A new formation theory explains the interstellar object Omoamoa

Researchers have calculated that there must be a very large population of interstellar objects like Omoamoa. "The discovery of Omuamoa implies that the population of rocky interstellar objects is much larger than we previously thought," said the lead author of the paper. "On average, each planetary system will emit a total of about one hundred trillion objects like Omoamua. We need to build a very common scenario to create this type of object."

Since its discovery in 2017, an air of mystery has surrounded the first known interstellar object to visit our solar system, an elongated, cigar-shaped body named "Umoamua" ("messenger from the distant past who arrives first" in Hawaiian). How was it created and where did it come from? A new study published April 13 in Nature Astronomy offers the first comprehensive answer to these questions.

First author Yun Zhang at the National Astronomical Observatories of the Chinese Academy of Sciences and co-author Douglas N. si. Lynn at the University of California, Santa Cruz used computer simulations to show how objects like Omoamua could form under the influence of tidal forces like those felt by Earth's oceans. Their theory of formation explains all the unusual features of Omoamoa.

"We have shown that Omoamua-like interstellar objects can form through massive disintegration by tidal forces during close encounters of their parent bodies with their host stars, and then be ejected into interstellar space," said Lin, professor emeritus of astronomy and astrophysics at the University of California, Santa Cruz.

Discovered on October 19, 2017 by the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1) in Hawaii, Umoamua is completely unlike anything else in our solar system, according to Zhang. Its dry surface, unusual elongated shape and incomprehensible movement have even made some scientists wonder if it is an alien probe. "It is really a mysterious object, but some signs, such as its color and the lack of radio emission, indicate that Umuamoa is a natural object," Zhang said.

"Our goal is to come up with a comprehensive scenario, based on well-understood physical principles, to connect all the exciting clues," Lin said.

Astronomers expected the first interstellar object they discovered to be an icy body like a comet. Icy bodies like those inhabiting the Oort Cloud, a reservoir of comets in the outermost region of our Solar System, develop at great distances from their host stars, are rich in volatiles, and are often thrown from their host systems by gravitational interactions. They are also highly visible due to the sublimation of volatile compounds, which forms the comet's tail as the sun heats it. Omoamoa's dry appearance, however, is similar to rocky bodies such as the Solar System's asteroids, and this suggests a different ejection scenario.

Other researchers have calculated that there must be a very large population of interstellar objects like Omoamua. "The discovery of Umuamoa implies that the population of rocky interstellar objects is much larger than we previously thought," Zhang said. "On average, each planetary system will emit a total of about one hundred trillion objects like Omoamua. We need to build a very common scenario to create this type of object."

When a relatively small body passes very close to a larger body, tidal forces of the larger body can tear the smaller one apart, as happened to Comet Shoemaker-Levy 9 when it approached Jupiter. The tearing processes by tidal forces can eject fragments into interstellar space, and this has been suggested as a possible source of Omoamoa. But there is still much uncertainty as to whether such a process could explain Omoamua's incomprehensible properties.

Zhang and Lin performed high-resolution computer simulations to model the structural dynamics of an object moving close to a star. They found that if the object gets close enough to the star, the star can tear it into very elongated fragments that are then ejected into interstellar space.
"The elongated shape is more convincing when you take into account the change in the strength of the materials during the encounter with the star. The ratio between the long axis and the short axis can be even greater than ten to one," said Zhang.

The researchers' thermal modeling showed that the surface of fragments originating from the rupture of the primary body would melt at a very short distance from the star and recondense at greater distances, thereby creating a cohesive membrane that would ensure the structural stability of the elongated shape.
"The dissipation of heat during the tearing process by the star's tidal forces also consumes large amounts of volatiles, and this explains not only the colors of Umoamua's surface and the absence of a visible tail, but also the presumed dryness of the interstellar population," Zhang said. . "However, some volatiles with a high sublimation temperature that are buried below the surface, such as water ice, can remain in condensed form."

Observations of Omoamoa have shown no cometary activity, and only water ice is a possible source of outgassing that would explain its non-gravitational motion. If Umoamua formed and was ejected by Zhang and Lin's scenario, a lot of residual water ice could be activated in its passage through the solar system. The resulting outgassing can cause accelerations that match Umoamua's comet-like orbit.

"The scenario of dispersal by tidal forces not only presents a path for the creation of a single Omoamoa, but also explains the large population of asteroid-like interstellar objects," Zhang said.
The researchers' calculations show the effectiveness of tidal forces in creating this type of object. Possible progenitors, including long-period comets, debris disks, and even super-Earths, could become Umoamua-sized chunks in stellar encounters.
This study supports the hypothesis that there is a large population of Omoamoa-like interstellar objects. Since these objects can pass through the domains of habitable zones, the possibility that they can transfer material that can generate life (called panspermia) cannot be ruled out. "This is a very new field. "These interstellar objects can provide critical clues about how planetary systems form and evolve," Zhang said.

According to Lin, "Umoamua is only the tip of the iceberg. We anticipate that many more interstellar visitors with similar properties will be discovered by future observations using the Vera C Observatory. Robin that will open soon."
US Naval Academy astronomer Matthew Knight, who is co-director of the International Space Science Institute's Omuamoa team and was not involved in the new study, said this study "excellently explains a range of unusual features of Omuamoa using one coherent model."

"When future interstellar objects are discovered in the coming years, it will be very interesting to see if any of them will display properties like Omoamoa's. If so, this could indicate that the processes described in this study are common," Knight said.

For a statement from the University of California at Santa Cruz

for the scientific article

More of the topic in Hayadan:

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• "If life spreads from one solar system to another we can discover the pattern of the spread"