Whipple Lecture: Cometary nuclei
After a great salad at an uncrowded, close, inexpensive lunch spot that you would have as much luck getting the location from me as my favorite fishing hole (if I fished) I attended the Whipple Lecture given by Prof. Whipple’s last PhD student, Joseph Veverka. Prof. Veverka discussed the Deep Impact and Stardust measurements of comet Tempel 1, the first comet with sufficiently high resolution images to explore the geology of the body.
The observations are a neat story because Deep Impact first visited Tempel 1, impacted it, but no observations of the resulting crater were possible as the dust didn’t settle fast enough. So they were lucky enough that 5.5 yr later they could return to the same spot with the Stardust spacecraft. And by some amazing orbital tinkering they came back at the right time for closest approach over exactly the spot they wanted. That being said, the results were, well, modest. More like “Cursory Impact”.
- Experts: Prof. Veverka suggested the dust could have resettled on the body filling in the hole, but it is a 6 km body, is the gravity field sufficient given the other motions (e.g. rotation) to bring the material back or would it disperse in a cloud about the body?
Anyway, there modeling work suggests the surface is similar to “lightly packed mountain snow”. A surprising thing I learned in the talk was the unlike mountain snow there is virtually no frozen water on the surface of this dirty snowball (sounds like one of those drinks on the bar menu I never order).
Another interesting results: the surface is covered with craters but they are not impact craters. They appear to be caused by material from the interior bubbling up to the surface. Also present on the surface are regions of melt which have flowed to the valleys of the surface (this little guy has a 850 m elevation gain on a body with a radius of 3 km!).
- Experts: Planetary science heavily rely on crater counts for all kinds of inferences about planetary bodies. Does one attempt to correct for this on larger bodies, or does this process not happen. For instance on the Moon could a significant number of craters be non-impact in nature?
So the hallmark of a good talk, it raised lots of questions in my mind.
Posters
1948: kudos to the University of Alberta who has begun a High Altitude Balloon program specifically designed for student participation. The have built a particle detector and have made a successful flight. Excuse the pun but I hope this program takes off!
260: hey experts need your help again. This posters by Daniels et al measured high altitude waves due to lightning on Venus. They said that lightning occurs on Venus due to sulfuric acid droplets creating charge separation on “other particles”. In my mind lightning is intimately tied to strong vertical convection. Dynamics not required on Venus?
276: Johnson et al., Energy and Power Spectrum of Thunder. Ms. Johnson has in my eyes a very interesting MSc thesis. I’ve seen lots of work on lightning but I didn’t realize that you can get important complementary information from the thunder (below 600 Hz). Apparently quantities due to charge compression can be discerned by these measurements.
187: experts need you yet again. Didn’t get to ask the authors, who have developed a model of what a habitable planet would look like from space, but want a mission to L1 to make these measurements on Earth to test it. I would think plenty of data sets exist that could be convoluted to the appropriate observing bias you want to test?
123: Hurst et al. had an interesting paper on stratospheric water vapor measurements. They showed using 2 long term data sets that the variability between the sets would cause a larger radiative forcing difference that the observer increases of stratospheric water vapor in the last decade. Lots of work to do here NDACC! I hope our stratospheric water vapor campaign with our colleagues at NASA will help in some small way with this important issue for climate modeling.
26: Scary poster: Mahlsten and Knotti argue that if the global mean temperature increases 1.2 K above the current value that should be sufficient to cause the lose of all the Arctic sea ice. This result is based by a linear dependence basically all models find on global mean temperature and sea ice extent. So Experts my question is, as you approach the limit of less and less ice and the amount of water vapor is increasing, dynamics changing etc. would you expect this relation to continue to be linear? My nose tells me no but I’m out of my league here.
1794: end with a planetary poster on Titan that answered something I was wondering, at least in the Arctic regions of Titan how much does it actually rain? Lorenz estimates it is cloudy 2.5-7% of the time and it only rains 1% of the time during these periods. Still that is a few meters per year, with a rate of about 0.1m/hr.
Evening science meeting now so gtg. Enjoy your science.
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