Random Tusks

Tusk prompts Grondine to query Napier on Dark, Dead comets and the effort to find them

From E.P. Grondine on Meteorite List:
Following a quote at https://cosmictusk.com from astronomer Bill Napier on the
abilities of WISE to detect dead comet fragments, I wrote him asking him about
it. As his reply also deals with some meteorites' parent bodies (Tagish Lake
being prominent) and the composition of comet cores, I think meteorite list
participants should find it of interest, and here it is:

"A population of extremely dark Earth-crossing comets in Halley-type orbits
is inferred to exist on dynamical balance grounds. These would be
undetectable visually but bright in the satellite infrared.

"Unfortunately these very dark bodies spend the great bulk of their time beyond
the orbit of Mars and it would take many centuries to map out the system to say
90% completeness with present-day technology, even with infrared survey

"Another class of dormant comets difficult to detect would be, fragments which
are simply too small to be seen easily, but which might
pack a punch either individually or collectively. If these have been around
awhile, the very dark organics on the surfaces might have disappeared
leaving a stony asteroid surface spectrum (the "asteroid" Phaethon, which
gives rise to the Geminid meteor stream, is a probable example of this).

"They can be regarded as part of the general population of sub-kilometre
near-Earth objects. Direct detection of these objects, sub-kilometre but
with higher albedos, should be possible with next generation telescopes, in
particular the Large Synoptic Survey Telescope, and even with present-day
Spaceguard telescopes if they run for long enough. The Comet Encke infrared
trail may contain a concentration of such bodies but we are a safe 600
years away from intercepting it.

"The best chance of detecting small bodies through occultation is probably
arises through orbits crossing the face of the moon and sun. Duncan Steel
and I had an exchange on this some years ago, and he told me that there are
many instances of dark objects having been reported to cross the face of
the Sun in the past. Unfortunately I don't think there has ever been a
systematic attempt to collate this information. But yes, in principle one
could put limits on the numbers of small fragments in this way.

"The 2022 (SW3) encounter will surely yield a meteor storm, and possibly an
enhanced risk of encountering a larger body within it, but I'm sorry that I
can't give any quantitative estimates -- the work simply hasn't been done, to
my knowledge.

Best regards,
Bill Napier"

E.P. Grondine
Man and Impact in the Americas
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