...Or Hit It With A Rock?

"How about just enough to start 'climate change'..any guestimate on how big and fast an impact would need to be - presumably would also depend on where it impacted?? Posted by pmn1 at Space.com" Any SINGLE impact to "...start 'climate change...'" to a significant degree would have to be something in the vicinity of the Cretaceous-Tertiary Event (AKA "bye-bye, dinosaurs!"), initiating a notorious period of mass extinction on Earth. Better make sure no-one's on the surface of Mars if you're dropping one of those! It left the approximately 300km wide Chicxulub impact basin in northern Yucatan, Mexico. It's believed that 65 million years ago, a 10 kilometer diameter asteroid penetrated Earth's crust at a speed of 15 to 20 kilometers per second; the kinetic energy equalled the energy of 300 million nuclear weapons and created temperatures hotter than on the sun's surface for several minutes. Incredibly, Mars has taken much bigger hits than this and survived (leaving the 2,300 km Hellas impact basin) - but probably lost its atmosphere in the process. Before we seriously consider a martian bombardment, we should consider the possibility of unintended side-effects. As previously pointed out, a really massive collision can entirely destroy a planet - where DID that asteroid belt come from...? A smaller, but still sizable collision might not destroy the planet, but could have undesired effects elsewhere on the planet's surface, not just at the impact site - check out the diagram here: http://books.google.ca/books?id=kAup0TOL09gC&pg=PA135&lpg=PA135&dq=impact+outgassing&source=bl&ots=218_rgLq6_&sig=qeYdV3FxlRk_i2v-XMJbeTiIRF8&hl=en&ei=pq-jSdXHAYmMsAPIjdmjAg&sa=X&oi=book_result&resnum=8&ct=result#PPA542,M1 and the text reads: "...an antipodal relationship between the Hellas impact basin and the Alba Patera volcanism on Mars was pointed out....the convergence of seismic waves was intense enough to fracture the Martian crust." Also consider the immediate cooling effect of the dust clouds in the atmosphere, along with other unpleasantness: http://www.lanl.gov/quarterly/q_spring03/asteroid_text.shtml

"Nuke the Red Planet?" (Sticknmuv, space.com)

The argument of terraforming versus ecopoiesis continues in Sticknmuv's posting at space.com (click on the title to link to the original posting). Fortunately, I wrote my dissertation on "...The Application of Desert Reclaimation Techniques To Ecopoiesis On Mars," so have studied the subject in depth. 'Ecopoiesis' is a 'softer' term for terraforming, meaning the 'making of a home,' without the invasive, transformative connotations of terraforming. Ecopoiesis supports the notion of protected, enclosed habitats, e.g. underground and/or dome-covered compounds, protected from the existing conditions of Mars, so that the presence of settlements would have a minimal impact on Mars itself. "Nuking Mars," in addition to having a negligible and short term effect on global surface temperatures (most of the thermal energy released is as a radiant flash, very little would be absorbed by the crust, and would cool rapidly) would result in massive clouds of lethally irradiated dust being kicked up into the atmosphere, probably covering Mars in a radioactive dust storm that would filter out the already scant sunlight, plunging temperatures at the surface even lower, and presenting any would-be future inhabitants with a less than desirable top-soil to grow their Martian crops in, should said radioactive dust storm ever settle. Furthermore, any interest in visiting Mars would most likely be scientific, with teams of geologists (soon to be areologists) eager to study rock formations in the Martian landscape. Not much to study if you blew it up.... And, as pointed out, there might actually be something living there already! Even if there isn't, why deny future generations the pleasure of trying to find the elusive "Loch Mars Monster?" The "loss of atmosphere," some people seem concerned with is a combined function of Mars' low gravity and incident sunlight, which very gradually depletes the water vapour in the atmosphere of hydrogen atoms; incoming photons 'knock' the atoms at the upper limits of Mars' atmosphere out in to space. The rest of the atmosphere is quite safe. The only other 'atmospheric loss' is through chemical weathering of the regolith, but this is not a loss to space, only to the ground; life cycles or processing could potentially release such gases back into the atmosphere again. One unaccounted for benefit of impacting the surface of Mars, be it with nukes, icy or metallic asteroids, is outgassing; a hard enough strike against the crust would vapourise gas-forming elements from the weathered regolith and breach to the Martian mantle, releasing further atmospheric elements in a similar way to vulcanism here on Earth. Since Mars no longer has vulcanism, die-hard terraformers might wish to consider a program of impact outgassing to replenish atmospheric elements and raise overall air pressure (and therefore surface temperature). Rather than randomly peppering the surface with redirected asteroids or comets, which would represent a considerable hazard to anyone on the surface, an exhaustively studied and remote site of little further geological interest could be selected as a repetitive outgassing target, and an orbital railgun could be used to accurately impact this target with metallic projectiles formed from mined asteroids or materials acquired from surface mining operations (William Gibson gave me this idea in one of his cyberpunk novels - "Mona Lisa Overdrive," I think...?). The Martian atmosphere is thin - around 6 millibars, depending on the season, but comprised mostly of carbon dioxide, so that there is roughly the same amount of CO2 in Mars' and Earth's atmospheres. Oxygen is not a greenhouse gas, so converting the available CO2 to oxygen via photosynthesis would result in further cooling at the surface of Mars. Adding atmospheric elements, e.g. nitrogen, water vapour (also a greenhouse gas) or oxygen not sourced from the existing CO2, and thereby raising the atmospheric pressure, would lead to an increase in the greenhouse effect of the existing CO2, which becomes more effective at higher pressures, leading to an increase in surface temperatures. Nitrogen makes up about 70% of Earth's atmosphere - instead of nuking Mars, if you were really committed to terraforming to the extent that humans could walk around on the Martian surface without any protection from the environmental conditions, you'd need to think of a way to pump Mars' atmosphere full of the missing nitrogen. Maybe there's enough nitrogen fixed in the soil there already to do the job....

Don Pettit's Saturday Morning Science

I was just perusing the video bar top left, here, as I was making a coffee, and I found this youtube video (http://www.youtube.com/watch?v=pk7LcugO3zg&eurl=http://gfreetek.blogspot.com/ in case it doesn't come up when you're here) about drinking coffee in space, which I've decided is the thing I'd most like to do right now! Well, maybe still the whole "World Peace," thing, but "Coffee In Space," is definitely in my top 10, now.... Anyway, a few years ago I was priviledged to attend the International Space Conference when it came to Vancouver, where astronaut Don Pettit (ISS exp 6 member) presented a seminar and a series of video clips he'd made of what he came to call his "Saturday Morning Science," experiments. The 'space coffee' thing jogged my special memory of that event, and in case you haven't had a chance to see them for yourself NASA has kindly posted them for posterity. Check out the clips, there's some AMAZING stuff! http://spaceflight.nasa.gov/station/crew/exp6/spacechronicles.html