What happens to interstellar objects captured by the solar system?

Oumuamua (L) and comet 2I / Borisov (R) are the only two ISOs that we know for sure. Credit: ESO / M. Kornmesser, nagualdesign

Now that we know that interstellar objects (ISOs) visit our solar system, scientists want to better understand them. How could they be captured? If they are captured, what happens to them? How many of them could be in our solar system?

A team of researchers are trying to find answers.

We know for sure two ISOs: “Oumuamua and comet 2I / Borisov. There must have been more, probably many. But we only recently acquired the technology to see them. We will probably discover many more soon, thanks to new facilities such as the Vera C. Rubin Observatory.

In a new document submitted to The Journal of Planetary Sciences, a trio of researchers have looked into the issue of ISOs in our solar system. The title of the article is “On the fate of interstellar objects captured by our solar system”. The first author is Kevin Napier of the Department of Physics at the University of Michigan.

As it stands, there is no reliable way to identify individual captured objects. If astronomers could capture an ISO being captured, that would be great. But the solar system is terribly complex, which makes identifying ISOs difficult. “Given the complex dynamic architecture of the outer solar system, it is not straightforward to determine whether an object is of interstellar origin,” write the authors.

What happens to interstellar objects captured by the solar system?

This study figure shows some simulation results. Each blue line is an individual ISO. The top represents the distance from the osculator pericenter in UA. The bottom shows the tilt in degrees. In their simulations, individual objects only become distinguishable after about 100 million years. When a blue line ends, that ISO has left the solar system. Credit: Napier et al 2021

There were not many opportunities to study “Oumuamua or Borisov. They were identified as ISOs by their hyperbolic speeding. This means that an object has the correct trajectory and a speed high enough to escape. the gravity of a central object In this case, the central object is, of course, the sun.

So could ISOs be captured? Rather likely. “The first step in a rigorous investigation of this question is to calculate a capture cross section for interstellar objects as a function of the hyperbolic excess velocity …”, write the authors.

But that’s only the first step, according to the authors. “Although the cross section is the first step towards calculating the mass of extraterrestrial rocks residing in our solar system, we also need to know the lifespan of the captured objects.” Researchers calculated the lifespans of objects using simulations, tried to understand what was happening to them over time in our solar system, and then made a current inventory of captured ISOs.

The researchers identified three general trends:

  • To survive for more than a few million years, the captured objects must somehow raise their pericenters beyond Jupiter. (In this case, to survive means to stay tied to the solar system.)
  • Objects in very tilted orbits tend to survive longer than those in planar orbits.
  • No object has reached permanent transneptunian status (i.e. q = 30 AU.)
What happens to interstellar objects captured by the solar system?

This study figure shows the surviving fraction of ISO captured over time. The black dots represent the simulation data and the blue line best matches the equation. It takes at least about 1 million years before enough orbits take place for an ISO to be ejected. Credit: Napier et al 2021

In the first case, if an ISO cannot raise its pericenter beyond Jupiter, it will likely be dragged into the gas giant and destroyed. In the second case, objects in very tilted orbits are less likely to encounter a planet because most of the time they are out of the plane of the solar system. Objects in planar orbits are more likely to encounter a planet and be disturbed and sent back into interstellar space. In the third case, it is difficult for an ISO to obtain a permanent trans-Neptunian status because it would require a very unlikely chain of events.

The simulations have certain limitations, which the authors explain. They only considered the four largest planets in the solar system and the sun. Smaller bodies are not massive to have much effect, or the effect they would have is overshadowed by the sun. They also ignore outgassing, radiation pressure from the sun, or drag from planetary atmospheres, which would be extremely rare anyway and shouldn’t affect the results. “Each of these approximations is rather modest, so including them would make relatively little difference in our conclusions,” they explain.

Overall, the simulation shows that over time most of the captured bodies would be ejected from the solar system. It takes time, however. This is because most ISOs would simply go through the system, and those that were captured in an unstable orbit of some type would go through many orbits, 30 in this job, before being ejected. This is because the captured objects generally have semi-large axes of 1000 AU with orbital periods of around 30,000 years. So it takes at least a million years before captured ISOs can be ejected.

The researchers also calculated the captured ISO populations that may currently be in our solar system. They point out that there are two distinct periods during which interesting objects can be captured. The first is in the early days of the solar system, when the sun is still in its birth star cluster and objects from that cluster could be captured. The second is when the sun resides in the field.

In their simulations, the trio of scientists used 276,691 captured synthetic interstellar objects. Of these, only 13 survived 500 million years, and only three objects survived a billion years. But these results come with detailed caveats that are best explained in the document itself.

The authors point out that their simulations could be useful in understanding panspermia. If the chemicals necessary for life, or even for life itself, can somehow travel between solar systems, ISOs probably play a role. Perhaps the most important role.

They also mention the Planet Nine storyline. One of the authors of this article, Konstantin Batygin, along with Michael E. Brown, hypothesized a so-called new planet. The Planet Nine hypothesis states that another planet about five to ten times the mass of Earth is in a wide orbit with a semi-major axis of 400 to 800 AU. Planet nine, if it exists, would take 10,000 to 20,000 years to orbit the sun.

According to this article, when included in the simulations, Planet Nine “… produced rich dynamics that did not appear in the simulations, including only the four known giant planets.”

Cosmic rays erode all interstellar objects except the largest

More information:
Kevin J Napier, Fred C Adams, Konstantin Batygin, On the fate of interstellar objects captured by our solar system. arXiv: 2109.11017v1 [astro-ph.EP], arxiv.org/abs/2109.11017

Quote: What happens to interstellar objects captured by the solar system? (2021, September 28) retrieved October 29, 2021 from https://phys.org/news/2021-09-interstellar-captured-solar.html

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Arline J. Mercier

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