Asteroid gets caught changing colours for the very first time

• Asteroid 6478 Gault, the solar system’s lone asteroid with a comet tail, was just caught changing colors.
• Astronomers at MIT speculate that its because the asteroid shed its outer layer as it spun.
• The two-tailed asteroid now glows blue instead of red in the near-infrared spectrum.

Asteroid’s aren’t supposed to leave two trails of dust behind them — and neither were they supposed to be able to change colours. But asteroid 6478 Gault is a rebel as it is going against the norm.

Gault was discovered last December and labeled an ‘active’ asteroid as it left two comet-like tails behind it. Now, astronomers at the Massachusetts Institute of Technology (MIT) have caught the same asteroid switching colours, from red to blue.

This is the first time that astronomers have seen any asteroid shift colours in real time.

"This was a very big surprise," said Michael Marsset, a part of the MIT team at the Department of Earth, Atmosphere and Planetary Sciences (EAPS) observing the asteroid from NASA’s Infrared Telescope Facility (IRTF) on the near-infrared spectrum.

Fifty shades of 6478 Gault

Astronomers aren’t quite sure what caused the colour to change. Their initial assumption is that Gault upper layer, composed mostly of dust, turned red after years of exposure to the Sun and simply withered away as the asteroid spun.

"About 10% of asteroids spin very fast, meaning with a two- to three-hour rotation period, and it’s most likely due to the Sun spinning them up," said Marsset.

The current blue tinge of the asteroid is the result of the less irradiated layer of the asteroid coming to light.

"Interestingly, you only need a very thin layer to be removed to see a change in the spectrum," stated DeMeo, the study’s co-author. "It could be as thin as a single layer of grains just microns deep," he explained.

Tailing similarities

As the MIT team tries to determine what caused Gault to shift colours, what they do know for sure is that the asteroid is rocky — unlike a comet, which is normally just loose bundles of ice and dust.

"It means that probably some mechanism responsible for dust emission is different from comets, and different from most other active main-belt asteroids," explains Marsset.

Most comets also emerge from much cooler regions of the solar system. It’s because they get hotter as they approach the sun that their surface starts to melt away. The melting ice is what creates the comet’s characteristic tail.

Gault can be found within the asteroid belt, between Mars and Jupiter. It’s a relatively average rock by all other accounts measuring around four kilometers as it orbits the Sun from 344 million kilometers away.

See also:
An asteroid only turns into a meteor if it falls to Earth

What happens when an asteroid actually hits Earth

An asteroid nearly half the size of Mount Everest might be on a collision course for Earth in less than a year