From Ethan Siegel at Forbes:
Based on everything we know, it seems like the conditions that make life possible are a lot more diverse and flexible than most people would expect.
Take Earth’s large moon, for example. The gravitational forces from it keep our planet rotating on the same axis over time. Our present axial tilt is 23.5 degrees, but this will vary over very long timescales between 22.1° and 24.5°. A world like Mars, on the other hand, has almost the same axial tilt as Earth: around 25°. But over tens of millions of years, this will vary by ten times as much as it does on Earth: from a minimum of 13° to a maximum of 40°.
This results in huge variations in the climate at various latitudes on Mars, far bigger than any ice age will deliver on Earth. But so long as life can either survive long-term temperature changes or migrate to more temperate climate zones, this shouldn’t be a dealbreaker. Interestingly, the tidal forces from our Moon have also slowed the length of our day: from ~8 hours to 24 hours over the past four billion years. This doesn’t seem to have affected life at all. More.
It’s convenient for Siegel that no one has found life anywhere but on Earth. He is free to assume whatever he likes about the extraterrestrial conditions that imagined life forms could survive, and still call it science. If we find do life elsewhere, later generations of physicist writers will not be so lucky.
See also:At Forbes: About extraterrestrial life, “fancy probabilistic analysis” just isn’t science All true. But that said, we have found complex organic molecules on Saturn’s moon Enceladus, which should provide a basis for genuine research. From a minimalist perspective, what if we encounter a number of instances where the setting seems to be right but life or intelligent life is markedly absent? In certain situations, persistently not finding something can be a source of information. (Ethan Siegel)
What becomes of science when the evidence does not matter?