Scientists find two huge red rocks with ‘complex organic matter’ in the asteroid belt that shouldn’t be there

203 Pompeja and 269 Justitia are thought to have moved into the belt from beyond Neptune at the start of the solar system

Adam Smith
Friday 30 July 2021 12:58 BST
(Getty Images/iStockphoto)

Scientists have found two huge, red objects in the asteroid belt that they believe are not supposed to be there – both of which have “complex organic matter” on their surfaces.

These two asteroids, called 203 Pompeja and 269 Justitia, were discovered by Jaxa, the Japan Aerospace Exploration Agency. Pompeja is approximately 110 kilometres wide, while the smaller Justitia has a diameter of only 55 kilometres.

Found in the cluster of rocks between Mars and Jupiter, these two objects are distinctly different from their neighbours. Both Pompeja and Justitia reflect more red light than other surrounding asteroids due to the increased presence of complex organic material on their surface – such as carbon or methane.

Asteroids like this are not usually found within the belt, which is generally made up of bluer debris, but they are common among trans-Neptunian objects and Centaurs (small bodies that orbit between Jupiter and Neptune) – which is where astronomers believe that they originated.

Jaxa believes that the movements of these asteroids came from the anarchy of the early solar system, where the movement of massive plants like Jupiter caused the gravitational fields to become more chaotic and sent these two bodies into the belt.

This occurrence must have happened during the early stages of our cosmic environment, because they both have stable circular orbits.

“In order to have these organics, you need to initially have a lot of ice at the surface,” Michaël Marsset, who worked on the recently published paper about these asteroids, told the New York Times. “So they must have formed in a very cold environment. Then the solar irradiation of the ice creates those complex organics.”

The existence of these asteroids could prove important to the Nice Model, which argues that Saturn, Uranus, and Neptune have been moving outwards from the solar system over a hundred-million-year period, while Jupiter has been moving slightly inwards.

The asteroid belt is estimated to contain between 1.1 and 1.9 million asteroids larger than one kilometre in diameter, and millions of asteroids even smaller. However, those larger than 100 kilometres in diameter are generally thought to have avoided the destructive physics of the early solar system, and as such can provide key insight into that age.

Not every scientist subscribes to this idea; Hal Levison, a planetary scientist at the Southwest Research Institute in Colorado who is the head of a Nasa mission (Lucy) to study Jupiter’s asteroids, told the NYT that the asteroids should have become less red as they approached the sun. As such, it is not entirely certain why the asteroids are so red but unlocking that secret may be related to understanding how they became a part of the belt.

To solve that mystery, it would likely be necessary to send a spacecraft to them for closer study – something that Jaxa believes is “worth considering as a candidate destination” in the future.

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