2I/Borisov

=== Observation ===

=== Observation ===

[[File:Video-NASA-InterstellarComet-2IBorisov-HubbleST-20191016.webm|thumb|right|Hubble started observations of 2I/Borisov in October 2019, two months prior to the comet's closest approach to the Sun.]]

[[File:Video-NASA-InterstellarComet-2IBorisov-HubbleST-20191016.webm|thumb|right|Hubble started observations of 2I/Borisov in October 2019, two months prior to the comet's closest approach to the Sun]]

The last observations were in July 2020, seven months after perihelion.<ref name=JPL-Data/> Observation of 2I/Borisov was aided by the fact that the comet was detected while inbound towards the Solar System. ʻOumuamua had been discovered as it was leaving the system, and thus could only be observed for 80&nbsp;days before it was out of range. Because of its closest approach occurring near traditional year-end holidays, and the capability to have extended observations, some astronomers have called 2I/Borisov a "Christmas comet".<ref name="NYT-20191224">{{cite news |last=St.&nbsp;Fleur |first=Nicholas |date=24 December 2019 |title=Watching an interstellar comet and hoping for a bang |quote=Seeing comet Borisov won't be easy for the typical sky gazer, but astronomers still have a lot to learn from this extrasolar tourist. |newspaper=[[The New York Times]] | url=https://www.nytimes.com/2019/12/24/science/interstellar-comet-christmas.html |access-date=28 December 2019}}</ref><ref name=NYT-20191001/> Observations using the [[Hubble Space Telescope]] began on 12&nbsp;October, when the comet moved far enough from the Sun to be safely observed by the telescope.<ref name=Hubble100719/> With its high angular resolution from above the Earth's atmosphere, Hubble could better separate the nucleus from the coma. The motion of jet-like structures in the coma indicate a 4.3 hr rotation period for the nucleus.<ref name="MNRAS-2020">{{cite news |last=Bolin |first=Bryce |date=27 July 2020 |title=Constraints on the spin-pole orientation, jet morphology, and rotation of interstellar comet 2I/Borisov with deep HST imaging|newspaper=[[Monthly Notices of the Royal Astronomical Society]] | url=https://doi.org/10.1093/mnras/staa2192 |access-date=24 April 2025}}</ref>

The last observations were in July 2020, seven months after perihelion.<ref name=JPL-Data/> Observation of 2I/Borisov was aided by the fact that the comet was detected while inbound towards the Solar System. ʻOumuamua had been discovered as it was leaving the system, and thus could only be observed for 80&nbsp;days before it was out of range. Because of its closest approach occurring near traditional year-end holidays, and the capability to have extended observations, some astronomers have called 2I/Borisov a "Christmas comet".<ref name="NYT-20191224">{{cite news |last=St.&nbsp;Fleur |first=Nicholas |date=24 December 2019 |title=Watching an interstellar comet and hoping for a bang |quote=Seeing comet Borisov won't be easy for the typical sky gazer, but astronomers still have a lot to learn from this extrasolar tourist. |newspaper=[[The New York Times]] | url=https://www.nytimes.com/2019/12/24/science/interstellar-comet-christmas.html |access-date=28 December 2019}}</ref><ref name=NYT-20191001/> Observations using the [[Hubble Space Telescope]] began on 12&nbsp;October, when the comet moved far enough from the Sun to be safely observed by the telescope.<ref name=Hubble100719/> With its high angular resolution from above the Earth's atmosphere, Hubble could better separate the nucleus from the coma. The motion of jet-like structures in the coma indicate a 4.3 hr rotation period for the nucleus.<ref name="MNRAS-2020">{{cite news |last=Bolin |first=Bryce |date=27 July 2020 |title=Constraints on the spin-pole orientation, jet morphology, and rotation of interstellar comet 2I/Borisov with deep HST imaging|newspaper=[[Monthly Notices of the Royal Astronomical Society]] | url=https://doi.org/10.1093/mnras/staa2192 |access-date=24 April 2025}}</ref>