2I/Borisov compared to Mount Etna

Second confirmed interstellar object, a true comet with unusually high carbon monoxide.

Can you see it?

No small telescope will show you this one; it is here to be understood, not spotted.

How big is 2I/Borisov compared to Mount Etna?

2I/Borisov is roughly 1/55 as wide as Mount Etna. That is for a width of about 632 m; its real size is only known to lie between 400 m and 1 km.

Worth knowing about 2I/Borisov

Its size: nucleus 0.4 to 1 km across. Hubble put an upper limit of 0.5 km on the radius from the shape of the coma; the way the comet was pushed off course by its own venting puts a floor of 0.2 km (Jewitt, Hui and Kim 2020).

Why it stands out: Discovered August 2019 by an amateur astronomer in Crimea.
What it is like: It has a glowing coma and tail, and is chemically similar to the solar system’s own comets.

2I/Borisov — No spacecraft has been there, so nobody knows what its surface looks like. What you see is only what has been measured of it: its size, and its shape and colour where anyone knows them.

The numbers

Mean diameter	400 m to 1 km
Discovered	2019

How anyone knows this

Games it appears in

Put them in size order

Show 2I/Borisov in the model ☀️ Everything the Sun holds 🌙 Plan an evening outside