There Are No Cows on Mars
Or, at least, less than 100. We know that, says Mike Brown, because the level of methane on Mars is less than 1 part per billion - about the amount that would be produced by 100 cows, burping. It's not exactly a shock that Mars is not prime cattle country, but the aforementioned result is also a major blow to one of Mike's favorite theories: that some kind of life on Mars was all but certain since life from Earth was very likely transported to Mars in the Early days by meteorites blown off the Earth in major collision, to land there when the planet was more hospitable. Even today, it seems likely that Mars has locales where methanogens would survive and reproduce.
Of course the reverse voyage scenario is also possible. In which case it would be a bit tragic that the planet that (perhaps) gave us birth, no longer supports life.