JWST characterization of fragmenting Oort cloud comet C/2025 K1 ATLAS

Oort cloud comet C/2025 K1 (hereafter K1) was discovered in 2025 May [1] and was observed to fragment on 2025 November 10, when it was ~1 au from the Sun [2,3]. Multiple fragments have been observed since its fragmentation [4, 5], denoted as K1, K1-B, and K1-C, were observed to be located 6 arcsec apart and 13 arcsec apart in mid-November 2025 [6]. A fourth fragment, called D, was observed in late November-early December [7,8]. Additionally, the comet is depleted in carbon-chain molecules such as C2 and CN [9]. Thus, the comet provides an ideal test of volatile heterogeneity within fragments of a recently disrupted comet, which may indicate the extent to which its parent body underwent differentiation through various evolutionary processes in the TND [10,11]. We present JWST observations taken in late 2025 December/early 2026 January when the comet was ~2 au from the Sun, well inside the H2O and CO2 ice lines. We observed the comet during multiple epochs using the NIRCam, MIRI, and NIRspec instruments covering wavelengths 0.7-18 microns. We present imaging and spectroscopy of the comet and its fragments. Our observations indicate multiple epochs of fragmentation that persist as the comet leaves perihelion. We will discuss the physical properties of the fragments, constraints on their volatile contents, and the potential for volatile heterogeneity in the comet.

 

References: 

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