Scientists believe they have spotted a rocky planet in the making around a young, sun-like star 1,200 light years away in the constellation Vela.
The violent process, marked by collisions of asteroids and other proto-planetary bodies, was detected by a dramatic change in telltale infrared radiation emissions coming from warm dust circling the 35 million-year-old star.
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Astronomers monitored the star, known as NGC 2547-ID8, with NASA's Spitzer infrared space telescope between May 25, 2012, and Aug. 23, 2015, taking a 157-day break when the star was behind the sun and not visible. During the gap, the star's disk of orbiting dust dramatically brightened, then slowly dimmed over the course of a nearly a year.
"The observed sudden brightening and the consequent decay would be very hard to explain, if at all possible, without the occurrence of a new impact," Huan Meng, a planetary sciences graduate student at the University of Arizona, wrote in an email to Discovery News.
Meng and colleagues turned to computer simulations to better understand what they were seeing. The best explanation is that in late 2012, a major collision took place among the star's orbiting proto-planetary bodies, producing vapor that condensed into a thick cloud of silicate spheres. Later collisions pulverized the small spheres into dust.
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The crash is believed to be similar to the one that occurred early in Earth's history which led to the formation of the moon.
While scientists have discovered brightening in stars' debris disks before, they did not have real-time observations to rule out other phenomena besides smashing proto-planets as the cause. A super-volcanic explosion on a young terrestrial planet, for example, or the breakup of a comet could brighten up a debris disk, but these events wouldn't cause variations over time like what was observed around ID8.
"This is the first detection of a planetary impact outside our solar system," Meng said.
Scientists estimate it takes 10 to 15 giant impacts of planetary embryos to form a rocky Earth-sized world.
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"We now directly witness a large impact around ID8, suggesting a reservoir of large asteroids and planetary embryos, but we still do not know whether ID8 has giant or ice-giant planets, or outer planetesimals analogous to Kuiper belt objects," Kate Su, associate astronomer at University of Arizona's Steward Observatory, wrote in an email to Discovery News.
"This study pioneers a new way to gain direct observational evidence for terrestrial planet formation," added astronomer Peter Plavchan, with Missouri State University "Because the debris disk from the star ID8 changes in brightness on particular timescales or periods, we can use Newton's version of Kepler's Third Law to infer the formation of planets at specific distances from the host star."
The research, which appears in this week's Science, also may shed light on the construction phase of Earth and the rest of the terrestrial planets in our solar system.