Many readers of this blog will be familiar with Bruce Moomaw who has been a long time commentator on planetary exploration. In a series of e-mails with several people, Bruce made some interesting points that I thought readers here also would find interesting. With his permission, I've assembled two threads here from e-mails over several weeks (with minor editing to increase cohersion).
On the value of the Mars Science Laboratory
The rationale for MSL is that its central purpose is to do something -- namely, look for organics -- which is difficult and maybe impossible for a less expensive mission to do. "SAM" is MSL's crucial core experiment; if I remember correctly, it weighs as much and uses more power than all the other experiments put together. A Raman spectrometer may or may not be sensitive enough to look for Martian trace organics; it certainly won't be as sensitive to them, or as capable of identifying them, as SAM is. So the real choice is to fly one cost-overrunning rover with great sensitivity to trace organics -- which will thus help us decide whether to set down a sample return mission or an "Astrobiological Field Lab" at the same landing site -- or a series of one or more smaller rovers which may very well not be able to detect organics at their landing sites even if Martian organics do exist. The rationale for the latter consists solely of the fact that we could send them to multiple landing sites (albeit with less organic sensitivity) if and only if MSL comes up empty-handed; if MSL comes up NOT empty-handed in its organic hunt, there is no point in wasting time launching a series of less capable rovers to different places before we move on to the AFL, or a sample return mission, sent to MSL's site. (Phoenix's unexpected discovery of those nasty perchlorates does little to change this argument, although I maintain that it does greatly heighten the rationale for trying to cram a Raman spectrometer onto MSL even at this late date.)
I repeat that the main [problem] of the Mars program, as far as I can see, involves not the cost overruns on MSL, but our [current] insistence on trying to fly a Mars probe at every Earth-Mars launch window rather than taking a fairly lengthy breather to examine MSL's results and only then resuming the planning and launch of Mars missions -- which, besides being good for the Mars program itself, would also free up more funds for the likes of Europa Flagship or New Frontiers.
You'll note that in their presentation "Potential MSL Outcomes and Discovery Response", Joy Crisp et al regard the launch of another rover -- with different instrumentation and/or a different landing site -- as the most likely followup of the MSL mission, with sample return being the followup only if MSL finds strong evidence of "interesting organics". But of course this means that that next rover must also have an ability to detect organics -- which will be difficult for a Mid-Rover, aka the "Mars Prospector Mission", to do, with Raman/fluorescence likely being the only instrument that could be crammed onto such a rover. And they also [state] that instrument design and landing site must be picked only after we get MSL's results. In this connection, of course, we also have ExoMars -- but remember that 2006 study made by JPL's summer school for interns ( http://adsabs.harvard.edu/abs/2006AGUFM.P51C1205C ) arguing that an ExoMars-sized rover with organic detection capability is likely to be practical only if the science payload is trimmed down almost to a single pyrolitic organic-detection instrument. If they're right -- and so far I see no reason to think they were wrong -- then "SCREAM", or something like it, could become the followup rover to MSL, but only if the followup rover has ExoMars' capabilities, which are currently greater than those for the projected Prospector Rover.
The "real problem in the early portion of the planning cycle" is the famous Camel's Nose Effect, in which you start by deliberately understating the cost and/or overstating the usefulness of a proposal, and then in succeeding years gradually raise your cost estimate and lower your usefulness estimate, all the while informing Congress (or whatever funding source you have) that if they don't go ahead and ante up that extra funding anyway, the money already spent on the proposal will have been wasted. NASA got both the Shuttle and the ISS funded in exactly this way, and it's hardly surprising to see the same thing happening to smaller unmanned space projects... JPL's utilization of the CN Effect to avoid MSL's cancellation is tiny by comparison -- and MSL's actual scientific usefulness relative to its cost is far greater than that of Shuttle and ISS. (Indeed, you probably all remember my previous statements that MSL, while it may end up being delayed, should under no circumstances be cancelled because it's a "watershed" mission whose results should and will be crucial in deciding what we ought to do next at Mars. The [real issue] in the Mars Program is the absurd insistence that we continue launching missions to Mars every two years, when in reality what we ought to do is sit back for about 6 years after MSL and let its results mold the next part of the Mars program. Personally, I'd be very happy if they utilized the MSL delay to add one more instrument, a Raman spectrometer, to its payload, given the possible nasty consequences from Martian perchorates.) As for whether JPL knowingly understated MSL's cost at the start, I simply don't know. If they did so, they were indeed counting on the Camel's Nose Effect to keep the funds flowing in -- but, to repeat, in this case that's not the primary count against them.
On the possible impact of perchlorate on MSL
Has anyone noticed just how devastating Phoenix's discovery of perchlorate salts on Mars is to all the current plans to look for Martian organics? See the LPSC paper by Ming et al at the LPSC ( http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2241.pdf ): "The presence of a strong oxidizer (i.e., perchlorate salt) in the soils at the Phoenix landing site will most likely combust organic materials during pyrolysis by TEGA [as the team established in detailed ground experiments]. Therefore, it is highly likely that no organic fragments will be detected by TEGA, unless they are present at concentrations that can overwhelm the oxidant." Both MSL and ExoMars utilize just such high-temperature pyrolysis (including the "Urey" instrument on ExoMars) -- and since it seems likely that Phoenix's perchlorates were produced by reaction of Martian atmospheric oxidants with chlorine in either gaseous or mineral form ( http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1567.pdf ), it seems likely that we'll find the stuff every place. The one instrument seriously proposed as a trace-organic searcher that is not vulnerable to this problem is the Raman spectrometer -- and in that connection, another LPSC paper found that Raman spectroscopy could detect beta-carotene at less that 1 part per million. ExoMars, lest we forget, carries a Raman while MSL does not, although I'm unsure of its sensitivity. Anyway, I intend to make some enquiries as to just how serious a problem the various researchers think this actually is -- it could be a real show-stopper.
I have yet to see anyone comment on the potentially devastating effect on Martian astrobiology made by Phoenix's discovery of perchlorates. It may provide actual Martian life with a boost by making it much easier for briny liquid water to exist near the surface; but it also makes it much harder to detect Martian organics, since it now appears that the use of any pyrolysis of Martian samples in an oven to look for organics will just end up chemically activating the perchlorates to destroy any Martian organics existing in the sample before the GCMS ever gets a chance to try and detect them. We may need an entirely different kind of organics analyzer than any planned for MRL (aka "Curiosity") -- such as a Raman analyzer that could look for trace organics without its laser light destroying the very thing it came to Mars to discover. One of ExoMars' strong suits is that -- unlike MSL -- it DOES have such Raman sensors.
Paul Mahaffy [SAM principle investigator] (kind of) answers my argument that Phoenix's discovery of perchlorates in Martian soil is very bad news for MSL's search for organics on Mars, given the fact that at pyrolytic temperatures the perchlorates are likely to react and destroy the organics before Mahaffy's instrument "SAM" has a chance of detecting them. Reading between the lines, however, it seems to me that the point he makes is really that we just don't know for sure yet whether perchlorates exist on other parts of Mars (and particularly inside Noachian rocks), so that SAM's chances of finding organics have indeed been reduced by Phoenix's find but are not yet "dismissed". I can't disagree with that, but then I myself was saying that SAM's goal is seriously endangered by this discovery but has not yet been totally wrecked. I still wish MSL had a Raman spectrometer.
"Why should we assume that Mars is not a very diverse place just like earth? Just because Phoenix found perchlorates in a specific location in the northern latitudes we should not assume that this chemistry will prevail all over the planet and especially in the ancient rocks that MSL may sample perhaps from early times when the chemical environment was much different.
"A key driver for selection of the MSL landing site will be the diversity of this site as established from our powerful orbital tools. I suggest the possibility of finding organics with the powerful MSL tools should not be dismissed based on this (certainly interesting) Phoenix detection. Also note that one organic detection now seems to be on firm footing – that of methane in the atmosphere."
Even though ExoMars' MOD instrument works at temperatures well below the combustion temperature for perchlorates, the latter will get mixed in with the possible organics in the subcritical water extract and so may well destroy them that way. Which, if true, returns us again to Raman spectrometry as the only reliable organic detector for Mars landers.
I've just run across a 2006 presentation by Henk Leeuwis ( http://www.planeetonderzoek.nl/documents/5_Leeuwis_NPP_Pasteur.pdf , pg. 5) which seems to say pretty clearly that another ExoMars instrument -- the Mars Organic Detector -- also does not require high-temperature pyrolysis: "...uses sublimation at Mars ambient pressures and temperatures to purify organic components from [its sub-critical] water extract." That "subcritical water extractor" apparently can be used at temperatures below boiling ( http://www.liebertonline.com/doi/abs/10.1089/ast.2007.0154?cookieSet=1&journalCode=ast ) and thus well below the pyrolytic temperature for perchlorates.
My thoughts as recorded by you contain one self-contradiction: the "Urey" experiment on ExoMars -- of which the "MOD" detector is the primary component -- does NOT raise the temperature of its samples to the combustion temperatures for perchlorates, and so may perhaps avoid the interference of perchlorates with the search for organics. However, it DOES use hot water -- maybe all the way up to 250 C. in a supercritical state -- and so the perchlorates may interfere with the search for organics when dissolved in such hot water. (The same thing is true for the "Life Marker Chip" on ExoMars.) I've enquired of the principal investigators for these two instruments whether perchlorates would indeed interfere with their search for organics, but so far have received no response.ReplyDelete
Make that "hot water in a SUBcritical state"; the water may be raised in temperature past its normal boiling point, but at high pressure so it doesn't boil -- but it will not be raised to supercritical temperatures. The possible problem of perchlorates interfering with its search for organics, however, remains.ReplyDelete