Solar systems, including ours, are thought to begin as massive clouds of dust and gas surrounding young stars; over billions of years, planets form from repeated impacts of rocky debris. Asteroids and comets are left-over chunks of debris from that process which didn’t coalesce together. Such debris clouds, or protoplanetary disks, have been found around many young stars. These are solar systems still in their infancy. Now, astronomers have been able to observe the actual collision between two large rocky bodies, most likely asteroids, in a protoplanetary disk surrounding a young, Sun-like star 1,200 light-years away.
The impact was apparently seen by the Spitzer Space Telescope as it observed the star NGC 2547-ID8, which is about 35 million years old, in the constellation Vela. A large surge of “fresh” dust was observed between August 2012 and January 2013, thought to be the result of a collision between two rocky bodies, such as 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,” said lead author and graduate student Huan Meng of the University of Arizona, Tucson.
It is these kinds of smash-ups which can eventually lead to the formation of planets around a star, so being able to see the process in action is exciting for astronomers. Spitzer has seen similar occurrences before, but this is the first time that data was able to be obtained both before and after the collision.
As George Rieke, a University of Arizona co-author of the new study, noted: “We are watching rocky planet formation happen right in front of us. This is a unique chance to study this process in near real-time.”
According to Kate Su of the University of Arizona and a co-author of the study: “We not only witnessed what appears to be the wreckage of a huge smash-up, 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. Spitzer is the best telescope for monitoring stars regularly and precisely for small changes in infrared light over months and even years.”
NGC 2547-ID8 was a subject of study by Spitzer, since variations in the amount of dust around the star had already been observed, a clue that asteroid collisions were happening on a regular basis. NGC 2547-ID8 is surrounded by a thick cloud of dust in the zone where planets are known to form.
Astronomers, therefore, hoped that they could see a larger collision at some point, and it seems that the strategy paid off nicely. After August 2012, Spitzer had to be pointed away from the star, as the Sun was in the way at the time. When observations resumed five months later, the larger-than-normal output of dust was seen by Spitzer’s infrared cameras. Spitzer has caught an asteroid collision in an young alien solar system.
Astronomers will continue to monitor the star; by studying how long the dust levels persist, they can calculate how often such collisions occur. NGC 2547-ID8 has provided a unique opportunity to be able to watch a crucial stage of planetary formation as it happens. And as we now know, planetary formation is common, with over 1,000 confirmed and thousands more candidate exoplanets having been discovered in recent years.
The results of the new study were published today in the journal Science. More information about Spitzer is available here.
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