For the first time, astronomers have observed an active asteroid changing color in real time from red to blue in the near-infrared spectrum as it undergoes self-destruction more than 322 million kilometers (200 million miles) away from Earth.
An out-of-this-world image captured by the Hubble Space Telescope shows the asteroid 6478 Gault with two narrow tails and bright streaking stars in the background in the asteroid belt between Mars and Jupiter. Scientists at the Massachusetts Institute of Technology (MIT) say this type of behavior from an asteroid is typical of comets but incredibly rare for their rocky asteroid cousins.
“That was a very big surprise,” said Michael Marsset, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences, in a statement. “We think we have witnessed the asteroid losing its reddish dust to space, and we are seeing the asteroid’s underlying, fresh blue layers.”
Measuring about 4 kilometers (2.5 miles) wide, Gault is mainly made up of a dry, rocky material called silicate. It is believed that the color shift is due to dust shedding off the planet as the asteroid becomes unstable. Typically, as sunlight heats an asteroid, infrared radiation escapes from its surface with angular momentum, which causes the asteroid to spin faster and faster. As this happens, the object becomes unstable and landslides release dust and rubble into space. Scientists aren’t exactly sure why the asteroid is behaving like a comet. Asteroids are mostly made of metals and rocky materials whereas comets contain dust and ice that typically kick up their well-known tails.
“It’s the first time to my knowledge that we see a rocky body emitting dust, a little bit like a comet,” Marsset added. “It means that probably some mechanism responsible for dust emission is different from comets and different from most other active main-belt asteroids.”
First discovered in 1988, an image of Gault was captured by astronomers in January. A paper describing the space object was published in Astrophysical Journal Letters. Estimates based on the photo suggest that the larger of the two tails measures about 805,000 kilometers (500,000 miles) long, while the shorter tail is about a quarter of its size. Altogether, the two likely contain tens of millions of kilograms of dust. Gault is one of the millions of objects within this asteroid belt, yet only about 20 of them are known to be active.