How about, "That bacteria is especially good at leaching gold out of rocks -- how can be put it to use" or "That bacteria makes one outstanding yogurt -- can we use it on Earth" or "That bacteria is amazingly efficient at degrading pollutant -- can we use it to solve a pollution problem" or "That bacteria can make hydrogen from water -- is it the solution to our global warming problem on Earth".

The point is that bacteria on Earth are very useful creatures, especially those that come from extreme environments.

Basically, we have a question in second-order probability, which isn't really even science.

I think there are good theoretical reasons to suspect that the shape of the second-order probability function (depending on biogenesis mechanisms of which we are solidly ignorant) spikes at the ends. Given 10^21 planets out there, the number that are at a given stage of habitation is probably either very high (within a couple orders of magnitude of the maximum; of course, some will be too hot, too cold, etc.) or extremely low.

Consider the exponents of p(L)... the probability of life (at some stage or another) on a planet and the exponent in the number of planets. It's quite unlikely that those two exponents are very near one another. (There would be absolutely no causal relationship between them.) If the exponent on the odds against life is considerably greater than the number of planets, then we probably ARE alone. (Eg, if there are 10^21 planets, and p(L) = 10^-40). If the exponent is considerably less (eg, 10^21 planets and p(L)=10^-5), then there are countlessly many planets with life at stage L.

It's either a mob or an empty house. People seem to have hunches about p(L), but I'll be darned if I've seen a lot of unbiased samples to point to as evidence. (Europa, here we come, one day.)

I'd say you've pretty much got it right, JRehling. Your argument is correct if we consider some finite volume of space over which we're counting planets and assigning probability for life, like for example our own galaxy. Unless you pick the volume specially, the two numbers should be unrelated and so you get either a huge or tiny (basically zero) number of planets with life.

So can we conclude from your argument that, since we do observe life on one planet in the Milky Way, and since the likely number of inhabitted planets in our galaxy is either miniscule or huge, then it must be huge?

Unfortunately we can't. What's missing is that the universe may be infinite in size (or just mind-numbingly bigger than what we can see now). Then no matter how small the likelihood that life arise on a given planet (as long as it's not zero), there will be lots of inhabited planets throughout the universe, in fact an infinite number of them! So even if we were ever able to reliably work out these probabilities and found that there was a 1 in 10^50 chance, say, of life developing in our galaxy, we shouldn't be surprized.

In other words, all bets are off, big time.

The probability of two bodies in a solar system
evolving life may be much smaller than the
probability of one body doing so. If so, not
finding other life in our solar system is no
indication of the probability of life arising in
other systems.

Could not the probability of life on one planet
in a solar system like ours be quite high, even
if the probability of life on two planets is very low?

Life looks possible on many bodies in our solar system, though we haven't as yet found evidence of it. I'd venture to say that as we continue to discover potentially habitable planets in places previously thought not likely - in binary systems, for example - the likelihood may swing towards it being more probable to find multiple life-bearing planets in a solar system.

If life were more easily apparent on several planets/moons in our solar system, I wonder what effect might that have on our theology? In the past few decades many astronomers have comfortably incorporated the likelihood of E.T. life into their religious beliefs, even without any direct evidence. Think how different it would be if there were some Martians clinging to their dying planet, as imagined a century ago.

Back to the news that began this thread, on this page you can find an interview with Andrew Knoll from the rover team discussing the prospects for life on Mars, from the Canadian radio program "Quirks and Quarks".

Hi
I must be missing something but aren't salt and acid mutually exclusive, and if so were there more neutral areas in between.
Roy

In principle, yes. We could hypothesize, for example, that Bode's Law tends to hold in a lot of cases, and therefore the "habitable zone" will be uncrowded.

But, just change the units in the discussion to "planetary system". That's the real interesting question. Of course there should be a lot of Mercurys and Plutos out there that seem to have no bearing on the issue.

See, that's what I find most fascinating about the entire issue. If we don't find life on Mars, Europa, Enceladus, or, let's say & why not, Titan, we've at least constructed the very first tentative set of boundary conditions to better resolve JR's probability plot.

One thing we can say with a high degree of confidence right now is that Earth is the only planet in the Solar System with an extensive macroscopic surface biosphere, which is largely a function of free O2 and abundant liquid/vapor H2O in a relatively dense atmosphere (causal relationships in the whole plant/animal interdependence noted but not addressed.) With respect to Mars, this to me means that life perhaps survives, but does not thrive there in the same sense that it does on Earth. It may be confined to oases of favorable conditions, much like the chemosynthetically-based communities of the ocean floor.

If we can find even one, count it, one possible hot spot on Mars that just might have a spring associated with it, then that would be the highest priority landing target on the entire planet. Not sure if our orbital armada is correctly equipped to precisely identify such a hypothetical feature, though...they can be quite small indeed.

Where's the mission to pinpoint methane "hot spots"?

It was one of the ones for the next round of Mars Scout. (MARVEL I think)

Doug

If MARVEL flies in 2013 and sends back very
intriguing results, I guess we'll have to plan for
another rover mission.

edit:
By the way, is MARVEL even still in the running? Or
are only "upper level" atmospheric missions without
the capability of pinpointing areas on the surface of
water vapor or methane release being considered?

MARVEL is not in the running. The Great Escape proposal apparently includes a spectrometer for measurements of methane and other trace gases. It is also possible that the MAVEN proposal would measure biogenic gases as part of addressing "key questions about Mars climate and habitability." However, the MSO science definition team put atmospheric chemistry as the prime goal of that now canceled mission, so the implications are that Great Escape's capabilities in this area are limited.

From the JPL press release http://www.jpl.nasa.gov/news/news.cfm?release=2007-002:

-- Mars Atmosphere and Volatile Evolution mission, or Maven: The mission would provide first-of-its-kind measurements, address key questions about Mars climate and habitability, and improve understanding of dynamic processes in the upper Martian atmosphere and ionosphere. The principal investigator is Dr. Bruce Jakosky, University of Colorado, Boulder. NASA's Goddard Space Flight Center, Greenbelt, Md., will provide project management.

-- The Great Escape mission: The mission would directly determine the basic processes in Martian atmospheric evolution by measuring the structure and dynamics of the upper atmosphere. In addition, potentially biogenic atmospheric constituents such as methane would be measured. The principal investigator is Dr. Alan Stern, Southwest Research Institute, Boulder, Colorado. Southwest Research Institute, San Antonio, will provide project management.

Oh, and I forgot to add to my previous post that I believe the Phoenix can also measure trace atmospheric gases such as methane. Not sure of this, though.

Roy - Acid (in liquid form) and rock are mutually reactive (i.e., mutually exclusive), on Mars as on Earth. The existence of salts implies that acids have been neutralized (by rocks). There is a great excess of rock (mainly basalt) on both planets. Therefore acids can be preserved only as non-reactive solids, such as jarosite or other ferric sulfates, or in the atmosphere (carbon dioxide). Personally, I doubt if liquid acids could ever have persisted as lakes or especially groundwaters. The ferric sulfates probably originated by sufide weathering (mechanism of Roger Burns) or as gas cloud condensates caused mainly by large meteorite impacts (although volcanic or post-impact fumarolic/hydrothermal input cannot be excluded). Acid lakes or groundwaters presumably weren't involved.

Salt water freezing or evaporation yields fresh water as ice or vapor (ice sublimation also yields vapor). So there must be plenty of fresh water on Mars, albeit in frozen form. That's a major reason why the planet appears so salty - the salts are a leftover of freezing. Of course, this is too commonsense to be news.

-- HDP Don

I really liked the following description of what MARVEL could
do. I haven't seen similar capabilities described for the
remaining mission candidates. Maybe NASA thinks these
claims are too difficult to achieve.

"a submillimeter spectrometer, would... seek localized atmospheric
concentrations of the chemicals of interest.

...Marvel could either detect and localize any existing life and active
volcanism on Mars or put extremely stringent limits on their existence....

The submillimeter spectrometer would also be used to seek localized
concentrations of water vapor in the atmosphere, a strategy to identify
places where subsurface water sources are actively venting."
http://mpfwww.jpl.nasa.gov/newsroom/pressr.../20021206a.html

NASA adopted these proposals for the now cancelled 2013 MSO mission (with the addition of a Hi-RISE class camera).

Studying the history and cyclic variations of Mars' atmosphere is great,
but how great would it be to identify a location exhibiting current production
of water vapor and/or methane? Maybe the low probability of finding such
a location is not judged to be worth the cost of looking at this point.

Would a dedicated mission for such a search be necessary, though? I'd think that one or two instruments would be sufficient: a high-res spectrometer & perhaps also a high-res IR sensor. Ideally, though, you'd want to put them on a polar orbiter for full coverage at minimal periapsis with a nadir view.

So, what else could we do from a polar orbiter? Radar mapping--particularly, pinging the permanent polar caps--and comm relay for high-latitude landers spring to mind, but not much else. Weather monitoring?

Hopefully further detailing of global and regional methane and
water vapor levels will spur the desire to look for point sources.
I wonder how far down the line that might be?

The methane levels are low and the signal is weak. A limb scanning instrument can detect it more easily due to long optical paths, but at shorter IR wavelengths, dust interference can reduce visibility of the lower atmospheric column. I don't know microwave, millimeter, and submillimeter remote sensing to know the spectral features and strengths in that part of the spectrum, and the instrumental limitations vs. shorter wavelengths.

What you'd LOVE to have is a Nadir viewing instrument that scans cross track to produce a global methane or whatever map once a day. It may not be possible with any spacecraft we can put in Mars orbit. Second best is a limb scanning instrument, preferably with multiple fields of view, to do essentially the same thing but with worse along track resolution.

You really want the ability to spot sporadic outbursts, as well as sources of steady state leakage. That level of sensativity may require a LARGE instrument on a dedicated spacecraft. It's unclear to me now if the requirements are worth the $$$$ at our current level of knowledge of the atmosphere's trace composition.

We'll have better ideas post-Phoenix (cross fingers). I don't know if they do expect to see the atmospheric methane or other trace molecules. The wet chemistry experiments will tell a lot, too, the first since the most curious results from Viking. A better understanding of soil chemistry and minerology, hampered by the lack of minerology specific experiments other than Crism, Omega, TES and Mini-TES, and the iron minerology seen by Mossbauer, will help a LOT.

We may just <frustrate> need to fly an interim instrument.... Something that (like Keplar will do for Terrestrial Planet Finders) will define the problem well enough to design the definitive instrument to crack this particular hard nut.

How did the famous martian meteor ALH48001 register? Too salty to have a possible fossil?