Earth was likely a rocky wasteland until comets smashed into it.
An international team of astronomers have found evidence of ice and comets orbiting a nearby sun-like star, potentially giving us a glimpse into how our own solar system evolved.
The results, which have been accepted for publication in the Monthly Notices of the Royal Astronomical Society, and were presented on May 18 at the ‘Resolving Planet Formation in the era of ALMA and extreme AO’ conference in Santiago, Chile, are one of the first major steps toward establishing the properties of comet clouds around sun-like stars just after their birth.
Comets, or ‘dirty snowballs’ of ice and rock, are formed early in the development of stellar systems, and within our solar system, they are typically found in its outer regions. However, when our solar system first formed, Earth was likely a rocky wasteland similar to how Mars is today. It is believed that as comets collided with early-Earth, they brought many elements and compounds with them, including water.
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The sun-like star in this study, named HD 181327, has a mass about 30 percent greater than the sun and is located 160 light-years away in the Painter constellation. It is also a fairly young system at just 23 million years old.
"Young systems such as this one are very active, with comets and asteroids slamming into each other and into planets," Sebastián Marino, a doctoral student from Cambridge's Institute of Astronomy and the paper's lead author, said in a press release.
Although the star likely has planets in orbit around it, they are impossible to detect with current telescopes. "Assuming there are planets orbiting this star, they would likely have already formed, but the only way to see them would be through direct imaging, which at the moment can only be used for very large planets like Jupiter," said co-author Luca Matrà, also a doctoral student at Cambridge's Institute of Astronomy, in the release.
Using data from the Atacama Large Millimeter Array (ALMA), the researchers observed a ring of ice and dust around the star caused by the collisions of comets, asteroids and other bodies, and were also able to detect very low levels of carbon monoxide gas around the star — in amounts consistent with comets found in our own solar system.
ALMA image of the ring of comets around HD 181327 (colors have been changed). The white contours represent the size of the Kuiper Belt, which is the region of our solar system beyond the orbit of Neptune, believed to contain many comets and asteroids. Photo credit: Amanda Smith/University of Cambridge
"This is the lowest gas concentration ever detected in a belt of asteroids and comets — we're really pushing ALMA to its limits," said Marino. "The system has a similar ice composition to our own, so it's a good one to study in order to learn what our solar system looked like early in its existence."
Impressively, given how far away the star is, the researchers were able to determine that the amount of gas they detected is equivalent to a 124-mile (200-kilometer) diameter ice ball. "It's amazing that we can do this with exoplanetary systems now," concluded Matrà.
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