it is also possible that the Martians have improved their planetary defense systems,
and are shooting our landers out of the sky before they reach the surface.
GORT KLAATU NARADA!
OT: Pillinger's facial fur reminds me of Asimov and Darwin... coincidence?
back on topic...
After the failure of Mars Polar Lander during descent,
NASA decided that future landers should signal on the way down
instead of after landing,
so Spirit and Opportunity will be sending tones during entry and landing,
hopefully allowing better confirmation of the success of each arrival phase.