The collision between two exoplanets of several to tens of Earth masses occurred at a distance of 2-16 AU (astronomical units) from the young solar-like star 2MASS J08152329-3859234, according to a team of astronomers led by Leiden Observatory.

2MASS J08152329-3859234 is a 300-million-year-old star located 567.2 parsecs (1,850 light-years) away in the constellation of Puppis.

In December 2021, the star underwent a sudden optical-dimming event and was assigned the identifier ASASSN-21qj by the All Sky Automated Survey for Supernovae (ASAS-SN).

“To be honest, this observation was a complete surprise to me,” said Leiden Observatory astronomer Matthew Kenworthy.

“When we originally shared the visible light curve of this star with other astronomers, we started watching it with a network of other telescopes.”

“An astronomer on social media pointed out that the star brightened up in the infrared over a thousand days before the optical fading. I knew then this was an unusual event.”

Dr. Kenworthy and colleagues analyzed both optical and infrared data collected by the Las Cumbres Observatory Global Telescope Network (LCOGT) and NASA’s Wide-field Infrared Survey Explorer (WISE) satellite for the years before and after the ASASSN-21qj dimming event.

They concluded the most likely explanation is that two ice giant exoplanets collided, producing the infrared glow.

“Our calculations and computer models indicate the temperature and size of the glowing material, as well as the amount of time the glow has lasted, is consistent with the collision of two ice giant exoplanets,” said University of Bristol astronomer Simon Lock.

“The resultant expanding debris cloud from the impact then traveled in front of the star some three years later, causing the star to dim in brightness at visible wavelengths.”

“Over the next few years, the cloud of dust is expected to start smearing out along the orbit of the collision remnant, and a tell-tale scattering of light from this cloud could be detected with both ground-based telescopes and the NASA/ESA/CSA James Webb Space Telescope.”

“It will be fascinating to observe further developments,” said University of Bristol astronomer Zoe Leinhardt.

“Ultimately, the mass of material around the remnant may condense to form a retinue of moons that will orbit around this new planet.”