The distance between stars is vast, but our first known interstellar visitor had plenty of time to get here. ‘Oumuamua left its home solar system millions of years ago, crossing into ours back in 2017. Scientists had a hard time classifying ‘Oumuamua, and there’s still some disagreement. Two astronomers from Arizona State University have published a paper that claims ‘Oumuamua is neither an asteroid nor a comet, but rather a pancake-shaped piece of a Pluto-like world.
Scientists discovered ‘Oumuamua in fall 2017, but it was already speeding out of the solar system at that point. We know ‘Oumuamua came from a different star because of its speed and trajectory, and at first, astronomers assumed it was a comet based on what we think we know about the structure of solar systems. However, ‘Oumuamua didn’t have a tail, known more properly as a coma, which you’d expect for a comet. Just when the prevailing opinion was starting to shift to ‘Oumuamua being an asteroid-like object, an ESA study showed that the object’s trajectory was being nudged by outgassing that was too faint to generate a coma. So, maybe a very old comet?
Alan Jackson and Steven Desch from ASU have devised a model that could change how we think about ‘Oumuamua’s appearance. According to their analysis, ‘Oumuamua is a planetary fragment composed mainly of frozen nitrogen. Yes, an exoplanet floating through our solar system.
The model from Jackson and Desch took into account the object’s size, shape, reflectivity, and motion. In addition to the revised pancake-like shape, they determined frozen nitrogen was the best match for what they were seeing, and we have some idea where you could get a giant chunk of frozen nitrogen thanks to New Horizons. When that probe flew past Pluto, scientists were treated to awe-inspiring views of its largely nitrogen ice surface. Jackson and Desch theorize that an impact on the surface of an icy world knocked ‘Oumuamua free and ejected it from its home solar system.
At the end of all this, we still don’t know for certain what ‘Oumuamua really is. Harvard’s Avi Loeb believes we cannot rule out artificial origins, and he’s got a book detailing his feelings on the issue. I don’t think it would be unreasonable to call this an outside possibility, but it is a possibility. ‘Oumuamua is speeding out of our solar system, never to return. So, this might be a mystery we never get to solve. Our best bet to understand ‘Oumuamua could be to keep an eye out for similar objects that we can study in greater detail before they zoom off into deep space.
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