From our esteemed guest blogger, Dr. David Levy
Skyward for August 2020.
Of a comet, a cosmic beacon, and the possibility of
extraterrestrial life
David H. Levy
A few months ago I wrote in
this space about Comet Atlas (C/2019 Y4), a comet that at the time showed signs
of becoming a bright comet visible without a telescope or binoculars with just
one’s eyes. I also repeated my maxim
that “Comets are like cats; they both have tails, and they both do precisely
what they want.” This comet indeed did
not live up to its billing, and neither did the next one, comet Swan (C/2020 F8).
The third Comet, however,
did! Comet Neowise (C/2020 F3) put on a
beautiful performance in the morning sky at the start of the Summer of
2020. (First picture.) It was a shining
cosmic beacon amidst the terrible time we are all having this year. Over the course of July, this comet faded
slightly as it moved into the evening sky, but it moved so far north that for a
time it was visible in the night sky all night long. (Second picture.)
When I look at a comet, my
thoughts often dwell on the role that comets have played in the origins of
life, and in particular why and how I am here looking up at the sky to ask. For a long time we have suspected that when a
comet strikes a planet, it leaves behind four of its substances—carbon,
hydrogen, oxygen, and nitrogen—CHON particles, the simple alphabet of life. For
impacts in the oceans, long-lasting
hydrothermal vents might have helped form prebiotic molecules which
began to replicate themselves before evolving into proteins, amino acids, then
RNA, and finally DNA.
Gene Shoemaker, the famous
geologist, loved to say the “we are the progeny of comets.” Comet Neowise itself had nothing to do with
it. This comet was formed when the solar
system was very young, and trillions of other comets formed at the same
time. Some of these other comets might
have. Certainly at least one of them did
collide with the Earth well over three billion years ago. If the impact were in an ocean, it could have
led to the start of one of those hydrothermal vents at the ocean bottom. So much time has elapsed, and we are still
here somehow. We also have the
opportunity to look at the sky and witness a cosmic cousin of the comet that
did collide, that cousin being comet Neowise.
In all its magnificence, this comet is visiting, to tell us its story,
and ours.
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| 1) Comet Neowise just after dawn, July 5, 2020 |
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| 2) Comet Neowise after dusk, July 18, 2020. |
