I was infamous for dozing off during lectures, but this one has kept my attention very well. To switch metaphors I think the brine splat hypothesis has gone the full 15 rounds and come out of its corner fighting every time. Certainly its true that it has been unfairly dismissed in some quarters. I would still say my gut reaction (and very possibly my earth bound predjudices) tell me that to account for several billion years of surface evolution with only one process is stretching even the best idea, but I can't find any specific objection. My gut, which is very talkative today because my brain knows little about either geology or chemistry, also finds the idea of a mars which is cold and slightly damp for a long time easier to digest than one which was recently warm and very wet. So congratulations Herr Professor, I'd say impact surge is a convincing alternative. I hope you can find time to post on some of the other discussions. I'd be very interested to hear your opinions on the features and processes of Titan for instance.

In rough order of personal preference:

Earth
Titan
Venus
Mars
Europa
Sol
Io
Enceladus
Saturn (Rings and wierd looking atmospheric features at its poles)
Jupiter
Luna
Yes I know its eleven, if that bothers any one take out mars for the reasons below.

Plus honourable mentions for:
Ceres
Pluto (and moons)
Vesta
Chiron
Just because ther could be interesting and no ones gone to look yet!

Most overrated? Paradoxically I'm gonna have to say mars; yes its fascinating geologically and atmospherically, yes it may have habitatable spots, and I post under it, and, yes I put it in my top ten, but it sometimes gets so much attention I wonder if we haven't all got a bit too hung up over it.

Forgive me for asking what may be a dumb question, but can the evidence for a northern ocean be squared with the view of mars as an ice ball? The evidence in question may not actually be of an ocean, but if it is then mars must have been warm and wet for at least part of its history, and if its not what is the simpler explanation?
Edit: I should make it clear that by 'evidence of a northern ocean' I'm referring to the traces of coastline around the northern basin, not any more subtle evidence for an ocean which I'm not aware of.

I'm no geologist or chemist but the impact surge argument seems very straight foward and logical, possibly more so than any other hypothesis I've heard. I understand that the chemistry of home plate is very suggestive of the presence of water. Could the chemistry of home plate be accounted for by the impact surge hypothesis alone, or would the occasional presence of water still be required?

This just appeared on the ESA website.

I seem to remember something in the rules about discussions about astrobiology and, although it's hardly possible to avoid the topic on a thread like this, I worry we might be pushing at the boundaries. I only mention this because I rate the detection of martian methane as one of this decades great unsolved mysteries and would like this discussion to continue! If its not appropriate I hope doug will let us know, or move the thread somewhere more appropriate.

Is there anything about the serpentinization process that is readily identifiable? If that hypothesis could be confirmed or eliminated it would be a big hint, although not conclusive. Also; as I understand it organisms only produce methane when active (although I could be wrong). The martian mantle is largely solid, so theres no heat supply to keep subsurface microbes active, and no new materials being brought from the surface. Given the scarcity of liquid water, radiation , low temperatures and pressures at the surface I would expect any martian biomass to be in hibernation across the planet with activity only in the rare locations and times where conditions are more clement. If that is true the 250 tons per year figure only indicates the total active biomass, and sites of activity might not be fixed adding further difficulty to detection. The more we learn about this puzzle the more I think it will take a dedicated mission to resolve this!

Serpentinization can involve water and heat, which spectulative martians would need, just to confuse things a bit more. Is there an applicable method of distinguishing between biologically produced methane and methane produced by serpentinization?

It'll happen guys too many people want it to happen for it not to! And look at the positives; our unmannned missions to the other planets may not be all we've dreamed of, but at least they mean we've got something to fuel those dreams! I've got a huge picture of gusev and when I look at it I can almost feel the rock under my feet and the dust devils on my face. Beautifull poem Stu, but you've damn near made me cry

Would that line of thought lead to a continuos scale of non luminous bodies , from grains of space dust to brown dwarfs, after the style of the Hertzsprung-Russel diagram for classifieyng stars?
Edit: I don't know what the scale(s) would measure, although mass is clearly the most obvious choice, but that would put the term planet into the proper context, and make the term valid for pluto, as it has the historical and cultural significance of the other eight.

I'm in full agreement, truly beautifull!

Hi I'm intruiged by a piece run by newscientist.com this morning, but I'm not subscribed to new scientist, could someone point me in the direction of more information on this topic please? The idea seems to be that everything a lunar base needs could extracted from lunar regolith using potassium fluoride crystals, which seems a bit to good to be true to me but I'd like to find out exactly what is being proposed. This is also my first attempt at posting a link so if it doesn't work please let me know!

I would guess that this is where the self replicating probe idea comes into its own, as a probe that could build a copy of itself could build a reactor and transmitter on site as well- if it could find suitable resorces.

also your bad to quote the whole of the preceeding post....read the rules on that one as well - doug

Sorry- my bad!

There seems to be no shortage of ideas and enthusiasm out there, just a shortage of suitable energy sources.
Perhaps minaturization will progress to the point where an interstellar payload would be small enough that such fearsome fuel requirements wont be needed. Could a a 1kg or less (payload mass) mission ever be practical?

Thu; Very nice summary, although if we had ET at the other end with a deceleration laser at least we'd be gauranteed someone for the probe to take pictures of at the other end! The problem of decellerating without a co-operative space alien at the destination has been looked at in a couple of papers: T. Taylor, R.C. Anding et al., “Space Based Energy Beaming Requirements for Interstellar Laser Sailing,” CP664, Beamed Energy Propulsion: First International Symposium on Beamed Energy Propulsion, ed. By A.V. Pakhomov (2003), American Institute of Physics 0-7354-0126-8. The original Forward paper — now considered a classic — is “Roundtrip Interstellar Travel Using Laser-Pushed Lightsails,” Journal of Spacecraft and Rockets 21 (1984), pp. 187-195. I'm still working out how to post links, sorry im a bit of a technophobe to be honest, but if you put 'interstellar laser sail' into google you should get a good sweep of material on the subject. Hope this is of some use.

While you're there do you think you could drop by home plate and give spirits solar panels a wipe?

Thats stunning!

I've always liked the idea of propelling a space-sail using lasers, and you could even decelerate at the target star by sending a secound sail/mirror ahead to reflect the laser back at the first.
However I have read a laser sail study (soz I can't remember the title or author) that the laser would need a titanic muzzle apeture to drive the sail across interstellar distances, something like 10,000 meters. If anyone else knows what I'm talking about could you direct me toward the study as I can't remember why the laser needed to be so large. After all even a ten km laser would look like a point source after travelling from earth to mars, never mind a fraction of the distance to alpha centauri.

Give it all of the above, lasers, layerd areogel shields, small cross section, and include huge shock absorbers.

Perhaps trying to make one probe proof against all possible disasters is the wrong approach. If we have our unfeasibly huge power supply why not split it between a couple of dozen probes, take some basic precautions with each (aerogel shields, small cross section ect) and accept that at least some of them won't make it?
If IEE comes to fruition it might open the door for missions to the interstellar medium that would tell us exactly what precautions are needed, and in what amount.

Edit: nprev point about the power supply is well made, clearly it is this more than engineering issues which will be a showstopper for any mission to another star. Although not forever I hope.

That would make much more sense than lugging tons of armour up to a percentage of c but having one huge laser seems very power intensive, and more power means more fuel and more mass. It might make more sense to have a very accurate radar system sweeping the flightpath ahead and linking this to an array of smaller lasers to pick off debris one peice at a time. Actually destroying a large peice of matter could result in it fragmenting in any case, which might actually compound the problem. Is there some means by which a particle of dangerous size could be 'nudged' out of the probes path? im thinking either a directed laser again or perhaps some kind of reverse bussard ramscoop using powerful electric or magnetic fields.

Edit: A single large laser would clearly overcome the problem of fragmentation; if it can breakup/ vaporize a big peice it could do the same for smaller fragments, but considering how widely spaced large grains are in interstellar space it would still be a very inefficient approach IMHO.

I'm not sure I'd consider either to by a true starship as both are at least a factor of 1000 away from being fast enough to reach another star in a human lifetime. It's still leaving the solar system though so I think the term interstellar sputnik is a good one for an IEE type mission(in the same way that sputnik didnt reach any other bodies but did make it into space).

All very true but I'm going to cross my fingers and hope a little anyway.

Hello everybody, I've been a long time lurker at UMSF, mainly because I didn't feel I had much to contribute, but I've finally run across something thats made me curious enough to step into the light. Space.com and Astrobiology.com are both running stories on how the viking life detection experiments are consistent with the presence of microbes with hydrogen peroxide as their internal fluid instead of water. I've got no background in chemistry but I have first hand experiance of how unpleasant hydrogen peroxide is (I once spilt some on myself and I stil have a faint scar on my hand) so I was wondering if someone could give my the short words and big pictures explanation of how such a creature would work? If this is already being discussed elsewhere many apologies.