Such violent confrontations are likely to be common in young solar systems — including our own. But this is the first time researchers have found evidence for it.

The formation of a planetary system is often a somewhat messy affair. For example, it is not uncommon for objects to collide. When this happens, the celestial bodies can merge, creating even larger planets. The Earth and the moon in our own solar system are also thought to be products of such gigantic collisions. Astronomers therefore suspect that these violent confrontations are common in young solar systems. But actually prove that? That’s another story.

HD 172555

Yet, surprisingly, researchers have now succeeded in doing so. In a new study they watched the white-hot star HD 172555; a young star about 23 million years old and about 95 light-years away from Earth. This star has long attracted the attention of scientists. That’s because the composition of the dust swirling around it is somewhat unusual. For example, the dust contains large amounts of unusual minerals, trapped in grains that are much finer than astronomers would expect. “Due to these two factors, HD 172555 is thought to be a peculiar system,” said study leader Tajana Schneiderman.

History

The researchers wondered what this dust might reveal about the system’s history. Using the Chilean Atacama Large Millimeter Array (ALMA), the team scanned for signs of carbon monoxide. “When studying gas in debris disks, carbon monoxide is usually the brightest and therefore the easiest to find,” explains Schneidermann. So the researchers set out to find it.

Carbon monoxide

And with success. Because after a careful analysis, the researchers managed to detect carbon monoxide around the star. They found that there is quite a bit of carbon monoxide orbiting the star, at an unusually close distance of only 10 AU (astronomical units; 1AU is the distance from Earth to the sun). The researchers considered several scenarios to explain this remarkable abundance of carbon monoxide so close to the star. In the end, there was only one possibility: the gas is the remnant of a gigantic collision. “Of all the scenarios, that’s the only one that can explain all the features,” said Schneiderman.

Crash

According to the researchers, the gas was released during a massive collision between a rocky planet – about the size of Earth – and a smaller impactor. Presumably, the Earth-like planet was hit by this smaller object at a speed of up to 10 kilometers per second. This confrontation took place about 200,000 years ago, so the star has not had enough time to clean up the gas. Given the amount of carbon monoxide the researchers detected, they suspect it must have been an immense blow. So severe, in fact, that one of the planets was – at least partially – dismantled from its atmosphere, which the researchers have now observed in the form of the gas.

Stripped Protoplanet

It means that researchers have now, for the first time, found evidence of violent clashes in young planetary systems. “This is the first time we have detected a stripped protoplantar atmosphere resulting from a massive impact,” Schneiderman concluded. “Many people are interested in studying such collisions because we expect them to be frequent. However, we hadn’t found any evidence for it yet. But now, thanks to the study, we are gaining more insight into the dynamics.”

In that respect, this research is an important stepping stone for other scientists. Because the detection of carbon monoxide in other systems may also provide more insight into their violent past. “We propose a new method to search for giant collisions,” said Schneiderman. “In addition, we are now also gaining a better understanding of how debris behaves in its aftermath.”