Through the Pan-STARRS telescope in Hawaii, the first interstellar object
from outside our solar system was found in 2017. Hawaiian words for "scout"
or "messenger" gave it the name "'Oumuamua." The object looked like a comet,
but it had some traits that made it hard to put into a category.
The strange traits of 'Oumuamua were studied by Steven Desch and Alan
Jackson of the School of Earth and Space Exploration at Arizona State
University. They came to the conclusion that it is most likely a piece of a
Pluto-like planet from another solar system. You can read about their
results in two new studies in the AGU Journal of Geophysical Research:
Planets.
Some things about 'Oumuamua made it look like a comet, but other things
about it made it so strange that people were guessing what it was, according
to Desch, a professor in the School of Earth and Space Exploration.
By looking at the object, Desch and Jackson found some things about it that
were not like what you would expect from a comet.
When the object entered the solar system, it was moving a little slower
than expected. This means it hadn't been going through interstellar space
for more than four billion years. When it came to size, its pancake form was
also flatter than anything else in the solar system.
They also saw that the object got a strong push away from the sun. This is
a regular "rocket effect" in comets that happens when sunlight melts the
ices that make them up, but it was stronger than they could explain. Last
but not least, the object did not have an escape gas that could be seen,
like a comet's tail. Overall, the thing looked a lot like a comet, but it
was different from any comet that had been seen in the solar system
before.
Then Desch and Jackson thought the object might be made of different kinds
of ice. To test this, they figured out how fast the ices would sublimate
(turn from a solid to a gas) as 'Oumuamua went by the sun. After that, they
figured out the rocket effect, the object's weight and shape, and how well
the ice reflected light.
Demsh said, "That was an exciting time for us." "We found out that a piece
of ice would reflect light much more than people thought, which meant it
could be smaller." Then, the same rocket effect would give 'Oumuamua a
stronger push than comets normally get.
Desch and Jackson discovered that solid nitrogen ice was the only ice that
perfectly matched all of the object's traits at the same time. It's also
possible that a comet-like object would be made of the same stuff because
solid nitrogen ice can be seen on Pluto's surface.
Researchers led by Jackson, an Exploration Fellow at ASU, were sure they
had the right idea when they figured out what albedo (how reflective the
body is) would make 'Oumuamua's motion match what they had seen. "That value
came out as being the same as we observe on the surface of Pluto or Triton,
bodies covered in nitrogen ice."
After that, they figured out how fast chunks of solid nitrogen ice would
have been thrown off the surfaces of Pluto and other things like it in the
early past of our solar system. They also figured out how likely it was that
chunks of frozen nitrogen ice from other solar systems would make it to
ours.
"It was likely knocked off the surface by an impact about half a billion
years ago and thrown out of its parent system," said Jackson. "The strange
shape of 'Oumuamua can also be explained by the fact that it is made of
frozen nitrogen." The body would have become flatter as the upper layers of
nitrogen ice melted, similar to how a bar of soap loses its shape as it is
used.
Could 'Oumuamua have been technology from other worlds?
It was quickly noticed that 'Oumuamua looked like a comet, but no one could
explain it in more detail. This led to rumors that it might be a piece of
alien technology, like in Avi Loeb's new book "Extraterrestrial: The First
Signs of Intelligent Life Beyond Earth."
The public is now talking about the scientific process and how experts
should not jump to conclusions that aren't true.
"Everybody is interested in aliens, and it was inevitable that this first
object outside the solar system would make people think of aliens," Desch
stated. "But in science, it's important not to give up too quickly." It took
two or three years to find a natural answer for 'Oumuamua that fits
everything we know about it. It's a piece of nitrogen ice. That's not very
long in the world of science, and it's way too early to say that we've found
no more natural answers.
As a piece of a planet like Pluto, 'Oumuamua has given scientists a unique
chance to study extrasolar systems in a way they haven't been able to do
before, even though there is no proof that it is alien technology.
Scientists are learning more about other planetary systems and how they are
like ours and how they are different. This is because they are finding and
studying more things like 'Oumuamua.
"This research is exciting in that we've probably resolved the mystery of
what 'Oumuamua is and we can reasonably identify it as a chunk of a
'exo-Pluto,' a Pluto-like planet in another solar system," Desch stated.
"Until now, we've had no way to know if other solar systems have Pluto-like
planets, but now we have seen a chunk of one pass by Earth."
They hope that in the future, bigger telescopes like the Vera Rubin
Observatory/Large Synoptic Survey Telescope in Chile will be able to
regularly look at the whole southern sky and find even more interstellar
objects that they and other scientists can use to test their ideas even
more.
"It's hoped that in a decade or so we can acquire statistics on what sorts
of objects pass through the solar system, and if nitrogen ice chunks are
rare or as common as we've calculated," he said. "Either way, we should be
able to learn a lot about other solar systems, and whether they underwent
the same sorts of collisional histories that ours did."
