It’s always good when a scientist is scratching their head, and Chelsea Whyte describes a fascinating one in NewScientist (18 February 2017, paywall):
Credit: NASA/JPL-Caltech
SOMETHING doesn’t add up. Mars has ice caps, and there is evidence in the terrain that water flowed in rivers and lakes there billions of years ago. We have a decent understanding of how water behaves on Earth, and there’s no reason to think the laws of physics are different on Mars. And yet, we can’t figure out how water could have existed in liquid form on young Mars.
Every time we try to replicate the conditions under which the liquid water could have existed, a new complication throws a wrench into our models. Last week, yet another paper tried to chip away at the mystery (PNAS, doi.org/bzjh). And like so many before it, instead of resolving the problem, it introduced another.
This 40-year-old mystery is known as the Mars paradox. If and when we resolve it, we might need to throw away a lot of textbooks.
Some folks might point at Venus and its thick atmosphere and ask what’s going on, on the assumption that Mars and Venus are similar, but they’re not. From Windows to the Universe I find that, as a handy way to express their masses, Venus is roughly .82 of Earth’s mass, while Mars is .11 of Earth’s mass, so that’s not a comparable, and that explains why Mars’ atmospheric pressure is light relative to Earth’s – and will remain so without a large addition of mass. Perhaps this also explains why the suggestion to replace the atmosphere with hot house gasses such as CO2 leads nowhere.
This disparity in mass opens the question of the possibility of a catastrophic removal of mass at some point after water had time to leave its mark on the surface of Mars. Beyond me. But it smells like von Däniken – blech.
So what did old fictional Holmes used to say? Chelsea walks down that path:
So is there some planetary mechanism we still don’t understand? A mixture of greenhouse gases we haven’t yet hit on? Perhaps the real trouble is our understanding of water itself. We already know it can bedevil a few laws of physics, like when colder water flows to the top of a glass. Whatever the answer, we’re running out of obvious solutions. We’re going to be in truly alien territory when the mystery is solved.
Sounds subtle and, if found, both fascinating and possibly useful.
