Rob McNaught's pics of Lovejoy taken from Siding Spring Observatory.
Some stunning shots here.
And David Sargeant's thoughts regarding Lovejoy's nucleus ...
Quote:
Hi all,
>> Just a few ideas to put before the group.
>> As I wrote previously, I suspect that the initial intrinsic faintness of
>> this comet was not so much a function of the small size of the nucleus,
>> but of the presence of a surface crust of refractory material. If the
>> nucleus was about 500 metres diameter (as against the 100 - 200 as
>> initially estimated) and covered by an insulating crust, this might
>> explain how it survived perihelion passage intact. If the insulating
>> layer was blown off around perihelion, this may even have formed a "sun
>> umbrella" of particles that shielded the freshly-exposed icy surface of
>> the nucleus, rather as is thought to have happened to Seki-Lines in 1962
>> (analysis of the dust tail suggests that this comet shut down for a few
>> hours at perihelion - q = 0.03 AU - which also helps to explain why
>> there were no daylight sightings of this intrinsically bright object).
>> In the case of Lovejoy, a similar event may have been a factor in
>> preserving its existence. Once the meteoric cloud dispersed, the comet
>> burs
> t into furious activity, however by then the worst of its ordeal was
> already over.
>> The presence of an ion tail clearly indicated an active nucleus
>> following perihelion. However, as this has this has now disappeared, it
>> may be that ice-driven activity has ceased. This could mean that the
>> nucleus has disappeared, or run out of ice or (I think the most likely
>> explanation) has had the ice cooked out of the surface layers. In other
>> words, the comet may by now have built up a new insulating layer that is
>> effectively keeping heat from underlying ice.
>> Yet, the "head" appears to be persisting as if some dust continues to be
>> released. Just a speculative thought, but electrostatic repulsion caused
>> by solar radiation can levitate fine dust on the surface of the Moon
>> (causing the unexpected crepuscular rays seen by the Apollo astronauts)
>> and is thought responsible for the small flare experienced by Phaethon
>> in 2009. With respect to the latter, David Jewitt called Phaethon a
>> "rock comet" - capable of low-level activity even in the absence of ice
>> - and suggested that this process may even be responsible for the
>> formation of the Geminid meteor stream. For what it is worth, I suggest
>> that the present weak activity of Lovejoy could be due to this process
>> lifting dust from what has again become a totally encrusted nucleus.
>> All very speculative I know, but comments welcome.
>> Cheers,
>> David
>>
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