"Colliding Planets" by NuclearVacuum / CC BY-SA 3.0

In a Distant Galaxy, Colliding Exoplanets Are Upending What We Knew About Solar System Formation

Oct 25, 2019

By Brandon Specktor

Solar systems form in a school of hard knocks.

Take ours, for example: Earth had barely cooled 4.5 billion years ago when it got slapped in the face by a renegade Mars-size rock, reducing both bodies to giant balls of lava. Scientists believe this cosmic collision spewed so much debris into the air that it eventually coalesced into Earth’s moon — a beautiful partnership born from chaos.

Collisions like these are common in young solar systems, but become much rarer as time rolls on: Large planets fall into line and host stars either swallow or blow away smaller chunks of debris. Now, NASA astronomers think they may be witnessing a violent exception to that pattern in a solar system far, far away.

In the star system BD +20 307 — a binary system roughly 300 light-years from Earth — it appears that two Earth-like exoplanets have crashed into each other, erupting in a hot cloud of dust and debris that’s visible to infrared telescopes. At more than 1 billion years old, the solar system being observed is fully mature, but according to conventional wisdom, that means it should not host planetary smashups like this one. This never-before-seen type of collision suggests that solar systems, like people, can still struggle to pull themselves together late in life.

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