Can someone with some understanding of this field explain, how do we know that this is a piece of Mars? Thank you!
I very much doubt it, myself. IMHO, the evidence for it is (at best) threadbare, hence my comment up in message 2.
Because it’s red?
No. That doesn’t work. It sounds to me like they’re just making a bunch of stuff up.
Meteorites are what remains of meteors which make it all the way through the atmosphere (everyone knows that I’m sure, but just so we’re all on the same page). Analyzing their composition is the way they are classified, and those with similar compositions are generally thought to be from the same source.
In the case of the Martian rocks, while there has never been a sample return mission (and I’d be against such a thing without certain precautions), the US has put probes on the surface which have analyzed the composition of Mars’ rocks.
http://en.wikipedia.org/wiki/Martian_meteorite
[snip] By the early 1980s, it was obvious that the SNC group of meteorites (Shergottites, Nakhlites, Chassignites) were significantly different from most other meteorite types. Among these differences were younger formation ages, a different oxygen isotopic composition, the presence of aqueous weathering products, and some similarity in chemical composition to analyses of the Martian surface rocks in 1976 by the Viking landers. [/snip]
meteorites from Mars:
http://www.newscientist.com/article/dn8004#.UpKoUMTrxfg
http://www.lpi.usra.edu/lpi/meteorites/mars_meteorite.html
http://www.imca.cc/mars/martian-meteorites.htm
annnnd, meteorites from Mercury:
http://www.npr.org/2013/04/11/176714430/origin-of-meteorite-is-a-puzzle-to-scientists
http://www.space.com/20426-mercury-meteorite-discovery-messenger.html
http://www.space.com/20547-mercury-meteorite-mystery-age.html
http://www.ctpost.com/local/article/Rock-said-to-be-from-Mercury-at-Peabody-5008188.php