Collisions between large bodies are an important part of planet formation, but they are usually rare and hard to observe. Astronomers have now directly imaged the dusty aftermath of two powerful collisions within about twenty years around the nearby young star Fomalhaut. These are the first directly imaged collisions between large objects outside the solar system.
Hubble images first showed a bright point near a dusty belt in 2004 and 2006; it was reported as a possible planet in 2008 and called Fomalhaut b. Later images showed motion that curved away from the star, behaviour consistent with small dust particles pushed by starlight rather than a true planet. A new 2023 HST image revealed another bright spot, Fomalhaut cs2, and the team analysed the 2023 and a poorer 2024 image.
Based on brightness, the colliding bodies were at least 30 kilometers (18 miles) across, at least twice the size of the object that struck Earth 66 million years ago. The team estimates about 300 million similar objects in the Fomalhaut belt and notes earlier detections of carbon monoxide that suggest the planetesimals are volatile-rich like icy comets. Researchers will track the clouds with the James Webb Space Telescope’s NIRCam and with HST over the coming three years, and they warn that dust clouds can mimic planets in exoplanet searches.
Difficult words
- collision — when two objects hit each othercollisions
- aftermath — what happens after a big event
- belt — a ring of material around a star
- planetesimal — a small solid body that forms planetsplanetesimals
- volatile-rich — containing many gases and ices
- mimic — to look like something else
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Discussion questions
- How could dust clouds make astronomers mistake them for planets in exoplanet searches?
- Why do you think scientists will track the clouds with Webb and Hubble over the next three years?
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