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.
The two illustrations:
1) Comet Neowise just after dawn, July 5, 2020.
12) Comet Neowise after dusk, July 18, 2020.
Be well and stay safe.