Tuesday, November 21, 2006

It wasn't a rock, it was a rock lobster!

I'm spending my last days on Mars for a while this week as I prepare to heard to Antarctica this Saturday! You can follow the exploits of the Antarctic Search for Meteorites over at the ANSMET weblog.

Just as I'm leaving, things are warming up in the Inner Basin and Spirit is getting the chance to stretch a little and look at some of the rocks and soil targets around her. She's looking at the white soil the wheels churned up on the way to where she is now. The white soils usually mean some kind of salt, and that usually means involvement of water. We're also looking at a rock layer that protrudes from Low Ridge like a fin. You can floow it all along the ridge to the rover. We tried to get the rover to move to break a piece off, but the sandy area where we are prevented the rover from doing that. Next week, we hope to actually drive a couple of meters to a basaltic rock and do a nice campaign there, looking at the vesicles (holes caused by escaping gas) in the rock and a detailed chemical analysis to see if these kinds of rocks are related to Home Plate. Then, it'll be off to Home Plate itself, a tantalizing feature we only zipped past last fall.

Opportunity has begun circumnavigating Victoria Crater, and every day there's a new, breathtaking vista. The team hasn't yet decided how far to go or when to try to go into the crater, so it's difficult for me to leave now knowing Opportunity could dive in at any time!

While you're missing me on this blog, keep up on what the rovers are doing through Steve Squyres' mission update, sites by passionate amateurs: MartianSoil, Mars Rover Blog and MarsGeo, and of course, the latest images direct from Mars are easily accessible from the Exploratorium web pages.

For other burning questions about all things planetary, spend some time at Planetary Science Research Discoveries, a fantastic site with very readable articles about current science.

Happy Holidays, everyone, and see you in February!

And still more on the Moon

Yikes. Here I am, trying to cram in all the work I have to do before leaving for Antarctica this Saturday, and the darn people out there get me talking about my favorite topic, the Moon.

"Riddle me this Science Girl: Does the moon have magnetic fields? I read somewhere that one problem with putting an outpost on the moon will be shielding astronauts from radiation. Is this true? I also read that future lunar missions would be longer than the Apollo program, but that they would not run into lunar night. Does being on the surface of the moon during lunar night bring about special problems for astronauts and jet setting planetary scientists? I hate to bring up the whole digging thing again, but what about putting in a subterranean bunker? I am just curious; after all, the new JB movie is out and "Moonraker" was one of my favorites! Are there natural caves on the moon? What about unnatural ones?"

The Moon doesn't have its own magnetic field like the Earth does. The Earth's magnetic field comes (very basically) from its spinning liquid core. No spinning liquid core in the Moon = no magnetic field. There are some rocks on the lunar surface that are magnetized though - these might have been magnetized by large, ancient impact events in some weird way of physics I won't even try to get into. Anyway, the upshot is that the Apollo astronauts were very lucky. They received low-level doses of radiation during their sorties, which is entirely recoverable, but by pure luck, did not encounter a solar flare that would have really dosed them. Now that we understand both the lunar radiation environment and the effects of radiation on humans better, you can bet there's a lot more work going into how to deal with this issue.

I have a great T-shirt that says, "I'm taking a lunar day off." Would be nice! A lunar day is a month long - the time it takes from full moon (which would be high noon if you stood on the near side) to full moon. So if you're on the surface, you've got pretty much 2 weeks of sunlight and 2 weeks of darkness. On the Earth, our atmosphere does a lot to keep our temperatures even. Think of cloudy nights that are warmer than clear nights, or the fact that when you're in the desert, the days can be very hot but the nights a lot colder because of the clear dry air. On the Moon, there's no atmosphere, so you've got the sun beating down on you during the day (surface temperature +100C) and absolute darkness at night (surface temperature -150C). So whether you plan your surface sortie during the day or the night, you have some extreme temperatures to deal with. It would be extra difficult to try to plan for both extremes during a single sortie.

What can you do to protect against both radiation and temperature extremes? A subsurface habitat will have a constant temperature equal to the Moon's mean surface temperature (-23°C) and protect against radiation and solar flares. People have speculated on how to construct these kinds of things for decades, and some people want to build habitats in lava tubes, the only kind of natural cave on the Moon. But don't expect to see them anytime soon. Excavating and building subsurface modules are the kinds of incredibly expensive architechture you'd be looking at for permanent bases, not for sorties like we're currently planning.

Monday, November 06, 2006

More about the Moon

Here's a comment I got recently: "We can also place a huge telescope on the moon which could replace the aging Hubble telescope. Would that not give us better resolution at greater distances? Or is this a waste of time due to the moon's orbit?" Actually, I thought this was prety obvious too, until our committee meeting a couple of weeks ago. The Moon certainly provides less atmosphere, so that's good, and the Moon's orbit is no big deal - remember that the Earth turns every 24 hours, so telescopes need to track on Earth anyway. Some people think you can get bigger collectors as well on the Moon, though a variety of techniques. But, the Moon has a lot of disadvantages too. It's still got dirt and gravity, which are inhibitors for large telescopes - gravity because you still need to build a big structure to hold and point the telescope, and dirt because it gets onto your collecting surface. Since the success of the Hubble mission, we've come to realize that there are great advantages for telescopes in free space that surpass even the Moon as the best platform. So, yes, there are some astronomy applications for which the Moon would be useful (like low-frequency radio astronomy), but for many, the advantages just aren't there. Here's a current article in Physics Today describing the pros and cons from two different points of view. The community's view on this is changing even in just the last year or two, so beware of older articles!

Another part of the comment is: "We could slowly develop mining on the moon using the iron and ore to build and launch future space missions." Well, yes and no. In-situ resource utilization (ISRU) on the Moon is a hot topic and many people are working in this area - they even holdan ISRU conference every year. One of the obvious ISRU uses is, of course, to support astronauts, bases, and continued missions. But, the Moon's resources are not like the Earth's. Here on Earth, many metals are concentrated in ore deposits. To make an ore deposit, you need a source, a transport mechanism, and a concentration mechanism or trap (hmmm, not unlike meteorites!). On Earth, by far the most common way to get these is by moving metal around in water, or less commonly, through igneous and metamorphic processes (for more, see the wiki on ore genesis). The Moon has been bone-dry since it formed and doesn't have plate tectonics, so both these major modes of ore formation are inoperable on the Moon, and there's no chance that we'll find metal deposits to mine. But, resources like oxygen and hydrogen do exist and may be able to be used to sustain humans and create rocket propellant. Read more about what the ISRU community is doing at the ISRU website.

Spirit busts a move!

Over the weekend, we commanded Spirit's first drive in over 200 sols, and she pulled through like a trouper, moving close to a meter. We basically pivoted around the current position about 30 degrees or so, in order to get some new material in front of the rover to look at. Through the winter, Spirit did a lot of interesting observations, but there wasn't a lot that was reachable with the arm instruments. Now, we're putting the arm down into the trenches that Spirit made when she dragged her wheel limping her way up to this position. The wheel drag basically made a trench in the soil, and in a number of places there is bright material exposed at the bottom of the trench. Usually the team gets all excited over bright material, because it frequently equates to salty, and by geologic inference, salty frequently means water in some form or another. Where we are right now, the water story is very slowly unfolding because of our lack of mobility, but we hope that doing some detailed work on the bright material in the wheel trenches will contribute to our understanding of where and how water was available in this area.