sciencehabit shares this article from Science magazine:
The comet is an alien intruder from another star system. But 2I/Borisov, the second known interstellar visitor after far smaller ‘Oumuamua, discovered in 2017, looks remarkably like a normal comet from our own Solar System: an object a few kilometers across spewing carbon monoxide gas, water vapor, and dust. Researchers who announced their analysis this week say the size of the two objects, along with the rate of their discovery and other factors, suggests that at any given moment more than a dozen interstellar visitors at least as large as ‘Oumuamua are passing through the Solar System.
“Our current telescopes are not powerful enough to detect all of these objects,” says Bryce Bolin, an astronomer at the California Institute of Technology in Pasadena and lead author of the new study. But in the future, he says, large telescopes will be able to catch these visitors more often, perhaps two or three times a year.
of this story at Slashdot.
Source:: Slashdot