[Outbackmanyep]

Originally Posted by CraigS

G'Day Liz and OBMY;

Re: Hartley 2 Obs

Interesting that OBMY's observation notes mentions that the coma is 'large and diffuse'.

I'm trying to figure out why they couldn't detect the (only recently announced) CO2 jets emanating from its dark side, prior to the flyby by Deep Impact.

Apparently, CO2 in the jets isn't detectable remotely by either our space bound scopes or ground based scopes. (Which is one reason justifying the probe's flyby).

Would've thought that if the coma was big, there'd be enough background light and hence we'd be able to pick up enough of the absorption spectrum to detect CO2 from Earth/orbit.

Big mystery this one. (We've been wrangling on the Science forum about it since yesterday).

Any thoughts/comments/ideas ?

Cheers

Hi Craig,

There's a few factors as to why we can't see the nucleus.
As you know comets are only visible due to either scattering of reflected sunlight from dust particles or flourescence from ionised gas.
The coma is split up into 3 main parts, the hydrogen envelope which is invisible at visual wavelengths, the outer coma (which is the part i measure) and the inner coma which is what we refer to as the central condensation or "false" nucleus. The nucleus is hidden within this central condensation. Ground based telescopes are able to image the inner coma and using a special computer program, the Larson-Sekanina filter (which was produced to study coma morphology), they can carefully produce maps of jets emanating from the nucleus which are projected into the coma.

http://users.libero.it/mnico/comets/ls.htm

A similar thing was done here:
http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/2010/pressRelease20100426/

So we know the jets are there but what constitutes the jets will be unknown until spectroscopic observations from in-situ spacecraft can do that for us. We can't really see them as the reflected sunlight from dust particles coming from the nucleus itself creates the false nucleus which shrouds the true nucleus from observation.

My observations describing "large and diffuse" means that through binoculars or the eyepiece the outer coma has a large angular diameter comparable with something such as the moon, i view many fainter comets with coma's between 0.5' to 5', so in regards to 103P it has a coma dia of around 20' which is larger than "normal".

Hope this helps.