Science Forums 2

[CraigD]

Originally Posted by LaurieAG

If you could drop a couple of large icy Kuiper belt objects on its surface you may just have a chance of making Mars habitable. Getting this same large amount of water from Mars itself would be a huge problem.

Originally Posted by Thunderbird

But even if you could somehow move these objects; Billions of tons across 100s of millions of miles, it would still take Billions of years for the planet to reform itself.

I don’t think this is true.

The various “watering/atmosphere-thickening” plans involving colliding KBOs (comets) with Mars don’t involve impacts that would damage Mars so much that it would need to “reform”, nor do they propose to duplicate the natural evolution of a biosphere. They simply propose to – quickly, within decades and centuries, not thousands and millions of years - add water and gas to create more human-friendly surface conditions.

Unlike the planet-moving examples in previous posts of this thread, the orbital mechanics of colliding large numbers of large KBOs with a planet, while obviously beyond humankind’s current engineering capabilities, are not energetically prohibitive for a fairly reasonable extrapolation of our near-future. KBOs regularly perform the trick on their own, with no artificial intervention, resulting in the appearance of new comets. Best speculation (we lack, by just a little, the instruments to actually observe these events) is that low-probability, effectively random gravitational encounters between large and small, or nearly equal mass KBOs transfer them from somewhat circular into very eccentric orbits, sometimes permitting stronger gravitational encounters with Neptune or other giant planets, that haphazardly transfer them to even more eccentric orbits. Though unlikely, there are a lot of KBOs, so these random events occur with enough frequency that new comets appear often.

Engineering comet strikes on a planet would be, I think, largely and observation and planning project, locating suitable KBOs that could be nudged into a series of gravitational passes with others, then one or more precisely guided passes with the giants, and some terminal guidance into target Mars.

Time-wise, comet orbits, which have semi-major axes from about 15 to 25 AUs, have orbital periods of 60 to 125 years, so these collisions could be engineered to begin happening about 30 years into a modest-energy program’s implementation.

Originally Posted by Thunderbird

It would be for more pactical to improve our way of living by reengineering how we live on this planet.

True. However, terrestrial reengineering is bound to occur regardless of any space engineering plans. IMHO, the promise of dramatic increases in available per-human power offered by space engineering - not precisely the same, but related to projects like comet-steering – makes it worth the high initial cost – and an inescapable necessity if our civilization is to climb the Kardashev scale.

Kim Stanley Robinson wrote a critically, popularly, and by-me lauded hard scifi trilogy on the subject of terraforming Mars, “the Mars trilogy”. Though one should be careful not to confuse scifi with real engineering, I recommend these books, not only for their engineering speculation, but for their cultural and sociological.