A planetary collision afterglow and transit of the resultant debris cloud

Matthew Kenworthy; Simon Lock; Grant Kennedy; Richelle van Capelleveen; Eric Mamajek; Ludmila Carone; Franz-Josef Hambsch; Joseph Masiero; Amy Mainzer; J Davy Kirkpatrick; Edward Gomez; Zoë Leinhardt; Jingyao Dou; Pavan Tanna; Arttu Sainio; Hamish Barker; Stéphane Charbonnel; Olivier Garde; Pascal Le Dû; Lionel Mulato; Thomas Petit; Michael Rizzo Smith

doi:10.1038/s41586-023-06573-9

A planetary collision afterglow and transit of the resultant debris cloud

Nature. 2023 Oct;622(7982):251-254. doi: 10.1038/s41586-023-06573-9. Epub 2023 Oct 11.

Authors

Matthew Kenworthy^#¹, Simon Lock^#², Grant Kennedy^#^{3

4}, Richelle van Capelleveen^#⁵, Eric Mamajek^#^{6

7}, Ludmila Carone^#⁸, Franz-Josef Hambsch^{9

10

11}, Joseph Masiero¹², Amy Mainzer¹³, J Davy Kirkpatrick¹², Edward Gomez^{14

15}, Zoë Leinhardt¹⁶, Jingyao Dou¹⁶, Pavan Tanna¹⁷, Arttu Sainio¹⁸, Hamish Barker¹⁹, Stéphane Charbonnel²⁰, Olivier Garde²⁰, Pascal Le Dû²⁰, Lionel Mulato²⁰, Thomas Petit²⁰, Michael Rizzo Smith²¹

Affiliations

¹ Leiden Observatory, Leiden University, Leiden, The Netherlands. kenworthy@strw.leidenuniv.nl.
² School of Earth Sciences, University of Bristol, Bristol, UK.
³ Department of Physics, University of Warwick, Coventry, UK.
⁴ Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK.
⁵ Leiden Observatory, Leiden University, Leiden, The Netherlands.
⁶ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
⁷ Department of Physics and Astronomy, University of Rochester, Rochester, NY, USA.
⁸ Space Research Institute, Austrian Academy of Sciences, Graz, Austria.
⁹ Vereniging Voor Sterrenkunde, Brugge, Belgium.
¹⁰ American Association of Variable Star Observers, Cambridge, MA, USA.
¹¹ Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne e.V., Berlin, Germany.
¹² IPAC, California Institute of Technology, Pasadena, CA, USA.
¹³ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
¹⁴ Las Cumbres Observatory, Goleta, CA, USA.
¹⁵ School of Physics and Astronomy, Cardiff University, Cardiff, UK.
¹⁶ School of Physics, HH Wills Physics Laboratory, University of Bristol, Bristol, UK.
¹⁷ Institute of Astronomy, University of Cambridge, Cambridge, UK.
¹⁸ Independent researcher, Järvenpää, Finland.
¹⁹ Variable Stars South, Nelson, New Zealand.
²⁰ Southern Spectroscopic Project Observatory Team, Chabons, France.
²¹ Department of Astronomy, The Ohio State University, Columbus, OH, USA.

^# Contributed equally.

PMID: 37821589
DOI: 10.1038/s41586-023-06573-9

Abstract

Planets 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 disk^1-3. 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 300 million years old), solar-like star ASASSN-21qj: an infrared brightening consistent with a blackbody temperature of 1,000 Kelvin and a luminosity that is 4 percent that of the star lasting for about 1,000 days, partially overlapping in time with a complex and deep, wavelength-dependent optical eclipse that lasted for about 500 days. The optical eclipse started 2.5 years 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.