Scientists using NASA’s Spitzer Space Telescope have likely observed a collision between two asteroids orbiting a young star. The dust and rocks from this impact could eventually coalesce and form a rocky planet. While scientists have previously seen extremely dusty conditions from similar events, this is the first time that before and after images have been obtained. The results of these observations have been published in Science.
The suspected impact occurred near the star NGC 2547-ID8, which is about 1,200 light-years away in the constellation Vela. The star is fairly young at only 35 million years old, and observations of dust accumulation hint at the possibility that planetary formation is underway.
The potential to learn more about the early stages of planetary formation prompted astronomers to use Spitzer to make regular observations of the star beginning in May 2012. Unfortunately, Earth came into a position behind the Sun in August of that year, preventing such observations from occurring. When they were able to look back at NGC 2547-ID8 in January 2013, images revealed a build-up of dust, hinting at collisions between asteroids.
"We think two big asteroids crashed into each other, creating a huge cloud of grains the size of very fine sand, which are now smashing themselves into smithereens and slowly leaking away from the star," lead author Huan Meng said in a press release.
Rocky planets like Earth are formed when discs of dust swirl around a young star. As bits of dust crash into one another, they stick together and get progressively larger. Just as snowflakes can smash together to form dense, tightly-packed snowballs, planets can be created from dust that's forced together. When larger objects like asteroids or proto-planets collide, a tremendous amount of dust and debris is generated. In fact, most people believe our Moon was formed out of the debris generated from the collision between the proto-Earth and a planetary body roughly the size of Mars.
"We not only witnessed what appears to be the wreckage of a huge smashup, but have been able to track how it is changing—the signal is fading as the cloud destroys itself by grinding its grains down so they escape from the star," co-author Kate Su added. "Spitzer is the best telescope for monitoring stars regularly and precisely for small changes in infrared light over months and even years.”
Unfortunately, the scientists’ observations are limited because of Earth’s vantage point. Even when the Sun isn’t in the way, the orientation of the dusty, elongated cloud encircling the star can interfere with data collection. When looking at the short end of the cloud, the amount of infrared light that can be picked up by Spitzer is obscured and limited. When the longer sides are facing Earth, more infrared light is visible. Astronomers will use data from these infrared fluctuations in order learn more about these types of collisions and about rocky planetary formation as a whole.
"We are watching rocky planet formation happen right in front of us," stated co-author George Rieke. "This is a unique chance to study this process in near real-time."
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