Oxidant used in rocket fuel found on Mars

(CNN) -- NASA's Phoenix lander has discovered a toxic chemical in soil near Mars' north pole, dimming hopes for finding life on the Red Planet, the probe's operators said Monday.
The chemical, perchlorate, is an oxidant widely used in solid rocket fuel. Researchers are still puzzling over the results and checking to make sure the perchlorate wasn't carried to Mars from Earth, the University of Arizona-based science team said.

However, the source of the perchlorate has not yet been evaluated fully, and may represent possible extra-Martian (Earth-sourced) contamination via the Phoenix lander itself. This is however unlikely since the Phoenix used ultrapure hydrazine for its retro rockets, and the perchlorate was found below the surface and at concentrations higher than would be expected from contamination during Earth launch operations.

www.cnn.com...

This is from Wikipedia:

NASA reports that: "Within the last month [July 2008], two samples have been analyzed by the Wet Chemistry Lab of the spacecraft's Microscopy, Electrochemistry, and Conductivity Analyzer, or MECA, suggesting one of the soil constituents may be perchlorate, a highly oxidizing substance." It is still unknown whether the perchlorate originates from the space ship or if it occurs naturally on Mars.

en.wikipedia.org...


Neither of these sites mention what type of perchlorate was found.
Can this mean that "someone" has been there before?
Are we just polluting another world without realizing it?
Does the fact that it was found below the surface mean that this occurred naturally?

Wikipedia lists 9 types or perchlorate, but is unclear which ones occur naturally. Do all of them? Most of them?

Ammonium perchlorate, NH4ClO4
Caesium perchlorate, CsClO4
Lithium perchlorate, LiClO4
Magnesium perchlorate, Mg(ClO4)2
Perchloric acid, HClO4
Potassium perchlorate, KClO4
Rubidium perchlorate, RbClO4
Silver perchlorate, AgClO4
Sodium perchlorate, NaClO4

I found this page which appears to have a lot of information on the subject, but I guess I need to go back to science class to understand a lot of it!

lib.bioinfo.pl...:15819211

I guess the reason why I am confused is that the CNN report states the following:
The new findings from Phoenix cast into further doubt the possibility that life exists on Mars' surface. But they do not rule out the possibility that life once existed, nor do they necessarily rule out the possibility of life existing now, perhaps in a deep underground aquifer.
If perchlorate is prevalent on Earth, found in seawater, and even turning up in urine and breast milk, why does this cast doubt on the possibilities of life?
Maybe it's not a good thing, but certainly life exists here in spite of it. Why should life have to be "in a deep underground aquifer"?

Well, maybe they were just trying to romanticize the theory. Here on Earth, sightings of teh unknown are always going on, but on mars, where the place is desolate (so were told) maybe the only place there would like be creatures would be the aquifer. I want to beleive, but with everything going on (including the info that nasa briefed the President on (ROCKET FUEL!?!? WERE GOIN TA MARS!)) will we ever really know?