Astronomers may be breaking out the cigars after the discovery of the first visitor from interstellar space, an asteroid that now bears the name of ‘Oumuamua, which is Hawaiian for “a messenger from afar arriving first.” The International Astronomical Union has given this cigar-shaped asteroid the designation of ‘Oumuamua: 1I/2017 U1.
‘Oumuamua was first spotted by the Pan-STARRS1 telescope in Hawaii on October 19th. When it showed no evidence of being a comet, astronomers assumed that it was an ordinary asteroid from our own solar system. Further analysis of its trajectory showed it to be on a hyperbolic path that will take it back into interstellar space. It hasn’t interacted with the gravitational fields of the planets in any way that’s significant enough to have effectively punted it on a trajectory that will take it out of interstellar space, which means that it probably came from interstellar space.
By extrapolating from trajectory data, astronomers determined that ‘Oumuamua made its closest approach to the Sun on September 9th, and then made its closest pass of Earth on October 14, coming within 24 million kilometers of Earth.
‘Oumuamua is believed to have formed in the outer system of another star and was probably booted out by the gravitational effects of planets that became big enough to play a game of cosmic billiards. It probably floated in interstellar space as an orphan for millions or billions of years before reaching our solar system. If ‘Oumuamua has anything in common with asteroids floating around in our outer solar system, it is likely to consist of more ice than rock.
Astronomers suspect that there may be more interstellar visitors in our solar system. ‘Oumuamua is simply the first to be found, thus the formal designation of 1I/2017 U1, in which the “I” stands for “Interstellar.”
“[I]t is expected that the discovery of 1I/2017 U1 (‘Oumuamua) will soon be joined by discoveries of more of such interlopers entering the inner solar system from interstellar space,” International Astronomical Union representatives said in a statement.
Astronomers are continuing observations with sensitive telescopes like the Hubble Space Telescope and NASA’s Spitzer space telescope as ‘Oumuamua continues its journey out of the solar system.