Europa vs. Titan Redux?

The presentations at the February OPAG meeting held statements that the Europa versus Titan decision may come back up for review. Last year, two teams competed to be selected for the next NASA Flagship mission and for a place in ESA's next large mission competition.  The review teams concluded that the science from either mission would be equally good, but that a decade of technology development made the Europa mission much more ready for development than the Titan mission.  A NASA Europa mission got the nod and an ESA Ganymede orbiter won a spot to compete against two astronomy missions (with the ESA decision to come next year).  Both space agencies promised to fund advanced mission planning and technology development to make the Titan mission ready for its own start later in the decade.  [Editorial note: The Survey could decide not to prioritize missions to either Europa or Titan, but I wouldn't take a bet on that outcome.]

Now, that decision on the American side is up for review as part of the Decadal Survey.  NASA has made it clear that it will take its priorities for planetary missions in the coming decade from the Survey's priorities.  Any mission that has not received a formal new start from Congress must be recommended by the Survey for NASA to procede.  That includes the Jupiter Europa orbiter.  

NASA's current budgets continue to fund the Jupiter-Europa for Phase A, which is the period of advanced development before final design, manufacture, and testing begin.  Funding beyond Phase A is contingent on the Decadal Survey making this mission a priority.  To do that, the Survey would have to deprioritize other elements in NASA's current roadmap.  At $3.2B, there simply isn't room in the budget for this mission and the current Mars program and the New Frontiers and Discovery programs (see here for analysis of latest NASA budget proposal).

At the same time, the proponents of Titan as the choice for outer planet exploration are working to be making their voices heard.  One of them, Ralph Lorenz, presented at the meeting.  He showed that Titan has been to subject of many more scientific articles than has Europa over time. (To be fair, the Cassini-Huygens mission has returned far more data on that moon than the crippled Galileo spacecraft did for Europa.)  He also complained that promised funding for advanced development of a future Titan mission has not been forthcoming.  As an example, he described how promised money to develop balloon technology for a Titan mission had gone instead to fund the Decadal Survey.

Cassini's continued exploration at Titan continues to build the case for returning to that world and to neighboring Enceladus.  The case also is being made that Titan could be home to exotic forms of life and one scientific paper has prioritized Titan ahead of Mars as the best place for astrobiological exploration in the solar system (Europa came in third).  Recent finds at Enceladus continue to build the case that that moon has an internal ocean that could host life.

Whether to return to Europa or Titan or both or neither in the coming decade looks to be one of the biggest decisions facing the Decadal Survey.

Editorial Thoughts: Europa-Jupiter and Titan-Enceladus-Saturn both are compelling targets for exploration.  Both destinations should be explored in the coming decade.  However, the radiation belts at Jupiter impose significant technical challenges to any mission that will meaningfully answer the question of whether Europa could be explored for life, either by finding a thin point in the ice to penetrate or by finding a location where recent eruptions have brought ocean material to the surface.  On the other hand, Titan-Enceladus-Saturn presents a relatively benign environment (if a bit chilly within the atmosphere of Titan), but the mission design and technology apparently aren't ready to fly for some of the most exciting mission concepts.

If the decision were up to me, I would commit to the $3.2B Europa-Jupiter mission and budget another $2B for Titan-Enceladus-Saturn, which might be expanded if other space agencies contributed.  I'd go ahead with the Jupiter Europa Orbiter as planned -- it's ready to go and the harsh environment at Europa doesn't favor cheap missions.  It would also do for the Jupiter system what Cassini is doing for the Saturn system and what Galileo with its crippled antenna couldn't.  Around $2B probably would fund a highly capable orbiter or a less capable orbiter (perhaps similar in scale to the proposed Io Volcano Observer)  and a Titan in-situ probe such as a lake lander.  


An alternative strategy would be to commit ~$3B to Titan-Enceladus-Saturn, perhaps for a combination of New Frontiers scale missions.  Perhaps a Saturn orbiter could execute a number of flybys of Titan and Enceladus with  instruments tuned to fill gaps in Cassini's investigations.  The orbiter could also act as a relay for one or two in situ Titan craft, perhaps the Titan Mare Explorer and the aerial AVIATR.  The Europa-Jupiter mission would then be constrained to a $2B mission.  Within that budget, a capable craft could perform a number of flybys of all the Galilean moons, study Jupiter from afar, and perhaps orbit Europe for weeks instead of the months planned for the Jupiter-Europa Orbiter.  However, the orbiter missions under investigation by the Decadal Survey do not currently include alternatives to the Flagship, ~ $3B, Europa Jupiter System Mission and the Titan Saturn System Mission for exploring those two moons.  The Survey is looking at a number of mission concepts to explore Enceladus, a Titan Lake lander, a Ganymede observer, and an Io observer.

Either of these plans could leave ~$5B for Mars exploration, which would fund the Mars Trace Gas orbiter and the 2018  ExoMars/Max-C mission and leave ~$2.5B for other Mars missions, presumably down payment on a sample return.  In this scheme, lunar, inner planet, and small body exploration would have to share the remaining ~$2B, which would fund perhaps a Discovery mission and a New Frontiers mission.

Baring breaking news on future planetary exploration, the next two blog entries will look at the planning for the science that the Jupiter Europa Orbiter could do for Jupiter and the Galilean moons other than Europa.

Resources:


Updates on NASA outer planets program and status of Jupiter Europa Orbiter funding from Feburary OPAG meeting

• Planetary Science Division Program Status
• Outer Planets Program Status

Ralph Lorenz's OPAG Presentation on status of Titan mission planning

Space News article on possibility of life on Titan http://www.space.com/scienceastronomy/titan-water-life-am-100323.html


Paper prioritizing Titan for astrobiology missions, The Search for Alien Life in Our Solar System: Strategies and Priorities

Hi-def Movies from Mars?

The Mars Science Laboratory originally was to have two cameras (for stereo imaging) that would both be capable of zooming and taking high definition movies.  In 2007, the zoom feature was removed in favor of two fixed focal length cameras, one moderately telescopic and one wide angle.  Now, with a push from movie producer James Cameron (who is a co-investigator on the MSL cameras), NASA is trying to restore the full zoom capability.  You can read the details at the Air & Space magazine website (Cameron's Camera).  Cameron already has experience making movies with remotely operated cameras.

A quote from the article gives us an idea of what the restored cameras might provide us: “The camera is looking down at the Mars rover... You can see the sample arm off to one side, and we pan up and see Mars in front of us. We’re rolling slowly along the surface. We pan back slowly so we see Mars going by, then look back at the tracks of the rover going off to the horizon behind us—in 3-D.”

Thanks to Emily Elakdawalla for the pointer to the article from her tweet.

Upcoming Events

At the last OPAG meeting in February, Jim Green, director of NASA's Planetary Science Division, gave an update on the program.  Included in that update was a schedule of upcoming planetary exploration events for the next three years.  I've slightly modified the list of events to include key mission selection events.  I was unable to find a definitive timeline for when ESA will select its next large mission; one of the candidate missions is the Jupiter Ganymede Orbiter.

Looking over this list, the next three years will be a wonderful time for those of us who follow planetary exploration.

2010

• June 13 - Hayabusa (JAXA) asteroid sample return
• Decadal survey: 2nd-3rd Quarter Prioritization and drafting of survey report 
• July 10 – Rosetta (ESA) closest approach for asteroid Lutetia
• Sept – Lunar Reconnaissance Orbiter transitions to Planetary Science Division
• Nov 4 - EPOXI encounters comet Hartley 2
• Late ‘10 Venus Climate Orbiter (JAXA) arrives at Venus
• Late ‘10- Early ‘11(?) – Opportunity gets to Endeavour
• Late ‘10- Early ‘11(?) – Down selection of Discovery missions?

2011

• Decadal Survey - 1st Quarter Report approved, NASA, NSF, OMB and Congress briefed and report released (prepublication-format)
• Feb 14 - Stardust NExT encounters comet Tempel-1
• Mar 18 - MESSENGER orbit insertion at Mercury
• April/May - New Frontiers mission selection
• July - Dawn orbit insertion at asteroid Vesta
• Aug - Juno launch to Jupiter
• Sept - GRAIL launch to the Moon
• Oct - MSL launch to Mars

2012

• Mid-year – Dawn leaves Vesta starts on its journey to Ceres
• Mid-year – Selection of next Discovery mission?
• Aug - MSL lands on Mars
• Oct - LADEE launch to the Moon

Making 1 + 1 > 2

Wags frequently blame designs that appear to be kludges to the deliberations of committees.  Camels and wildebeests have been held up as examples.  When it was first announced that ESA and NASA would deliver two separate rovers to the same location on Mars in 2018, many commentators on message boards would apparently concluded that attributing this to design by committee might be generous.

The basic deal was that NASA and ESA would combine their landing technology demonstration (ESA), Mars Trace Gas Orbiter (NASA), ExoMars rover (ESA), and MAX-C astrobiology and caching rover (NASA) missions.  The first two elements would fly in 2016 in a mission led by ESA, while the latter two elements would be delivered to Mars in a mission led by NASA.  To keep the 2018 mission within fiscal bounds, NASA would do a single launch and a single landing on Mars that would deliver two rovers to the same location.

 The rovers would have different missions.  The ExoMars rover would have a sophisticated analysis lab (a la NASA's 2011 Mars Science Laboratory rover) with sample delivered via drill from as deep as 2 m below the surface.  The MAX-C rover would have a suite of contact instruments to study the surface soils and rocks and would also collect a cache of samples for latter return to Earth.  Still, two rovers to one location seemed like a stretch of credibility.  I suggested that NASA's rover be delayed and the ESA rover could be enhanced with the MAX-C contact instruments.  (This blog entry also had a lot of background on the two rovers.)

ESA and NASA have moved forward to look at how the two missions could be combined.  The first question appears to have been whether or not a modified MSL entry capsule and the skycrane descent and landing system could deliver two rovers to Mars.  A team has looked into this question and concluded it could, although future studies will also look at airbag landings and landers with legs a al Viking and Phoenix.

The next question is how the two rovers could operate synergistically on the surface of Mars.  That apparently is proving to be a harder question.  To understand the tradeoffs, here are some basic facts about the two missions:

ExoMars

• Primary goal: Acquire and analyze samples from up to 2 m beneath the surface
• Be capable of operating for a total traverse path length of at least [3] km.
• Be capable of conducting Mars sample location selection, sub-surface sample collection down to 2m depth, and sample analysis operations at [6] different locations for at least [180] sols.

MAX-C

• Find locations of interest for sampling and characterize composition, mineralogy, and presence of organic materials to allow sampling decision at many locations
• Select, acquire, and cache at least [38] core samples ([2] caches of at least [19] cores each) from surface materials
• Traverse path length capability of at least [20] km.
• Conduct Mars surface sample selection and coring/caching operations for at least [500] sols.

Based on the design goals, MAX-C will rove almost six times further and operate almost three times longer than ExoMars.  It will also be able to use its instruments to investigate many more sites.  If the experience of the MER rovers with their 90 day planned lifetimes is any example, then both of these rovers may operate for many years and travel many tens of kilometers.

A team has been chartered to look at joint mission opportunities.  They used a couple of analogies, apple orchards and marriage to describe the options and issues.  First, the apple analogies were used to describe how two children in an orchard looking for apples might divide the work:

In the first option, “One looking for apples, the other picking them,” MAX-C scouts for locations that ExoMars will sample with its more sophisticated instruments.  This option makes use of MAX-C’s greater mobility, faster analysis capabilities, and larger limit on the number of sites it can analyze.

In the second option, “Have a 2nd opinion on your best apple,” the two rovers would operate independently, but would combine analytic capabilities when one finds an interesting “apple”.

In the third option, “Are the apples better on different trees?,” rovers separately examine the landing area to maximize the changes of stumbling on the best “apples.”

In the fourth option, “Give you best apple to your friend to take to town,” interesting samples collected by ExoMars would be transferred to MAX-C for caching and eventual return to Earth.

In the fifth option, “Scouting to help choose the best trees to pick,” MAX-C would receive additional instruments too allow it to more efficiently search for ExoMars sampling sites.

In the sixth option, “Make sure not to run into the trees,” the landing system would be enhanced so it could land in more geologically diverse and otherwise hazardous regions to better exploit the capabilities of both rovers.

The marriage analogy comes in as the costs of the two missions getting married.  First, operating together would require extra time and complicate mission operations for both rovers.  Second, finding a landing site that would meet the two rovers engineering constraints and science objectives becomes much harder.

The team did not make any final recommendations, but suggested that the most compelling advantages for using the rovers as a team would be for MAX-C to scout for locations to study, use their different instruments suites (MAX-C surface, ExoMars subsurface) to study interesting sites, and to allow ExoMars to pass samples to MAX-C for caching.

The recommended hardware changes to the missions to enable their cooperative exploration (and most of these would be considered major changes except as noted) would be:

• Improve landing hazard avoidance to allow landing at a site that better addresses both rovers’ goals
• Modify ExoMars and MAX-C sampling handling to allow transfer and caching of samples
• Extend ExoMars roving distance to ~ 10 km and double its planned lifetime (this might be a major change; not noted in the team’s report)
• Allow two telecommunications sessions per sol with each rover to reduce conflicts for available communications bandwidth (this might be a minor change; not noted in the team’s report)

 From 2 Rover International SAG presentation to MEPAG, March 2010

Editorial Thoughts: If all of this makes you worry that this is a mission designed by a committee and possibly a kludge, remember that camels and wildebeests are highly successful species.  I suspect that the combined efforts of these two rovers will be greater than the sum of their separate contributions.  And without this marriage, the Mars Trace Gas Orbiter would be a minimalistic endeavor instead of the highly capable mission now planned and ExoMars might not fly at all.   That's a "committee" decision I have grown to like.

Resources: The following presentations form the basis of this report and were presented at the March 2010 MEPAG meeting

2018 mission update

2 Rover International Science Advisory Group

Preparing for Japan's Akatsuki Venus Orbiter

Note: A crush of deadlines is largely behind me and I should be able to begin more regular postings again.

Japan is in final preparations for the May 18 launch of its Akatsuki orbiter.  This mission will use a innovative orbit to allow it to study the super rotation of Venus's atmosphere.  While Venus itself rotates at a brisk walking pace (6.5 km/hour or 4 miles/hour), the upper atmosphere rotates at 400 km/hour.  Current models of atmospheric circulation cannot explain the super rotation, suggesting that Venus can teach us some fundamental lessons about how atmospheres work.

The mission will study Venus in a number of wavelengths to study the atmosphere at different levels.  One band will see all the way to the surface and will be used to look for signs of active volcanism.

Akatsuki's five cameras will be optimized to probe phenomenon at different levels of the atmosphere and on the surface.  From Planet-C 2008 VEXAG update

The entire budget for the mission is just $280M (¥25.2 billion), although it's not clear what all is included in that cost beyond the spacecraft (launch vehicle? instruments? mission operations?).  Whatever the full burdened cost of the mission, it appears to be within the scope of what would fit within NASA's Discovery program.  This suggests that there are still interesting missions to the inner planets that would be relatively inexpensive.

As the launch date approaches, articles are beginning to appeal, and I posted a blog entry on the mission some time ago that includes some nice illustrations:

My blog: http://futureplanets.blogspot.com/2009/03/vexag-part-2-japanese-venus-climate.html

Journal Nature: http://www.nature.com/news/2010/100315/full/news.2010.126.html?s=news_rss

Aviation Week and Space Technology: http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/asd/2010/03/18/04.xml

Additional resources:

JAXA Planet-C website

Planet-C 2008 VEXAG update (with information on scientific goals)

Planet-C 2009 VEXAG update (mostly engineering and schedule) Large file!

BBC Article on Jupiter Europa System Mission

The BBC has an in-depth interview with Dr. Robert Pappalardo from NASA's Jet Propulsion Laboratory.  Dr. Pappalardo has led JPL's efforts to define the Jupiter Europa Mission.  This interview provides a very nice perspective on the science goals of the proposed NASA and ESA missions to the Galilean moons.  I learned some interesting tidbits after following these proposed missions for a year and a half.  You can read the interview here: http://news.bbc.co.uk/2/hi/science/nature/8537992.stm

Decadal Survey Update

I've been busy with various projects so that recent posts have focused on process which are quicker to write.  Within the next week, I'll start posting again on possible future missions.

At the just completed Lunar and Planetary Science Conference Steve Squyres provided the most complete explanation and update of the Decadal Survey I've seen yet.  (Go to the Decadal Survey webpage, and look for 'View the Presentation given by Decadal Chair Steve Squyres to the LPSC on the status of the study' about a quarter of the way down the page.  This is a Java link, so I can't provide a normal link.)

His presentation discusses the scope of the Survey, which will prioritize all Flagship and New Frontiers missions.  If New Frontiers missions are prioritized by rank as opposed to just identifying a candidate pool of targets, this will be change in how these missions are selected.  The last Decadal Survey selected a pool of (if memory serves me correctly) four missions that was latter expanded to six to eight missions.  Any target within the pool -- which ranged across the solar system -- was an allowable target.  Squyres' slide suggests that instead, this Survey may actually designate which specific targets are priority #1, #2, and so forth.

Discovery missions will continue to be selected by competition, but the science goals by which they will be selected will be identified by the Survey.  Only missions that have received formal budgetary new starts and therefore are in development are exempt from review (these are Juno [Jupiter interior and atmosphere], GRAIL [lunar gravity], Mars Science Laboratory rover, LADEE [lunar atmosphere], MAVEN [Mars upper atmosphere]).  All other missions including the Mars Trace Gas orbiter and the Jupiter Europa Orbiter are subject to Survey review and prioritization.  A key requirement is that the recommended list be able to be implemented within expected budgets.  NASA has made it clear that it will use the Survey's prioritization as its priorities.

Squyres included a schedule for completing the survey:

2010

• 1st- 2nd Quarter Final Panel meetings, Panel reports finalized
• 2nd-3rd Quarter Prioritization and drafting of survey report
• 4th Quarter Draft survey report to reviewers, Report revised

2011

• 1st Quarter Report approved, NASA, NSF, OMB and Congress briefed and report released (prepublication-format)
• 3rd Quarter Printed report released

Editorial Thoughts: The presentation suggests a difference in the way New Frontier missions are selected.  In the past, they have been selected from a list of missions.  In any given decade, only a third (and later after the list was expanded a quarter) of the missions could be selected.  If the survey is prioritizing New Frontiers missions, the list of missions would likely be constrained to just those that could be afforded within the coming decade.  It is also possible that the Survey will recommend one or more small Flagship missions at around $1 - 1.5B (compared to ~$3B for a full scale Flagship mission).  If this occurs, the coming decade could have a much more focused program than the last decade.

A couple of weeks ago, the subscription-only journal Nature had an article discussing the Astronomy Decadal Survey, which is in progress but somewhat ahead of the Planetary Decadal Survey.  Nature held a round table with several prominent astronomers who were not members of that Survey.  The participants emphasized the importance of a 'narrative' to provide a story behind the recommendations of a Survey.  The search for life in the universe and understanding the origins of the universe were discussed as possible astronomy narratives.  (As a side note, a strawman poll of the Nature discussion participants gave priority to the Large Synoptic Survey Telescope, the Giant Segmented Telescope, the Terrestrial Planet Finder, and the Constellation-X Observatory/International X-ray Observatory.)

If the planetary survey selects a narrative, then prioritizing the larger Flagship and New Frontiers class missions makes sense.

I don't think it's hard to predict a likely Planetary Survey narrative: The search for possible habitats for life, past or present, in the solar system.  This would give priority to missions to Mars, Europa, Titan, and Enceladus.  Venus, Ganymede, and Callisto might gain supporting roles as worlds that help us understand the evolution of terrestrial planets and icy moons.  If this becomes the narrative, the target worlds are easy to predict.  What is harder to predict is how the Survey will recommend that dollars and therefore mission resources be divided between them.

Appendix: This is the list of missions that the Survey is considering for the next decade (from Squyres' presentation). The institution performing the analysis of each mission is also given: Goddard Spaceflight Center, the Jet Propulsion Laboratory, the John Hopkins Applied Physics Laboratory, and the Marshall Spaceflight Center.

• SAGE (NASA New Frontiers 3 Candidate)
• Venus Mobile Explorer (GSFC)
• Venus Tessera Lander (GSFC)
• Venus Climate Mission (GSFC)
• Moonrise (NASA New Frontiers 3 Candidate)
• Lunar Polar Volatiles Lander (APL)
• Lunar Network Mission (MSFC)
• Mars Trace Gas Orbiter (JPL)
• Mars Polar Mission (JPL)
• Mars Network Mission (JPL)
• Mars Sample Return (JPL):
• Mars Astrobiology Explorer with Cacheing
• Mars Sample Return Lander
• Mars Sample Return Orbiter
• Europa Flagship Mission (JPL)
• Io Mission (JPL)
• Ganymede Mission (JPL)
• Saturn Probe (JPL)
• Titan Flagship Mission (JPL)
• Titan Lake Lander (JPL)
• Enceladus Mission (JPL)
• Uranus System Mission (APL)
• Neptune System Mission (JPL)
• OSIRIS REX (NASA New Frontiers 3 Candidate)
• Main Belt Asteroid Lander (APL)
• Chiron Orbiter (GSFC)
• Trojan Asteroid Tour (APL)
• Comet Surface Sample Return (APL)

Additional Studies

• NEO target study. (Assess NEO targets that can be reached with an electric propulsion spacecraft.)
• Reactor-Based thermoelectric generator technology study.
• Saturn Ring Observer technology study.
• Comet cryogenic sample return technology study.

Beyond describing a prioritized set of NASAplanetary missions, the survey report will address several other issues:

• NSF-funded ground-based telescopes
• Technology development for future NASA
• planetary missions
• The NASA and NSF planetary R&A programs
• Education
• Public Outreach

State of the Program

At major meetings of planetary advisory meetings, NASA headquarters gives a state of the planetary presentation.  A couple of readers have written asking me to provide updates on when New Frontiers competitions, etc. are expected to be completed.  So about twice a year I'll summarize the state of the program.  (These updates happen every few months, usually with little change from presentation to presentation.)

The most recent presentation was by James Green, Director of NASA Planetary Science Division, to the Decadal Survey Steering Committee at the end of February.

The biggest news was the proposed FY11 budget, which I've covered in depth in previous blogs.  As a side comment, though, Green said that the proposed budget for about $1.4B was substantially less than the budget for the Solar System Exploration and Mars programs earlier in the decade (when these were two separate programs).  I went back and checked old budgets, and the combined FY04 FY05 budgets for the two programs was $1.9B.  Given inflation, today's budget is a substantial loss in purchasing power.  Unfortunately, the programs that NASA is trying to fit into today's budget -- an aggressive Mars exploration program leading to a sample return, the New Frontiers and Discovery principal investigator led mission programs, and an outer planets flagship mission -- was sized for the budgets of mid last decade.  Something will have to give in the coming decade.

Good News

Here's a list of the funded programs in the new budget:

• Continued operation of all in 11 in flight missions including Cassini and the Mars MER rovers
• Juno (Jupiter interior and atmosphere), GRAIL (lunar gravity), Mars Science Laboratory rover, LADEE (lunar atmosphere), MAVEN (Mars upper atmosphere) continue development
• Continues advanced funding for Europa Jupiter System mission pending recommendation from the Decadal Survey
• Restart of Pu-238 (if Congress approves; they withheld approval last year)

Mars Science Laboratory on track for 2011 launch with only minor issues remaining. [Am I'm glad to write that at last!]. No major titanium issues found.

Next New Frontiers mission will be selected in April/May 2011 between MoonRise (lunar sample return), OSIRIS-Rex (asteroid sample return), and SAGE (Venus lander)

Final schedule for selection of the next Discovery mission remains open (From the draft Announcement of Opportunity released last December, a downselection to a small number of candidate missions would likely occur by early next year with final final selection in mid 2012 and launch no later than 2016.  However, this is subject to change.)

NASA has committed to the joint mission with ESA for the Mars Trace Gas orbiter and request for proposal for instruments has been released.  (NASA has also agreed to participate in ESA's 2018 ExoMars rover mission.  NASA's current plans are include a capable lander of its own to cache samples for eventual return, but the scope of that involvement presumably is subject to change based on the Decadal Survey's recommendations.)

Not so good news:

The Europa Jupiter System Mission appears to still require Russia to fulfill its contracts to supply additional Pu-238.  Restarted production apparently would not supply new material in time for this mission.  Right now there is enough Pu-238 on hand for a Discovery mission, a lunar network mission, and about half of the Jupiter Europa Orbiter requirements.  [The lunar network mission costs have exceeded expectations, so a small amount of Pu-238 may become available to cover a small part of the JEO shortfall or to power another Discovery-class mission.]

The Promise of MSL

I had planned to post this blog entry a couple of weeks ago, but then budget news intervened.  One piece of news that came out of the Decadal Survey meeting last week was that the Mars Science Laboratory (MSL) rover Curiosity is on track for its 2011 launch.  About a week before that meeting JPL released information on one of the possible landing sites for MSL, Gale Crater.  Currently there are four finalists for the landing site with two additional sites under consideration for the short list.  (Final selection of the landing site is planned for early 2011.)  The goal of the mission is to use the new precision landing system to place MSL within a terrain that shows obvious evidence of a watery past.  Ideally the location will have access to ancient clay and sulfate minerals that formed in the presence of water.

I don't know whether Gale Crater will be ultimate choice for the landing site.  Similar studies to the one reported below are underway for all the candiates sites.  However, this early look at one of the candiates suggests what a stunning scientific bonnanza awaits MSL.

When you finish reading the portion of the press release below on Gale Crater, you might want to check out the recent BBC article on MSL and its development travails, read this  write up on the current four candidate landing sites, read a mission summary on Wikipedia, or go to the candidate landing site website for more details on Gale Crater and the other candidate sites.

The complete press release can be found at http://www.jpl.nasa.gov/news/news.cfm?release=2010-044

PASADENA, Calif. -- Near the center of a Martian crater about the size of Connecticut, hundreds of exposed rock layers form a mound as tall as the Rockies and reveal a record of major environmental changes on Mars billions of years ago.

The history told by this tall parfait of layers inside Gale Crater matches what has been proposed in recent years as the dominant planet-wide pattern for early Mars, according to a new report by geologists using instruments on NASA's Mars Reconnaissance Orbiter.

"Looking at the layers from the bottom to the top, from the oldest to the youngest, you see a sequence of changing rocks that resulted from changes in environmental conditions through time," said Ralph Milliken of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This thick sequence of rocks appears to be showing different steps in the drying-out of Mars."

Using geological layers to understand stages in the evolution of a planet's climate has a precedent on Earth. A change about 1.8 billion years ago in the types of rock layers formed on Earth became a key to understanding a dramatic change in Earth's ancient atmosphere.

Milliken and two co-authors report in Geophysical Research Letters that clay minerals, which form under very wet conditions, are concentrated in layers near the bottom of the Gale stack. Above that, sulfate minerals are intermixed with the clays. Sulfates form in wet conditions and can be deposited when the water in which they are dissolved evaporates. Higher still are sulfate-containing layers without detectable clays. And at the top is a thick formation of regularly spaced layers bearing no detectable water-related minerals.

Rock exposures with compositions like various layers of the Gale stack have been mapped elsewhere on Mars, and researchers, including Jean-Pierre Bibring of the University of Paris, have proposed a Martian planetary chronology of clay-producing conditions followed by sulfate-producing conditions followed by dry conditions. However, Gale is the first location where a single series of layers has been found to contain these clues in a clearly defined sequence from older rocks to younger rocks.

"If you could stand there, you would see this beautiful formation of Martian sediments laid down in the past, a stratigraphic section that's more than twice the height of the Grand Canyon, though not as steep," said Bradley Thomson of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. He and John Grotzinger of the California Institute of Technology in Pasadena are Milliken's co-authors.

NASA selected Gale Crater in 2008 as one of four finalist sites for the Mars Science Laboratory rover, Curiosity, which has a planned launch in 2011. The finalist sites all have exposures of water-related minerals, and each has attributes that distinguish it from the others. This new report is an example of how observations made for evaluating the landing-site candidates are providing valuable science results even before the rover mission launches.