Mars Images Reveal Evidence of Ancient Lakes 128
Matt_dk writes "Spectacular satellite images suggest that Mars was warm enough to sustain lakes three billion years ago, a period that was previously thought to be too cold and arid to sustain water on the surface, according to research published today in the journal Geology. Earlier research had suggested that Mars had a warm and wet early history but that between 4 billion and 3.8 billion years ago, before the Hesperian Epoch, the planet lost most of its atmosphere and became cold and dry. In the new study, the researchers analysed detailed images from NASA’s Mars Reconnaissance Orbiter, which is currently circling the red planet, and concluded that there were later episodes where Mars experienced warm and wet periods."
We'll Never Know For Sure (Score:2, Insightful)
Re:We'll Never Know For Sure (Score:4, Interesting)
Why? (Score:1)
What is so special about humans manipulating measuring equipment versus robots? This notion that we must send people into space is just romantic.
Without romanticism exploration will stagnate (Score:1)
What is so special about humans manipulating measuring equipment versus robots? This notion that we must send people into space is just romantic.
The romanticism of the adventure is one of the strongest motivators of exploration. Take that away, and it's just work.
Besides, there are practical reasons for sending humans into space. One day, in order for the human species to survive, we will have to move off this rock and travel to other regions of our galaxy. We might as well start our baby steps now.
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What is so special about humans manipulating measuring equipment versus robots?
We do it better.
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Because people can wander around navigating the terrain a lot better and quicker. Now imagine the person is in fact a geologist. They can immediate analyze what they are seeing, move around looking for interesting things, all the time E.g. "Ooh, that's an interesting rock". WHACK. "Hmm, look at that...". Now compare that to an incredibly slow robot that has to inch around, take a picture, send data home, have it processed here, wait, wait, wait. Experts here decide to move the robot 2 feet to the left. wait
Re:Why? (Score:4, Informative)
The limitations of our current robots were based on space, cost, and durability. A geologist might be able to search the terrain faster, but they won't be able to be there for more than a few days or weeks at best, and each geologist could really only search one general area. In the same space as your single geologist and all the food and resources he/she will need, we could explore multiple places on the surface of Mars with a generous handful of Spirit-type robots, and they could all stay there for years collecting data.
The reason Spirit and Opportunity are so slow is because they operate on a small solar array, that generates (at peak) 140 watts for the 4 hours of daylight they get in a Martian day. That's about 560 watt/hours an m-day at best, and that's all the energy they need to do what they do. That's a lot of science packed into that amount of energy. They are currently getting a fraction of that due to dust on the arrays, and yet they are still collecting good science, six years in.
If you want enough energy to support a human being there, you're talking nuclear engines. If you're going to make that kind of energy available, you might as well power the robots with nukes - they will then be able to move faster than a human could, and there could be hordes of them for the same cost and resources expended sending one human. And they could stay for years.
To get a single human to mars, on the surface, and back to Earth, you'll need about a half ton of dehydrated food, enough water to recycle so they have a continuous supply, and probably a few thousand watt-hours a day minimum for the entire trip for heat, light, etc. You'll also need radiation shielding (likely tons of it) for the multi-year trip, room for them to exercise, many tons of fuel for the two-way trip, etc.
Spirit weighs about 400 pounds, or a little over twice the weight of a human. But you save the half-ton of food, the water, more than half the fuel (no return trip, no need to re-orbit it), and almost all the energy needed to sustain life during the voyage. The ship is simpler, since you need almost no shielding, no living space - just strap a few (or a few hundred) robots around the outside of a rocket engine.
Take a science team of a dozen, and you could probably have at least 50, maybe 100 robots take their place. And those robots would be able to work there for years. Each could have its own nuclear plant and probably have power and functioning instruments for decades (energy starvation from the solar cells is what is slowly killing off the current robots).
Plus, robots can make a one-way trip. No need to store fuel to bring them all back, just enough for a few dozen of them to send a sample back to a central ship in orbit, which can then pack up the samples and send them back on a relatively small rocket that weighs a few hundred pounds.
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Take a science team of a dozen, and you could probably have at least 50, maybe 100 robots take their place.
No, you couldn't. My view on this is simple. A human presence on site is superior to sample returns which in turn are much superior to probes controlled remotely from Earth. We only need to look at how we do science on Earth to see that. Most of it is done directly by humans. In a sufficiently large project where the overhead of using humans (and the cost of putting mass on Mars) is reduced greatly by economies of scale, I see humans occupying the same research and exploration roles they take on Earth.
Fu
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Now compare that to an incredibly slow robot that has to inch around, take a picture, send data home, have it processed here, wait, wait, wait.
Yeah, but if you sent a human with enough food and resources for a 3 month mission, what do you reckon the chances are that they will still be around doing the same thing six years later?
Robots might indeed be slower, but on a cost and support basis, they utterly hands down smash any human in a support scenario. Also, the rovers touched down in a module around the size of a small car from memory. Also the support habitat didn't need to move with the robot.
Lastly, why do you think really makes somethin
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Because a robot can be powered down and require no resources for the flight there and back. They can also be stacked neatly into boxes. They also don't fight, or make little robots. They can stay at Mars forever, and no one will clamor to bring them back to Earth. And if your measurements are off and you kill one, you send another.
Heck, you could fit Spirit, Opportunity, and probably a few hundred similar robots in the same amount of space and weight you'd need to provide a single human with food, water
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Because a robot can be powered down and require no resources for the flight there and back. They can also be stacked neatly into boxes. They also don't fight, or make little robots. They can stay at Mars forever, and no one will clamor to bring them back to Earth. And if your measurements are off and you kill one, you send another.
Which is really suboptimal, because it takes a lot less cost to manufacture humans.
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LOL. True.
Unfortunately, it takes a lot more to get a human to Mars in a condition where it can be useful. And then they expect to be able to get back, which is even costlier.
I wonder how much it costs to get a ton to Mars?
Let's say we have a payload of ten tons on a one-way rocket.
In ten tons, you could fit:
5 humans at 200 pounds each = 1/2 ton.
Food for all ten humans at 1/2 ton each = 2 1/2 tons.
Water for all five humans, spacesuits, control instruments, bathroom facilities, water recycling plant, perso
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Food for all ten humans at 1/2 ton each = 2 1/2 tons.
I'm guessing that's a typo, and was meant to read "Food for all five humans at 1/2 ton each = 2 1/2 tons."
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Yup, sorry. I started with 10 and quickly realized that a 10-ton payload couldn't possibly accommodate ten people.
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Which is really suboptimal, because it takes a lot less cost to manufacture humans.
It would take somewhere in the ballpark of half a million dollars to manufacture a human suitable for the mission. Do you really think the price of a mass-produced robot is going to be that high ? Not to mention building the robot will take a few weeks, or maybe months, whereas building the human will take 25-30 years.
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Heck, you could fit Spirit, Opportunity, and probably a few hundred similar robots in the same amount of space and weight you'd need to provide a single human with food, water, and entertainment for the multi-year mission. And you'd get a LOT more science done.
Until the robot gets stuck in a hole and is unable to figure out how to remove dust from solar panels.
The problem with a robot, vs a human, is that one is depressingly static while the other is highly adaptable. For known and/or repetitive tasks, robots can't be beat. For exploration... I'm unconvinced.
If there were a human on Mars, Spirit would likely have all of its wheels working.
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If there were a human on Mars, we wouldn't possibly have had him/her there for 6 years. Not with our current technology. Not with our current resources.
For the cost of one human on mars for 6 months, we could have 10 Spirits there for years. Or more. And if one broke, it would be disposable.
Eventually, we want humans there. But to learn about the terrain, the most efficient and effective way is to send robots. When humans go there, our target should be a one-way trip.
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3.8 billion years is a long ways for humans to time travel and see. guess we'll just have to continue to make educated guesses off the data provided by the rovers and current orbital observers.
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At the risk of being serious... (Score:3, Insightful)
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And we can't explore both...why exactly? (plus mission to Europa is being worked on; though it will be not an easy feat)
As a matter of fact, why do you want to limit us to Europa? Why do you dismiss Mars outright? (there are still those weird methane emissions we have to sort out; and possibility of subsurface water) Also, what makes you think Europa is more likely to harbor life than Ganymede, Callisto, high atmosphere of Venus or even Enceladus?
Mars has one big advantage of being relatively easy to get th
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I didn't say anything about limiting us to Europa, you did. It would be a very good thing to explore not only Europa but the other moons you list. The reason we keep going back to Mars isn't so much for the science because there is a hell of a lot of other and possibly more interesting science that could be better served by going to Europa, or maybe Enceladus. The reason I dismiss Mars outright, on its face, and with no reservations is that given our budget it would be better to let Mars rest for a time,
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We could learn a lot from Europa because Europa has a small iron core which is heated by tidal friction, and under the the 3km of ice there may in fact be 100-200 kilometers of salt water . Now it is odd, that our space agencies, that claim to be searching for life willfully have ignored Europa other than a few flybys.
Maybe they're put off by that 3km of ice. How exactly are they going to drill through that ice, when the best we've managed so far with remote probes is to launch a few wheeled rovers to a dr
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It's hard, but if we put an effort and money into it, I have no doubt would could solve those problems. Solutions have been proposed.
Studying Europa isn't impossible, nor is it harder then Mars, just different.
We can, and should study Europa, it has a strong likelihood of life, right now, not the possible of life millions of years ago.
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Again, "walk before run" applies here. We're having a lot of trouble just getting some simple wheeled rovers to operate reliably on a DRY planet that's only 30 light-minutes away. Don't you think we should figure out how to make our autonomous space hardware work a little better before we attempt to take on a mission involving a moon many light-hours away, which involves drilling through 3km of ice (a serious feat here on Earth), and then exploring what's most likely an under-ice ocean?
And second is the m
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Ahh, we can melt through that with a small self contained probe that is RTG powered. It could be designed it to melt its way in, and climb down the hole as it goes. I don't see that as hard.. It could then release a probe or a number of gliders to roam about. The gliders could even be powered by their own small RTG's which would allow them to be driven!
As far as communications fhrough the ice well there is research in this area like this that utilize high loss. Take this article for instance: "Underwater c [theiet.org]
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That's a good idea about melting through the ice, though I do wonder if an RTG would generate enough heat to do that. But the rest of the things you're talking about are still fairly new here on Earth, let alone on another planet. Wheeled rovers are comparatively simple, and we're still having trouble with them on Mars with some simple dirt.
I imagine the reasons they're focusing on Mars are 1) it's very close, much closer than Europa; 2) it's all dry land. It's much easier to operate stuff on dry land, f
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Another interesting point: NASA and ESA (with JAXA and Roscosmos expressing interesting in joining in) are planning a mission to the Jupiter moons, with a focus on Europa, Ganymede, and Jupiter's magnetosphere: http://en.wikipedia.org/wiki/Europa_Jupiter_System_Mission [wikipedia.org]
So they're not completely ignoring Europa.
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Mars is just too easy
Your rant was actually doing pretty good until there. Check the mars mission failure rate... If Europa were say, a hundred times more difficult, then the odds of total mysterious failure in Europa currently approach 100%. But if we can improve our reliability by trying stuff in easier mars missions, maybe someday a Europa mission wouldn't be a guaranteed failure, and might even work, maybe.
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I didn't say anything about limiting us to Europa, you did.
Uh, you said "forget Mars", so it seems pretty clear that whatever unlimited space program you're imagining, it is limited to not-Mars.
In short Mars has received a disproportionate number of missions yet we keep sending rovers and landers to Mars!
Because we still have a ton of things to learn and it's low-hanging fruit. Relatively cheap missions with a relatively high measure of success and an enormous payoff in science. We will be sending rovers
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No, we can't forget about mars, because we still have a crap-ton of stuff left to learn about it. So much so that just about everything we do there results in us learning something new. Hell, just a day or two ago, I learned that the Spirit rover trying to work its way free from some sand had revealed sulfate deposits. And that was quite literally just scratching the surface.
As others have pointed out, Europa missions are in the works, but are quite a bit harder to do than Mars, especially if you think t
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*nod*
We need to learn a ridiculous amount about a few other places too. But, yeah.. :)
Global Warming? (Score:2)
So would 'global warming' have prevented this type of disaster?
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So would 'global warming' have prevented this type of disaster?
Uh, no. Or do you really believe global warming would've magically allowed Mars to hold on to its atmosphere?
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No. The problem with mars is that it lacks the gravity to keep gaseous particles bound to it's atmosphere, such that the solar wind removes a really small % of it's atmosphere annually.
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So if you were generating the same % of gas annually, would it not be in equilibrium?
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Correct, which is why we can still breathe :) Realize that most of a planet's mass is not involved in the generation of the atmosphere, and that aside from Volcanos not much change occurs on a 1000 year scale unless biological processes are involved. Volcanic activity has also substantially reduced on Mars, which would have been the other major factor in producing atmospheric gases from minerals / rocks.
The off-set of having a warmer atmosphere though is that warm things expand, which makes them easier
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From Charged particles, yes. Not all space particles are charged, or are slowed down by magnetic fields.
Mars is lacking a magnetic field, which is also believed to be why volcanism has stopped. (molten core not large enough, or maybe fully solid )
Yeah, that's great Mars (Score:2)
liquid exchange between craters? (Score:1)
Are we next (Score:2, Funny)
So, the aliens have successfully stolen all of the water from Mars (as reported in thousands of lousy science fiction movies and TV dramas). Is the Earth next on their list of planets to steal the water from? I mean, it's not like you could possibly manufacture your own water by taking a couple of common elements in the universe, like hydrogen and oxygen, and combine them using a stupid trick like fire.
This nerd's theory (Score:1)
Sorry, too much Clarke and Heinlein as a kid I suppose.
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I love the way scientists talk... (Score:1)
"Channel connecting depressions in bottom right providing clear evidence of liquid exchange between depressions."
Around here, we call that a "river"... XD Most lakes have one or two connecting them to other bodies of water.
I can see your boobs... (Score:1)
...aaaaaaand...now we're safe from terror...
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Your ex is over 3 billion years old? That must have chafed..
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I'd prefer a non-polluted life-sustaining planet.
I am an environmentalist, but I don't think that we have to live in caves and grow our own food to keep Mother Gaia and all Her Creatures in something something, I kind of lose interest at that point too.
If you consider terraforming pollution, then you and I have different views. Adding carbon dioxide and water to Mars to make it habitable for humans is perfectly acceptable. We require more earths to sustain our lifestyle, and we've only got the one tiny litt
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Adding CO2 and water to Mars is going to involve industry. And energy. Shitloads of both. Industry is going to involve, by necessity, many of the chemicals you mention, either to run the machinery or as a byproduct of it. Therein lies the problem. Mankind isn't going to wait around for hundreds of years for a long, slow, low-energy terraforming system to work, so by the time we've turned the dial to 11 for enough years to have reached a semi-breathable atmosphere, it'll be polluted.
Now add in your comm
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I wondered about that as I was posting. Where would we get all this water and CO2 from? We can't really export it from Earth because that'll fuck up our ecology here.
We'd have to make it on site once we get to Mars, and that means industry, like you say. I've never had a problem with industry -- I like the fact that I don't have to spend all day every day growing / chasing food and finding water. You're conflating environmentalism with Ludditism. Technology and industry are fantastic. However, we can be mor
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What proof would satisfy you?
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--
Universal health care is a good thing. It's not socialist. Get over it.
Sorry to post off topic to your sig, but universal helthcare is socialist. whether or not it is a good thing remains to be seen.
Off Topic (Score:5, Funny)
Your post reminds me of the day a coworker came into my office with a look of deep thought on her face, asking why we need to use money. Not getting where she was going, I started explaining that money is just an accounting system. That didn't satisfy her, so I started to explain how it evolved from barter.
She stopped me, and saying that she understood that, followed by a but "Why can't we just go to work, and when we need something just go to the store and get it? Why do we need to keep track of it with money? That's what I think we should do."
At that point I got what she meant, and told her that theoretically we could. And said "What you are describing is communism." She then puffed up and angrily said "YOU are a communist." and stomped out.
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The proper response is, "And you are as dumb as a box of rocks."
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At that point I got what she meant, and told her that theoretically we could. And said "What you are describing is communism."
She is also describing a lack of scarcity.
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Sorry to post off topic to your sig, but universal helthcare is socialist. whether or not it is a good thing remains to be seen.
NO. It's a social program, but it not socialist. Unless you consider the police, army, judicial system and public schools also to be socialist.
Socialism is very different than social programs.
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Don't forget: Firemen - The Red Truck Menace!
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Kind of right I guess. Although it's not as much of a misnomer as calling the US's current system Capitalist.
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its no more socialist than the police force is, even if you never need to use haelthcare (which is extremely unlikely) most rational people are happy to contribute in case they do need it.
at least thats how it works over here in europe.
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There are many first world countries with universal healthcare. Why are they not good examples of the effects? I am not arguing for or against. I simply stating that countries like Canada and Germany can serve as examples.
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It is Government-run healthcare that is intrinsically oppressive and untenable to freedom loving peoples.
Just like a government run judicial system and military forces.
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As a Canadian, I have to quirk my eyebrow at that.
You realize that we have supplementary coverage up here, right? Hear me out.
The government provides basic health coverage. They cover almost everything, from emergency treatment to birth and annual physicals.
We don't get coverage for private rooms, eyeglasses, Rx medication (unless you spend $3k a year or more, long story), massage, physio, etc. There's a long laundry list of things that aren't covered. Ambulance rides aren't covered, but that's because too
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And here again you prove the anti-healthcare arguments. You're healthcare is up to the whims of a politician. Compared to how it should be, I buy the amount of healthcare I want. Something we mostly don't have in the US but should be working towards not away from.
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And it's fantastic! Healthcare is a major election issue. Politicians are spineless attention seekers who will do anything to get elected. You can't get elected on a platform of reducing healthcare, and every election cycle the opposition parties pick apart the performance of the health system and loudly promise to improve it. Then whoever is elected sets the health budget at the lowest they think they can get away with and lets the doctors get on w
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That was my point. In Canada, you buy whatever coverage you want. If you can't afford any, you get a base coverage of medically required procedures.
To summarize Canuck Health Care:
1. The basics are paid for.
2. You can buy more insurance.
That's all there is to it. If you don't make enough money, you get taken care of. If you make enough, you get the same care for the same price*, but you can buy more. I can get coverage that'll cover a massage every day and chocolate mints on the pillows in a private suite i
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If my choice is health care up to the whims of a politician or up the whims of an insurance executive I'll choose the politician.
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I'd much rather have health care up to my health care provider, and health insurance up to my insurance provider. Why should I be required to have maintenance and insurance in the same policy? It's these bundlings that really cause faults with any system.
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Wow, you seem terribly defensive over what is a pretty reasonable question. This is slashdot, you are allowed to ask things here...
Anyways, from what I understand (and this is in no way my field), they usually date these sorts of things by observing what kind of geological features are on top. If a crater has numerous smaller craters in it, then you know the larger crater is older. With the crater distribution they can make pretty reasonable estimates about the age of something. Similar methods techniqu
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The article does address this:
"The researchers determined the age of the lakes by counting crater impacts, a method originally developed by NASA scientists to determine the age of geological features on the moon. More craters around a geological feature indicate that an area is older than a region with fewer meteorite impacts. In the study, the scientists counted more than 35,000 crater impacts in the region around the lakes, and determined that the lakes formed approximately three billion years ago. The sc
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Aha! No, you want room 12A, next door.
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Re:How do they determine those dates? (Score:5, Informative)
The researchers determined the age of the lakes by counting crater impacts, a method originally developed by NASA scientists to determine the age of geological features on the moon. More craters around a geological feature indicate that an area is older than a region with fewer meteorite impacts. In the study, the scientists counted more than 35,000 crater impacts in the region around the lakes, and determined that the lakes formed approximately three billion years ago. The scientists are unsure how long the warm and wet periods lasted during the Hesperian epoch or how long the lakes sustained liquid water in them.
So to answer your question the moon is the reference point.
It has large error bars, but it's the best we have until we can send radiometric dating to these areas. [Crater Counting [wikipedia.org]]
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It has large error bars, but it's the best we have until we can send radiometric dating to these areas. [Crater Counting]
If you'd like a somewhat more detailed explanation, try Dr. Hartmann and Herres six year old explanation at:
http://www.psi.edu/projects/mgs/cratering.html [psi.edu]
Re:How do they determine those dates? (Score:5, Insightful)
Contrary to what the "internet" likes to tell you, many people question what scientists say because they want to see actual proof to support the claims rather than just additional layers of theories and educated "guesses".
And the people who are legitimately intellectually curious rather than simply delighting in taking jabs at the "scientific orthodoxy" don't universally phrase their questions as "Do you know what you're talking about or are you making shit up that supports your preconceived notions?"
"How do they determine those dates?" is a fine question, one I am curious about as well. "Gee, in the scientific method I'm used to, you have to have a known reference. Do they have one? Have they been following the scientific method?" kinda makes you sound like the kind of person you are implying you aren't. Maybe you're just being defensive, or using modding reverse-psychology. But really, just leave that part out.
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You must be new here... ;)
Unfortunately, not reading TFA is pretty par for the course here. Comments like this get modded up because often the moderators haven't RTFA either. "Playing a martyr to get easy modpoints" seems to be getting pretty popular as well. (note: I'm not accusing the GP of karma whoring... at least intentionally)
Re:How do they determine those dates? (Score:5, Informative)
How are these dates determined?
Basically, they're counting craters.
The idea is that everything in the solar system is being steadily bombarded by random bits of debris. More craters means that something has been exposed to the elements for a longer amount of time.
In this case... If you have a once-lakebed that's now covered with craters, it must have been a while since there was water in it.
No, it isn't perfect. But it isn't too horrible either.
And, of course, the numbers will be refined as more/better data and measurements become available.
Re:How do they determine those dates? (Score:4, Insightful)
I'm probably going to get modded down or flamed for being a heretic for daring to question modern scientific orthodoxy
Ah, the classic cry of the rebel without a clue.
Listen up, kid: you are not an iconoclast. You are not boldly speaking truth to power. You are not Martin Luther nailing his theses to the cathedral door. You are not a special snowflake.
Everyone who has ever worked in this project has thought of, and answered, every single one of your questions long ago. And those answers are easily available with a small amount of digging, which you would do if you had any interest in the actual answers instead of just self-aggrandizing puffery.
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I agree, it's not because you have an engineering degree that you know so much about something that you have never had contact with, as well they are using earth type examples to template off of, thinking there could never be any similar thing that would cause water like patterns in the sand, so it must be water, what about liquid gasses...they are liquid too, but not water...anyways, I lost interest in what they were doing a long time ago....when I saw some of the presumptions they made about so many space
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A) Most people question scientists because the conclusion from studies are different them the sacred cows.
B) Most people wouldn't understand the data
C) " based on supposition to support a hypothesis?" this seldom lasts long.
D) Your question are all good one, the type of questions a 5 year old asks. That's not an insult, 5 year olds ask the best questions.
Unlike a 5 eyar old, you could easily get the answers to those question, so I won't hold your hand.
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If you read my other response, I'm suggesting that the dates are not based on anything other than a very limited time period of observation and scientists have extrapolated from that limited data set a rate of impacts. They then used that to provide an educated guess on the age.
The problem with this is t
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any effort to seed the martian atmosphere would at best be a temporary(ok, a few million years) improvement. Mars lacks the gravity to hold the atmosphere. what's more, the warmer the atmostphere the faster it will disipate off into space.
in the 3 billion years since the lakes existed, mars has reached an equilbrium.
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any effort to seed the martian atmosphere would at best be a temporary(ok, a few million years) improvement.
A few million years would, of course, be more than enough time (by a factor of 10000 or so) for colonies to flourish and grow. And presumably, if we figured out a technique that we could use to do it once, our many-times-great-grandchildren could repeat the process if the air started to get a little thin.
Mars lacks the gravity to hold the atmosphere.
Okay, here's something I've always wondered about:
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The Earth's magnetic field protects the atmosphere to some extent, and Mars and Venus don't have much of one. Venus has lost most of its original water (or rather the hydrogen that was in the water) to space.
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Lost its water, sure, but not the rest of its atmosphere. What I'm wondering about is the overall mass and density of the atmosphere which a planet of a given size can maintain, and again, based on the example of Venus, it seems like neither Earth nor Mars can be anywhere near the upper limits for those numbers.
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Mars once had a much thicker atmosphere, so it must have gone somewhere. A mechanism for its loss to space has been proposed [nasa.gov], but this is not settled science. Still, there is no obvious place on the planet for most of the old atmosphere, presumably mostly carbon dioxide, to be sequestered (carbonates or what not).
Re: (Score:1, Interesting)
No, you're not missing anything. The "not enough gravity" explanation is completely bogus. Titan is a lot smaller than Mars, hell it's only half as massive as Mercury, and holds on to an atmosphere with a surface pressure 50% greater than earth. In fact, the atmosphere is so thick and the gravity so low, that a human could strap on a pair of wings and easily flap their way to self-powered flight.
The real culprit behind Mars' lack of atmosphere is twofold.
1. no magnetific field
2. the sun
The Solar wind is not
Iceteroids! (Score:2)
In the long term, iceteroids in the outer solar system seem to be a reasonable source of replacement hydrogen and oxygen for a terraformed Mars.
The nice thing about them is that, assuming you have nuclear rockets of sufficient size and durability, an asteroid made of ice is essentially made of reaction mass.
Other places you could get hydrogen (or water - strip out the oxygen if you don't want it) include the gas giants themselves or some of their satellites. The inner Jovian moons are unlikely to have sign
Re: (Score:2, Funny)
Where was the last place you saw it? You must have lost it somewhere between here and there. Don't forget to check under the sofa cusions.