Scientists go to all this trouble for the purpose of “planetary protection”—which usually means protecting other planets from contamination by microbes originating on Earth. Most spacefaring countries have agreed to follow guidelines from the International Council for Science’s Committee on Space Research to reduce the chances of their vehicles carrying Earth organisms to other planets. The clean room procedures also safeguard against scientists mistaking Earthly microbes as extraterrestrial in origin if they are discovered on another planet, having caught a ride with a man-made spacecraft. “The whole idea of collecting information about what kind of bugs we have in the spacecraft assembly facility is to have baseline information so that in the future, if you find it on Mars, you have some grounds to rule out the possibility that it came from Mars,” Vaishampayan says.
Being able to make the distinction between panspermia induced by human activity, and panspermia that occurred through some other mechanism is important. The possibility that life jumped the gap on meteorite strike debris does not make protecting against contamination any less important.
Actually, I would say that it makes it more important. If there was no possibility for non-human related panspermia, then if we found an organism on Mars that appears closely related to an earth organism, then we could write it off as contamination and ignore it. However since non-human related panspermia could conceivably happen, it would be more difficult to pin such a discovery on contamination.
Citation please (sounds interesting, but yeah), and does it get exchanged at the speed that this stuff does, or does it take thousands^x years to arrive?
Not that I disagree. Just wondering if there are a few orders of magnitude that need to be considered.
Looking back for the specific citation, I can't find it. Looking naively to find the source, it seems like it was an estimate (I mean, we know there are meteorites, but the actual frequency and when they landed, and the total amount isn't known exactly).
http://arxiv.org/pdf/1205.1059v1.pdf
(ignore the part about lithopanspermia. I'm just discussing the facts of the matter, not the crazy speculation part).
OK. Turns out I was using the wrong search term. It's "meteorite flux",
and here are several sources. Unfortunately, Google obscured the PDF link, so do:
[ mars earth meteorite flux ]
In particular,
"Assessment of Planetary Protection Requirements for Mars Sample Return Missions" has data.
1) agreed. there's solid evidence that Mars sends junk to us - not sure about the other way around.
2) does that matter, since they're in orbit, thus zero/microgravity? You still need energy to leave an orbit, whether up or down, I don't see how it makes a difference. There's no friction to speak of to make "down" a direction that things are predisposed to move in. Over ridiculous time scales sure, but ridiculous time scales are nothing like human time scales, so we still have many orders of magnitude difference if we fling stuff at Mars intentionally.
orbit. gravity is canceled out by orbital velocity, as far as distance-from-sun is concerned. it costs Mars nothing to stay in orbit, and to go down to a -100m/s orbit or up to a +100m/s orbit costs the same amount of energy: (mass of mars) * (100m/s velocity change)
if Mars and the Earth were not orbiting, I would completely agree. drop something from Mars and it'll land on Earth, and the reverse is not true. but they're not - drop something on Mars and it's just in Mars' orbit.
Delta-v requirements for transfers in space are generally symmetrical. It takes the same amount of delta-v to go from Earth's orbit to Mars's orbit, for example, regardless of direction.
The one thing that changes this equation is aerobraking (or, when dealing with stuff whose structural integrity isn't important, lithobraking). Because drag works in one direction, that means that you can take advantage of it when arriving but not departing. For that reason, for example, it takes more delta-v to reach a transfer orbit to Mars from Earth than it takes to reach Earth from a transfer orbit to Mars. Technically that's not true, but when arriving at Earth, a great deal of delta-v can be provided by the atmosphere or the ground.
It's true tat it's been a long time since I played with this stuff, I work out for a circular orbit
Total energy of an orbit is -G mp mS /(2 r)
mp = mass of planet
mS = mass of sun
r = distance of planet from sun
Even though this is a circular orbit, the basic result should be the same: the greater the distance from the sun the more energy the planet has, per unit mass.
I think I understand your basic point, however, which is that whether we speed it up or slow it down we have to do something to the mass, and how much we do depends only on difference of the orbit radii.
But note that adding 100 m/s or subtracting 100 m/s gives two different differences in r.
About #2, it may be the other way round, anything escaping Earth is easily pulled in towards Mars' orbit by the Sun's gravitational pull. The other way round, it requires more energy to escape.
BTW, I found the source of this quote- it's from Craig Venter (he cites it as a reason for sending his DNA sequencer to Mars). I can't find anything supporting his statement, however.
Scientists go to all this trouble for the purpose of “planetary protection”—which usually means protecting other planets from contamination by microbes originating on Earth. Most spacefaring countries have agreed to follow guidelines from the International Council for Science’s Committee on Space Research to reduce the chances of their vehicles carrying Earth organisms to other planets. The clean room procedures also safeguard against scientists mistaking Earthly microbes as extraterrestrial in origin if they are discovered on another planet, having caught a ride with a man-made spacecraft. “The whole idea of collecting information about what kind of bugs we have in the spacecraft assembly facility is to have baseline information so that in the future, if you find it on Mars, you have some grounds to rule out the possibility that it came from Mars,” Vaishampayan says.