LPSC 2017 Trip Report, 2/4

[Back to the first part]

HOW DIELECTRIC BREAKDOWN MAY WEATHER THE LUNAR REGOLITH

Not only meteorite impacts reshuffle lunar surface. Solar wind, especially during long lunar nights, probably makes a comparable contribution to that process. How? Via a flow of energetic electrons. Which can reach the night side of the Moon and hit and charge regolith particles up to electric field strengths of ~106 V/m. Which would cause electric breakdowns within particles, resulting in their destruction or partial re-melting. Which amounts to slow mixing and resurfacing of the lunar soil. The darker and the colder it is, the better this process presumably works (in “warmer” locations, electric charges dissipate via normal conductivity).

We don’t know for sure whether this actually happens as described. But it would be worth figuring that out. Who knows – maybe in countless millions of years the astronaut’s footprints would disappear not under the dust of nearby meteorite impacts, but via trillions of microscopic discharges?


[This is an electric discharge, too. Just a larger one. Image Copyright: Eugene V. Bobukh]

===

SPACECRAFT IMPACTS ON THE MOON: CHANG’E 1, APOLLO LM ASCENT STAGES
Electronic poster

Over the past 60 years, Solar System exploration has gotten its own history… and archaeology. Yes, people search for landers of 1970s in contemporary satellite imagery from other planets, and sometimes find them, as that wonderfully happened with the mysteriously silenced Mars-3 Soviet probe.

The author of this presentation specializes on lunar impacts and has built a whole collection of them. This year, four more were added to it: ascent stages of Apollo-12 and -14, Chinese Chang’E 1 and (very recently) European SMART-1.


[Impact traces from ascent stages of Apollo-12. Image Credit: NASA / Philip J. Stooke]

I found it surprising that many impacts leave behind not craters, but streaks. Apparently, grazing collisions at velocities of ~1 km/s just result in violent rotation and breakup of the impactor, scattering the debris over long distances along the orbital path.

===

SIZE AND SOLAR INCIDENCE DISTRIBUTION OF SHADOWS ON THE MOON

It may be hard to accept that after studying the Moon for hundreds years, walking on it, making 12-inch resolution photos of it, and dumping 180 tons of trash on its surface we can still have something unclear about it. Especially about such a seemingly trivial thing as shadows.

Yet it appears to be the case.

The authors conducted a research that may look like a simple and boring activity. They studied the distribution of lunar shadows by size. This is pure statistics – but with a twist. Shadows sizes and shapes could be rather complex and depend on lunarscape characteristics in non-obvious ways. That is particularly pronounced at lunar “mornings” or “evenings”, when the sunlight is parallel to the surface and minute roughness variations cause great impact on the projected shadows.

They found that the number of shadows with sizes between 3 and 100 meters (10 to 300 feet) does not depend on their size. More importantly, they saw no clear good explanation for that. So perhaps there is something in the distribution of lunar bumps and ditches that we don’t understand well? This conclusion caused some serious discussion at the conference, with people was trying to interpret it via crater size statistics, but I did not quite capture all the details so can’t convey them here.

So yes, this is a seemingly trivial statistic of black and white patches. But done right, it reveals something enigmatic about our well-studies Moon – something hidden within its shadows…


[Shadows area distribution from the discussed work. Image Credit: Oded Aharonson, Paul O. Hayne, Norbert Schorghofer]

===

PENITENTES AT TARTARUS DORSA, PLUTO

Penitentes are bizarre needle-like snow formations known so far only on Earth:


[Image Credit: Wikipedia]


[Image Credit: Wikipedia]

But, according to the presentation, they may also exist on… Pluto! While we haven’t seen them close enough to be 100% confident, these longs stripes “are well described by the theoretical penitente models of [4] with spacing, orientation and growth rates matching well with observations for the methane ices observed by New Horizons (NH) [5] on Pluto”. And yes, they most likely are made of methane (CH4) ice.

[Tartarus Dorsa are on Pluto. Image Credit: NASA/JHUAPL/SWRI]

To part 3/4

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