Chris Peterson wrote:
Buddy wrote:I've read that the meteor impact that killed the dinosaurs is estimated to have deposited in the order of a tonne of material on the Gliese 5 planets, so if there wasn't life there before, there is now.
However, some simple analysis reveals that this is complete nonsense. You could vaporize the entire Earth and send the debris spherically outwards, and at 20 light years (the distance to Gliese 581) the mass density would be 10-5
. An Earth-sized planet at that distance would collect 360 kg of material. Of course, the Earth wasn't destroyed 65 million years ago. And even if the entire contents of the Chicxulub crater were ejected spherically from the Solar System, the mass density at 20 ly would be just 4 x 10-5
. An Earth-sized planet would capture a few hundred milligrams of material.
In reality, however, almost none of the material from that impact would have even escaped Earth's gravitational pull, and less yet the Sun's.
Remember, too, that if some of that life-bearing debris was indeed capable of travelling all the way to the Gliese 5 planets, much more of it would have been able to travel to Mars, which is many orders of magnitude closer to us than Gliese 5.
Also bear in mind that the very much shorter journey to Mars would mean that the bacteria in the Earth fragments had a reasonable, perhaps even good, chance of surviving. What would be the chances of Earth life forms surviving for, we must assume, millions of years travelling slowly through the dry ice cold and cosmic ray-ridden wastes of interstellar space?
any debris from the Chicxulub crater has made it to the Gliese 5 planets, if its load of life form has survived, and if that life has managed to establish itself and grow a colony on that planet, then surely many more life-bearing "spaceships" should have made it to Mars and delivered Earthly life forms to Mars. There should be many thriving and extended colonies of Earth bacteria on Mars by now. That bacteria should make their presence known to our instruments, both to those that monitor Mars from Mars orbit and to those that have reached the surface of Mars. We should probably even detect clear signals from the Earth that the Martian atmosphere had been modified by all the planet's bacteria.
Where is that very clear evidence of present life on Mars?