If you draw Mars with 20% of the surface covered in water
Why are there lots of craters, but no rivers or clouds?
NASA boffins have popped out a new paper, Strong water isotopic anomalies in the martian atmosphere: Probing current and ancient reservoirs, in which they advance a theory that Mars once had substantial oceans. The theory outlined in the paper relies on measurements of the types of water found on Mars. Yes, we do mean “types …
"So, the next lander will be a nuclear tank with a big fricking laser and dynamite?"
It wouldn't be out of the question. Some of the Apollo landers brought mortars for seismic investigations. Oh, wait, how should I say that Reg style...
"NASA assaulted the moon with mortar barrages, I doubt Mars is any safer."
One theory I have read in some places blames the lack of Martian magnetic field, which allows particles from the Sun to blast away gases from the upper atmosphere. So the first step in terraforming Mars should be building a humoungous superconducting coil around the equator, and a big nuclear power plant to feed it :-)
hah - I once tried that out in a physics tutorial, getting the students to work through the numbers, estimate currents, power requirements, etc. Only for earth, mind, it'd obviously be much "easier" for the smaller Mars.
"First, assume a spherical Mars... " :-)
Efficient martian yeasts, and advanced distillation technology enabled the inhabitants to turn all the water into the mars version of scotch. It's currently maturing in oak barrels, in ther giant maturation cellars. The lack of trees on mars points towards loads of barrels of this red planet firewater, as they only had a finite supply of wood to create the casks. Thinking about it, it's the only logical explanation that can account for no water AND deforestation of the planet. Future human visitors to Mars can almost certianly look forward to cracking open a barrel of 'Glen Syrtis Major' on their arrival.
> Thinking about it, it's the only logical explanation that can account for no water AND deforestation of the planet. Future human visitors to Mars can almost certianly look forward to cracking open a barrel of 'Glen Syrtis Major' on their arrival.
You may be on to something there ... perhaps it's no coincidence that the surface of Mars is marginally less desolate than the average Scottish High Street.
"So why has Earth's magnetosphere lasted 4GY longer than Mars?"
Earth has a couple of factors going for it:
1) Higher proportion of iron. Earth is significantly denser than Mars because of a high iron percentage. This gives Earth a bigger iron core for its magnetic field.
2) Bigger. Earth is ten times as massive as Mars and has twice the radius, but only has about 4 times the surface area. It takes more time for a watt of heat to escape, and Earth has a lot more watts to begin with. This keeps Earth's core molten for its magnetic field.
"So why has Earth's magnetosphere lasted 4GY longer than Mars?"
Because Mars is tinier than most people think:
http://mars.nasa.gov/images/20030728_marsClose02-fi.jpg
If Earth was basketball sized, Mars would be grapefruit sized.
Much less mass, greater surface area proportionately, means its core cooled quite rapidly compared to Earth's.
"So why has Earth's magnetosphere lasted 4GY longer than Mars?"
Short answer, because of the size difference. Mars masses about 1/6 as much as the earth. The active field like the eath has chilled down. Longer answer is, it's still there. Mars occasionally has auroras which don't occur without a magnetic field. Even longer answer is that most of Mars' water may still be there, trap in glaciers covered by dust and at the south pole. Mars has quite a few sinkholes and they can't be due to the same kinds of action that cause sinkholes in Florida and Central America. The best bet is subliming ice (either water or methane).
"Core still hot and rotating."
Probably factually correct, but why? Earth has four times the surface area but its dynamo has lasted 9 times as long. Come up with a model to convince me that make sense. And, while you're at it, explain why the Earth-sized Venus lacks one? (Venus, too, has lost all its water, BTW.)
My impression is that some critical process got started on Earth that didn't happen on either Mars or Venus, and that that means our dynamo will run a lot longer. It could be that Mars cooled down too quickly for this process to start. It could be that subduction of water is important and that Earth mopped up so many comets that Venus didn't get enough. It could be that the moon has a role: the core must experience tides forces which generate heat.
But I don't buy the simplistic arguments on offer here.
My impression is that some critical process got started on Earth that didn't happen on either Mars or Venus .... It could be that the moon has a role: the core must experience tides forces which generate heat.
I'm no astrophysicist, but Earth's moon certainly pumps some energy into the crust and mantle. Does that contribute significantly heating the liquid outer core? I don't know, but stuff I've read suggests that radioactive decay is a much larger contributor to the Earth's overall heat.
If you're looking for critical processes, the obvious one would be the formation of the Earth's moon in the first place. Some whacking huge thing (probably about the size of Mars) hit the Earth and carved off a moon that's much, much bigger than anything any of the other inner planets have; among the natural satellites of the gas giants, only half a dozen are comparable.
A whack like that is going to linger. Earth's rotational speed is ~250 times that of Venus, if I'm not mistaken. Mars has roughly the same sidereal day as Earth but a much smaller radius, obviously. So Earth's core has a hell of a lot of angular momentum.
And, of course, versus Mars it has a much better mass to surface area ratio; versus Venus it's 30% further from the sun, so less tidal drag on its rotation. How much do those contribute? Dunno, but they could be significant.
"Probably factually correct, but why? Earth has four times the surface area but its dynamo has lasted 9 times as long."
When Earth was young, a planet roughly the size of Mars crashed into it. Much of the lighter elements splashed off into orbit and became the moon. All the heavier elements - like Uranium, Thorium and other radioactives - sunk to Earth's core. Earth has not the radioactive power of one planet, but two. combined with it's higher size, the remnant heat from that catastrophic impact and the fact that it was spun up both by Theia and the Late Heavy Bombardment, and, well....
"Probably factually correct, but why? Earth has four times the surface area but its dynamo has lasted 9 times as long. Come up with a model to convince me that make sense. "
Well, you left out a key number: Earth is 10 times as massive as Mars. Everything else being equal, that's 10 times the number Joules stored as heat to leak through proportionally less surface area. If I did the math correctly, Earth only has 40% of the area per unit volume. That'd be 2.5x as long to cool Earth's core to Martian levels.
But everything else isn't equal on several counts.
First, Earth has twice the radius of Mars. This compounds the matter of lower proportional surface area. Joules at Earth's core have twice as much material to conduct and convect through to reach the surface.
Second, ten times the mass means every kilogram got treated to a larger dose of gravitational energy when the Earth was piled together out of the proto-solar nebula. Earth's escape velocity is ~2.2x that of Mars, which means Earth's infalling material accumulated about 4.8x the kinetic energy, which manifested as heat. Flipped around, each kilogram of Mars only started with about 21% of Earth's heat of formation.
Third, the larger, hotter iron core of Earth is likely to have a larger percentage of radioactive elements, though I couldn't put numbers to that.
To summarize: Mars has proportionally 1/10th the starting mass; only 21% of the initial joules per kilogram imparted by gravity; 250% more surface area per unit volume; and (at most) half the distance for heat to leak out. I'm not sure how you want to combine those factors, but they can easily get you above 9x the dynamo lifespan.
"And, while you're at it, explain why the Earth-sized Venus lacks one? "
Theia pumped a lot of angular momentum into Earth to keep Earth's core spinning, while Venus's superrotating atmosphere damped Venus's rotation. As I understand it, planetary rotation is critical for the core dynamo effect.
The problem with the Mars missions at the moment is similar to how the space programme was in the mid 70's in that people got bored of it. Same old, same old. Because of that the NASA budget was slashed and we didn't go to the moon anymore.
With NASA's budget again on a proverbial shoestring, rather than constantly send rovers to look at the geology of the red planet which the majority find boring (not me) why can't they stick a HD camera on top of one and stream it live 24/7 back to earth which will surely get the kiddos interested again and hence obtain a budget increase?
I know we currently suffer from bandwidth limitations but surely if they can land a rover on Mars in one piece then it's not beyond the realms of possibility is it?
It's not beyond any realms, but it looks like we are several orders of magnitude down on what you'd need for an HD camera, even with compression.
e.g.: http://www.astrosurf.com/luxorion/qsl-mars-communication3.htm
There's a table at the end of that article suggesting that we currently manage 5.7KB/s at a cost of 15W in power, but if you had 100W to play with then you might manage 4.8MB/s, which would support a video signal.
Bear in mind also that (as noted at the start of that article) Mars is sometimes quite a long way away and when it is you are also trying to transmit the signal past a nearby Sun.
On the other hand, for the inner solar system it might be practical to build some relays. Each relay's reception dish would have to be a similar diameter to the dishes used on Earth because the inverse square law doesn't grant exceptions to spacecraft, but (freed from gravitational constraints) that would not require as much metalwork as an Earth-based dish. Power would be another issue but again not insurmountable because we have solar power in the inner solar system and a relay could actually be quite close to the Sun and still be usefully half-way between (say) Earth and Mars in the worst-case scenario.
Pffft. Boring.
I want to see some close-ups of the Martian Caves.
My understanding of plate tectonics on earth is that it is driven by the water allowing the plates to lubricate when they slide over each other, it has also been suggested that microbial life is also important for this process.
Venus had no plate tectonics and Mars exhibits pre-plate tectonics which suggests that water wasn't there in the abundance that we find on Earth or for very long.
Given the above, if water wasn't around long enough to get plate tectonics going properly, much as I'd love to find evidence of life on Mars it's probably very unlikely :(
"plate tectonics"
They got sick of all the Marsquakes and welded all the plates together. That stopped the quakes but the stresses still carried on building. That lead to Mons Olympus popping like the ultimate zit and the creation of Valles Marineris. And the rest is history. Like the Martians.
If there is water, heat and C,N,S around, it is possible (but we do not know how probable) that life can arise.
A system under a net positive energy flow has to dissipate that gradient somehow. If it can't just radiate that energy away (which is what "net positive" means), it has to become more complex. That's just a consequence of thermodynamics.
With sufficient variety and concentrations of various elements, that means you get increasingly complex chemicals with increasingly complex interactions. With sufficient time, you get something that can reasonably be called "life" - defined as something like self-assembling collections of complex molecular structures.
So it's not so much a matter of "can arise" as it is of "will arise, if you stuff enough of the ingredients in the pot" (said ingredients including time and energy). Reactions will produce more and more complex structures until you reach whatever arbitrary limit you set for "living". The problem is nailing down those "sufficient"s.
(Many people have wondered what the purpose of life is. To paraphrase Scott Sampson, among others, it's to dissipate energy. Problem solved! The real question, of course, is what the meaning of life is. Alas, that is not a matter for thermodynamics.)
This was my thinking too, build a huge MgB2 or something with a higher Tc coil around the equator and use it to jump start Mars's existing (weak) magnetic field.
I calculated that the magnetic field strength needed for a basic dipole field to be about 5 times what is routinely used in an MRI scanner ie 45T as it is spread out over a very large area.
The power consumption would actually be quite low once the coil was energized as superconductors conduct electricity with virtually no losses as long as the field does not vary much.
Once the field is stable we can start to add an atmosphere using existing surplus nuclear devices at the poles to vaporize volatiles and voila!