Interstellar Object 2I/Borisov Double
ATel #13611; David Jewitt (UCLA), Max Mutchler (STSCI), Yoonyoung Kim (MPI), Hal Weaver (JHU-APL), Man-To Hui (U. Hawaii)
on 2 Apr 2020; 16:05 UT
Distributed as an Instant Email Notice Comets
Credential Certification: David Jewitt (djewitt@gmail.com)
Continuing Hubble Space Telescope images of interstellar object 2I/Borisov (GO Program 16087) show a distinct change in appearance. Images from UT 2020 March 23 show a single inner brightness core, like that observed in all previous HST images of 2I/Borisov (Jewitt et al. (2020) ApJLetters, 888:L23(8pp)). In contrast, images from UT 2020 March 30 show a clearly non-stellar core, consistent with two unresolved components separated by 0.1 arcsecond (180 km at the distance of the comet) and aligned with the main axis of the larger dust coma. The double appearance, indicating the ejection of a nucleus fragment, is confirmed in HST data from UT 2020 March 28 (GO 16040). If the ejection occurred on March 23, then the estimated sky-plane speed is 0.3 m/s. This is typical of the separation speeds observed in split (solar system) comets and comparable to the gravitational escape speed of the sub-kilometer radius nucleus of 2I/Borisov. Additional HST observations are planned to monitor the development of this event. http://www2.ess.ucla.edu/~jewitt/HST_Borisov_March_23.28.30.jpg
