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Collision robbed an exoplanet of atmosphere – ring of carbon monoxide gas around a nearby star indicates a catastrophic planetary collision

Planetary catastrophe: A severe impact could have stolen large portions of its atmosphere from a nearby exoplanet. This is indicated by an unusual cloud of dust and carbon monoxide around a star about 95 light-years away, astronomers reported in the specialized “Nature” magazine. The position and composition of the gas ring indicates that this gas originates from the atmosphere of a planet and was torn apart in space in a high-speed collision.

Violent collisions are common in young planetary systems – and this was also the case in the early solar system. Planetary researchers doubt that MercuryVenus Jupiter And Uranus Once witnessed such clashes. On Earth, the collision with the protoplanet Theia about 4.5 billion years ago gave rise to parts of our planet and collide evaporated Earth’s moon came out from under the rubble.

Dust disk with unusual features

Astronomers working with Tajana Schneiderman of the Massachusetts Institute of Technology (MIT) could discover another consequence of planetary collisions. The spectacle of the event is the young star HD 172555, which is about 95 light-years away from us. A few years ago, astronomers discovered a disk of dust with unusual features around it. Among other things, spectroscopic measurements indicate a particularly fine grain size of glassy solid silicate and silicon monoxide.

Both are somewhat unusual for the disk of dust around young stars: “Because of these two features, HD 172555 was a mystery,” says Schneiderman. To get to the bottom of the matter, she and her team have now targeted the star and its dust disk using the Large Millimeter/ Submillimeter Array (ALMA) radio telescopes in Chile. Since dust and gases generate spectral signals especially in the radio band, this provides more detailed information about the structure and composition of the dust disk.

carbon monoxide ring

The analyzes revealed something surprising: in the dust ring there is a region where a high density of carbon monoxide (CO) gas can be detected. This gas ring extends from 3.3 to 7.5 AU from the star – surprisingly close. Because at this distance, the star’s radiation should cause carbon monoxide to decay very quickly, astronomers explain. It is normal for there to be very little carbon dioxide inside the dust disk or planetary system

“The presence of carbon monoxide so close to the star requires an explanation,” Schneiderman says. One possibility is that carbon dioxide is constantly replenished, for example by impacts of asteroids or comets falling from the outer system. However, both scenarios do not match the features of the dust and star disk, the team found with the help of model calculations.

Collision as a source of carbon monoxide?

But there is still another possibility: Carbon monoxide could have been released when two protoplanets collided in orbit around the star. “Out of all the scenarios, this is the only one that can explain all the characteristics of the monitoring data,” Schneiderman says. “The time horizon fits, the age of the star as well as the morphological and chemical parameters of the system.”

In this scenario, a planet roughly the size of Earth with a large gas envelope would have to collide with a smaller protoplanet at high speed. This collision released so much energy that most of the gaseous envelope on the larger planet was torn apart and thrown into space. The astronomers wrote: “The mass of carbon dioxide detected in the system corresponds to about ten times the mass of the Earth’s atmosphere – this corresponds to the collision-related release from the atmospheres of the planets.”

Young planet has lost its atmosphere

The unusual dust disk and ring of carbon monoxide gas around HD 172555 are the legacy of a planetary catastrophe, in which a young, gas-rich exoplanet lost its heliosphere. According to the research team’s calculations, this collision could have occurred about 200,000 years ago – which is why carbon dioxide has not yet been completely decomposed by stellar radiation.

“This is the first time we’ve detected a planetary atmosphere ruptured in a collision,” Schneiderman says. The team believes that the discovery of this phenomenon indicates that large-scale collisions and impacts could also deprive planets of their atmospheres in many other cases – and that at least some of these events are identifiable by their gaseous effects.

“This offers us a new approach to looking for major impacts and collisions in planetary systems,” Schneiderman says. At the same time, observations on HD 172555 provide valuable information about the nature of the gas and debris of such a planetary catastrophe and how it developed. (Nature, 2021; doi: 10.1038/s41586-021-03872-x)

Coyle: MIT