Demise of Kreutz Sungrazing Comet C/2024 S1 (ATLAS)

TL;DR

This study observed the Kreutz sungrazing comet C/2024 S1 (ATLAS) before perihelion, revealing ongoing nucleus disintegration, unpredictable activity variations, and coma fading due to refractory grain sublimation, providing insights into its physical decay processes.

Contribution

First detailed pre-perihelion observations of C/2024 S1, demonstrating nucleus disintegration and coma fading, advancing understanding of sungrazing comet physical evolution.

Findings

Nucleus disintegration was ongoing at 0.7 au pre-perihelion.

Coma scattering cross-section peaked near 0.075 au and faded significantly.

Fading attributed to sublimation of refractory grains at ~1000 K.

Abstract

Most Kreutz family sungrazing comets are discovered only days before perihelion, severely limiting observational opportunities to study their physical nature and decay. Kreutz sungrazer C/2024 S1 (ATLAS) was discovered a month before reaching its perihelion distance of 0.008 au, allowing physical observations from both ground- and space-based telescopes. We present observations from 0.9 au to 0.4 au using the Nordic Optical Telescope showing that 1) nucleus disintegration was on-going already at 0.7 au pre-perihelion, 2) the activity varied unpredictably with distance and 3) the nucleus radius was $<$600 m (red geometric albedo 0.04 assumed). We also use coronagraphic observations from the STEREO-A spacecraft to study C/2024 S1 at heliocentric distances $\lesssim$0.1 au. We find that the coma scattering cross-section peaked near 0.075 au and faded progressively, by a factor $\sim$20, towards the last observation at 0.02 au. We interpret the near-perihelion fading as a result of the sublimation of refractory coma grains, beginning at blackbody temperatures $\sim$1000 K, consistent with olivine composition. The comet was not detected after perihelion. We consider processes operating to destroy the nucleus when near perihelion, concluding that rotational instability and sublimation losses work together towards this end, even before entry of the comet into the Roche lobe of the Sun.