Wednesday, May 23, 2007

When the heck are you going into Victoria Crater already?!?!

OK, I've gotten that question more than once - in hallways, by email, on the phone. You've probably noticed on the rover traverse maps that Opportunity got to the dark streaks, then turned around and headed back past the Valley Without Peril. No, the valley did not live up to its name, presenting some very steep slopes that were a little bit scary to contemplate. We're headed back the way we came, to the very first valley called Duck Bay. Still no guarantees we'll go in - depends on a thorough assessment of the rover's health and the safety situation when we arrive - but the tentative plan is to make a "toe-dip" into the crater there, as the gently-sloping valley appears to be lined with bedrock for some ways into the crater.

Of course, when we arrived here at this huge hole in the ground, like all good adventurers we immediately want to leap into it. But in the trek around Victoria Crater, we've learned tons about the crater and its interior and sharpened our idea of what science can only be done by entring into the crater. For instance, this and other gorgeous Pancam images show that the bottom of the crater is covered with rippled black sand. Big sand dunes are unfriendly rover territory, as exampled by Purgatory Dune where Opportunity was stuck for 5 weeks in 2005. So, driving across the bottom of the crater is right out. But, then we went over to where that dark sand is streaming out of the crater and examined it from a safe vantage point. So we got the science along with the safety in that case.

One of the more visibly fascinating things to see is the rock that makes up the cliff faces of the crater rim, like above in one of my favorite false-color images. We think it is pretty clear that the stuff at the top is normal Meridiani surface rocks, jumbled up as ejecta blocks. But then there's some thin and thick layering, followed by spectacularly crossbedded rocks underneath those. Crossbedding is an indicator of sedimentary processes operating in a fluid environment (here I'm using fluid to mean either wind or water, can't tell which yet) forming dunes and ripples. I was going to try to explain it more, but here's a *fantastic* animation showing how crossbeds form. Though it would be da bomb to drive up to the crossbeds and put the Microscopic Imager right on them, we don't want the rover to tumble to its death extending a giant lever arm on a slope. So, we're doing a lot of what's called superresolution imaging of the cliff faces - taking multiple images from the same location but offset a fraction of a pixel. This allows you to combine the information and subsample below the pixel size, sharpening up edges in the image. We're getting some fantastic views of the stratigraphy this way.

But still, everyone wants to go into the crater, of course! The one thing we can't do anywhere else is understand the relationships between mineralogy, chemistry, texture, and physical properties of the rocks (like hardness or flakiness) in situ. That's why the paved valley of Duck Bay is extra attractive. When Opportunity went into Endurance Crater, we stopped to examine all the rock layers going in, leaving a trail of RAT holes behind. We hope we can do something similar here at Victoria if we get the ok to go in, so stay with us on our trek back!

Wednesday, May 16, 2007

What is up with the lunar robotic program?

Check out this great explanation of the state of the lunar robotic program from InterplanetSarah. I couldn't agree more - if Congress wants NASA to explore the Moon, Congress needs to give NASA the money to do so, and then let NASA do it. LRO will go in 2009 and human landings are scheduled for 2018 - what will we be doing at the moon in the interim? It's the perfect opportunity to show we can land on another planet robotically and retrieve samples, and learn more about the environment we're sending humans into to boot.

Tuesday, May 15, 2007

Meteorite Mania: the followup

This week, we find out that the object that crashed through that house in New Jersey is not a meteorite. When a test for nickel was conducted at the American Museum of Natural History, it turned out to be made of a human-made stainless steel alloy. So, density and magnetism are good indicators for meteorite, but they are also properties of many, many chunks of rock, ore, and slag here on Earth.

In fact, the most definitive test of the meteoritic origin of metal is the nickel content. When the Earth differentiated, forming a crust, mantle, and core, nearly all the iron, nickel, gold, platinum, and other metallic elements went into the core. That's why there aren't big chunks of metal in the crust. The metal we get through ores is in small quantities and usually collected in mineral form, which is why they are scarce and valuable. The process of smelting can convert the ore iron into its metallic form, but there won't be any nickel associated with it. Now, the same differentition happened on some large asteroids - but the iron meteorites come from the asteroid core itself, where all the metals went. So the iron in meteorites contains a lot of nickel - usually 5% but up to 35% - plus traces of lots of other metals. No rock on Earth has all the metals wrapped up into one. Even further, the iron and nickel in some iron meteorites cooled slowly from the molten state and formed two different minerals, kamacite (low-Ni) and taenite (high-Ni), and you can see these mineral crystals in the meteorite when you etch a cut surface (called Widmanstatten pattern). No rocks but meteorites have slowly-cooled Fe,Ni minerals in them. But to be able to tell Ni content and Widmanstatten pattern, you need to open the rock up and run some tests on it. So density and magnetism aren't the whole story.

Want more information on how you can tell if you have a meteorite? Glad you asked. Also, see more about metal in meteorites, including nice photos.

Thursday, May 10, 2007

Meteorite mania

OK, here's a couple of meteorite topics for today:

Did a meteorite fall from the recent Kansas tornado? I have a pretty intense tornado-phobia, so my heart goes out to the residents of Greensburg, Kansas and everyone who is helping them recover from the massive tornado that struck this week. But tornadoes have nothing to do with meteorites. In this case, part of the massive Brenham pallasite, which was found nearby in 1949, was on display in the Greensburg Big Well Museum. The Museum was one of the buildings destroyed in the massive tornado, but contrary to some reports out there that the 1000-lb Brenham chunk was blown away and recovered east of Greensburg or in some farmer's field, the meteorite was in fact recovered in the rubble of the destroyed museum building. No flying meteorites associated with the tornado.

Riddle me this Science Girl: What is up with the meteorite that crashed into the house in New Jersey? Hmm, I was out in the frozen wasteland when this happened, but it was apparently thought to be a meteorite that week by the group at Rutgers. The news articles only say that the Rutgers group considered the density and magnetism of the sample and haven't been able to do a definitive test for nickel concentration, the true fingerprint of an iron meteorite, so there may be more news coming. Up to 100 fist-sized meteorites fall to Earth every year, so that part isn't unusual. The majority of meteorites that fall are ordinary chondrites, so a falling iron is unusual. The chances of a meteorite falling into a piece of your property are remote - there's only a few accounts of that ever happening anywhere. So though the meteorite itself may not be scientifically spectacular, the circumstances (fresh fall, iron meteorite, human interest story) are highly unusual and are likely to drive the price up for collectors (the piece of crap car that was hit by the Peekskill meteorite went on tour and eventually sold for $12K!).

Finally, I've very pleased to announce our new UNM Meteorite Museum web pages, including a Virtual Tour of our collection, photos of hand specimens and thin sections, tons of information about meteorites and their parent bodies, and links to our collections catalog. The information level is aimed pretty low because our physical audience at the Museum is mostly gradeschool field trips, but you might find it interesting anyway!

Wednesday, May 09, 2007

Science results at Home Plate

Last week, we published the results of last fall's science campaign at Home Plate, including the evidence for and against a couple of our hypotheses for its formation - see the Science article here (most people need a subscription to download the full article online, but you can also visit your library or bookstore to see it in print). I love alphabetical order sometimes - I get to be 4th author on this Athena team publication :)

If you've been following along, you'll already know we think it is a volcanic feature formed when lava met wet terrain, like a maar volcano (hey! Maars on Mars!). If lava interacts with groundwater, the water can flash into steam and make shallow eruptions. These eruptions don't make normal volcanic cones, but looke like low rings or craters. Zuni Salt Lake in New Mexico is a well-preserved example of a maar, which is why it was a stop on our MER field trip last summer. Check out team intern Megan Ennis' terrific poster comparing Zuni Salt Lake to Home Plate to see some of the interesting and diagnostic features of each.

It's good to keep an open mind among the team, though, and we're doing all a lot of new work with the rover to look for more evidence that would help us rule scenarios in or out. For instance, one of the things many people find compelling is this photo, which shows a dark rock and some apparently bending layers. To many, this is a bomb sag, formed when the lighter rock was still wet or deformable, and the dark rock got plunked down onto the layers, bending them under it like when you sit on a soft chair. I'm still a little skeptical though - to me the dark rock looks like the other dark rocks in this frame, which might be weathering out of the light rock or might just be rolled onto the light rock later. We can't tell which from this photo and we didn't have time last fall to investigate more thoroughly. It would be great to find another example like this one!

We are planning a throrough characterization of the rocks as we guide Spirit up the side of Home Plate in the next couple of weeks. And then we've got an exciting area ahead of us - the Home Plate surface itself! We just scooted on by as we headed for Winter Haven and we're all anxious to get on up there and check it out.