Another Twist in the Debate Over the Origins and Structure of Mysterious Interstellar Object ’Oumuamua

Artists Impression Interstellar Asteroid Oumuamua

This artist’s impression shows the first interstellar object discovered in the Solar System, `Oumuamua. Credit: ESA/Hubble, NASA, ESO, M. Kornmesser

Scientists Determine ‘Oumuamua Isn’t Made From Molecular Hydrogen Ice After All

The debate over the origins and molecular structure of ‘Oumuamua continued with an announcement in The Astrophysical Journal Letters that despite earlier promising claims, the interstellar object is not made of molecular hydrogen ice after all.

The earlier study, published by Seligman & Laughlin in 2020—after observations by the Spitzer Space Telescope set tight limits on the outgassing of carbon-based molecules—suggested that if ‘Oumuamua were a hydrogen iceberg, then the pure hydrogen gas that gives it its rocket-like push would have escaped detection. But scientists at the Center for Astrophysics | Harvard & Smithsonian (CfA) and the Korea Astronomy and Space Science Institute (KASI) were curious whether a hydrogen-based object could actually have made the journey from interstellar space to our solar system.

“The proposal by Seligman and Laughlin appeared promising because it might explain the extreme elongated shape of ‘Oumuamua as well as the non-gravitational acceleration. However, their theory is based on an assumption that H2 ice could form in dense molecular clouds. If this is true, H2 ice objects could be abundant in the universe, and thus would have far-reaching implications. H2 ice was also proposed to explain dark matter, a mystery of modern astrophysics,” said Dr. Thiem Hoang, senior researcher in the theoretical astrophysics group at KASI and lead author on the paper. “We wanted to not only test the assumptions in the theory but also the dark matter proposition.” Dr. Avi Loeb, Frank B. Baird Professor of Science at Harvard and co-author on the paper, added, “We were suspicious that hydrogen icebergs could not survive the journey—which is likely to take hundreds of millions of years—because they evaporate too quickly, and as to whether they could form in molecular clouds.”

Interstellar Asteroid Oumuamua

An illustration of ‘Oumuamua, the first object we’ve ever seen pass through our own solar system that has interstellar origins. Credit: ESO/M. Kornmesser

Traveling at a blistering speed of 196,000mph in 2017, ‘Oumuamua was first classified as an asteroid, and when it later sped up, was found to have properties more akin to comets. But the 0.2km radius interstellar object didn’t fit that category, either, and its point of origin has remained a mystery. Researchers focused on the giant molecular cloud (GMC) W51—one of the closest GMCs to Earth at just 17,000 light years away—as a potential point of origin for ‘Oumuamua, but hypothesize that it simply could not have made the journey intact. “The most likely place to make hydrogen icebergs is in the densest environments of the interstellar medium. These are giant molecular clouds,” said Loeb, confirming that these environments are both too far away and are not conducive to the development of hydrogen icebergs.

An accepted astrophysical origin for solid objects is growth by sticky collisions of dust, but in the case of a hydrogen iceberg, this theory could not hold together. “An accepted route to form a km-sized object is first to form grains of micron-size, then such grains grow by sticky collisions,” said Hoang. “However, in regions with high gas density, collisional heating by gas collisions can rapidly sublimate the hydrogen mantle on the grains, preventing them from growing further.”

Although the study explored destruction of H2 ice by multiple mechanisms including interstellar radiation, cosmic rays, and interstellar gas, sublimation due to heating by starlight has the most destructive effect, and according to Loeb, “Thermal sublimation by collisional heating in GMCs could destroy molecular hydrogen icebergs of ‘Oumuamua-size before their escape into the interstellar medium.” This conclusion precludes the theory that ‘Oumuamua journeyed to our solar system from a GMC, and further precludes the proposition of primordial snowballs as dark matter. Evaporative cooling in these situations does not reduce the role of thermal sublimation by starlight in the destruction of H2 ice objects.

‘Oumuamua first gained notoriety in 2017 when it was discovered screaming through space by observers at Haleakalā Observatory, and has since been the subject of ongoing studies. “This object is mysterious and difficult to understand because it exhibits peculiar properties we have never seen from comets and asteroids in our solar system,” said Hoang.

While the nature of the interstellar traveler is currently an unsolved mystery, Loeb suggests it won’t remain so for much longer, especially if it’s not alone. “If ‘Oumuamua is a member of a population of similar objects on random trajectories, then the Vera C. Rubin Observatory (VRO), which is scheduled to have its first light next year, should detect roughly one ‘Oumuamua-like object per month. We will all wait with anticipation to see what it will find.”

Reference: “Destruction of Molecular Hydrogen Ice and Implications for 1I/2017 U1 (‘Oumuamua)” by Thiem Hoang and Abraham Loeb, 17 August 2020, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/abab0c

25 Comments on "Another Twist in the Debate Over the Origins and Structure of Mysterious Interstellar Object ’Oumuamua"

  1. I read the article twice and still don’t understand it. When writing your next article, presume that your readers don’t have PhDs in Astrophysics. e.g. “The object is not likely made of ice because the ice would have melted in the millions of years it took get to our solar system. The object is more likely made of “sticky space dust” (or whatever they think the thing is made of)

  2. I thought it was a fine article.

    John, your lack of understanding reflects on you, not the author.

  3. Linda Fitzpatrick | August 19, 2020 at 11:45 am | Reply

    I believe that ice could be part of its structural make up since space is sub zero temperatures. Yet it seems more of a rocky structure like from the break up of a previous planet or moon.

  4. How about a plant core splinter from a collision?

  5. In the interior Alaska area I live most of the ice and snow are lost to sublimation and not much melts. Four feet of snow disappear and the ground is not even damp.
    Minimal physics and chemistry, dropped out and went to work back in the booming 1960’s.
    The science taught then is in direct conflict with the H2 ice lasting for hundreds of millions of years sucking in the cosmic microwave background radiation as well as surfing through fields of hydrogen gas without sublimating.

    What ever the object is, if it were volatile it would not have gotten here.
    The ability of light to peel electrons off atoms was one of Einsteins major papers. 100,000 miles per second for 100,000,000 years in an abrasive environment is sharpening a knife until there is no knife left, just a thin wire than folds over. Ice would be eroded one ion at a time until it was no more.

    Waiting for answers along with all of us. Could it somehow have acquired a coating of high melt carbon compound?

  6. Dan Clemmensen | August 19, 2020 at 1:56 pm | Reply

    Stories that mention the “terrific speed” of ‘Oumuamua bother me. As best I can tell, ‘Oumuamua was almost at rest relative to the center of mass of the nearest stars other than our Sun. The Sun is travelling fairly fast (“terrific speed”) relative to those other stars. ‘Oumuamua is now travelling faster than it was because of gravitational interaction with the Sun.

  7. The fields of science are filled with two types: One, the naive in search of the truth, and two the knowing who lies.

  8. So cant be an advanced spacecraft? Im sure its not just curious if anyone has disproven this idea?

  9. Sergey Brin, sick burn bro. totally agree.

  10. Oh Stan! You are twisted my dude. Those games in highlights are pretty hard though.

  11. When in doubt, the answer is aliens… it’s always aliens!!!

  12. Too many misanthropes on the internet. Or does my pointing that out make me one too?

  13. Lol. Physicists everywhere, everyday: “ITS NOT FREAKING ALIENS!
    Me: ” Are you SURE? Damn.”

  14. Like the building of the pyramids we pressume the obvious but impossible…,man made..let’s assume it’s an advanced alien ship..prove its not…find that difficult aswell. We are the only advanced race. Mathematically impossible.we are the least evolved race seems more plausible…no contact till maybe we prove we can do something besides destroy.

  15. DOUGLAS GLADDEN SR | August 20, 2020 at 9:30 am | Reply


  16. Richard Carter | August 27, 2020 at 3:44 pm | Reply

    I solved the mystery of most “Dark Matter” years ago, but no one wants to admit it.. Matter is composed of quantum bound energy and quantum bound space, and whenever matter is converted to quantum free energy, matter is also converted to quantum free space, and this is the basis for the continuing spacial expansion of the universe which started with a colossal matter/ antimatter reaction of the Universal Superparticle. Most missing matter of the universe actually resides in quantum free space. The remaining missing antimatter of the Universe was blown down into a Universal black hole by the Big Bang explosion, the long recognized Dark Spot where no stars can be seen.

  17. Richard Carter | August 27, 2020 at 4:30 pm | Reply


    I solved the mystery of most “Dark Matter” years ago, but no one wants to admit it. Matter is composed of quantum bound energy and quantum bound space, and whenever matter is converted to quantum free energy, matter is also converted to quantum free space, and this is the basis for the ongoing spacial expansion of the universe which started with the colossal matter/ antimatter reaction of the Universal Superparticle known as the Big Bang. Believe it or not, most missing mass of the Universe actually resides in quantum free space. The remaining missing mass of the Universe takes the form of the “missing antimatter” of the Universe which was blown down into a Universal Black Hole by the original Big Bang explosion of the Universal Superparticle, and the long recognized Dark Spot where no stars can be seen is actually where that Universal Black Hole still resides.

    Rick Carter

  18. Richard Carter | August 27, 2020 at 4:46 pm | Reply

    In short, prior to the Big Bang explosion of the Universal Superparticle, there was no quantum free energy or quantum free space in existence. The Universal Superparticle simply resided in higher dimensional hyper space. Everything in our Universe (including quantum free energy and quantum free space) is the result of the colossal matter/antimatter explosion of the Universal Superparticle known as the Big Bang.

    Rick Carter

  19. Richard Carter | August 27, 2020 at 4:55 pm | Reply

    Guess what, I also know about gravity, too. What we call gravity is actually a temporal gradient in space/time, and it is a universal property of all matter in our Universe to seek its lowest temporal state in space/time.

    Rick Carter

  20. Richard Carter | August 27, 2020 at 5:01 pm | Reply

    You can actually accelerate matter (i.e., make it fall) in any direction in space/time by generating a local temporal gradient in space time.

    Rick Carter

  21. Richard Carter | August 27, 2020 at 7:17 pm | Reply

    Do you all understand? There is a large volume of missing antimatter which corresponds to all the matter in our Universe, which in turn resides at the bottom of a Universal Black Hole, which was created at the time of the Big Bang, which was a colossal matter/antimatter reaction. It was blown down into the bottom of the Universal Black Hole by the Big Bang and can still be seen as the well known Dark Spot where no stars can be seen. But most of the remainder of the missing mass of our Universe can actually be found in quantum free space itself, which was and is created at the same time as quantum free energy, and is the reason for the ongoing spatial expansion of our Universe.

    Rick Carter

  22. Regardless of ones scientific opinion is, your delusional if you think this was an alien spacecraft. There already here and have been for a minimum of this past century. Their spacecraft designs do not follow this configuration and furthermore any spacecraft traveling trillions on miles would have a protective field around it. I have been observing their spacecraft for 57 years. Trust me on this. This object Is not Alien made. My daytime 4k HD photo’s will be released, before years end. Completion, is being finalized at a lab. Regardless what you believe, they are here and have been silently observing this planet’s inhabitants and NO their not interested in contacting our species. Would you? Lol.

  23. If I admit my ignorance up front can I ask a dumb question? If it is tumbling end over end, don’t any “jets” continually alternate facing opposite directions? How does that add speed to one direction instead of canceling each direction out? Does my question make sense, I could try to clarify.

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