Two strange red rocks live in the asteroid belt, and they don’t belong to it



In the asteroid belt between Mars and Jupiter, it appears that two interplanetary visitors have made their home there.

203 Pompeja and 269 Justitia are much redder than any other object we’ve seen lying around in the densely populated area. In fact, according to new research, their profiles are much closer to those of objects much more distant: the Kuiper Belt, beyond Neptune, where Pluto has taken up residence.

If the discovery can be validated, it suggests that these two asteroids formed much further from the Sun before migrating to the asteroid belt, possibly very early in the history of the solar system.

In turn, this could be evidence that the early stages of the planets in the solar system (when they were only planetary “seeds” known as planetesimals) first emerged far from the Sun before heading towards inside, which is consistent with some models of the formation of the planetary system.

“The spectroscopic results suggest the presence of complex organic materials on the surface layer of these asteroids,” the researchers wrote in their paper, “implying that they may have formed near Neptune and be transplanted to the region of the main belt during a phase of planetary migrations. “

The solar system may look beautiful and tidy, but it was literally a hot mess in its early years. Chunks of dust and rock in the remnants of the molecular cloud that gave birth to the Sun moaned together to form planetesimals, asteroids, and comets – all the big, good things we have flying today.

This period, astronomers believe, was an eventful one. Planets began to form in different places and migrated to their current positions, with larger planets forming further away and moving inward. The movements of the planets would have created gravitational chaos, in particular the planetary giant of the solar system, Jupiter.

Eventually, things calmed down, giving the configuration we have today: a nice selection of rocky planets in the inner solar system, the asteroid belt beyond Mars, then the gas and ice giants, followed by the Kuiper Belt.

The asteroid belt is located between 2.1 and 3.3 astronomical units from the Sun. It’s a very populous place, relatively speaking: it contains up to about 1.9 million asteroids over a kilometer in diameter (0.62 thousand) and several million smaller ones.

203 Pompeja was discovered in 1869 and 269 Justitia in 1887, so we have known and observed them for some time. They are also both quite important objects; in fact, 203 Pompeja is designated as a minor planet. Both, however, were considered fairly typical D-type asteroids that contain a lot of silica and carbon and make up most of the bodies in the asteroid belt.

A team of researchers led by astronomer Sunao Hasegawa of the Japanese Space Agency’s Institute for Space and Astronautical Sciences (ISAS JAXA) found the opposite when they began to take a closer look.

Initially, they were trying to learn more about planetesimals; objects in the asteroid belt over 100 kilometers in diameter are considered planetesimals that never came all the way.

When they arrived at 203 Pompeja, which is approximately 116 kilometers in diameter, they found it to be much redder than expected. So, they went to see if anything else in the asteroid belt had a similar color profile and found 269 Justitia.


The spectrum that these two objects presented was very far from any other asteroid in the belt for which we have spectral data. But that didn’t mean there was nothing like it in the solar system.

In fact, they were right in the middle of the road for Kuiper Belt objects (also known as Transneptunian objects, or TNOs), like Arrokoth (pictured at the top of this article), the most common object. remote from the solar system visited to date.

This reddish hue is attributed to the presence of tholins, organic compounds that form when ultraviolet radiation cooks simple carbon-containing compounds, such as methane, ethane, and carbon dioxide. They are found in great abundance on the outer icy bodies of the solar system, but not so much in the asteroid belt.

This led the researchers to conclude that 203 Pompeja and 269 Justitia did indeed form in the outer solar system and traveled to their current position.

They must have done this some time ago because their orbits are stable and circular and their positions are anchored in the asteroid belt.

The researchers concluded that the established presence of 203 Pompeja and 269 Justitia suggests that they moved during the period of planetary migration before the solar system stabilized in its current configuration.

If the two objects formed in the far reaches of the solar system, that means two important things. First, it validates the model of planetary migration, which means that we have more information about the formation of the solar system than before, which helps us understand how we got here.

Second, it means that there are external solar system bodies within much more accessible range of our probes.

“By exploring such objects, it is quite possible that information regarding the outer regions of the solar system beyond the snow line composed of organic compounds during the formation of the solar system can be obtained without having to travel to on the outskirts of the solar system, ”ISAS JAXA said in an article posted on its website.

“It is worth considering as targets for candidate destination missions in the future. “

The research was published in Letters from the astrophysical journal.


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