A Colossal Impact Destroyed the Atmosphere of an Alien World

Early planetary systems are thought to be full of havoc as infant bodies collide and fuse to form larger planets. In fact, in our own solar system, the Earth and moon are thought to be the product of this type of giant collision. Although these impacts are thought to be common occurrences, astronomers have struggled to observe them around other stars until now.

Astronomers at MIT, the National University of Ireland Galway, Cambridge University, and elsewhere have spotted evidence of a giant impact that occurred in a nearby star system. The star, named HD 172555, is about 23 million years old, and is located just 95 light-years from Earth. 

An atmosphere stripping impact

“This is the first time we’ve detected this phenomenon, of a stripped protoplanetary atmosphere in a giant impact,” said lead author Tajana Schneiderman, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences, in a statement. “Everyone is interested in observing a giant impact because we expect them to be common, but we don’t have evidence in a lot of systems for it. Now we have additional insight into these dynamics.”

The team has determined that the collision likely occurred at least 200,000 years ago, at a speed of about 22,000 miles per hour (10 kilometers per second). The impact was between a roughly Earth-sized terrestrial planet and a smaller impactor.

They also estimated that the high-speed impact likely blew away part of the larger planet’s atmosphere.

To draw these conclusions, the astronomers looked to data taken by ALMA, the Atacama Large Millimeter Array in Chile, which consists of 66 radio telescopes, the spacing of which can be adjusted to increase or decrease the resolution of their images. The team evaluated data from the ALMA public archive, searching for indications of carbon monoxide around nearby stars.