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An Interstellar Holiday Visitor

This article first appeared in the 12/6/19 edition of the Davis Enterprise.

An Interstellar Holiday Visitor

Hubble's view of interstellar comet 2I/Borisov. Photo credit NASA, ESA, and D. Jewitt (UCLA)



An Interstellar Holiday Visitor

by Vinita Domier (


Comet Borisov, the Christmas 2019 comet, is a very special object in the sky as it is the first known comet to have originated in another star system. Discovered on August 30, 2019 by amateur astronomer Gennadiy Borisov, the interstellar comet is hurtling at a great speed towards our sun in a hyperbolic orbit indicating it is not gravitationally bound to the sun. The comet is formally designated as 2I/Borisov, with the ‘I’ indicating it is an interstellar object that originated beyond our solar system, and it will eventually exit our solar system after its foray past the sun.


The comet will make its closest approach to the sun on December 8, 2019 at a distance of 190 million miles, and its closest approach to earth later in the month on December 28 at a distance of about 176 million miles. Observations made by the Keck Telescope in Hawaii in late November show that the comet has already developed a 100,000 miles long tail. However, because of the relatively small size of the its nucleus, the comet will not be visible in binoculars or small telescopes. 


Comet Borisov is only the second object detected in our solar system that is confirmed to be a visitor from interstellar space. Extrasolar body ʻOumuamua was first observed on October 19, 2017 when it was exiting our solar system after making its nearest approach to the sun 40 days earlier on September 9. Officially designated 1I/2017 U1, this elongated object may be an asteroid, a comet, or a comet remnant. 


Comets are small icy bodies that are composed of frozen gases surrounding rocky dusty cores, and asteroids are small, mostly rocky objects. Comets become visible when their icy surfaces heat up close to a star. The frozen gases in their nuclei vaporize and shroud them in diffuse halos of gases and dust particles that gradually become bigger and more reflective. If enough material outgasses, the comets develop bluish ion tails and whitish dust tails comprised of gaseous charged and dust particles respectively. The charged particles in the solar wind and photons in sunlight push on the diffuse particles in both tails, resulting in straight ion tails and curved dust tails that always point away from the star.


Comets and asteroids are millions of small remnant bodies that exist in a star system after the formation of planets in that system. They are, thus, fossilized remains of the very early evolutionary stages of that star system, and studying their compositions are one of the main ways to determine the existing conditions during planetary formation. Spectroscopic analyzes of interstellar Comet Borisov indicates presence of water, cyanide, and diatomic carbon which are also detected in comets from our solar system.


Join the Davis Astronomy Club on Saturday, December 7 starting at 7pm at Explorit Science Center (3141 5th Street, Davis) at the free public meeting for all ages where we will discuss the interstellar visitors to our solar system indoors followed by a star party outdoors, weather permitting.



Explorit's coming events:


  • Looking for a great gift for family and friends?  Explorit Memberships are usable for an entire year, and card holders also receive discounted or free entry to hundreds of other museums across the country with the ASTC Passport Program.  For more information or to purchase visit or call Explorit at 530-756-0191.  Purchase soon as membership prices increase January 1, 2020.


  • Explorit has a number of events and a workshop during winter break.  Check them out here


  • Explorit’s Nature Bowl team is still enrolling for the school year.  This is an afterschool science team from students grades 3-6.  Call (530) 756-0191 to register.  The $25 fee covers weekly meetings and a t-shirt.



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