In 2017, the first interstellar object from beyond our solar system was discovered using the Pan-STARRS astronomical observatory in Hawaii. He was named ‘Oumuamua, which means “scout” or “messenger” in Hawaiian. The object was like a comet, but with features strange enough to defy classification.
Two astrophysicists at Arizona State University, Steven Desch and Alan Jackson of the School of Earth and Space Exploration, set out to explain ‘Oumuamua’s strange features and determined that it is likely a piece of a Pluto-like planet from another solar system. Their findings were recently published in a pair of papers in the AGU Journal of Geophysical Research: Planets .
This painting by William K. Hartmann, who is a Senior Scientist Emeritus at the Planetary Science Institute in Tucson, Arizona, is based on a commission by Michael Belton and shows a concept of the ‘Oumuamua object as a pancake-shaped disk. Credit: William Hartmann
“In many respects, ‘Oumuamua resembled a comet, but it was peculiar enough in several respects that mystery surrounded its nature, and speculation ran wild as to what it was,” said Desch, who is a professor at the Space Exploration School. Earth and Space.
From observations of the object , Desch and Jackson determined several features of the object that differed from what would be expected of a comet.
In terms of speed, the object entered the solar system at a slightly slower speed than would be expected, indicating that it has not traveled in interstellar space for over a billion years or more. In terms of size, its pancake shape was also flatter than any other known object in the solar system.
They also observed that while the object acquired a slight push away from the sun (a common “rocket effect” in comets when sunlight vaporizes the ices they are made of), the push was stronger than could be explained. Finally, the object lacked detectable escaping gas, which is usually represented visibly by a comet’s tail. Altogether, the object was very comet-like, but unlike any comet ever observed in the solar system.
Desch and Jackson then hypothesized that the object was made of different ices, and they calculated how quickly these ices would sublimate (changing from a solid to a gas) as ‘Oumuamua passed by the sun. From there, they calculated the rocket effect, the object’s mass and shape, and the reflectivity of the ice.
“It was an exciting time for us,” said Desch. “We realized that a chunk of ice would be much more reflective than people were assuming, which meant it could be smaller. The same rocket effect would give ‘Oumuamua a bigger boost than comets usually experience.”
Desch and Jackson found one ice in particular – solid nitrogen – that provided an exact match for all of the object’s features simultaneously. And since solid nitrogen ice can be seen on Pluto’s surface, it’s possible that a comet-like object is made of the same material.
“We knew we had the idea right when we completed the calculation of what albedo (how reflective the body is) would make ‘Oumuamua’s movement match the observations,” said Jackson, who is a research scientist and researcher at ASU. “This value turned out to be the same as what we observe on the surface of Pluto or Triton, bodies covered by nitrogen ice.”
They then calculated the rate at which chunks of solid nitrogen ice would have been ripped off the surfaces of Pluto and similar bodies early in our solar system’s history. And they calculated the probability that chunks of solid nitrogen ice from other solar systems would hit ours.
“It was probably ripped from the surface by an impact about half a billion years ago and knocked out of its original system,” Jackson said. “Being made of frozen nitrogen also explains ‘Oumuamua’s unusual shape. As the outer layers of nitrogen ice evaporated, the body’s shape would have become progressively flatter, just as a bar of soap does when the outer layers are removed through use.
Could ‘Oumuamua be alien technology?
While ‘Oumuamua’s comet-like nature was quickly recognized, the inability to immediately explain it in detail has led to speculation that it is a piece of alien technology, as in the recently published book “Extraterrestrial: The First Signs of Intelligent Life”. Beyond the Land” by Avi Loeb of Harvard University.
Illustration of a plausible story for ‘Oumuamua: Origin in its parent system, about 0.4 billion years ago; erosion by cosmic rays during their journey to the solar system; and passage through the solar system, including its closest approach to the Sun on September 9, 2017, and its discovery in October 2017. At each point throughout its history, this illustration shows the predicted size of ‘Oumuamua, and the ratio between its longest and shortest dimensions. Credit: S. Selkirk / ASU
This sparked a public debate about the scientific method and the responsibility of scientists not to jump to conclusions.
“Everyone is interested in aliens, and it was inevitable that this first object outside the solar system would make people think about aliens,” said Desch. “But it’s important in science not to jump to conclusions. It took two or three years to find a natural explanation – a piece of nitrogen ice – that matches everything we know about ‘Oumuamua. That’s not very long in science, and far too soon to say we’d exhausted all natural explanations.
While there’s no evidence that it’s alien technology, such as a fragment from a Pluto-like planet, ‘Oumuamua has given scientists a special opportunity to look into extrasolar systems in a way they couldn’t before. As more objects like ‘Oumuamua are found and studied, scientists can continue to expand our understanding of what other planetary systems are like and how they are similar to or different from our own solar system.
“This research is exciting because we’ve likely solved the mystery of what ‘Oumuamua is and can reasonably identify it as a piece of an ‘exo-Pluto’, a Pluto-like planet in another solar system,” said Desch. “Until now, we had no way of knowing if other solar systems had planets like Pluto, but now we’ve seen a piece of one pass by Earth.”
Desch and Jackson hope that future telescopes, such as those at the Vera Rubin Observatory/Large Synoptic Survey Telescope in Chile, which will be able to take regular surveys of the entire southern sky, may start to find even more interstellar objects than they and other scientists can. use to further test your ideas.
“Hopefully, in a decade or so we’ll be able to acquire statistics on the types of objects passing through the solar system and whether chunks of nitrogen are rare or as common as we’ve estimated,” Jackson said. “Either way, we should learn a lot about other solar systems and whether they’ve gone through the same kind of collision history as ours.”