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2I/Borisov is the second interstellar object (ISO) after Oumuamua (Meech et al. 2017), but differs from Oumuamua drastically with its extensive cometary activity. A key ingredient to understand the nature of this comet is its size. However, due to its cometary activity and extended coma in the optical, only rough estimates and upper limits can be made for 2I/Borisov, ranging in a wide spread from 0.7 to 3.8 km (Guzik et al. 2019; Fitzsimmons et al. 2019; Jewitt, & Luu 2019; Bolin et al. 2019). It has been shown that observations at longer wavelengths (i.e. infrared) are less susceptible to the effects of coma, and can provide a better estimate of the size of the comet nucleus (see, e.g., Fernandez et al. 2013; Bauer et al. 2017). Here we present an estimate of the nucleus of 2I/Borisov from infrared observations by FLAMINGOS-2 on-board the Gemini South telescope (under Fast Turnaround program GS-2019B-FT-207), and infer a comet nucleus size of 1.5 km, comparable to but more stringent than the estimate from Keck AO imaging by Bolin et al. (2019).
The composition of comets in the Solar System come in multiple groups thought to encode information about their formation in different regions of the outer protosolar disk. The recent discovery of the second interstellar object, 2I/Borisov, allows fo
We present high resolution imaging observations of interstellar comet 2I/Borisov (formerly C/2019 Q4) obtained using the Hubble Space Telescope. Scattering from the comet is dominated by a coma of large particles (characteristic size 0.1 mm) ejected
2I/Borisov is the first-ever observed interstellar comet (and the second detected interstellar object). It was discovered on 30 August 2019 and has a heliocentric orbital eccentricity of ~ 3.35, corresponding to a hyperbolic orbit that is unbound to
We present Hubble Space Telescope observations of a photometric outburst and splitting event in interstellar comet 2I/Borisov. The outburst, first reported with the comet outbound at 2.8 AU (Drahus et al.~2020), was caused by the expulsion of solid p
The discovery of the first active interstellar object 2I/Borisov provides an unprecedented opportunity to study planetary formation processes in another planetary system. In particular, spectroscopic observations of 2I allow us to constrain the compo