A new object from interstellar space has been found within the solar system, only the second such discovery of its kind, according to the International Astronomical Union (IAU).
The object, given the name 2I/Borisov by the IAU, offers a tantalising glimpse beyond the solar system, and raises some puzzling questions, IAU said in a statement.
On August 30 this year, amateur astronomer Gennady Borisov from MARGO observatory, Crimea, discovered the object with a comet-like appearance.
The object has a condensed coma, and more recently a short tail has been observed, IAU said.
Borisov made this discovery with a 0.65-metre telescope he built himself, according to IAU.
After a week of observations by amateur and professional astronomers all over the world, the IAU Minor Planet Center was able to compute a preliminary orbit, which suggested this object was interstellar -- only the second such object known to have passed through the solar system.
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The orbit is now sufficiently well known, and the object is unambiguously interstellar in origin; it has received its final designation as the second interstellar object, 2I, the statement said.
The IAU has decided to follow the tradition of naming cometary objects after their discoverers, so the object has been named 2I/Borisov.
Of the thousands of comets discovered so far, none has an orbit as hyperbolic as that of 2I/Borisov, IAU said.
This conclusion is independently supported by the NASA JPL Solar System Dynamics Group, the statement said.
Coming just two years after the discovery of the first interstellar object 1I/"Oumuamua, the new finding suggests that such objects may be sufficiently numerous to provide a new way of investigating processes in planetary systems beyond our own.
2I/Borisov will make its closest approach to the Sun, its perihelion, on December 7, when it will be two astronomical units (AU) from the Sun and also 2 AU from Earth.
By December and January, it is expected that it will be at its brightest in the southern sky. It will then begin its outbound journey, eventually leaving the solar system forever.
Astronomers are eagerly observing this object, which will be continuously observable for many months, a period longer than that of its predecessor, 1I/"Oumuamua.
Astronomers are optimistic about their chances of studying this rare guest in great detail.
Estimates of the sizes of comets are difficult because the small cometary nucleus is embedded in the coma, but, from the observed brightness, 2I/Borisov appears to be around a few kilometers in diameter.