Ask the experts…

I think many of you will agree that one of the best things about the whole MER mission is the way that members of its science team have made themselves so accessible to members of the media and the public, granting interviews, sharing images, information and news as much as possible, and generally making sure that everyone feels involved in the mission. And speaking personally, one of the most fun things about writing this blog is cheekily emailing those scientists and asking them questions about Opportunity and what she’s doing, and always – always – getting an answer. I always get a real “wow!” feeling whenever one of them takes the time to write back and share information with me for RtE! 🙂

So much has happened on Cape York recently that I thought it was time we caught up again with two of the scientists who’ve been kind enough to chat to me in the past – NASA scientist James Wray and Ray Arvidson, (role here). Simply because I wrote to, and received a reply back from, James first, I’ll ‘chat’ to him first here, then we’ll hear what Ray has to say about Oppy’s continuing adventure…!

Since we last talked with James   things have changed for him. He’s moved from Cornell to Georgia Tech, and isn’t as heavily involved in things MER as he was, but of course he is still an expert in the geology Oppy is studying on Mars so his insights and opinions are always going to be valuable and fascinating to MER followers. Anyway, I’ll let him explain…

I was at Cornell from 2006 until July of this year, completing a PhD and then a postdoctoral position with Steve Squyres.  Most of my research during those years actually used *orbital* Mars data, especially the HiRISE and CRISM instruments on the Mars Reconnaissance Orbiter.  But as Steve’s student and postdoc, I was also officially a MER “science team collaborator”–I would frequently sit in on the rover science meetings (they happened in the room right next to my office!) and I did help plan a Spirit imaging sequence once when we were trying to coordinate with an upcoming HiRISE image.  Probably my biggest contribution was identifying the phyllosilicates at Endeavour crater; again, this was based on analysis of *orbital* (not rover) data, but of course it has become highly relevant to Oppy’s ongoing activities!

Now that I’m at Georgia Tech, my role is more that of an “interested outside observer”–I correspond with team members about what Oppy is finding and I continue to contribute to analyses of the orbital data around Endeavour.  But I can no longer go next door and sit in on the science ops meetings!

Ok, now that’s cleared up, let’s talk to James about what Oppy’s been up to…!

Can you believe we’ve been at Cape York for three months? It seems more like 3 days! What are your impressions of the place?

Yes, the time has flown by = three months is one nominal mission lifetime!  My impression is that it is more complex than I had expected, but that I should have expected it to be complex.  Just look at the Columbia Hills, which are probably the oldest terrain explored by either rover prior to Oppy reaching Cape York.  The Hills were tremendously complex, with some rocks containing carbonates, some rocks and soils containing sulfates, others nearly pure opaline silica, and still others showing very little evidence for alteration by water of any kind.  This was all within an area not too much larger than what Opportunity has already traversed across Cape York.  So the fact that Cape York has rocks that appear diverse in terms of texture, color and composition, which are requiring some time to figure out, is really not surprising based on our prior experience in ancient Martian terrains.  Fortunately, we were clearly right in predicting that these rocks would be quite different from those that dominate the plains.  And the other good news is that the views here (especially into and across the crater) are spectacular.  It’s a pretty nice place to hang out for awhile and make detailed science measurements.

Oppy certainly spotted some fascinating-looking rocks around Odyssey Crater, with Tisdale 2 really catching everyone’s eye with its bizarre shape and beautiful layering. You’ve had time to dissect the data gathered there now – anything new turn up? What is Tisdale 2’s significance?

Beyond being different—in both texture and composition—from anything we had seen before with Opportunity, I think the major distinguishing feature of Tisdale 2 remains its anomalously high zinc abundance.  It was noted back in September that this could indicate formation in a hydrothermal system.  I think this takes on even greater significance following a recent report (http://www.jpl.nasa.gov/news/news.cfm?release=2011-337) that most Martian phyllosilicates may have formed beneath the planet’s surface, perhaps in hydrothermal systems, not on the surface due to weathering as is most common on Earth.  Importantly, that recent study shows that the major element chemistry of clay-bearing rocks on Mars may not differ much from the chemistry of basaltic rocks that have never seen water.  So for Oppy to spot potential clay-bearing rocks with her APXS instrument, we may need to pay extra attention to minor elements, such as zinc.  Tisdale 2 showed us that zinc-enriched rocks exist on Cape York, but we will need to study more examples to piece together a coherent story.

On Landfall Day, Oppy saw a bright vein on the ground almost as soon as she rolled up onto Cape York – but she rolled right on past it. Why? Did you not realise the significance of these veins at the time, or were you confident you’d get a chance to see one – maybe a better one – later and just wanted to get to Odyssey, with all its ejecta, as quickly as possible?

The veins were definitely intriguing from the moment we first spotted them, but yes, the goal back in August was to reach Odyssey crater and then head toward the locations where our orbital data give the strongest indications of clay minerals.  It turns out those locations are on southeast-facing slopes, and since August we’ve become increasingly aware of the need to reach north-facing slopes before winter.  We started driving toward the north-facing slopes early enough that we could afford a brief stop or two for science, so the team kept their eyes open and had the good fortune to come across another vein: Homestake.

Now, Homestake seems to have you all buzzing! It looked different and important from the very moment we first saw it. There’s been lots of speculation about it (In the MI images released so far it looks quite layered and crystalline, and I’ve spent ages going through galleries of geological specimens, and my local museum’s geology section, trying to spot something that looks like it!), and I’m sure you can’t tell us everything about it in advance of official statements, etc, but can you tell us how such a vein would have formed, and when?

Veins typically form when water flows along a crack within a rock, and then evaporates, leaving something behind.  This “something” could be one or more salts (sulfates, chlorides, carbonates, etc.), which can either entirely fill the crack or just cement together other material that had previously fallen into the crack.  I recently wrote about such crack-filling deposits on Mars here: http://www.psi.edu/pgwg/images/may11Image.html

As that post describes, Opportunity has previously found “fins” of material cemented together along crack walls in the rocks of the Meridiani plains.  But those fins were dark, whereas Homestake is bright.  And as you note, the texture of Homestake is pretty distinctive as well.  So it appears to be an entirely new manifestation of water on Mars that we have not encountered before.

Any chance you could give us at least a rough idea of how important it is, and why? Is it because of its age? Its composition?

The composition will tell us a lot.  In the few meteorites we have from Mars, most of the secondary minerals (those formed by water-rock interactions, e.g. salts and clays) occur along veins within the rocks.  The minerals in Homestake and any other veins we might encounter will tell us something about the chemistry of fluids that might have flowed through these cracks long ago.  How acidic were those fluids, and how salty?  As you note, the age of Homestake relative to the sulfate-rich rocks of the plains is another key question, although for now I would say that remains a subject of active study.  Stay tuned!

Are you hoping to find a larger Homestake-like vein further north, one big enough to use the RAT on?

That would be fantastic, but mainly we’re just hoping to survive the winter!  If we find a good north-facing slope, we might be able to make brief “sorties” throughout the winter to nearby targets of geologic interest, and if we happen to see a large vein nearby this could certainly be of interest.  But the main reason to drive north is because that’s where the best north-facing slopes are on Cape York.

The ground around Homestake appears to be littered and strewn with what look like dark, rounded stones. What process made them that shape?

 Good question.  Oppy has previously studied rounded stones (the “blueberries”) that formed as “concretions” via groundwater processes.  But volcanic or meteoroid impact fallout can also include rounded pebbles, and on Earth the most common way to round off a stone is to transport it a long distance, typically in rivers but maybe also via wind.  To gain more insight, it would be great if we could find a location where these rounded stones have collected (like the “berry bowl” in Eagle crater) where we could measure their composition.  For now, we must continue to entertain multiple hypotheses.

 Deadwood looks very different to Homestake…darker, less layered, more lumpy. Can you give us a Geology #101 and explain how two such very different-looking rocks can be situated so close to each other?

Well, if Deadwood was indeed an older rock (of any type) that had cracks in it through which water flowed, and this water evaporated and left behind some salts, then that could lead to a very different appearance; the secondary minerals in Homestake may have little or nothing to do with whatever minerals are present in the preexisting rocks, such as Deadwood.  Comparing the compositions of these two materials should be informative.

Pretty soon Oppy will be heading north, looking for a Winter Haven – then what? With phylosilicates hardly thick on the ground on Cape York, will she go check out Sutherland Point or just head straight to Solander and Tribulation, where we are much more certain there are larger deposits waiting to be studied?

 That will be a decision to make in the spring.  But if it were up to me, I would first explore Cape York for awhile longer.  The fact that we haven’t yet found phyllosililcates definitively does not mean they aren’t here on Cape York.  Remember that Oppy’s payload was selected before we had detected any phyllosilicates on Mars, so it was not designed with them in mind … and now the two best instruments for confirming phyllos (MiniTES and Moessbauer) are non-functioning and severely weakened, respectively.  That’s not to say that we won’t confirm the presence of phyllosilicates … but it will take some time even in the best of circumstances.  Since we do see orbital evidence for phyllosilicates at Cape York, I hope that we’ll conduct a more thorough search for them in the spring before we head out across the plains again toward Cape Tribulation (a journey which, of course, we might not be able to complete!  Remember that Oppy is way past her warranty!)  A cape in the hand is worth two in the bush.

We’re now just two weeks away (note: this was written a week ago) from the launch of Curiosity… do you wish you had that rover sitting on Cape York? If you did what would you be doing differently? Obviously there wouldn’t be such a pressing power problem, no need to find a Winter Haven, but what would you have done with or to Homestake, for example?

Having Curiosity at Cape York would indeed provide additional opportunities.  If we didn’t need to worry about power, then we would probably be sitting on the most promising spots for phyllosilicates on Cape York right now; we might not have driven to Homestake at all!  With Curiosity’s payload, we could confirm the presence of phyllosilicates definitively (if they are sufficiently abundant) and determine whether any organic matter is preserved within them.  Or if we did drive to Homestake, then we could acquire more detailed mineralogical and microscopic data than Opportunity can provide.  That said, I’m very happy that Curiosity is not headed to Endeavour, but instead to Gale crater!  At Gale we will have access to a much thicker sequence of sedimentary layers than Opportunity has encountered, allowing us to read many more pages in the book of Mars’s geologic history.  And as for Opportunity, using her instrument suite at Cape York allows us to make direct comparisons to the Meridiani plains that Oppy has explored for over seven years now.  So there are no regrets in our current situation.

Oppy is doing well, exploring a fascinating place, doing great science. The MER team must be feeling very happy right now. Quite a contrast to the Russian scientists who have to sit and wait to hear if Phobos Grunt is lost. How has that affected the MER team? Is it hard not to think “That might have been me if things had gone differently…”?

Space exploration—whether robotic or human-tended—is very difficult!  It is all too easy (at least for the scientists) to forget this after a string of recent missions have been successful.  But in 2003 and 2004, there was a very real fear of failure; NASA’s most recent attempt to land on Mars had failed, ESA’s Beagle 2 and JAXA’s Nozomi failed just weeks before Spirit and Opportunity landed.  Every agency has had both successes and failures.  The fact that Opportunity not only reached Mars successfully but is still operating today is a testament to the job performed by JPL’s engineers in building and testing the spacecraft … but also partly due to luck!  For example, who could have anticipated that winds would blow the dust off our solar panels from time to time?  So while we have every reason to believe that Curiosity has been engineered and tested with the same care as Oppy, we’re still crossing our fingers for the launch and landing next summer.  In the meantime, yes, the MER team is very happy and fortunate to still be roving Mars after all these years.

 Thanks!

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Regular readers will recall that back in May – when Oppy was still heading towards Cape York, and it was by no means certain she would get there – the Deputy Principal Investigator of the MER mission, Ray Arvidson, was good enough to take time out of his insanely busy schedule to talk to us about what the plans were for Oppy after Landfall on Cape York. Ray has been kind enough to talk to me again, post-Landfall, and to give us some information about what Oppy’s been up to since she rolled up onto the Cape, triumphantly, in August…

After three months of driving across and over it, what are your initial impressions of Cape York? And are you happy you went to Cape York instead of driving right to Solander / Tribulation?

I am quite happy that we went to Cape York because the geology of this portion of Endeavour’s rim, based on HiRISE and CRISM data, is basically the same as we see for the larger rim segments to the south. We would not have had time to make measurements like the ones on Tisdale, Charter Lake, Homestake, and Deadwood, had we been driving a couple more kilometers to get to Cape Tribulation. Remember we are now looking for a winter haven. Aphelion is in Feb and the winter solstice is in March.

We all watched Endeavour Crater growing larger and larger on the horizon and wondered what it would be like once … if… we got there. Now we’re essentially inside its rim, what have you learned about Endeavour itself since arriving at Cape York? You’ve photographed the central “mound “ a lot – what have you learned about that?

We have not done a lot of central mound imaging except to monitor dunes. It is too far away to get detailed imaging of strata. There is a lot of the floor in our imaging because whenever we take pan images to the east there it is! From CRISM data we see evidence for hydrated sulfates and from HiRISE there is clear layering.

We were all delighted to see the rocky debris around Odyssey Crater appear on the horizon as Oppy drove up onto Cape York, and Oppy spent quite a while there. What did we learn about the history of this part of Mars by studying Odyssey?

That this part of the Noachian crust is basaltic and Tisdale has been lightly modified in a water-rich environment that deposited the Ni, Zn, Br, S, Cl, and P.

What has it been like for the team to be driving around and amongst rocks again, after all those months of slogging across the wide open Big Country plains of Meridiani?

Exciting and frustrating, both at the same time. To preserve the rover we need to get to a winter site with a northerly tilt for the winter. This meant passing up very interesting rock targets to get to the northern part of Cape York where the 10 to 20 deg north facing slopes are located.

What is the feeling amongst the science team now about Oppy finding those precious phyllosilicates at Cape York? Nothing obvious seems to have jumped out on the ground, so the deposits here might be very small. Are you starting to think that you’ll have to head south to Solander and Tribulation before finding what you’re looking for?

Smectites are probably all around us in the Noachian rocks on Cape York. How to confirm their presence? Moessbauer spectrometry and that will take many hours of integration because of depletion of the Co57 radioactive source. Mini-TES would have already told us about smectites but it no longer works. Pancam cannot see the water and OH in this mineral because the vibrational features are longward of 1 micrometer.

And going back to Solander and Tribulation, what do you think about it as a driving area? Think Oppy can get up there for a grandstand view of Endeavour?

Opportunity will be able to climb the southern rim segments. It will be like Spirit ascending Husband Hill in slope and elevation.

…and finally… Homestake… we’re all looking forward to the science that comes out of Oppy’s studies of that fascinating feature. But why did you run over it like you did?

We ran over Homestake to break it up to see its interior. We did what I call a “triple crunch” drive in which the rover backed over it, drove forward, and turned in place over it before driving toward the winter haven site for topographic mapping. We exposed very bright surfaces, presumably not exposed to the Martian environment, and acquired Pancam 13F observations of the disrupted Homestake before driving away.

Thanks again for talking to Road to Endeavour!

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So, there you go, the latest news from two of the people who had a hand in making it. More interviews soon, I hope.