked into interstellar space?

That is possible. Another explanation is that it could have been in orbit around a star that was more massive than the Sun. When that star became a red giant, it would have lost some of its mass, and the object could have become unbound to the star.

Do the available spectra match any other class of asteroids? Are there other similar objects that visit our solar system but don’t fit into the asteroid or comet category?

The spectra match either comets or red, organic-rich asteroids. We have seen a second interstellar object, and it is clearly a comet – with detection of gas and dust, and it too is red.

Where is ‘Oumuamua headed?

A. It is headed towards the constellation Pegasus.

This was discovered by accident, right? Are there any surveillance programs that are now intentionally looking for interstellar objects like ‘oumuamua? What is the expectation for how many we are likely to see?

I prefer to say that it was a serendipitous discovery. I am not aware of any dedicated surveys for interstellar objects. The next interstellar objects will likely be discovered by the Near-Earth Object surveys or by LSST with the Rubin Observatory. We have learned a lot from `Oumuamua, so we might be more efficient at finding similar objects in the future.

Have we learned everything we can about ‘Oumuamua based on the data we were able to select? Is this research over or might new insight materialize?

We have obtained all the data we will ever get. There are still papers being produced from a wide range of astronomers with different backgrounds — proposing new theoretical models to explain the data. This is the first I’ve seen this in planetary astronomy! There are probably over 200 papers written on this one object now, and they still keep coming.

What was your personal involvement in the detection and analysis of ‘Oumuamua?

Richard Wainscoat: I was probably the second person on the planet to see the images of `Oumuamua. I work closely with Rob Weryk,　who discovered it. I immediately scheduled observations of `Oumuamua with the Canada-France-Hawaii Telescope (CFHT), and these observations showed that it appeared to be asteroidal (point-like) rather than cometary (fuzzy). Shortly after the discovery, I had to leave for a conference in South Korea (very bad timing) and continued to create observations with CFHT using the in-flight wi-fi. There was a period of poor weather in Hawaii, and after that, I obtained a long time-sequence of observations with CFHT that showed that `Oumuamua had a dramatically changing light curve. Those observations were closely monitored remotely as I left the conference, including from the hotel lobby and the taxi to the airport.

Karen Meech: Richard called me at home on Sun. Oct 22 saying that Robert Weryk had found a NEO on Oct 19 that, with added data from CFHT and other telescopes, looked like it was on a hyperbolic orbit — coming from outside the solar system. I have mobilized large groups of planetary astronomers using big telescopes for planetary missions before, so my role was to do this again. We started immediately and had telescope time on the Very Large Telescope in Chile (8m) the very next day, with other observatories following quickly after that. I also coordinated all the observations and began setting up and writing the paper so that everyone could contribute.

Robert Jedicke: I managed the Moving Object Processing System (MOPS) development that was used to detect `Oumuamua and published a paper predicting the orbit distribution of discovered asteroidal and cometary interstellar objects about a year before `Oumuamua was discovered. I was also a co-author on Karen’s Nature paper, for which I calculated the number of objects like ‘Oumuamua that are in our solar system at any time.

What was your personal involvement in the detection and analysis of ‘Oumuamua?

Richard Wainscoat: I was probably the second person on the planet to see the images of `Oumuamua. I work closely with Rob Weryk,　who discovered it. I immediately scheduled observations of `Oumuamua with the Canada-France-Hawaii Telescope (CFHT), and these observations showed that it appeared to be asteroidal (point-like) rather than cometary (fuzzy). Shortly after the discovery, I had to leave for a conference in South Korea (very bad timing) and continued to create observations with CFHT using the in-flight wi-fi. There was a period of poor weather in Hawaii, and after that, I obtained a long time-sequence of observations with CFHT that showed that `Oumuamua had a dramatically changing light curve. Those observations were closely monitored remotely as I left the conference, including from the hotel lobby and the taxi to the airport.

Karen Meech: Richard called me at home on Sun. Oct 22 saying that Robert Weryk had found a NEO on Oct 19 that, with added data from CFHT and other telescopes, looked like it was on a hyperbolic orbit — coming from outside the solar system. I have mobilized large groups of planetary astronomers using big telescopes for planetary missions before, so my role was to do this again. We started immediately and had telescope time on the Very Large Telescope in Chile (8m) the very next day, with other observatories following quickly after that. I also coordinated all the observations and began setting up and writing the paper so that everyone could contribute.

Robert Jedicke: I managed the Moving Object Processing System (MOPS) development that was used to detect `Oumuamua and published a paper predicting the orbit distribution of discovered asteroidal and cometary interstellar objects about a year before `Oumuamua was discovered. I was also a co-author on Karen’s Nature paper, for which I calculated the number of objects like ‘Oumuamua that are in our solar system at any time.

What does it mean to be an astrobiologist?

Astrobiology is a field that explores life in the universe. This includes how life originates (on Earth or elsewhere), how the ingredients for life are synthesized in space, the search for habitable environments in our solar system and elsewhere (and what constitutes a habitable environment), and the search for life elsewhere. The latter includes missions in our solar system (Mars, subsurface oceans on Europa), to the search for technological signatures.

What role does UH play in detecting near-Earth objects?

UH operates two major surveys for Near-Earth Objects: Pan-STARRS (Haleakala) and ATLAS (Haleakala and Mauna Loa, with additional telescopes being constructed in South Africa and Chile). Another program, run by David Tholen, obtains additional observations of objects that potentially could impact Earth in the future to refine their orbits. UH also operates the NASA Infrared Telescope Facility, which is extensively used to characterize Near-Earth Objects. Much of the UH work on Near-Earth Objects is funded by the NASA Near-Earth Object Observations Program, part of NASA’s Planetary Defence Coordination Office.

What is the best estimate of how often significant interstellar objects pass through our solar system?

In Karen’s Nature paper on ‘Oumuamua we estimated that there is, on average, about one object of about ‘Oumuamua’s size closer to the Sun than Earth at any time. The problem is that these objects are small, probably dark, and moving fast, so they are difficult to detect with existing ground-based asteroid search programs. So the answer to the question is “all the time,” but you have to be looking at the right place at the right time with the right instrument.

Avi Loeb has gained a lot of attention for proposing a light-sail hypothesis, for suggesting that we should take seriously the possibility that ‘Oumuamua was designed and launched by another civilization? What is the strongest argument for this view? What is the weakness? 

This was discussed in the webinar. Loeb argues that the only plausible explanation for the acceleration of ‘Oumuamua out of the solar system was that it was a light sail because he discarded all other explanations for acceleration other than solar radiation pressure. Solar radiation pressure requires a large area to mass ratio (a density so low it does not occur in nature). Comets outgas unevenly, often in jets of material. This acts like a rocket thruster, imparting an acceleration. This is seen all the time with comets. The amount of acceleration seen for ‘Oumuamua which pointed radially away from the sun was consistent with the amount of acceleration seen with comets, and also decreased by the inverse of the square of the distance, just as you would expect from a process driven by the heat of the sun. He argues against this because we didn’t detect gas or dust. We didn’t have any experiments sensitive enough to detect the gas to rule its presence out. We did have sensitive measurements of tiny dust, usually expected to be pushed off the comet with the gas. There was no tiny dust. However, this could have been eroded during the passage through the interstellar medium gas and dust clouds. I see no strong evidence for his view; he is being selective in how he supports his arguments.

Avi Loeb has gained a lot of attention for proposing a light-sail hypothesis, for suggesting that we should take seriously the possibility that ‘Oumuamua was designed and launched by another civilization? What is the strongest argument for this view? What is the weakness? 

This was discussed in the webinar. Loeb argues that the only plausible explanation for the acceleration of ‘Oumuamua out of the solar system was that it was a light sail because he discarded all other explanations for acceleration other than solar radiation pressure. Solar radiation pressure requires a large area to mass ratio (a density so low it does not occur in nature). Comets outgas unevenly, often in jets of material. This acts like a rocket thruster, imparting an acceleration. This is seen all the time with comets. The amount of acceleration seen for ‘Oumuamua which pointed radially away from the sun was consistent with the amount of acceleration seen with comets, and also decreased by the inverse of the square of the distance, just as you would expect from a process driven by the heat of the sun. He argues against this because we didn’t detect gas or dust. We didn’t have any experiments sensitive enough to detect the gas to rule its presence out. We did have sensitive measurements of tiny dust, usually expected to be pushed off the comet with the gas. There was no tiny dust. However, this could have been eroded during the passage through the interstellar medium gas and dust clouds. I see no strong evidence for his view; he is being selective in how he supports his arguments.

You’ve been quite critical of Avi Loeb’s claims about ‘Oumuamua as alien technology. Why?

It is certainly intriguing to creatively speculate what the physical nature of something is when it is the first of its kind – this is part of exploration and discovery (and our team tossed around some questions of that nature when it was first discovered). However, one has to follow scientific principles. ‘Oumuamua had most of the world’s large telescopes observing it for only about a week in October 2017, and then it got too faint. Our Hubble space telescope program observed it in Nov, Dec and early January to get its position, and the Spitzer space telescope tried to observe it in late Nov, but it did not detect it (it was too faint). This is all the data we will ever have. The data was consistent with it being a comet from another star system. It was observed to be accelerating out of the solar system at a rate that we often see for comets. Comet acceleration is caused by uneven outgassing that acts like rocket thrusters. We didn’t detect either gas or dust near ‘Oumuamua and on this basis, Avi Loeb has declared it is alien technology. None of the attempts to measure gas were sensitive enough to rule out the amount of gas that would be needed for the acceleration. There were sensitive measurements for small dust and none was seen; normally escaping gas pushes small dust off the surface of a comet. We have examples in our solar system, however, of asteroids and some comets which have big “dust” or rocks on the surface and no small dust – so ‘Oumuamua was a little unusual, but not extraordinary in this sense. There are models that show if ‘Oumuamua passed through a dust / gas cloud in space it would remove small dust. Everything we have seen with ‘Oumuamua is entirely consistent with it being a comet. We can’t prove it, because we had too little time and it was too faint to get all the data we would like, but that is a poor reason to declare it is alien technology!

Avi Loeb also presents factually incorrect information in his arguments, and this is harmful to the scientific process. He claims that the reflectivity of ‘Oumuamua is so bright it cannot be natural. First, the reflectivity was not measured. The Spitzer telescope tried, but they didn’t detect anything. Based on the non-detection they made some models of what it *could* be – and suggested 5-20% reflectivity (with ~10% most likely). Loeb maintains that natural bodies are not this reflective. Comets reflect about 5% of the light, Asteroids range between 5-40%, most are between 20-30%, and the dark regions on the moon reflect up to 10% of the light. Metals typically reflect nearly 100%. So Loeb’s statement (from various interviews) that it is so bright that it can’t be natural and is more likely a spaceship is completely wrong.

‘Oumuamua was found at precisely the local standard of the rest of stars in our region of the Galaxy. (The chance of that occurring by accident is less than 500:1.) With an unprecedented post perihelion acceleration, with NO outgassing observed within the most demanding tolerances, and with its unprecedented aspect ratio, why is the tumbling light sail hypothesis not dynamically consistent with what was observed?

Objects moving more quickly would be more difficult to discover. So there may be selection effects at play — we might have found the “easy” one. The acceleration is consistent with solar radiation pressure, but requires very low density that is not consistent with a natural solar system object.

How sooner or later is it likely to visit us? 

‘Oumuamua passed through our solar system a few years ago and will *never* come back.

I’m interested in the acceleration that was noticed late in the passage, specifically in the angle between that acceleration vector and the velocity vector – presumably, the 2-dimensional projection onto our observing plane (i.e. perpendicular to line-of-sight). And did the strength or orientation of that acceleration vary with time?

The acceleration was in a direction away from the Sun. The acceleration decreases inversely as the square of the distance as `Oumuamua moved away from the Sun.

Do we have any, or enough, information to trace its backward path to guesstimate its last port-of-call?

It came from the general direction of the constellation Vega. However, all the stars have their own motions. So we don’t really know where it came from. Vega, too, is moving.

Some unusual aspects of ‘Oumuamua (especially aspect ratio and non-gravitational acceleration) have been given … unusual … explanations which the media latches on to. What are some leading explanations for its unusual properties based on known science?

You have hit on the two most unusual aspects of ‘Oumuamua with a third aspect being the fact that the first interstellar object was not cometary. Let’s look at natural, and the most likely, explanations for each of these aspects.

Asteroidal appearance – the ‘binary’ distinction between asteroids and comets is changing as we discover objects that are intermediate between them and/or difficult to classify. e.g. The asteroid Bennu visited by NASA’s Osiris-Rex spacecraft is ejecting particles from its surface. Does this make it a comet? Some objects on cometary orbits from the Oort cloud show little to no activity despite coming close to the Sun. Does this mean they are asteroids? In our own solar system most objects that have been detected coming from the Oort cloud appear like comets but we have found some ‘dead’ or ‘dying’ comets and at least one that may be an ‘asteroid’. So maybe Oumuamua is just a statistical fluke, an asteroidal object ejected by another solar system. Or maybe it is a dead or dying comet ejected from its home system.

Aspect ratio – there is no known object in our own solar system with an aspect ratio like Oumuamua. However, not many objects in our solar system in Oumuamua’s size range have been carefully studied to determine their aspect ratio. Maybe small objects like Oumuamua are more likely to have odd shapes? A few objects come close to Oumuamua. There is also the possibility that the derived aspect ratio is due to albedo (surface material reflectivity) variations across the surface. Saturn’s moon Iapetus has a surface that changes in reflectivity by more than a factor of 10, so albedo may play a role in explaining Oumuamua’s apparent aspect ratio. Finally, in our solar system, by definition, we have not detected objects that have been ejected in some kind of gravitational interaction. Perhaps the event that ejects interstellar objects affects their shapes.

Acceleration – There are many factors that can cause acceleration: 1-outgassing, 2-solar radiation pressure, 3-impulsive changes in velocity (e.g. from a collision or breakup), 4-measurement error (e.g. if this were a binary object and we had changing view of the center of light in our measurements), 5-Yarkovsky effect (small force on a rotating body due to uneven emission of heat), 6-friction like effects (think of a golf ball in air), and, 7- magnetic fields acting on a magnetically ‘active’ object.

Ruling out six of these explanations : (2) would require a density that is implausible for a natural object (and the reason some claim a spaceship solar sail – but then you could not explain the rotational light curve), (3) is inconsistent with observations which showed smooth acceleration, (4) Our resolution was good enough with HST observations to show that it was not a binary with enough separation to cause the observed changes in its trajectory (5) the observed acceleration was too big, and in the wrong direction, (6) any friction or drag force would slow it down, not accelerate it, and (7) the acceleration was about 100,000 times too large to match this effect.

The only remaining and best explanation is comet outgassing. Critics say “but you didn’t see gas” but our measurements were not sensitive enough to detect this tiny amount of gas, Critics also say “you didn’t see any dust” (which should get lifted off the surface by the escaping gas). The lack of dust is puzzling but our measurements were only sensitive to tiny dust which could have eroded from the surface as Oumuamua passed through molecular clouds.

If ever encountering ‘Oumuamua what would you do next? Any chance we could come into contact with ‘Oumuamua again?

‘Oumuamua will never come back to our solar system. Future interstellar objects will require an intensive and internationally coordinated observing campaign to get as much information as possible about the objects before they leave our solar system. Detecting them early, long before they reach their closest point to the Sun, will provide the most time to follow them as they fall into, and then escape, our solar system.

Will it be possible with any of the newer telescopes being deployed to image this object and glean any further information about it? 

It is now too faint for any telescope – including the Hubble Space Telescope. Hopefully we find another, and get a chance to study the next one in more detail.

What would be required of any spacecraft we might possibly deploy to overtake it and to take some measurements?

It would be a very expensive mission and it would have to launch *now*. We do have the technology but it would be pushing the limits and require spacecraft with a speed faster than any current mission. What would be better would be to be ready for the next one. But this requires a new type of mission style that NASA doesn’t have yet – i.e. build a spacecraft and have it ready and waiting to launch when something is discovered, or waiting in a ‘parking’ orbit around Earth

How have your theories from when ‘Oumuamua was initially observed, until now, changed?

Most astronomers expected interstellar objects to look like comets, so the first surprising aspect was that ‘Oumuamua looked like an asteroid. As the data accumulated it became curiouser and curiouser. So now we have many different ideas about how interstellar interlopers are formed and travel through our galaxy.

What has been remarkable has been how much of the astronomical community has been interested in ‘Oumuamua. Initially it was mostly planetary astronomers but now we have people who study galaxies and the movement of stars, theoreticians and a wide community exploring the science. This is healthy and exciting and can lead to new theories and ideas.

As we have missed the opportunity to get more details on this, how well are we prepared for the next visitor?

Some people have prepared telescope observations in anticipation. It also seems likely that the Hubble Space Telescope will be used more extensively to study the next one.

What is the current United States policy on claiming territories and resources in Space? For example could the US claim the moon or future planets to be discovered? What international treaties regulate our relationships in space? 

U.S. companies can claim ownership of resources extracted from objects off Earth’s surface but can not claim ownership of those objects (https://en.wikipedia.org/wiki/Commercial_Space_Launch_Competitiv eness_Act_of_2015#:~:text=The%20law%20was%20passed%20on,%2C %20any%20celestial%20body.%22%20Some) “The Commercial Space Launch Competitiveness Act, sometimes referred to as the Spurring Private Aerospace Competitiveness and Entrepreneurship (SPACE) Act of 2015,[2] is an update of the United States Government on its commercial space use, legislated in 2015. The update to US law explicitly allows US citizens and industries to “engage in the commercial exploration and exploitation of space resources” including water and minerals. The right does not extend to extraterrestrial life, so anything that is alive may not be exploited commercially.”

If the TMT was built would it have found an object such as Oumuamua farther out than the telescope that first found it ?

The TMT has a narrow field-of-view, so it is not likely to discover interstellar objects. However, TMT would be very powerful for obtaining spectra of interstellar objects, and help us to learn more about their composition. Our present telescopes weren’t quite big enough to learn about its detailed composition – simply that it is reddish.

Is there something in the light curve that says geometry is a more likely explanation than geography?

I will interpret your question as geographical changes in brightness (albedo) vs geometric changes in the observed shape of the object. Actually, if we have a nearly spherical object that is dark on one side and bright on another – the light curve will be very sinusoidal looking. The light curve of `Oumuamua had wide, rounded, bright peaks and very narrow “V-shaped” minima. This is the signature of geometry. A combination of albedo and geometry could explain the light curve variations but then it becomes a lot of speculation; we just don’t have enough data.