Scientists determine the origin of the extrasolar object ‘Oumuamua


Scientists determine the origin of the extrasolar object 'Oumuamua

This painting by William K. Hartmann, a scientist emeritus at the Planetary Science Institute in Tucson, Arizona, is based on a commission from Michael Belton and depicts a concept of the Oumuamua object as a pancake-shaped disk. Credit: William Hartmann

In 2017, the first interstellar object beyond our solar system was discovered through the Pan-STARRS astronomical observatory in Hawaii. It was named ‘Oumuamua, which means “scout” or “messenger” in Hawaiian. The object was like a comet, but with features that were strange enough to defy classification.

Two Arizona State University astrophysicists, Steven Desch and Alan Jackson of the School of Earth and Space Exploration, set out to explain the strange features of ‘Oumuamua and have determined that it is likely a part of a Pluto-like planet from another solar system. Their findings have recently been published in a couple of articles in the AGU. Journal of Geophysical Research: Planets.

“In many ways, ‘Oumuamua resembled a comet, but it was quite peculiar in many respects that mystery surrounded its nature, and speculation ran rampant about what it was,” said Desch, who is a professor at the School of Exploration of Earth and Space.

From observations of the object, Desch and Jackson determined several characteristics 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 expected, indicating that it had not traveled in interstellar space for more than a billion years or so. 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 “rocket effect” common in comets when sunlight vaporizes the ice they are made of), the push was stronger than could be explained. . Finally, the object lacked a detectable gas leak, which is usually visibly depicted on the tail of a comet. Altogether, the object looked very much like a comet, but unlike any comet that had been observed in the solar system.

Desch and Jackson then hypothesized that the object was made of different ices and calculated how quickly these ices would sublimate (from a solid to a gas) when ‘Oumuamua passed through the sun. From there, they calculated the rocket effect, the mass and shape of the object, and the reflectivity of the ice.






Credit: Arizona State University

“It was an exciting time for us,” Desch said. “We realized that a chunk of ice would be much more reflective than people assumed, which meant it could be smaller. The same rocket effect would give ‘Oumuamua a bigger push, bigger than what comets often experience. “

Desch and Jackson found one particular ice, solid nitrogen, that provided an exact match to all of the object’s features simultaneously. And since solid nitrogen ice can be seen on the surface of Pluto, it is possible that a comet-like object is made of the same material.

“We knew we had the right idea when we completed the calculation of what albedo (how reflective the body is) would make ‘Oumuamua’s motion match the observations,” said Jackson, who is a research scientist and exploration fellow at ASU. . “That value turned out to be the same as what we observed on the surface of Pluto or Triton, bodies covered in nitrogen ice.”

They then calculated the speed at which chunks of solid nitrogen ice would have detached from the surfaces of Pluto and similar bodies early in the history of our solar system. And they calculated the probability that chunks of solid nitrogen ice from other solar systems would reach our own.

“It was probably knocked down by an impact about 500 million years ago and blown out of its original system,” Jackson said. “The fact that it is made of frozen nitrogen also explains the unusual shape of ‘Oumuamua. As the outer layers of nitrogen ice evaporated, the shape of the body would have become progressively more flattened, much like a bar of soap when the outer layers fade through use. “

Could ‘Oumuamua have been alien technology?

Although the comet nature of ‘Oumuamua was quickly recognized, the inability to immediately explain it in detail 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 Earth” by Avi Loeb. from Harvard University.

Scientists determine the origin of the extrasolar object 'Oumuamua

Illustration of a plausible story for ‘Oumuamua: Origin in its main system around 400 million years ago; erosion by cosmic rays during their journey to the solar system; and the 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 in its history, this illustration shows the predicted size of ‘Oumuamua and the relationship between its longest and shortest dimensions. Credit: S. Selkirk / ASU

This has sparked a public debate about the scientific method and the responsibility of scientists not to jump to unwarranted conclusions.

“Everyone is interested in aliens, and it was inevitable that this first object outside the solar system would make people think of aliens,” Desch said. “But in science it’s important not to jump to conclusions. It took two or three years to find a natural explanation, a chunk of nitrogen ice, that matches everything we know about ‘Oumuamua. That’s not that long in science, and too early to say that we had exhausted all natural explanations. “

Although there is no evidence that it is extraterrestrial technology, such as a fragment of a planet similar to Pluto, ‘Oumuamua has given scientists a special opportunity to observe extrasolar systems in a way that they have not been able to 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 the ways in which they are similar or different from our own solar system.

“This research is exciting because we’ve probably solved the mystery of what ‘Oumuamua is and can reasonably identify it as a chunk of an’ exo-Pluto, ‘a Pluto-like planet in another solar system,” Desch said. “Until now, we have had no way of knowing if other solar systems have planets similar to Pluto, but now we have seen a piece of one pass by the 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 survey the entire southern sky on a regular basis, may begin to find even more interstellar objects than they do. and other scientists can use it to further test their ideas.

“It is hoped that in a decade or so we will be able to acquire statistics on what kinds of objects pass through the solar system and whether chunks of nitrogen ice are rare or as common as we have calculated,” Jackson said. “Either way, we should be able to learn a lot about other solar systems and whether they went through the same type of collision history as ours.”


‘Oumuamua probably came from a binary star system


More information:
Alan P. Jackson et al. 1I / ‘Oumuamua as a N 2 ice fragment from an exo-Pluto surface: I. Size and compositional constraints, Journal of Geophysical Research: Planets (2021). DOI: 10.1029 / 2020JE006706

S. J Desch et al. 1I / ‘Oumuamua as a N 2 ice fragment from an exo-pluto II surface: Generation of N 2 ice fragments and the origin of’ Oumuamua, Journal of Geophysical Research: Planets (2021). DOI: 10.1029 / 2020JE006807

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