THE SOUTHWORTH PLANETARIUM
70 Falmouth Street Portland,Maine 04103
(207) 780-4249 usm.maine.edu/planet
43.6667° N 70.2667° W 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.
[image:
ngscience-2109-largest-comet_annotated-comet-image_ai2html-desktop-small.jpg]
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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