Sky & Telescope - September 2024 - 4

SPECTRUM by Peter Tyson
Lasting Impressions
COMETS REALLY MAKE you ponder the concept of longevity.
Take Comet Tsuchinshan-ATLAS, the focus of our cover story this
month. Also known as C/2023 A3, this comet formed, along with
the Sun and planets, around 4.6 billion years ago. It has lingered
ever since in the distant Oort Cloud, which encapsulates our solar
system. Even by astronomical standards, it's been around for quite a while.
Yet, considered from our human perspective, Comet Tsuchinshan-ATLAS's
life might be rather brief. We only discovered it in January of last year, and it's
possible that it could disintegrate during this month's perihelion, when it makes
its first and perhaps only approach to the Sun.
As Arwen Rimmer writes in her article on page 12, " Once a comet starts its
journey toward the inner solar system, its days are numbered. " In all of those
4.6 billion years, C/2023 A3 has never passed near our star, and we have no idea
how it will respond. As other comets before it, it might go poof at perihelion,
disappointing observers. If that happens, then for us this new comet will effectively
have " lived " for less than two years.
On the other hand, after it passes the Sun late
this month, Comet Tsuchinshan-ATLAS might
last into a truly venerable old age. If it survives
perihelion, it will either remain within the solar
system, journeying for more than 80,000 years
before nearing the Sun again, or it will be flung
Comets Leonard (C/2021 A1,
on the cover) and NEOWISE
(C/2020 F3, above) dazzled us in
recent years. Will C/2023 A3 do
the same in 2024?
into interstellar space. If that happens, it might
" live " essentially forever - that is, until it slams
into another object or comes near enough to
another star that it crumbles into dust.
This paradoxical quality of comets - should
we consider them short- or long-lived? - adds to their allure. Hopefully, Comet
Tsuchinshan-ATLAS will be long-lived from our viewpoint. If it survives grazing
the Sun on September 27th, it will make its nearest passage to Earth 15 days
later, on October 12th. If all goes well, it could put on quite a show.
Alas, all tenures, whether of comets or editors, must come to an end at some
point, and I plan to retire this fall. My 10th anniversary as editor in chief of
S&T falls on the 29th of this month - the very day that, as Bob King notes on
page 48, Comet Tsuchinshan-ATLAS will be at its highest in the morning sky for
observers at mid-northern latitudes. It feels like an auspicious time to pass the
reins to the next editor in chief. (See the posting for my position at skyandtelescope.org/about/job-opportunities.)
As
it's been for C/2023 A3, it's been one helluva ride for
me. I'll share more thoughts on that in a coming issue.
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Sky & Telescope - September 2024

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