First identified comet to visit our solar system from another star

Comet 2I/Borisov is only the second interstellar object known to have passed through the solar system. These two images, taken by NASA's Hubble Space Telescope, capture the comet appearing near a background galaxy (left) and soon after its closest approach to the Sun (right).

When astronomers see something in the universe that at first glance seems like one-of-a-kind, it's bound to stir up a lot of excitement and attention. Enter comet 2I/Borisov. This mysterious visitor from the depths of space is the first identified comet to arrive here from another star. We don't know from where or when the comet started heading toward our Sun, but it won't hang around for long. The Sun's gravity is slightly deflecting its trajectory, but can't capture it because of the shape of its orbit and high velocity of about 100,000 miles per hour.

Telescopes around the world have been watching the fleeting visitor. NASA's Hubble Space Telescope has provided the sharpest views as the comet skirts by our Sun. Since October the space telescope has been following the comet like a sports photographer following horses speeding around a racetrack. Hubble revealed that the heart of the comet, a loose agglomeration of ices and dust particles, is likely no more than about 3,200 feet across, about the length of nine football fields. Though comet Borisov is the first of its kind, no doubt there are many other comet vagabonds out there, plying the space between stars. Astronomers will eagerly be on the lookout for the next mysterious visitor from far beyond.

These two images, taken by Hubble, capture comet 2I/Borisov streaking though our solar system and on its way back to interstellar space. It is only the second interstellar object known to have passed through the solar system.

Nov. 16, 2019, photo

The comet appears in front of a distant background spiral galaxy (2MASX J10500165-0152029). The galaxy's bright central core is smeared in the image because Hubble was tracking the comet. Comet Borisov was approximately 203 million miles from Earth in this exposure. Its tail of ejected dust streaks off to the upper right. The comet has been artificially colored blue to discriminate fine detail in the halo of dust, or coma, surrounding the central nucleus. It also helps to visually separate the comet from the background galaxy.

Dec. 9, 2019, photo

Hubble revisited the comet shortly after its closest approach to the Sun where it received maximum heating after spending most of its life in frigid interstellar space. The comet also reached a breathtaking maximum speed of about 100,000 miles per hour. Comet Borisov is 185 million miles from Earth in this photo, near the inner edge of the asteroid belt but below it. The nucleus, an agglomeration of ices and dust, is still too small to be resolved. The bright central portion is a coma made up of dust leaving the surface. The comet will make its closest approach to Earth in late December at a distance of 180 million miles.

"Hubble gives us the best upper limit of the size of comet Borisov's nucleus, which is the really important part of the comet," said David Jewitt, a UCLA professor of planetary science and astronomy, whose team has captured the best and sharpest look at this first confirmed interstellar comet. "Surprisingly, our Hubble images show that its nucleus is more than 15 times smaller than earlier investigations suggested it might be. Our Hubble images show that the radius is smaller than half a kilometer. Knowing the size is potentially useful for beginning to estimate how common such objects may be in the solar system and our galaxy. Borisov is the first known interstellar comet, and we would like to learn how many others there are."

Crimean amateur astronomer Gennady Borisov discovered the comet on Aug. 30, 2019, and reported the position measurements to the International Astronomical Union's Minor Planet Center in Cambridge, Massachusetts. The Center for Near-Earth Object Studies at NASA's Jet Propulsion Laboratory in Pasadena, California, working with the Minor Planet Center, computed an orbit for the comet, which shows that it came from elsewhere in our Milky Way galaxy, point of origin unknown.

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Hubble observes first confirmed interstellar comet

Hubble photographed comet 2I/Borisov at a distance of 260 million miles from Earth. This Hubble image, taken on Oct. 12, 2019, is the sharpest view to date of the comet. Hubble reveals a central concentration of dust around the nucleus (which is too small to be seen by Hubble). The comet is falling toward the Sun and will make its closest approach on Dec. 7, 2019, when it will be twice as far from the Sun as Earth. The comet is following a hyperbolic path around the Sun and will exit back into interstellar space.

NASA's Hubble Space Telescope has given astronomers their best look yet at an interstellar visitor -- comet 2I/Borisov -- whose speed and trajectory indicate it has come from beyond our solar system.

This Hubble image, taken on Oct. 12, 2019, is the sharpest view of the comet to date. Hubble reveals a central concentration of dust around the nucleus (which is too small to be seen by Hubble).

Comet 2I/Borisov is only the second such interstellar object known to have passed through the solar system. In 2017, the first identified interstellar visitor, an object officially named 'Oumuamua, swung within 24 million miles of the Sun before racing out of the solar system. "Whereas 'Oumuamua appeared to be a rock, Borisov is really active, more like a normal comet. It's a puzzle why these two are so different," said David Jewitt of the University of California, Los Angeles (UCLA), leader of the Hubble team who observed the comet.

As the second known interstellar object found to enter our solar system, the comet provides invaluable clues to the chemical composition, structure and dust characteristics of planetary building blocks presumably forged in an alien star system a long time ago and far away.

"Though another star system could be quite different from our own, the fact that the comet's properties appear to be very similar to those of the solar system's building blocks is very remarkable," said Amaya Moro-Martin of the Space Telescope Science Institute in Baltimore.

Hubble photographed the comet at a distance of 260 million miles from Earth. The comet is falling past the Sun and will make its closest approach to the Sun on Dec. 7, 2019, when it will be twice as far from the Sun as Earth.

The comet is following a hyperbolic path around the Sun, and currently is blazing along at an extraordinary speed of 110,000 miles per hour. "It's traveling so fast it almost doesn't care that the Sun is there," said Jewitt.

By the middle of 2020 the comet will streak past Jupiter's distance of 500 million miles on its way back into interstellar space where it will drift for untold millions of years before skirting close to another star system.

Crimean amateur astronomer Gennady Borisov discovered the comet on Aug. 30, 2019. After a week of observations by amateur and professional astronomers all over the world, the International Astronomical Union's Minor Planet Center and the Center for Near-Earth Object Studies at NASA's Jet Propulsion Laboratory in Pasadena, California, computed a trajectory for the comet, which confirms that it came from interstellar space.

Until now, all cataloged comets have come from either a ring of icy debris at the periphery of our solar system, called the Kuiper belt, or the hypothetical Oort cloud, a shell of comets about a light-year from the Sun, defining the dynamical edge of our solar system.

Borisov and 'Oumuamua are only the beginning of the discoveries of interstellar objects paying a brief visit to our solar system, say researchers. According to one study there are thousands of such interlopers here at any given time, though most are too faint to be detected with current-day telescopes.

Observations by Hubble and other telescopes have shown that rings and shells of icy debris encircle young stars where planet formation is underway. A gravitational "pinball game" between these comet-like bodies or planets orbiting other stars can hurtle them deep into space where they go adrift among the stars.

Future Hubble observations of 2I/Borisov are planned through January 2020, with more being proposed.

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Naming of new interstellar visitor: 2I/Borisov

On 30 August 2019 the amateur astronomer Gennady Borisov, from MARGO observatory, Crimea, discovered an object with a comet-like appearance. The object has a condensed coma, and more recently a short tail has been observed. Mr. Borisov made this discovery with a 0.65-metre telescope he built himself.

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.

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. In this case, 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. This conclusion is independently supported by the NASA JPL Solar System Dynamics Group. Coming just two years after the discovery of the first interstellar object 1I/'Oumuamua, this 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 (reach its perihelion) on 7 December 2019, when it will be 2 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 kilometres in diameter. One of the largest telescopes in the world, the 10.4m Gran Telescopio Canarias in the Canary Islands, has already obtained a spectrum of 2I/Borisov and has found it to resemble those of typical cometary nuclei.

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