Well, even a large mirror close to the Sun would just appear to be a bright speck from the distance to Mars, compared to the Sun.
As for a gravity well, everything has a gravity well, including the Moon. The Moon still doesn't have an atmosphere. This is because the gravity well isn't deep enough to keep the atmosphere from being lost to the solar wind or to sunlight pressure. The atmospheric pressure is mostly a function of how much the gravity can compress the atmosphere at the bottom; so Mars is never going to have a thick enough atmosphere to be breathable.
See, this is why Jupiter has a very deep, very thick atmosphere, and the pressure at the bottom is so high; it's got a huge gravity well.
Warming Mars would just make it worse; the atmosphere would tend to fly away even more. As for moholes, it would be easier just to live underground - no terraforming required. And speeding up rotation? How would you manage that?
Terraforming Mars is a popular idea but it's just not going to work. Martian gravity is about a third of Earth's and Mars is never going to be able to hold any kind of atmosphere. The Martian atmosphere is about 1/100th as thick as Earth's and bringing that up to breathable would be nearly impossible. Plus Mars receives only 43% of the sunlight Earth does and it would need a very thick atmosphere to trap enough heat to be livable. Some people suggest solar mirrors to increase heat but these would need to be moon-sized structures before they'd produce any perceptible difference.
What we need to do instead - and yes, this will take a *long* time - is terraform Venus. Venus has a surface gravity 90% of Earth's and already has a thick atmosphere. Venus is obviously far too hot at present to even explore, but we can take steps toward terraforming it if we're willing to take a long-term approach.
First off, we can stick Venus in the shade. This isn't going to require another gigantic structure to accomplish, since we don't need to focus the sunlight. Something as simple as a series of paint bombs set off between Venus and the Sun would produce a cloud that would scatter quite a bit of incoming sunlight. Obviously the solar wind would blow it away sooner or later, but if we were to move a few asteroids into position and set up automated (solar-powered!) factories to slowly convert them into dust clouds, we could keep Venus shaded continously.
Once the surface temperature drops, we can seed the atmosphere with microbes to break up the CO2 and sequester the carbon, releasing the O2 and making the atmosphere eventually breathable.
Slashdot Mirror
Well, even a large mirror close to the Sun would just appear to be a bright speck from the distance to Mars, compared to the Sun.
As for a gravity well, everything has a gravity well, including the Moon. The Moon still doesn't have an atmosphere. This is because the gravity well isn't deep enough to keep the atmosphere from being lost to the solar wind or to sunlight pressure. The atmospheric pressure is mostly a function of how much the gravity can compress the atmosphere at the bottom; so Mars is never going to have a thick enough atmosphere to be breathable.
See, this is why Jupiter has a very deep, very thick atmosphere, and the pressure at the bottom is so high; it's got a huge gravity well.
Warming Mars would just make it worse; the atmosphere would tend to fly away even more. As for moholes, it would be easier just to live underground - no terraforming required. And speeding up rotation? How would you manage that?
Terraforming Mars is a popular idea but it's just not going to work. Martian gravity is about a third of Earth's and Mars is never going to be able to hold any kind of atmosphere. The Martian atmosphere is about 1/100th as thick as Earth's and bringing that up to breathable would be nearly impossible. Plus Mars receives only 43% of the sunlight Earth does and it would need a very thick atmosphere to trap enough heat to be livable. Some people suggest solar mirrors to increase heat but these would need to be moon-sized structures before they'd produce any perceptible difference.
What we need to do instead - and yes, this will take a *long* time - is terraform Venus. Venus has a surface gravity 90% of Earth's and already has a thick atmosphere. Venus is obviously far too hot at present to even explore, but we can take steps toward terraforming it if we're willing to take a long-term approach.
First off, we can stick Venus in the shade. This isn't going to require another gigantic structure to accomplish, since we don't need to focus the sunlight. Something as simple as a series of paint bombs set off between Venus and the Sun would produce a cloud that would scatter quite a bit of incoming sunlight. Obviously the solar wind would blow it away sooner or later, but if we were to move a few asteroids into position and set up automated (solar-powered!) factories to slowly convert them into dust clouds, we could keep Venus shaded continously.
Once the surface temperature drops, we can seed the atmosphere with microbes to break up the CO2 and sequester the carbon, releasing the O2 and making the atmosphere eventually breathable.
Some useful stats on planets can be found here
http://www.sciam.com/2000/0400issue/0400tsien.html It's interesting, if a bit technical.