Mysterious Asteroid Is Really Two Rocks That Look Like Comets

An asteroid is cruising through our solar system is actually two space rocks, based on images from NASA’s Hubble Space Telescope.

The asteroids are orbiting each other and look a lot like comets, with a halo of material called a coma surrounding them and a tail of dust trailing behind, according to the space agency’s Goddard Space Flight Center. They are unique because of this comet-like appearance and their other characteristics — both pieces are about the same size and are widely separated.

“Understanding its origin and evolution may provide new insights into the early days of the solar system,” NASA said. “Main-belt comets may help to answer how water came to a bone-dry Earth billions of years ago.”

They are called a binary asteroid because of how they float through space in a pair and they are in the asteroid belt between Mars and Jupiter, the ring of material separating the inner and outer sections of the solar system.

Researchers have estimated that the rocks have been married to one another for about 5,000 years. It’s possible that the union started when a quickly rotating object broke into two, and then they were pushed apart from the force of their water transforming directly from ice to gas, a process that skips the liquid phase and is called sublimation.

According to NASA, if water molecules are “ejected” as gas in one direction, it would force the rock the other way.

Hubble spotted the duo last year as they were reaching the point in their orbit that is closest to the sun.

“Hubble’s crisp images revealed that it was actually not one, but two asteroids of almost the same mass and size, orbiting each other at a distance of 60 miles,” NASA said.

It wasn’t the first time scientists had detected the asteroids — they were discovered 10 years before that encounter, although astronomers at the time thought they were one object. It was 2011 when researchers observed “cometary activity” and gave them a classification as an asteroid belt comet. They are now the first binary asteroid to have such a designation.

“We detected strong indications for the sublimation of water ice due to the increased solar heating — similar to how the tail of a comet is created,” team leader Jessica Agarwal, of the Max Planck Institute for Solar System Research, said in the NASA statement.

All these observations were made through the space agency’s Center for Near-Earth Object Studies.

The scientists are investigating how common such an asteroid pairing could be.

“We need more theoretical and observational work, as well as more objects similar to this object, to find an answer to this question,” Agarwal said.

Asteroids can appear is more than just parties of two. Scientists have found triple asteroids, in which there are three of the rocks orbiting together. One recent discovery was an asteroid that shot by Earth earlier this month, at which point astronomers observed it had two moons in orbit around it.