Interstellar comet Borisov has an unexpected amount of carbon monoxide
Second visitor from the stars has three times the CO relative to H2O than any local comets
![comet 2I/Borisov](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2020/04/041720_cc_borisov_feat.jpg?fit=1028%2C579&ssl=1)
A wispy tail of gas and dust trails behind interstellar comet 2I/Borisov, seen about 420 million kilometers from Earth in this Hubble Space Telescope picture from October 12, 2019.
D. Jewitt/UCLA, ESA, NASA