Rare Water-Rich Mars Meteorite Discovered

The article is very short on explanations. For instance:

1/ When they say 'Martian meteorite' do they mean that it actually came from the surface of mars or rather than it's general origin was near to the orbit of mars?
2/ What guarantees are there that this rock is actually from mars?
3/ If so, how can you explain the parent meteor escaping the gravity well of mars? If this piece of rock is about a kilogram, then its entry mass must have been be quite large. The meteorite in California that was tracked with radar (the Sutton Mill's meteorite in 2008) and later collected had an estimated mass of 40,000 kg but only about 1 kg was recoverable from pieces much smaller than the one in the story.
4/ Following this, it would seem an improbable event that a/ there would be some impact on mars that would send ejecta as large as 40000 kg out of mars orbit and that b/ this orbit would be towards the earth. Any impact that could send ejecta into escape velocity would almost have to be tangential to the surface, and even then it is difficult to see how such an impact could even produce large ejecta as the impact would skim more across the surface rather than into the interior of the planet.
5/ usually dating of the material and its mineral composition leads to a supposition that it is of planetary origin. And yet this rock has a different material composition than martian rocks, as per the article. Thus it seems that the entire hypothesis that it came from mars should actually be questioned instead of inferring that mars had more water than because of the composition of this meteorite.

Just how can they actually prove that the rock came from mars? It seems Occam's razor needs some sharpening.

I remember not long ago that they were saying that the Corvid meteoroids were ejecta from the Giordano Bruno impact. This was proven false: http://adsabs.harvard.edu/abs/1993JGR....98.9145H [harvard.edu]

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/oTUELNKKjAc/story01.htm

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