Astronomers using the NASA/ESA Hubble Space Telescope have captured two new images of 2I/Borisov, the first known interstellar comet to travel through the Solar System.
This Hubble image, taken on November 16, 2019, shows the interstellar comet 2I/Borisov in front of the spiral galaxy 2MASX J10500165-0152029. Image credit: NASA / ESA / D. Jewitt, University of California, Los Angeles.
2I/Borisov was discovered by Ukrainian amateur astronomer Gennady Borisov on August 30, 2019.
Also known as C/2019 Q4, the comet formed in a planetary system beyond ours and was ejected into interstellar space as a consequence of a near-collision with a planet in its original system.
2I/Borisov has taken on a ‘ghostly’ appearance after it began reacting to the Sun’s warmth. It continues to evaporate as it sails close to Earth, releasing gas and fine dust in its tail.
In October 2019, Hubble observed the comet at a distance of approximately 420 million km (261 million miles) from Earth.
The new observations of the comet at a closer distance provide clearer insights into the details and dimensions of the interstellar visitor.
The first image, taken on November 16, 2019, shows 2I/Borisov in front of 2MASX J10500165-0152029, a background spiral galaxy that’s located 390 million light-years away from Earth. The galaxy’s bright central core is smeared in the image because Hubble was tracking the comet.
At the time of observations, 2I/Borisov was 326 million km (202.5 million miles) from Earth. Its tail of ejected dust streaks off to the upper right.
Hubble revisited 2I/Borisov on December 9, 2019, shortly after its closest approach to the Sun where it received maximum heating after spending most of its life in frigid interstellar space. Image credit: NASA / ESA / D. Jewitt, University of California, Los Angeles.
The second image, captured on December 9, 2019, is Hubble’s revisit observation of the comet near its closest approach to the Sun. There it was subjected to a greater degree of heating than it had ever experienced, after spending most of its life in the extreme cold of interstellar space. The comet also reached a breathtaking maximum speed of about 161,000 kmh (100,000 mph).
2I/Borisov is 298 million km (185 million miles) from Earth in the second photo, near the inner edge of the asteroid belt. The comet’s nucleus is still too small to be resolved.
“Hubble gives us the best measure of the size of 2I/Borisov’s nucleus, which is the really important part of the comet,” said University of California, Los Angeles Professor David Jewitt.
“Surprisingly, our Hubble images show that its nucleus is more than 15 times smaller than earlier investigations suggested it might be. The radius is smaller than 500 m (1,640 feet).”
“This is important because knowing the size helps us to determine the total number, and mass, of such objects in the Solar System, and in the Milky Way.”
“2I/Borisov is the first known interstellar comet, and we would like to know how many others there are.”
