Slashdot Mirror

See also "The case against Hubble"..

http://www.spacedaily.com/news/hubble-04p.html

What slows down the nuclear-powered reactors in space is not much the technological problem involved but the political issue related to the use of nuclear energy in space. For a good report on thermoionics read e.g. http://www.nap.edu/books/030908282X/html/ (Thermionics Quo Vadis?) Also keep an eye on the eccentric but pragmatic Nobel laureate Carlo Rubbia who brought up the novel concept of utilizing the highly energetic fragments produced by nuclear fission to heat a gas. Extremely high temperatures produced in this reaction would enable faster interplanetary travel. Though interestingly he also states that this technology is not suited for interstellar travel (see http://www.spacedaily.com/news/fuel-01a.html The Italian Space Agency has started feasability studies on this.

"And while it might be feasible for us to add iron to the ocean to stimulate blooms, for every ton of it we throw overboard, we'd need to add at least 5,000 tons of silicate to enable the blooms to persist for long enough to impact on atmospheric carbon dioxide levels," he [Philip Boyd] said.

2. Doesn't pay for itself? No new reactors? Then why is France building more plants? And why is over 78% of French electricity demand produced by nuclear power?

Nuclear power works. Get over it.

One of the more interesting uses for jamming satellites coming real soon now is Galileo, the European/Chinese GPS constellation, coming on line in a couple of years. The U.S. is most unhappy that there will be a GPS system with 1 meter resolution, with wider coverage, they don't control, because it will break their monopoly on GPS guided weapons and navigation during a conflict unless they have the capbility to jam it. The U.S. GPS system can be selectively crippled/encrypted by the U.S. to deny its use to its enemies.

I wouldn't be surprised if the U.S. is making this threat public to send a signal to the Europe/China that if they proceed with a GPS system free of U.S. domination the U.S. is going to counter with the technology necessary to cripple it.

China's Xinhua has a pretty biting commentary on the subject that appeared on SpaceDaily a couple days ago.

It is a further indicator that as the U.S. continues to seek its global empire and world dominion it is going to continue to place itself against and at odds with the entire rest of the world.

Apparently only the U.S. is allowed to decide who can use and deploy basic technology.

This is part of the threat the senior US official made at a London conference on Galileo.

The senior official promised that in the event China used the Galileo system against the US, the US would attempt what they called reversible action, but, if necessary, they would use irreversible action, to knock out the Galileo system.

Article on the threat

On the contrary. The evidence is quite good.

I have no freaking clue what you are talking about the Earth's magnetic field. For one, it has *NOTHING* to do with global warming.

Read this and this and then get back to me. The magnetosphere blocks solar radiation from penetrating the lower levels of the atmosphere.

About the sun, well, let's see. Sunspots are actually cooler areas of the Sun. So the more sunspots, the cooler the sun!

Read this and then get back to me. Sunspots are indicators of higher solar activity.

Thank you Ghost of Wernher von Braun!

Hmmm... I'm not sure Von Braun's ghost is the best entity to summon here. Von Braun had more than a little to do with putting the shuttle on NASA's technology roadmap. Mars Direct is called Direct partly because it deliberately abandons a big chunk of the Von Braun architecture, which is that you have a space station, serviced by shuttles, where you assemble your outward bound spaceships. Even when you take out the station, Von Braun's 1969/1970 Mars architecture relies on shuttles to cover the gap between LEO and the ground. This article entitled The Von Braun Master Plan: National Dream or National Nightmare? sums up the objections to Von Braun's architecture -- and NASA's long term adherence to it -- concisely.

BTW, Here's Von Braun's 1950's vision

They've been constantly considering the viability of the Shuttle program since it began in the 70s, and it's always been under the threat of having the plug pulled at any moment.

If Nasa had been up front about the shuttle's limitations, it probably never would have been approved

I don't know why it's so "hip" to hate the shuttle program around here. If you look past the cost,

The cost is why we hate it. It's expensive as hell, and frankly doesn't deliver much that couldn't be done better and more cheaply in other ways. The International Space Station is rapidly becoming another of these projects - the cost has been cut to the point that the thing is nearly useless, but it still costs a fortune.

the shuttles are pretty damned cool, and have a better safety record than any commercial passenger jet.

Really. I wasn't aware commercial passenger jets crashed once every 57 flights, killing all passengers aboard. I'd challenge you to find a commercial jet with a _worse_ safety record.

Not only will the Cassini be taking pictures, but its ion and neutral mass spectrometer will "scoop up" and sample Titan's atmosphere as it passes at a distance of 1,200 kilometers (745 miles).

"One important goal of this flyby is to confirm scientists' model of Titan's atmosphere to prepare for the Huygens probe descent," according to this article at SpaceDaily.com.

This is going to be a fascinating event - however I do have some questions.. The total mission cost is around $4 billion - is this good value for money? For example look at New Horizons, a Jupier/Pluto/KBO mission with a total projected cost of $600 million. I also wonder, given the scale of the mission, if a RTG should have been put on board Huygens so that it could stay longer and observe the Titan environment over a longer time? (Yes I know it could only relay data when Cassini passes by, but that could still be useful..) Listening to thunderstorms is all well and good, and adding a mic is worth doing because its a cheap thing to do in such a system, but what about a lander that spends more time there looking at the chemistry of Titan?

I think that the smaller, cheaper missions return much better scientific return for the money. For instance, most of the function of the proposed $10 billion JIMO mission could be done by a cheaper Europa-only orbiter that would cost less than $1 billion. (See: http://www.spacedaily.com/news/hubble-04p.html ) Also take a look at the SMART-1 ESA mission - less than $100 million for a complete mission featuring many new technologies.

For example the camera on the $4 billion Cassini mission is only 1 megapixel - if we had a larger number of smaller, cheaper missions, would we be there now with a much better imaging system. Cassini had a much delayed launch, so the design was outdated by the time of its launch in 1997. The same mission launched on a later window could have used ion propulsion (SEP/RTG combo) saving weight (1/2 the 4 tons Cassini weight is fuel)

The same thing could happen with JIMO - if NASA spend $10 billion on that, they could forego many other missions, such as a New Horizons II mission, which would give us a chance to look at Uranus (not always a good word to say on Slashdot) with modern instruments, as well as Jupiter & some more KBO's..

Also think about Hubble - is it worth spending $2 billion on a robot to repair the aging telescope, when the same money could buy better new space telescopes.. (see link above)

I dont want to belittle the work of the scientist working on Cassini - it will be a fascinating mission, I just wonder if we could get more return by rejigging the beurocracy.. The X-Prize, New Horizons and SMART-1 prove that more smaller & competitive missions return much more bang-per-buck..

Before you start jumping up and down here,

Seems to me you are the one doing the jumping.. :-)

(Wouldnt we get better performance long-term from a larger number of smaller probes?)

Most of the cost goes into getting to these very far away places and holding enough propellent that you can slow down enough to be captured into orbit after you've been going very fast for a few years. It's not feasible to launch probes to outer planets all the time because you lose the ability to "sling shot" past other planets as a cheap way to pick up a lot of speed. These gravity assist (or more accuratley, angular momentum assist) moves make a little ship go whole heck of a lot faster which means you don't need as much propellent to get you somewhere. You have to go really fast to someplace that several billion miles away in a few years.

Yes, I understand that. In fact its not all that bad - an opportunity to use Jupiter to sling-shot comes round every 13 months. For example, New Horizons will launch Jan 2006 for Pluto, mission cost $600 million. If a second identical probe is built for a follow up around 2008, we can get a fly-by of Uranus and then some more KBO's, for an even smaller cost. Probes like SMART-1 also conserve power by making careful use of other celestial mechanics & tricks - "lunar resonances", check the ESA site. There are "interplanetary highways" that could even provide "free" trips between planets, all be it slowly..

(and hence would have more up-to-date sensors. For example, the CCD on the Cassini camera is only 1 megapixel!)

The way to get better quality pics is NOT to have more pixels but to have better optics. The cameras in the "eyes" of the Mars Exploration Rovers (the pancam) are only about 1 megapixel and they have returned VERY high resolution pics that look great if you have to blow them up 10 times their size. That's because NASA spends a lot of money to use phenomonally good optics. In addition, more megapixels means larger files which requires higher data transfer rates which requires more power to your antenna which means less electricity to do other stuff. (whew)

Even within limited Bandwidth, higher resolution can prove useful - remember Galileo which busted its high gain antenna, and could only send data to earth at a low data rate? It still did 90% of the science it was supposed to do anyway, by careful use of resources.. I am not saying Cassini is not worthwhile - the results are/will be fascinating. I just believe that smaller/cheaper missions turn around faster and actually put up more modern devices within a given timescale..

(I have heard it suggested that most of the useful function of the JIMO $10 billion orbiter could be done with a simpler $1 billion direct-to-europa mission.. And look at New Horizons, with a mission cost less $1 billion, or SMART-1 less than $100 million..)

Dude, compare apples to apples here. SMART-1 is a test of new technology (ion drive) that is meant to see how well it works and if it useable in other missions. It was meant to be a cheap way to get to the moon. You don't need a whole lot of force to get the moon and orbit it if you're willing to wait a few years...like SMART is. To get to Jupiter and then ORBIT it, you have to go very fast to get there, then be strong enough to slow down to be captured into orbit. Then maybe you'd want a few kilos of propellent left to actually move around near Jupiter for a few year. That is a completely different scope than crusing along to the moon for several years or flying by Pluto-Charon before the atmosphere freezes out.

This is not something I am just pulling out of the air here - for example check this article from SpaceDaily. http://www.spacedaily.com/news/hubble-04p.html
We could get to orbit Europa (the main satellite of interest) with a much cheaper mission than JIMO - about 1 billion should do it. In fact, and this is my origin

It is important to remember the difference between deterministic effects (the minimum dose needed for depilation, skin burns, marrow suppression, death) versus stochastic effects (relative risk increases in cancer). From what I understand, there doesn't seem to be a risk of death, but there may be a relatively increased risk of fatal malignancies in the future.

Personally, for me, the trip would still be worth it (though I would probably bank my sperm). Also, someone can probably help on this, I understand that there are transient increases in ionizing radiation levels, from solar flares, and from some deep space sources that have screwed up satellites from time to time. I don't know if unshielded exposure to these sources would be 'deterministically' fatal.

new way to harness the power of the sun

this is at least viable alternative to biodisel

one more link is Center for materials research in energy conversion

This guy predicted a major earthquake in Southern CA by early September 2004. At the time, he was 2 for 3. I guess his average just took a serious hit.

So it is amoral and shortsighted to invest in developing local technology so that local industry thrive and help catch a pie of the multi-billion dollar satellite launch market by proving their capabilities, so they get foreign business, creating thousands of jobs in the process, and bringing in billions of foreign capital to grow their economy?

So it is amoral and shortsighted to invest in communications systems to help boost education levels in poor rural areas?

A space program isn't a pissing contest - all countries depend on space technology in one way or another. For a country with more than a sixth of the worlds population it would be lunacy to depend on other countries for things like military surveillance, communications, weather monitoring, etc. It would also be lunacy to let other nations cement their technical superiority and hold onto their grip on a market that is growing extremely rapidly, and will be a vital revenue source in a few decades.

I've been harping on the idea of using nuclear batteries in cell phones and laptops for the past year or so. To date I've been called a variety of names for it, the least of which is "crazy". Yet here we are. Researchers are SERIOUSLY talking about using radioisotopes as power sources!

In case anyone is wondering how these work, the idea is that the radiation from a small amount of radioactive material (NOT fissable material!) is captured and converted into electricity or other forms of energy. There is very little radiation emitted by these devices, because the radiation IS the power! Letting it escape would be poor economy.

NASA has used these sorts of devices in spacecraft for 40+ years, starting with the Apollo missions. NASA's earlier designs produced about 75 watts utilizing a few pounds of Plutonium-238. Pu-238 was an excellent choice because it is useless for bombs, and has a short half-life (~80 years). With the public finally calming down about nuclear technology, NASA is now developing a more efficient device called an SRG. These devices get about 55 Watts per 600 grams of PU-238. This is way more efficient than current RTGs, like the ones used on Apollo.

The primary downsides to Nuclear Batteries is that they are expensive and they don't scale. They are expensive because the nuclear materials are very rare and expensive to process. If we started using these materials in massive quantities, it's a certainty that the prices would drop. They are not scalable, because the amount of materials required means that a few hundred watts is the largest device one could construct with a reasonable size, weight, and expense.

As for anyone who's worried about dirty bombs, I suggest you read this and this. The threat has been greatly overstated, and is actually less effective than a regular bomb. The real problem is the issue of keeping the materials out of landfills. Even today, there's a big problem with Lead, Cadium, and other dangerous materials ending up in landfills. Radioisotopes wouldn't be much worse, but there is an upper limit on how much you want to add to the sub-soil.

1. Just load an ICBM with gallons of white paint and smash the missile onto the asteroid. (This method works for small asteroids.) The light from the sun will push the newly painted asteroid onto a different flight path.

2. Load an ICBM with a hydrogen bomb. Smash the missile into the asteroid.

All is well.

This is not bad, but what about the incredible feat the software engineers at JPL and elsewhere regularly pull off with the deep space probes? Example

There was an interesting article on spacedaily.com (The case against Hubble) which proposes that 2 new cheaper modern telescopes could be built for the price of "repairing" hubble.. I was in favour, until I heard about the costs.. Its had a damn good run, and will continue to do good science, but its like an old car that is costing more and more to put through its MOT each year..

There was an interesting article on spacedaily.com (The case against Hubble)
which, although primarily about Hubble, mentioned the fact that NASA rejected a much cheaper mission option for a Europa-only orbiter costing around $1 billion in favour of the $8 billion JIMO mission. You could have 10 or more SEP/RTG missions for the cost of JIMO.. Solar can even be used for getting to Jupiter-Neptune, by swinging in close to the sun first & picking up momentum with SEP or a solar sail.. Just carry enough fuel to enter orbit on arrival, like Cassini..

Something like JIMO will come eventually, but is it worth sacrificing so many possible missions for that one option?

It may be a lot sooner than you think

"China has started developing its first unmanned lunar exploration craft in order to meet its own tight timetable of reaching the moon before 2007, state media said Tuesday.

Work on the craft, named "Chang'e 1" after a moon traveler of ancient legend, is going smoothly, making members of the moon program confident the launch will go ahead as planned, the Xinhua news agency reported."

There are 6 going on 10 Trillion people overpopulating the planet, better armed than fed, with diminishing resources and religious animus to fuel their desire for war over what remains of those resources.

Engineers and Scientists can't solve those problems, but we CAN go out to the asteroid belt to collect metals, to orbit to build Satellite Solar Power Stations, to the gas giants for methane... and in the doing of these things, just by the way, spread ourselves around the entire Solar System so that accidents to the one planet we have MIGHT not be fatal to the species

We can do this and deserve to survive as a species, or we can take this view that there is nothing out there worth having and deserve to go the way of the Dinosaurs

What can I tell my children's children as they are starving to death, facing bio-chemical-nuclear ruin, being overrun by some quasi-human mob with spears bent on cannibalism... the "real returns were questionable"? Looking at the question from the viewpoint of money and science and from that viewpoint you are correct, but that view is completely innocent of troubles outside those two areas, and like the billiard player saying "8 ball in the corner pocket" just before a Richter 8 quake, it'd be right IF nothing else were happening to us

After saying that, it is a LOT cheaper than most of the things we spend on anyway. Check this little op-ed piece. An excerpt "$31 billion go annually in the US on tobacco products - twice the NASA budget -, and $58 billion is spent on alcohol consumption -almost four times the NASA budget. Forget space spin-offs - here are genuine tangible benefits: $250 billion are spent annually in the US on the medical treatment of tobacco- and alcohol-related diseases - only sixteen times more than on space exploration."

You'll excuse me if I don't come along

Bah!! If this was true, why haven't we started mining asteroids "by now"?? Scientists theorize that there can be Trillions of dollars worth of raw materials within a single near-earth asteroid. A new theory proposes that Neptue and Uranus rain diamonds. Why hasn't deBeers jumped all over this? If Mars were gushing oil, it's still cheaper and easier to get it from Earth, just like our other resources.

Mars does experience much greater obliquity variations. The values usually cited are an oscillation between 15 and about 35 degrees, over a cycle of about 124,000 years.

Recent speculations have led to suspicions that on longer time scales, there may be even greater swings in obliquity, ranging from zero right up to 60 degrees. Jeffrey Kargel has speculated about what a Mars under these conditions would be like. Linked is a PDF of a brief paper on Mars' climate during periods of high obliquity.

Neat stuff. My apologies to the grandparent poster for unnecessary flamage.

"...please read this overview."

TRANSLATION:

...please support and increase Roland Piquepaille spam and advertising clickthrough rates.

If you really want more details and pictures about the Mars Underground Mole then you can

• read this SpaceDaily four-part article on Mars Drillers
• read the Mars Underground Mole PDF with diagrams, photos and tables
• look at a whole range of Mars-related projects from the 2003 Sixth International Conference on Mars
• read a Deutsche Welle interview with German Aerospace Center Chairman Sigmar Wittig - DLR developed the Mars Express mole that inspired the MUM project
• read a National Space Society two-part interview with Dr. Brian Glass, MUM co-investigator
• read about a MUM inspired student project or
• watch a NASA Mars Underground Mole Quicktime movie animation.

It's much better than supporting craven self-interested people who are just after advertising like Roland Piquepaille, blog spammer.

According to some scientists Mars had a much thicker atmosphere when its magnetic field was still completely up. When Mars's magnetic dynamo died, solar winds carried most of its atmosphere away. The same thing would happen here if the magnetic field would just stop. You can check up on research on the interaction of Mars's magnetic field and it's atmosphere here

We're all missing it. Luanch a bird with a nuclear reactor in it and when the sludge builds up or the core is depleted, send it on a trajectory for the sun. Keep the platform small so that it won't have a large impact at the sun. References include:

• Nuke launch accidents
• Japan wants to do this by 2040
• Space Nuclear Auxilary Power (SNAP) and RTGs

The other point mentioned briefly in the Japan article is that even if high-energy beams were used, they could be pointed out to sea. Put it out far enough and bouys would be easy to post or, better yet, a small unmanned receiving platform with a cable to the land.

That reminds me... Pizza Hut was getting ready to fund a proton space rocket, though I think the deal went sour.

I submitted a story to /. on this a while back. Rejected - but there is more info here

Ariane: unreliable, and run by a baby NASA that speaks French

Russian launchers: you're kidding right?

All this bickering over nuclear power being the only environmentally-friendly solution in the next 50 to 100 years has me thinking of another solution: oribital solar power .

Okay, there's the cost. It'll be expensive.

But if we put that aside for the moment, the orbital solar power seems to make more and more sense for the near future. The idea is to have vast arrays of solar cells in orbit, which can collect solar energy the vast majority of the time (since Earth will block their view of the sun only a small percentage of the time) and then beam that energy back down to earth.

One of the big advantages some see in this is that you could, feasibly, transmit energy to regions that needed it on an on-demand basis, much moreso than we have today.

And it'd get more stuff happening in space. But that's a different story...

BTW, a few links for you:

http://www.spacedaily.com/news/nuclear-blackmarket -02d.html
http://www.llnl.gov/csts/publications/sutcliffe/

The end result is very few (if any) people would die from the radiological effects. Of course, maybe the public would know better if Nader had done something useful and taken the nuclear challenge.

Lotta birds gonna fry going through the microwave beams that send the power to earth, not to mention the james Bond style money making opportunities having a spaced base microwave beams would lead too. 1 billion dollars!

This is cool and all but the article is a bit misleading about the demands of a Moon suit as opposed to a Mars suit.

- Radiation. Mars has little to no magnetosphere but it does have some atmosphere. This provides some protection that the Moon does not. Also, the Moon is much closer to the sun so the levels of radiation from it are higher. There are also little baby north and south poles around the planet. Landing in one of those will provide a bit more protection.

- Temperature. The Moon has much higher and lower temperatures to worry about than Mars

- Sandstorms. True, the Moon doesn't have these but with the low gravity, thin atmosphere and fact that they won't be sleeping in hammocks, explorers/settlers should be able to handle them as long as they wear something thicker than a windbreaker.

In short, Mars suits have fewer extremes to deal with than Moon suits. The article exhibits some FUD about Mars.

It appears that energy is a major factor that is pacing Chinese economic development. Have the Chinese established some other energy sources through R&D(say some results in some other form of hot fusion) or diplomatic arrangements(i.e. a deal with the Russians or Islamic oil exporters)?

Select quotes from Is Space Exploration Worth the Cost?"

"For instance, this year, total pet-related sales in the United States are projected to be $31 billion - the double, almost to the cent, of the $15.47 billion NASA budget. An estimated $5 billion worth of holiday season gifts were offered - not to the poor - but to the roving family pets - six times more than NASA spent on its own roving Martian explorers, Spirit and Opportunity, who cost the American taxpayer $820 million both."

"Instead of betting on the future, Americans spend $586.5 billion a year on gambling. It is perhaps immoral to criticize one's personal choice, so instead of kicking the habit and feeding the poor with this money, one should stop instead the enormous waste in space who stands at a scandalous amount of 40 times less than gaming tokens."

"Speaking about personal choice, $31 billion go annually in the US on tobacco products - twice the NASA budget -, and $58 billion is spent on alcohol consumption -almost four times the NASA budget. Forget space spin-offs - here are genuine tangible benefits: $250 billion are spent annually in the US on the medical treatment of tobacco- and alcohol-related diseases - only sixteen times more than on space exploration."

These figures represent how, as a society, how lowly we value space exploration. If we spent 50% as much on space exploration as we spent on Hollywood entertainment, Orbitz would selling weekend passes to the most popular lunar resorts.

Here is another article about cold fusion experiments. It uses sound cavitation to collapse acetone vapor. It sounds quite promising. I'm personally fond of the idea of using sound as a controlling force for the reaction. The experiments were funded in part by DARPA.
"The research team used a standing ultrasonic wave to help form and then implode the cavitation bubbles of deuterated acetone vapor. The oscillating sound waves caused the bubbles to expand and then violently collapse, creating strong compression shock waves around and inside the bubbles. Moving at about the speed of sound, the internal shock waves impacted at the center of the bubbles causing very high compression and accompanying temperatures of about 100 million Kelvin."

One can calculate the minimum size body that will become rounded by its own gravity starting from very basic principles of physics. Doing so, you find the boundary is a diameter of a few hundred kilometers.

Better sources for space related stuff:
spaceref.com
space.com
spaceflightnow.com
spacedaily.com
the rovers' homepage
and just for fascinating pics and educative descriptions: Astronomy Picture of the Day

They often carry the same stories, but usually one of them will have the scoop. There are more sites, but these ones are definately worthy of a daily visit, and some have plenty links to other interesting sites. Have fun :D

As with so many rare finds, the real question is How to not contaminate or destroy what we've found, while still getting access to the knowledge we want.

On the other hand, there is this article, about the Rio Tinto in Spain, which supports life despite a pH of around 2. It might not be totally separate or isolated, but that's a pretty alien environment. (another similar story, including a brief discussion of astrobiology, is here.

They never take into account disposal fees. The energy industry is counting on Uncle Sam to build them a free disposal facility in Yucca Mountain. The Nuclear power would be about as free as the roads I drive on. Taxpayers (not rate-payers) flip the bill.

I'm not a tree hugger. But I do realize that Nuclear power still has a HUGE disposal problem. ALL the energy from EVERY plant in the US has yet to find a final resting place. Even the Yucca mountain proposal still has some possibility for contamination.

We need to find a way to bottle that re-process the fuel and imprison the stuff in solid inert mixtures. Either that, or find create disposal units that drill one way trips down past the earth's crust into hot/squishy rock layers.

Until then, nucular power is still risky until they deliver on the ultra-sonic fusion concepts.

At least all those other technical areas have had even less money invested in them than space launch - so there's good reason to hope all the needed breakthroughs can be made soon - with some R&D money.

Would this be completely unconnected with the Hypersonic Cruise Vehicle (Falcon) concept? DARPA's idea for a global hypersonic bomber that could pre-emptively bomb a country back to stone age before Letterman.

Still, the Germans beat DARPA to this idea by about 60 years - meet the Sanger Amerika bomber... an aircraft that would fly right around the planet skipping off the atmosphere like a stone thrown across a pond.

Best wishes,
Mike.

Short answer, temperature. It's way, way, way too warm for any liquid like N2 or methane or ammonia to form as a liquid. And it's always been too warm. So the probability that the rock formations occured from any of those liquids is precisely zero.

Secondly, H2O2 is highly unstable, it quickly decomposes into plain-old H2O and O2 in sunlight and/or temperatures above freezing. Both conditions exist and have existed on Mars for billions of years so there is zero probability that H2O2 had anything to do with it.

2. How much, if any, of the present evidence could be explained by flows of liquid CO2, nitrogen, methane, ammonia, or some other liquid?

Zero evidences for all of those substances. Again, its far, far, far too warm. First, carbon dioxide does not exist in liquid form at atmospheric pressure at any temperature. It requires a temperature of 20 degress Celsius and a pressure of 30 atmospheres to form. Mars has never had such conditions so there is again, zero chance liquid CO2 had anything to do with Mars' sedimentary rocks.

The other compounds on your list require extremely cold temperatures to form into liquids. Far, far colder than it EVER gets on Mars for most of them. It also requires a much higher atmospheric pressure than Mars had for most it's existence. Finally, there isn't sufficient quantities of some of these compounds to form rivers, lakes or oceans, nor is there any evidence of that there ever was enough.
Here's the list of temperatures:

• Nitrogen == -196 degrees Celsius @ 1 atmosphere of pressure
• Methane == -162 degrees Celsius @ 1 atmosphere of pressure
• Ammonia == -33 degrees Celsius @ 1 atmosphere of pressure
  It gets cold enough on Mars for this, but there is very, very little amounts of it.

Which evidence, if any, points most strongly to the presence of large amounts of H2O as the liquid in question? I know there are currently thought to be large, polar caps of solid H2O, but how much of the current evidence precludes the existence of large seas of some other liquid in the distant geological past?

Part 3

Nope. (Relevant bit about halfway down the page). My guess based on the information in the link is that the obliquity variations occur over a period of hundreds of thousands of years, so the ice migrates slowly toward the equator, while the seasonal variations occur over a period of just hundreds of days, so the ice doesn't have time to migrate back.

One correction: The obliquity cycle would seem to not exactly be highly chaotic, but rather a slow oscillation.

Scientists think they have a handle on why. Low atmospheric pressure means that water can't exist in liquid form on the surface any more. Mars' atmosphere was denser billions of years ago during what is called its Noachian period. For various possible reasons (such as a lack of a magnetic field to protect against the stripping solar wind) Mars' atmosphere was mostly lost, and all the water boiled off into vapour, and was either lost to space or deposited in the ice caps.

A lengthy and detailed overview of current theories can be found here: Part 1, Part 2. Especially cool is the stuff about Mars' "obliquity cycles", namely the fact that the planet's axial tilt appears to be chaotic, and may have been completely tipped over on its side several times in the past. During such a period Mars would not have ice caps at the poles, but rather an ice belt around its equator.

Scientists think they have a handle on why. Low atmospheric pressure means that water can't exist in liquid form on the surface any more. Mars' atmosphere was denser billions of years ago during what is called its Noachian period. For various possible reasons (such as a lack of a magnetic field to protect against the stripping solar wind) Mars' atmosphere was mostly lost, and all the water boiled off into vapour, and was either lost to space or deposited in the ice caps.

A lengthy and detailed overview of current theories can be found here: Part 1, Part 2. Especially cool is the stuff about Mars' "obliquity cycles", namely the fact that the planet's axial tilt appears to be chaotic, and may have been completely tipped over on its side several times in the past. During such a period Mars would not have ice caps at the poles, but rather an ice belt around its equator.