The biggest comet ever discovered, the lecturing astronomer told us, is speeding toward the sun at 22,000 miles per hour. I sat up straighter, as I’d guess did most of us in this Zoom class. We were here to learn why Pluto is no longer a planet and this was news. But, he continued, we don’t need to worry since this comet, larger than the state of Rhode Island, won’t come any closer than a billion miles away. That’s the distance to Saturn. This comet is named Berardinelli-Bernstein C/2014 UN 271 or BB for short. BB will cross our solar system between the orbits of Saturn and Uranus before whipping around the sun and back into deep space. Also, BB won’t arrive until 2031. So much can happen in nine years, our instructor intoned sagely.
But comets can cause major damage if they hit a planet. In 1994, the huge gravitational field of Jupiter tore the Shoemaker-Levy comet from its orbit when it strayed too close. The comet crashed to the surface, leaving an imprint larger than the earth on the surface of Jupiter.
Also, some astronomers now think a comet, not an asteroid, crashed into earth some 65 million years ago, blotting out the sun and wiping out the dinosaurs. For decades, most astronomers thought an asteroid slammed into the coast of Mexico at Chicxulub. New research from Amir Siraj and Avi Loeb of Harvard, however, suggests that a comet caused the Cretaceous-tertiary mass extinction.
The comet BB is about 80 miles across or 50 times the size of typical comets. In contrast, the unusually bright 1997 Hale-Bopp comet, the most viewed comet ever, is half the size of BB. Halley’s comet, the best-known comet, is just about 7 miles across. BB has a mass of 500 trillion tons or about the mass of 2800 Mount Everests. Astronomers Pedro Berardinelli and Gary Bernstein discovered BB in 2010, when it was about 3 billion miles from the sun. In a new study, David Jewett of UCLA, says, “It’s big and it’s blacker than coal,” describing the rocky surface charred by intense radiation. They figure BB has a long elliptical orbit that takes 3 million years to complete. And on this trip, it has been heading toward us for about a million years. So don’t expect to see BB again after it barrels through our solar system this trip.
Will we be able to see it? Astronomers tell us it will be difficult to see with the unaided eye or even good binoculars. We should not expect the high visibility of Hale-Bopp or Halley’s Comet. Higher-end amateur telescopes have enough power to see BB and many observatories will post pictures and video as BB draws closer.
What is a comet, anyway? Yale astronomer Debra Fischer once described a comet to me as a “dirty snowball.” Loosely packed ice and rocky material comprise the core of a comet, its nucleus. The black surface of a comet absorbs massive amounts of radiation from the sun. This radiation causes the surface of the nucleus to vaporize and produce the coma, the haze surrounding the comet, and its trademark tail. The sun shining through the ionized gases streaming from the coma produces a colorful comet’s tail. The hues of the tail depend on the chemical composition of the comet. Some comets even have two tails. And comet tails always point away from the sun because of the pressure from the solar wind–a topic for another day.
Comets are ancient and contain materials left over from the formation of the universe 4.5 billion years ago. We believe BB originated in the Oort Cloud, a gigantic sphere encasing our solar system, 4.6 trillion miles from the sun. Billions of pieces of space junk, including icy masses larger than mountain ranges, make up the Oort Cloud. Some of these may be even larger than BB. Sometimes, the gravitational field of the Oort Cloud ripples enough that one of these icy masses breaks free. Swooping in from the edges of the solar system on a highly elliptical orbit, this new comet tours the solar system, trailing its tail of ionized gas (plasma) and dust.
Historically, the ancients viewed comets as omens, usually bad omens. The record-breaking comet, BB, is not a bad omen for earth, at least on this trip around the sun. And there may be comets even bigger than BB coming our way, says Jewett. Now with the Hubble telescope, we’ll be able to learn more about comets, our solar system, and the formation of the universe from the biggest comet ever — so far.
- New York Times