Our solar system contains a myriad of comets and asteroids. Gravitationally bound to the Sun, hundreds of thousands of them have been discovered and catalogued by astronomers over the past few centuries.
For at least several decades, it was expected that some would be sighted inbound from the depths of interstellar space. The first such object, 1I/'Oumuamua (Hawaiian for “scout”), was found as it was leaving our planetary system almost two years ago. Likely asteroidal in composition, its velocity of about 30 miles per second and hyperbolic trajectory were clear indications of an origin from a star system other than our own.
A second interstellar visitor has now been identified speeding toward our solar system. On August 30, Gennady Borisov, an amateur astronomer in Crimea, discovered a faint comet in the constellation of Cassiopeia.
Within two weeks, additional observations confirmed that Comet Borisov was not a member of our Sun’s retinue of comets, estimated to number 1 trillion, but instead an interloper from deep interstellar space. It has been provisionally designated C/2019 Q4 (Borisov).
Like ‘Oumuamua, Comet Borisov has likely spent billions of years wandering through the vastness of space between the stars. Probably ejected from an alien stellar system during the chaos of its early stages of formation, its path and speed are evidence that it originated from somewhere within our Milky Way galaxy. The object’s spectrum, obtained by Spain’s Grand Telescope in the Canary Islands, shows a reddish surface, with a composition similar to our own solar system’s comets.
Although it has been imaged by amateur and professional astronomers, Borisov is far away and faint, and will pass closest to the Earth and the Sun in December, missing both by about 200 million miles. It will take a fairly large amateur’s telescope and clear dark skies to visually spot this “faint fuzzy.” Borisov will pass the Sun traveling at 27 miles per second, and the solar gravity will bend its path by 36 degrees, slinging it back into the black from whence it came.
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While these interstellar visitors come to us from a long time ago, they do not come from a galaxy far, far away, but our own: the Milky Way.
Resource: HVA club
The Heart of the Valley Astronomers is a group of amateur astronomers dedicated to sharing our passion for the sky with the local community. We meet on the second Tuesday of each month (next: October 8 at 7 p.m.) at the Walnut Community Room, 4950 NW Fair Oaks Drive in Corvallis. Meetings are free and open to everyone. For more information, see www.hvaastronomy.com, or visit us on Facebook.
Astronomy Question of the Month
During the 1990’s not one but two Great Comets graced our skies. They were bright enough to be noticed at night even by casual observers in the Northern Hemisphere who were not looking for them. What were their names?
Answer to Last Month’s Question: When is the Earth closest to the Sun?
The Earth is closest to the sun (the point is called “perihelion”) on or about January 3 of each year, primarily depending upon whether or not the previous year is a leap year. Our next perihelion occurs on January 4, 2020. This sounds counterintuitive, but the seasons are much more due to the Earth’s axial tilt, rather than its distance from the sun, which only varies by about 3%. However, if you live in the Southern Hemisphere, perihelion and summer do coincide, since the seasons “down under” are reversed compared to ours.
Richard Watson is on the board of directors of Heart of the Valley Astronomers.