Our solar system stole asteroids from interstellar space when it was young, scientists say

Centaurs haven't been studied directly, but some scientists suspect they may look like this asteroid, called Mathilde.
Centaurs haven't been studied directly, but some scientists suspect they may look like this asteroid, called Mathilde. (Image credit: NASA/NEAR Shoemaker)

A cache of interstellar asteroids may have been hiding under scientists' noses for billions of years, researchers say.

That's according to new research focused on a handful of strange space rocks known as Centaurs, which orbit the sun in the neighborhood of Jupiter and Saturn. Astronomers have long been puzzled by Centaurs because their orbits are very unpredictable, with simulations suggesting that they should bang into things or fly out of the solar system. The new research suggests that's because they were stolen by our solar system when it was very young. With so much less expansion under the universe's belt, stars were closer together.

"The close proximity of the stars meant that they felt each others' gravity much more strongly in those early days than they do today," Fathi Namouni, lead author of the study and an astronomer at Observatoire de la Cote d'Azur in France, said in a statement. "This enabled asteroids to be pulled from one star system to another."

Related: Photos: Asteroids in deep space

The new research focused on 21 objects in the outer solar system: mostly Centaurs and a few other strange space rocks. Using a computer program, the scientists virtually cloned these objects tens of thousands of times over to understand likely scenarios for their escapades.

According to the researchers, that analysis suggests that the Centaurs' strange-but-steady orbits are a hint they were born beyond our solar system and trapped here. Scientists have long hypothesized that objects move between solar systems, and saw the first confirmed interlopers in our neighborhood in the past few years, with 'Oumuamua and Comet Borisov.

Both of those objects only passed through our solar system and weren't caught by the sun's gravity. The scientists on the new research think early asteroids may have been more likely to wander into other star systems and get stuck because in the early days of the solar system, with more than 4 billion years less of expansion, things were closer together.

And identifying originally interstellar asteroids in our cosmic neighborhood is important because they are much easier to study than objects in distant solar systems.

"The discovery of a whole population of asteroids of interstellar origin is an important step in understanding the physical and chemical similarities and differences between solar system-born and interstellar asteroids," co-author Maria Helena Morais, an astronomer at Universidade Estadual Paulista in Brazil, said in the same statement. "This population will give us clues about the sun's early birth cluster, how interstellar asteroid capture occurred, and the role that interstellar matter had in chemically enriching the solar system and shaping its evolution."

The research is described in a paper published today (April 23) in the journal Monthly Notices of the Royal Astronomical Society.

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook. 

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Meghan Bartels
Senior Writer

Meghan is a senior writer at Space.com and has more than five years' experience as a science journalist based in New York City. She joined Space.com in July 2018, with previous writing published in outlets including Newsweek and Audubon. Meghan earned an MA in science journalism from New York University and a BA in classics from Georgetown University, and in her free time she enjoys reading and visiting museums. Follow her on Twitter at @meghanbartels.

  • rod
    Modeling Centaur orbits is difficult. From the abstract cited "...Here, we examined 17 multiple-opposition high-inclination Centaurs and the two polar trans-neptunian objects 2008 KV42 and (471325) 2011 KT19. The statistical distributions show that their orbits were nearly polar 4.5 Gyr in the past, and were located in the scattered disc and inner Oort cloud regions. Early polar inclinations cannot be accounted for by current Solar system formation theory as the early planetesimal system must have been nearly flat in order to explain the low-inclination asteroid and Kuiper belts. Furthermore, the early scattered disc and inner Oort cloud regions are believed to have been devoid of Solar system material as the planetesimal disc could not have extended far beyond Neptune’s current orbit in order to halt the planet’s outward migration. The nearly polar orbits of high-inclination Centaurs 4.5 Gyr in the past therefore indicate their probable early capture from the interstellar medium."

    Centaur modeling showed a polar inclination orbit some 4.5 billion years ago, something not explained by the solar protoplanetary disk model, also something not observed in astronomy either for the present location of the Centaurs. Here is another link, New discovery: First asteroid population from outside our solar system Table 1. in the report cited shows what time issues are involved. My note, the report attached in Table 1. shows what is taking place with the 19 Centaurs studied. Short orbital times when extrapolated over long periods, collisions and ejections take place.

    "Table 1. Clone statistics at −4.5Gyr. Orbital inclination is denoted by I, eccentricity by e, semimajor axis by a, and perihelion by q. RGD stands for the relative generalized deviation of the Centaur’s orbit. T0 and Tm are the minimum and median lifetimes. Orbital elements are not given to nominal orbit precision to avoid an overcrowded table."

    My comment, prograde Chiron is shown. Using the orbital elements provided and my trusty spreadsheet, Chiron has a period about 50.49 years. In a time span of 1E+9 years, Chiron could complete 19.8E+6 perihelion passages but will never survive this long as shown in the report and table calculations, most lifetimes < 100E+6 years in the solar system. Centaur present locations and their orbital stability over 4.5 billion years is the problem, this new model offers a possible solution. Other objects in the solar system like the ring age of Saturn, etc. are issues too in reconciling with the radiometric ages of meteorites used to establish the 4.5 billion years time line.