Meet the 2 reddest asteroids in the asteroid belt



Artist’s concept of transneptunian objects in the outer solar system. They are generally much redder than the asteroids in the main asteroid belt because they have more complex organic materials covering their surface. Could the 2 reddest asteroids in the main asteroid belt – named 203 Pompeja and 269 Justitia – come from beyond Neptune’s orbit? Image via Lynette Cook / WM Keck Observatory / SALLE.

The 2 reddest asteroids

The main asteroid belt between Mars and Jupiter is estimated to contain more than a million objects over a kilometer in diameter. Plus, there are millions of smaller pieces of rock debris in the belt, all swirling around the sun. And, for the most part, these millions of asteroids are quite similar in composition and appearance. But now, with new observations, astronomers say they’ve found two asteroids in the belt that, frankly, shouldn’t be there. These rocky bodies are the two reddest asteroids ever seen in the asteroid belt.

Peer review Astrophysics Journal published the new work on July 26, 2021. The Japan Aerospace Exploration Agency (JAXA) announced the discovery in a press release on July 27. Veteran science writer George Dvorsky featured it in an article in Gizmodo on July 30.

Rich in organic matter

The intriguing discovery was made by astronomer Sunao Hasegawa and his team at the Japan Aerospace Exploration Agency (JAXA). Asteroids as red as these – 203 Pompeja and 269 Justitia – are generally not seen in the asteroid belt. This is because asteroids closer to the sun have little organic matter on their surface, while asteroids further away are covered with complex organic matter. These are believed to be produced from simpler organic compounds like methane and methanol ice.

Other low albedo asteroids in the belt, called D-type asteroids, have long been considered the redder. But it seems that is no longer the case.

Ring of rock objects around the distant sun.
Artist’s illustration of the main asteroid belt between Mars and Jupiter. Astronomers have discovered two asteroids that are the reddest ever seen in the belt. They probably came from beyond Neptune. Image via NASA / JPL-Caltech / NPR.

Transneptunian objects?

For this reason, researchers believe they could be transneptunian objects (TNO), asteroids that inhabit the distant outer solar system beyond Neptune. Their surface composition is very similar to that of the NWT. According to the paper:

These two asteroids have a redder spectral slope than any other D-type body, which are the reddest objects in the asteroid belt. The spectroscopic results suggest the presence of complex organic materials on the surface layer of these asteroids, implying that they could have formed near Neptune.

But then, how did they end up in the main asteroid belt?

Researchers say these objects likely drifted inward when the solar system was still young. It’s not clear exactly why this happened, but it does indicate that the early solar system was a very chaotic place.

Graphic with many small dots and colored circles on black background with marked distance to sun, and lots of labels.
Transneptunian objects (TNO) orbit the sun well beyond Neptune’s orbit. They include the plutinos and the Kuiper belt. Image via Wikipedia (CC BY-SA 3.0).

The first of many?

Because these objects are so much redder than the typical asteroids in the main belt, they stood out like a sore thumb. It seems likely that they are also more numerous. It could be that many of the main belt asteroids actually originate from further out in the solar system. If so, identifying them could provide valuable clues to the formation of the early solar system.

The main asteroid belt, therefore, can be a mixture of asteroids that formed closer to the sun and others that drifted from elsewhere. The solar system can be a messy place.

Cataloging large asteroid populations

The two unusually red asteroids were noticed following a new study to catalog the composition and distribution of large asteroids in the main belt. The installation of the NASA infrared telescope (IRTF) and the Seoul National University (SAO) astronomical observatory were used in this effort. Scientists from MIT, the University of Hawaii, Seoul National University, Kyoto University and other institutions collaborated on the study.

Diagram of the solar system with the orbits of the planets and ring of thousands of tiny white dots, as well as a few spots of colored dots.
The main asteroid belt lies between the orbits of Mars and Jupiter. Based on the new findings, scientists believe that some transneptunian objects may have migrated inward from the outer solar system. They ended up in the asteroid belt when the solar system was still young. Image via Wikimedia Commons.

203 Pompeja and 269 Justitia are both larger asteroids, so they were included in the observations. The 203 Pompeja has a diameter of 68 miles (110 km) and the 269 Justitia is about half its size.

The surprising discovery of these red asteroids, and possibly more in the future, will provide valuable clues to the formation of the early solar system. It was a chaotic place back then, maybe even more than initially thought.

The future

There is also another bonus. If some TNOs found their way to the asteroid belt, then it would be easier to study them with future probes. NASA’s New Horizons probe is currently exploring the distant Kuiper Belt beyond Neptune. But studying some TNOs up close can now be as easy as traveling to the asteroid belt, which is much closer. A probe could study the two the typical bodies of the asteroid belt as well as the NWT.

Bottom line: Astronomers have discovered two asteroids in the asteroid belt between Mars and Jupiter that are much redder than any of their neighbors. Researchers say they likely migrated inland from the far reaches of the solar system.

Source: Discovery of two TNO-type bodies in the asteroid belt


Via Gizmodo


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