Two Extremely Red Asteroids Discovered Far from Home

None of the asteroids in the primary belt are fairly like the 2 that astronomers have simply found. These extraordinarily red oddballs may imply that planet formation theories are heading in the right direction.

Between Mars and Jupiter lies the primary asteroid belt, which is generally comprised of darkish, carbon-rich or stony, silicate-rich rocks. But whereas these varieties are the commonest, they’re not the one class of asteroids dwelling within the belt. D-type asteroids – carbon-rich rocks that include volatiles corresponding to water and carbon dioxide — are sprinkled all through the primary belt however are extra frequent towards the large planets and may even be discovered caught alongside Jupiter’s orbit as Trojans.

an asteroid like object floats through space with a bright star in the background
An artists impression of an icy trans-Neptunian object that orbits previous Neptune, with the faraway Sun within the background.
NASA / ESA / G. Bacon (STSci)

These D-type asteroids, in contrast to their cousins, are very red, and till now, they have been the reddest objects recognized to exist within the asteroid belt.

Now, a workforce of astronomers led by Sunao Hasegawa (Institute of Space and Astronautical Science, Japan) has discovered two even redder objects in the primary belt, named 203 Pompeja and 269 Justitia. Objects this red will need to have journeyed inward from past Neptune’s orbit, and their presence in the primary belt strengthens the case for large planet migration early within the solar system’s historical past. Hasegawa and colleagues have revealed this examine within the July twentieth Astrophysical Journal Letters.

Outer Solar System Origins

Hasegawa’s workforce discovered Pompeja serendipitously whereas utilizing NASA’s Infrared Telescope Facility and the Seoul National University Astronomical Observatory (Republic of Korea) to survey asteroids bigger than 100 km (60 miles). At 110 km vast, the red Pompeja stood out from the group and prompted the examine of the recognized asteroid Justitia, which is smaller in dimension. The evaluation of those objects led to the sudden discovery of their red colour.

a chart of the solar system shows where the snow line are in relation to types of asteroids.
This diagram exhibits how completely different asteroids and centaurs are organized within the solar system and the place they type in relation to the snow strains.

Until Pompeja and Justitia got here alongside, astronomers thought D-type asteroids have been the reddest objects within the asteroid belt — however not the reddest within the solar system. Outer solar system objects can beat out the D-types, since asteroids’ colours are inclined to redden the farther they orbit from the Sun. The presence of advanced natural compounds – molecules with numerous carbon atoms in them, like benzene – causes this elevated floor redness.

For advanced organics to exist on an asteroid, the physique should type previous sure snow strains, the place the molecules exist as ices somewhat than vapors. The water snow line, the place water freezes, is correct previous the primary belt. The carbon dioxide snow line is farther out, towards Saturn. Simple carbon-containing compounds corresponding to methane type even farther than that. This growing distance to the ice boundaries signifies that probably the most advanced natural supplies freeze solely within the outermost reaches of the solar system.

The two newly found asteroids resemble two redder courses of objects within the outer solar system: Centaurs and trans-Neptunian objects (TNOs), which orbit close to the large planets and out previous Neptune, respectively. For Pompeja and Justitia to be so red, they need to hail from the solar system’s edge. So how did the newly found oddballs find yourself the place astronomers discovered them?

Migration Patterns of Planets

Current planet formation theories state that, after the early phases of planet progress created a compact giant-planet lineup, these outer planets started emigrate and unfold out, interacting with each other and mixing up asteroids alongside the way. This stirring implanted objects close to Jupiter and past into the asteroid belt from time to time.

the spectra of Pompeja and Justitia is shown as clearly more red than other asteroids and as red as TNOs and Centaurs
When an asteroid could be very red, this implies it will get extra reflective to mild as its wavelength will increase. In these plots, it’s clear that Pompeja and Justitia are a lot redder than different sorts of important belt asteroids previous the seen mild vary (Left), and are simply as red as TNOs and Centaurs (Right) regardless of their placement within the asteroid belt.
Hasegawa et al. 2021

The presence of Pompeja and Justitia in the primary asteroid belt implies that distant objects migrated inward, far-off from house. The migration of Jupiter and different big planets will need to have coaxed these outer solar system our bodies into making such a protracted journey, as predicted.

“I interpret this discovery as further, very strong circumstantial evidence in support of these current models,” says Sean Raymond (Astrophysics Laboratory of Bordeaux, France), who was not concerned within the examine.

If Pompeja and Justitia are really red wanderers from outdoors Neptune’s orbit, they affirm scientists’ present understanding of planet formation. By visiting the primary belt, these asteroids supply a possibility for astronomers to review the situations of the outer solar system from afar.


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