OotM 4.ii: GRAIL and lunar gravity

[kaberett]

F MARIA ZUBER -- GRAIL AND LUNAR GRAVITY
Gravity Recovery and Interior Laboratory
- 2-spacecraft mission that senses the Moon's graivty field by measuring the change in distance between 2 spacecraft 60-225km apart in the same ~55km altitude orbit for a period of ~3 months, then at 25-75km, and then for 10 days at ~11km
- spacial blocksize 6km at best
- at degres corresponding to lunar basins, GRAIL shows 3 to 6 orders of magnitude over Kaguya & LP

[that makes two women who've been interrupted and no men. One "I can't hear you" (from near the front, by a dude), one "is that the radius" (ditto).]

- woo Bouguer anomalies
-- pretty smooth
- get out some crustal porosity, solve for crustal thickness, etc (34-43km)
-- less than previous estimations but consistent with Apollo seismic results
-- two basins have thicknesses near zero, wow

Rest of talk: identification of lunar basins.
- lots of Bouguer gravity. Now looking only at long-wavelength part.
- are there basins buried but not identified? let's have a look, work out impact history, etc

Procellarum BAsin
- not supported by geophysical and relative age data
- gravitational evidence does not correlate with previously mapped boundaries
- south border post-dates Humorum
- East border pre-dates Serenitatis
--> protracted period of formation (100s Ma) i.e. NOT the largest single impact crater on the Moon! -- or at least the evidence used to say it's there... doesn't hold up. Need more info.

I am sorry I do not care enough about gravity anomalies it is a bad pain day and I am underslept. However it is very pretty and I want many of the pictures framed and on my walls.
- discovered only a handful of new basins

Summary & status:
- current gravity field resolution SH degree and order 900 (spacial blocksize 6km) improved by over a factor of two from Zuber et al Science 2013
- errors at length scales sampled by lunar gravity models from all previous missions improved by 3-6 orders of magnitude
- improved low-degree gravity enabling more confident models of deep interior tructure
- evidence fro extensive impact-generated fracturing of the lunar crust
-- high coherence between gravity and topography
-- low (highlands) crustal density (2516 kg m^-3) } for GRGM0720
-- high (highlands) crustal porosity (13.5%) }
- mantle uplift confined within peak rings
- definitive assessment of impact basin inventory
- significant unmodeled signal remains in lowest-altitude regions

Discussion:
- implications for the late heavy bombardment... very few of impact craters being debated are actually real
- okay, so strange polygonal structure around Procellarum? -- "plumbing system for mare basalts, thermal cracking" says speaker
- ... Moon isn't fully solid _now_? Huh. Liquid outer core. Maybe a layer of mush. There you go.
- ... there are now two people on the floor standing up with microphones, facing each other talking. ... one of them is a woman and the other is a brown man and they are BEING ENCOURAGED IN THIS :D (I am kind of weirded out by the way I am treating this whole thing as an opportunity to Sociology of Science, where e.g. S. is very much using it to talk shop. I suppose I am, too, in my way, it's just a very different *kind* of shop...)

Comments

[calissa]

I think I enjoy your notes on the audience just as much as your notes on the talks.