Thanks Jeremy.
C/2016 R2 was the spectacularly blue-tailed comet
that attracted a lot of attention because of the amazingly low ratio of H2O to
CO of just 0.32%, which is even more unusual than its N2/CO ratio.
The abstract of this paper concludes: Our scenario indicates that comet C/2016 R2 (PanSTARRS) formed in
a colder environment than the other comets that share more usual compositions.
Our model also explains the unusual composition of the interstellar comet
2l/Borisov.
The link mention of the interstellar comet might
hint that C/2016 R2 was also interstellar at one time but was captured by the
Oort Cloud.
One thing that isn't spelt out is the way in which
the different chemical species become separated out. Turns out that the early
solar nebula had a boundary between material attracted towards the Sun and
volatile species blown away from the Sun a bit like gas in the tail of a comet
blown by the solar wind. This boundary or 'centrifugal radius' is not fixed in
space as in time (0.1-1 million yr) it moves outwards from 6 AU to 45 AU. Also
gas is much more likely to move outwards than are dust particles. This means
that H2O condenses out near the 'ice line' leaving more volatile species to
migrate further out. Eventually they condense near the boundary when it has
moved to a sufficiently cold region.
There's a talk tomorrow evening at 10.30pm GMT by
Michele Bannister on this very subject.
It's hosted by the U of Arizona/Steward
Observatory:
If you can't manage to link in then let me know
as there is a proprietary link available.
Richard
----- Original Message -----
Sent: Wednesday, March 03, 2021 11:09
AM
Subject: [BAA Comets] Cold traps of
hypervolatiles in the protosolar nebula at the origin of comet C/2016 R2
(PanSTARRS)'s peculiar composition
|
Recent observations of the long period comet
C/2016 R2 (PanSTARRS) indicate an unusually high N2/CO abundance ratio,
typically larger than 0.05, and at least 2-3 times higher than the one
measured in 67P/Churyumov-Gerasimenko. Another striking compositional
feature of this comet is its heavy depletion in H2O, compared to other
comets. Here, we investigate the formation circumstances of a ...
arxiv.org |
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