We processed images taken with the Hubble Space Telescope ( HST ) to investigate any morphological features in the inner coma suggestive of a peculiar activity on the nucleus of the interstellar comet 2I/Borisov .
The coma shows an evident elongation , in the position angle ( PA ) \sim 0 ^ { \circ } -180 ^ { \circ } direction , which appears related to the presence of a jet originating from a single active source on the nucleus .
A counterpart of this jet directed towards PA \sim 10 ^ { \circ } was detected through analysis of the changes of the inner coma morphology on HST images taken in different dates and processed with different filters .
These findings indicate that the nucleus is probably rotating with a spin axis projected near the plane of the sky and oriented at PA \sim 100 ^ { \circ } -280 ^ { \circ } , and that the active source is lying in a near-equatorial position .
Subsequent observations of HST allowed us to determine the direction of the spin axis at RA = 17h20m \pm 15 ^ { \circ } and Dec = - 35 ^ { \circ } \pm 10 ^ { \circ } .
Photometry of the nucleus on HST images of 12 October 2019 only span \sim 7 hours , insufficient to reveal a rotational period .
The morphology exhibited by the interstellar comet 2I/Borisov is very similar to that of comet C/2014 B1 suggesting that the activation processes are the same observed in the Solar System native comets .