THE SOUTHWORTH PLANETARIUM
70 Falmouth Street Portland,Maine 04103
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Altitude: 10 feet below sea level
Founded January 1970
2021-2022: XXI
"People say nothing is impossible, but I do nothing every day."
-A.A. Milne
THE DAILY ASTRONOMER
Thursday, September 30, 2021
A Monster Comet!
is heading our way!!!
Yet, before you clasp your desk's underside in a desperate panic while casting frightened glances skyward (or, in our case, dome-ward), be well assured that this ice-coated interloper will veer nowhere near our pristinely beautiful planet. That first line "is heading our way" is somewhat misleading. Ok, yes, well, completely, intentionally and obnoxiously misleading! It is heading our way in that it will infiltrate the inner solar system and draw "close" to the Sun in 2031. However, we care-burdened Earthlings need not add this monstrous comet's appearance to our burgeoning collection of soul dampening anxieties. It will give us a miss.
Now for the astronomical aspect of the story and, believe you me, this comet, called Comet Bernardinelli-Bernstein, is still going to be one for the record books. In fact, it already is.
SIZE
First, consider its size: the comet's nucleus is estimated to be 93 miles wide, making it larger than the two Martian moons (Phobos and Deimos) combined. That size estimate, which could change as the comet approaches, makes it one of the largest comets on record.
DISTANCE
Secondly, when first imaged, Comet Bernardinelli-Bernstein, was farther away from Earth than any other detected comet. Here, the issue becomes slightly tricky. On October 20, 2014, a telescope in Chile's Atacama Desert captured wide image of the southern sky. Contained within that image was a minute point of light: a faint glimmer of sunlight reflected from a comet that was, at that moment, 2.7 billion miles from the Sun! (29 times farther from the Sun than Earth!) However, seven years elapsed before postdoctoral researcher Pedro Bernadinelli and his adviser Own Bernstein, identified that point as a comet.* By IAU (International Astronomical Union) convention, the comet was named after its two discoverers. Since their announcement, this still-distant comet has become a prime observational target for astronomers around the world.
The image below, courtesy of National Geographic, shows the comet when it was 25 AU (astronomical units) away from the Sun. (An astronomical unit equals Earth's mean distance from the Sun, or about 93 million miles.) As one can readily see, it is not a particularly conspicuous object.
This comet originates from the Oort Cloud, an immensely large series of spherical shells enclosing the solar system. Containing perhaps as many as a trillion cometary nuclei, the Oort Cloud's inner shell is about 2000 AU from the Sun, while its outermost regions could extend as much as 50,000 AU. Oort Cloud comets often require thousands of years to travel between the cloud and the inner solar system, Some subscribers might remember Comet Hyakutake, which blazed across our sky in 1996 and became the most spectacular comet living memory.** Another Oort Cloud object, Hyakutake started its lethargic trudge toward the inner solar system around the time that the Stonehenge builders brought back their first IKEA shipment.
Comet Bernardinelli-Bernstein left its home perch thousands of years ago and is only now becoming visible. It is highly likely that a veritable armada of long period Oort Cloud comets are inexorably moving toward the inner solar system. Most remain concealed from view, like a degradation of shadow wraiths loitering in the midnight forest. How many of them could pose a threat to Earth remains to be seen.
DURATION OF VISIBILITY
Well, that is why astronomers are so giddy with excitement. This comet will remain within telescope range for years. It is expected to reach perihelion, its closest point to the Sun, in January 2031. At that time, it will be a billion miles from Sol, about equal to Saturn's distance. It will then be within our sights until approximately 2040 as it begins its unfathomably long journey back to the solar system's rarefied outer reaches. Astronomers will have about twenty years to scrutinize, analyze and admire this monster comet before it vanishes from view.
Unfortunately, it will likely never become a naked eye comet for us. According to recent estimates, it might become as bright as Titan, Saturn's largest moons. While that brightness will put it in the range of even lower grade telescopes, it will not bedazzle us as Comet Hyakutake did.
Yes, a monster comet is speeding toward the inner solar system. As it draws closer to the Sun, it will continue to accelerate until it swoops by the Sun at a comparatively breakneck clip. It won't harm us and will pass unnoticed by those who only scrutinize the sky with the unaided. However, something enormous has been approaching us since the inception of recorded history. How exciting that it's finally about to arrive.
Brain of Portland quiz tomorrow!
I can't wait, either.
*This observation wasn't a simple matter of looking, but of using a cluster of computers to extract from the data those images that didn't match any known solar system objects. These calculations require eye-wateringly complex computer algorithms and months of computations. Astronomy isn't as much an act of simple eyesight anymore.
**And, indeed, it was. That comet covered 30 degrees of the sky and was even visible from many major cities. It was nature's way of apologizing for the pathetic Halley's Comet apparition from nearly a decade earlier. Halley's Comet, hyped above and beyond all proportion, was scarcely visible. Imagine waiting a year to see your favorite rock star only to find out that your seats aren't just in the nosebleeds, but in the geosynchronous orbit section.
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