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Rupert Goodwins

Now that's what I call service.

So dust and fading cells may do for the MERs, but so could a wrong turning or an unintended command sequence. I'd bet on the latter - didn't something like that can one of the Viking landers?

I think, however, that the dangers of the extended mission are concomitent with the benefits - even in the narrow sphere of mission control. If we are going to explore on the ground, then we will need to know how to run rover missions that go on for many months, and frankly the money spent on keeping the team running that long is going to be far better value than sending new mops up to the caretakers on the ISS. Given that the Shuttle has slipped to 2005, I'd imagine that ongoing good news from Mars will find ready sponsorship.

Now, what I'd *really* like to see is something spectacular. Not too wild. A trilobite would be nice.

R

Bruce Moomaw

Rupert, a trilobite is very "wild" indeed. The odds are overwhelming that, even if Mars evolved one-celled life, it did not evolve multicellular life.

Joel McKinnon

Multi-cellular life may be unlikely, but I wouldn't think the odds against it were "overwhelming."

Here's a snippet from an article I wrote for New Mars after a chat with Chris McKay at NASA Ames:

The other big advantage on Mars had to do with something we don’t often associate with modern Mars – the presence of oxygen. The development of complex lifeforms on Earth had to wait until there was sufficient oxygen generated by early anaerobic (non-oxygen breathing) lifeforms. This process took about 700 million years. On Mars, due to a variety of factors such as a greater initial quantity of volatiles including water, the lower gravity letting more hydrogen escape, less volcanic outgassing, and the lack of plate tectonics as on Earth, all combine to create a situation in which Mars could have become sufficiently oxygenated to allow development of multicellular life in only 10 to 100 million years. With these kinds of advantages, how advanced could life have become on Mars before the surface became uninhabitable?

“It could have been as advanced as small animals and plants – if evolution was faster on Mars. It could have gone up to the Precambrian level – trilobites and palm trees; fern trees would have been possible. That’s not saying that they’re there, but theoretically it’s possible. We should include in our research the ability to be able to see fossils of things like that.”

The full article is available at https://www.newmars.com/archives/000066.shtml

Bruce Moomaw

I know about that, Joel -- my argument is that the oddds are overwhelming that Mars did not have time to evolve the one-celled photosynthetic organisms that could pump out that oxygen. It took a good 1.5 billion years for cyanobacteria to appear on Earth; Noachian Mars was conceivably habitable for such organisms for only around 700 million years -- and that was the same period in which both planets were being savagely bombarded every few hundred thousand years with giant asteroids which would very often have vaporized much or all of their surface water, which in turn may have prevented any significant evolution of any kind of one-celled life forms during that period. (While there is still some dispute over how long Mars' Noachian era lasted, there does seem to be general agreement that it ended very soon after the end of the Terminal Bombardment period for Mars, and maybe simultaneously.)

Now, if you want a REAL mind-bender: David Grinspoon, at last September's DPS meeting, pointed out that there is now very great uncertainty over how long early Venus had liquid-water oceans. The consensus view has been that they could only have lasted a few hundred million years. But James Kasting has pointed out that that is an extreme lower boundary (thanks to the fact that a dense water-cloud cover on Venus would have had a high enough albedo to greatly reduce the amount of sunlight reaching its CO2 greenhouse) and that it is quite possible that Venus didn't lose its surface liquid water for as much as 2 billion years! If so, then there might have been much more time for life to evolve on Venus than on Mars -- perhaps even enough for Venusian cyanobacteria to appear (although that same ocean would probably have allowed Venusian plate tectonics to operate back then, preventing any speedy buildup of photosynthetic oxygen in Venus' atmosphere just as on Earth's). The trouble is that this will very likely always be a shaggy-dog story, though -- unprovable either way. Venus, thanks both to the incredible difficulty of exploring it and to the fact that almost all its crust has undergone at least one episode of remelting, is a singularly dismal place to look for any trace of fossils.

Joel McKinnon

OK, Bruce, I'll concede you've probably studied this subject in a lot greater depth than I have. One thing I might not have been clear of, however, is that I was paraphrasing Dr. McKay in the first paragraph and the second was a direct quote. My understanding, arising from my conversation with him, was that the cyanobacteria would have an easier job doing their oxygenating work due to the factors I mentioned (greater volatiles, lower gravity, etc.) and the one big factor I didn't mention- lack of a moon forming event such as Earth experienced, and could therefor have accomplished the task much faster than on Earth.

It's pretty cool to think about the Venus possibilities (perhaps Perelandra did once exist?). Another thought is that, though fossils would never likely be found, interplanetary exchange due to asteroid bombardment could mean that we are the Venusian's direct descendants. It'd be funny if it turned out that Earth was the only one of the three planets where life didn't originate. The odds against that particular scenario I have no problem considering "overwhelming."

Bruce Moomaw

Actually, I have one of McKay's essays on the subject in an anthology, "Circumstellar Habitable Zones", which I definitely recommend as a crucial book for anyone interested in astrobiology. I'll reread it to see if he thinks there are any loopholes in my argument above. I suppose it's possible that -- by pure luck -- photosynthetic bacteria might have time to evolve on Noachian Mars; but I will say that the odds are definitely longer than on Earth. The very early inner Solar System was simply a much nastier place, thanks to the continuing giant impacts.

One other corollary: even if we find fossil -- or extant -- life on Mars, it may well always be totally impossible to determine whether it evolved there as a native, or originated on Earth and then got sent to early Mars via meteorite transfer. (Of course, the same is true the other way around -- or, conceivably, life could have begun on Venus and been transported to one or both other worlds!) As one scientist said at the first Ames Astrobiology Conference back in 2000, the idea of such transfers of live microbes between worlds via meteorite has already become so accepted at this point that it is "virtually a truism".

But my overall point -- on which at least one scientist agreed with me at the DPS -- is that the discovery of life on Europa may actually be far more important scientifically than the discovery of Martian life. If we find the latter, it will not come anywhere near ruling out the possibility that life originated on only one world in this Solar System -- by an extremely rare long-shot chance -- and then got transferred to a second inner world via meteorite. It will thus do nothing to rule out, or perhaps even measurably decrease, the odds that life is actually an extremely rare chance occurrence in the Universe as a whole. But meteorite transfers between any of the inner worlds and Europa (or vice versa) are extremely rare. If we find life there, the odds are extremely high that it evolved there separately -- in which case it really will constitute solid evidence that the evolution of life from nonliving compounds is actually a very common phenomenon throughout the Universe.

Joel McKinnon

Of course, Robert Zubrin would say that it doesn't matter where we find it here in our solar system because it's far more likely it came from somewhere else via astronautically adapted bacteria. Still, that's an important point about the rarity of meteorite transfers between inner planets and Europa that hadn't occurred to me.

Bruce, I'll be sure to check out Circumstellar Habitable Zones once I get finished with the one I've just started into which bears heavily on the subject: Life on a Young Planet by Andrew Knoll. It's mostly about Cambrian & Precambrian Earth, but he does get into some astrobiology discussions. I bought it because of a tip on some space blog- may even have been this site.

Bruce Moomaw

I'll have to read Knoll's book myself -- it just got a rave review in "Science".

Oliver Morton

Interesting discussion. A few extra points. The first is that we shouldn't write off the possibility of working out what happened on Venus completely. If it had oceans for a couple of billion years and life evolved in them, then there is a chance that there is still life in the clouds above. I wrote something on this idea for Science back in November 2002. On the earth there are bacteria in clouds -- not just spores, but viable bacteria actually using their metabolisms as they drift around. And though the clouds of Venus are very acidic, earthlife can hack it in pH 0 sulphuric acid. So cloud life on Venus -- as Grinspoon and a few others have pointed out -- is not inconceivable. It's the opposite of the story imagined for Mars; life would start in surface water, but when that went away the bugs would migrate upwards into the sky in search of cooler climes, rather than downwards into the rocks in search of warmth as they may have done on Mars.

If there is cloud life on Venus, genomics might be able to tell us something about the ocean conditions it evolved in.

Transfer of life from Venus to the earth, or Mars, is possible, but as a life exporter Mars is always the best bet. Escape velocity is low, and it's downhill from Mars orbit to the rest of the inner planets. I would guess the rate of transfer of meteorites from Mars to the earth is at least one or two orders of magnitude higher than the rate of transfer of Venus meteorites to the earth. The fact we haven't found any venusian meteorites seems to bear this out.

Over and above ease of transport, though, the idea that Mars was habitable *very early* is a key part of the life-from-Mars-to-the-earth notion. We know there was life on the earth from 3.8 billion years ago or so, and so if we think it came from somewhere else it has to be somewhere that was habitable prior to that. Comparatively recent oceans on Venus don't make transfer from Venus more likely. And a lot of water on Venus makes an early origin of life less likely; on wet planets really big impacts of the sort we see in the late heavy bombardment boil the oceans to create planetary steam baths that last for thousands of years and send >100 degree C heat pulses deep down into the crust. This is thought to have been what happened on earth repeatedly over the first 500 million years, frustrating the evolution of life.

The idea that life came from Mars is appealing because Mars may have been continuously habitable significantly before the earth was. I don't think the same claim can be made for Venus.

As to early *complex* life on Mars, there's an interesting dilemma. If you want a warmer martian surface for all this to take place on, as I think most people would, your best bet is a Mars with a biogenic methane greenhouse. But if you start pumping oxygen out in such a world, you burst the greenhouse (the methane and oxygen react) and everything gets very cold very quickly. Joe Kirschvink at Caltech thinks this is what happened on earth about 2 billion years ago; oxygen from blue-green algae would have started to build up, the methane levels in the atmosphere would have crashed, and the earth would have frozen over in the first and worst of the "snowball earth" events. On the earth there was enough volcanic activity for CO2 to build up in the atmosphere during the snowball event and eventually bring the reign of ice to an end. On Mars that might well not have been the case, and the first snowball would have lasted to this day...

Rupert Goodwins

The trilobite was by way of a joke -- I've got one on my desk here, watching events with crystalline stoicism. I'd no more expect to find one on Mars than a Macdonald's Happy Meal.

If there had been an era of biotic oxygen generation on Mars, could this be deduced by the spread of oxgyen-containing compounds present now? I don't know what the current thinking is on the evolution of the peroxides in the regolith, but I presume they don't form just through water vapour acting on iron.

R

Aloysius

Something about "NoImpact" man struck me as funny.He is giivng a talk.What I see, is that giivng 'a talk' involves an audience. Each member of the audience has made an extra trip that day, a voyage, that was in addition to their normal patterns of energy usage.That voyage for all consume energy. Those that walk consume food calories, and unless they are growing their own food, all of it, they are relying at least partially on petroleum-powered transport to get the food to their distribution center or grocery store, and on the energy-consuming grocery store to keep that food fresh and available, and to discard the remnants and spoiled food.Those that drive also consume energy, either directly fossil fuel powered, or indirectly (electricity must be considered fossil fuel energy until the last coal, oil, and gas fired plants are retired), Or they flew or otherwise increased the total energy and fossil fuel use on the planet.Which, like consolidating school districts, for the same reason, strike me as about the last way to measure "no impact".The outcome might be to influence people. If "talks" were all that were needed to instigate wide-spread change, I imagine that would have been blindingly obvious by now. Most talks preach to the choir, that is the crowd is motivated for change, and looking for technical details, that some will actually use. About those that attend a talk, that aren't already embracing the topic, that might change their thinking - again, success doesn't seem to be blindingly obvious to me.No Impact Man might not be consciously choosing a career catering to people interested in the environment, but he seems to be measuring success in terms of revenue and crowd count. In one sense the wealth of today's world - money - is a direct expression of the consumption of cheap energy. With the end of cheap energy (Peak Oil), the validity of measuring wealth in dollars gets to be an interesting question. And measuring success in terms of burning oil for Earth Day seems a bit . . ironic.Chrunchy, I think you raise the caliber of the group at TreeHugger.

Federico

I have never seen a Venus flytrap in real life! That is so cool you have one in your cloaorssm! I like that it comes back to life after it dies, I have a bad habit of killing plants. I think I may need one of these because I live in Alabama, USA, and we have a lot of flies here. You know what we do to keep flies away? We hang ziploc baggies full of water over doors and windows that are open. Think a Venus flytrap may look less redneck!! Thanks for the tip!

June

Beethoven wo stthie-iru hito nara Dovrak mo stthie-iru hazu desu. Dovrak no slavic mo tottemo yu~mei desu! Zehi kiite mite kudasai!Kare no seika wo mireru nante urayamashii kagiri desu! wo daihyousuru ongakuka no Smetana mo tottemo yu~mei desu.Praha wa machi jitai ga sekai isan de, sekai no housekibako to iwarete imasu.600 nen tsuzuita Hapsburg teikoki no shyuto deshita. Watashi no akogare no machi desu.Zehi iro iro na mono wo miteoite kudasa~i!Maria

Ashwini

Another article I read said the athrspmeoe of Mars is equivalent to the athrspmeoe on Earth 20 miles above the ground. This is much,much higher than your average jetliner. Even the Concorde, when it was operating, flew at an altitude of about 60,000 ft which is far, far shy of 20 miles.

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