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A planetary collision afterglow and transit of the resultant debris cloud
Nature | Vol 622 | 12 October 2023 | 251ArticleA planetary collision afterglow and transit of the resultant debris cloudMatthew Kenworthy1,21 ✉, Simon Lock2,21, Grant Kennedy3,4,21, Richelle van Capelleveen1,21, Eric Mamajek5,6,21, Ludmila Carone7,21, Franz-Josef Hambsch8 ,9,1 0, Joseph Masiero11, Amy Mainzer12, J. Davy Kirkpatrick11, Edward Gomez1 3 ,1 4, Zoë Leinhardt15, Jingyao Dou15, Pavan Tanna16, Arttu Sainio17, Hamish Barker18, Stéphane Charbonnel19, Olivier Garde19, Pascal Le Dû19, Lionel Mulato19, Thomas Petit19 & Michael Rizzo Smith20Planets grow in rotating disks of dust and gas around forming stars, some of which can subsequently collide in giant impacts after the gas component is removed from the disk1–3. Monitoring programmes with the warm Spitzer mission have recorded substantial and rapid changes in mid-infrared output for several stars, interpreted as variations in the surface area of warm, dusty material ejected by planetary-scale collisions and heated by the central star: for example, NGC 2354–ID8 (refs.4,5), HD 166191 (ref.6) and V488 Persei7. Here we report combined observations of the young (about 300million years old), solar-like star ASASSN-21qj: an infrared brightening consistent with a blackbody temperature of 1,000Kelvin and a luminositythat is 4percent that of the star lasting for about 1,000days, partially overlapping in time with a complex and deep, wavelength-dependent optical eclipse that lasted for about 500days. The optical eclipse started 2.5years after the infrared brightening, implying an orbital period of at least that duration. These observations are consistent with a collision between two exoplanets of several to tens of Earth masses at 2–16 astronomical units from the central star. Such an impact produces a hot, highly extended post-impact remnant with sufficient luminosity to explain the infrared observations. Transit of the impact debris, sheared by orbital motion into a long cloud, causes the subsequent complex eclipse of the host star.