[X] My Assistant

[remcook]

http://www.timesonline.co.uk/article/0,,2089-1697332,00.html

FAR from discovering life on Mars, Nasa may have put it there. The American space agency believes the two rover spacecraft scuttling across the red planet are carrying bacteria from Earth, writes John Harlow.

Probably isn't the first time either. Can't believe old russian probes had any policy with that respect.

[tty]

Interesting idea. According to the latest biological ideas, the Earth actually is of both types! This theory claims that most of life (in mass and in numbers) can be found deep below the surface, up to 3 or 5 kilometers deep. Life on top of the surface should be regarded as 'icing on the cake'. From time to time, the icing is destroyed and for a short while the Earth is a pure type 1 planet. (Like after the impact that created the Moon or when our planet is covered with ice from pole to pole) However, it doesn't take long for those critters underground to find their way up and colonize the surface once more.

The impact that created the Moon almost certainly sterilized the Earth completely. In any case it is doubtful if life had had time to develop (it probably happened 4.45 bya). The Late Heavy Bombardment c. 3.85 bya may well have sterilized the surface, but probably no incident since then, not even the extreme neoproterozoic ice ages. A number of macroscopic metazoan lineages go back before that time, and so must have survived somewhere (deep sea vents? hot springs?). As far as can be judged from the sparse data (mostly acritarchs) a lot of lineages did become extinct.

tty

[Bob Shaw]

The impact that created the Moon almost certainly sterilized the Earth completely.

Although the proto-Earth was, it appears, dealt a mighty whack, and the whole place became untenable as an abode of life, presumably much debris was ejected which then returned to the planet over a period of a few tens of millions of years - just as it would today. Much debris would have landed on a very hot and inhospitable planetary surface, but as time went on things would have improved. I suspect that while Earth may have been sterilised, any rock-dwelling life from before the big impact might have returned to the planet in due course. A good proportion of such returnees probably got hit by the next pile of junk falling onto the surface, but...

Additionally, if life did gain a foothold here before the big whack then imagine how much debris from Earth contaminated the whole inner Solar System! From what I've read, the collision which is accepted as creating the Earth/Moon system must have been just about the biggest ever in our locale, and would have generated a commensurate amount of rocky spaceships!

[dvandorn]

If by "our locale," you mean Earth or the inner Solar System, you're right. But for the Solar System in general, I bet the impact that tilted Uranus on its side was a bigger, more violent event.

-the other Doug

[AndyG]

If by "our locale," you mean Earth or the inner Solar System, you're right.  But for the Solar System in general, I bet the impact that tilted Uranus on its side was a bigger, more violent event.

-the other Doug

At number #3 in the charts there's the one that ate up (and then some) Venus' rotational energy.

Number #3?

Let's see - lifting the Moon to lunar orbit = ~4*10^30 joules
Cancelling the spin of Venus (assuming initial 24hr rotation period) = ~4*10^28 joules.

That's a lot!

Andy G

[tty]

Two other big (though somewhat hypothetical) collisions:

1. The one that stripped the mantle off Mercurius

2. The one (or maybe more than one) that differentiated the northern and southern hemispheres on Marss.

Additionally, if life did gain a foothold here before the big whack then imagine how much debris from Earth contaminated the whole inner Solar System!

And the same thing happened again on a somewhat smaller scale (and perhaps a little less violently) during the Late Heavy Bombardment, at which time lots of material must have been exchanged between all four inner planets. Also at that time it is rather more likely that life had had time to evolve somewhere. I suppose Mercurius has always been a pretty hopeless case, but who knows about Venus back then when the sun was weaker and perhaps less CO2 had outgassed....

Incidentally an awful lot of rocks from Earth must have landed on the Moon during the LHB and the Moon is quite possibly the best place to find out what happened on Earth pre-3.85 bya. It seems there is little chance that we will ever find much more than detrital zircons from pre-LHB days here on Earth.

tty

[Bob Shaw]

Incidentally an awful lot of rocks from Earth must have landed on the Moon during the LHB and the Moon is quite possibly the best place to find out what happened on Earth pre-3.85 bya. It seems there is little chance that we will ever find much more than detrital zircons from pre-LHB days here on Earth.

tty

I've always thought that when/if He3 mining takes place on the Moon then in the spoil tip will be some real treasures!

[Sdetton]

ESA: Lichen survives in space (temporarily)

... During the Foton-M2 mission, which was launched into low-Earth orbit on 31 May 2005, the lichens, which came from two different species (Rhizocarpon geographicum and Xanthoria elegans) were exposed for a total 14.6 days before being returned to Earth. At the conclusion of the mission the lid of Biopan was closed to protect the lichens from the conditions of reentry.

...lichens have the capacity to resist full exposure to the harsh space conditions, especially high levels of UV radiation. Analysis post flight showed a full rate of survival and an unchanged ability for photosynthesis.

This is pretty interesting. I wonder if the lichen communities would survive in deep space though and for how long. What would happen if this got transported (safely) to the martian surface?

[hendric]

What would happen if this got transported (safely) to the martian surface?

Should be a fairly easy experiment to do on the ground, at least the atmosphere and Uv portion of it. The rock/soil composition might be harder.

An enterprising young PhD should take this up, with simulated variations in the atmosphere and irradiance based on martian years, for different locations on Mars.