Mars Had Big Rivers For Billions of Years, Study Suggests (space.com)

A new study suggests that Mars once had giant rivers larger than anything on Earth after the planet lost most of its atmosphere to space. "That great thinning, which was driven by air-stripping solar particles, was mostly complete by 3.7 billion years ago, leaving Mars with an atmosphere far wispier than Earth's," reports Space.com. "But Martian rivers likely didn't totally dry out until less than 1 billion years ago, the new study found." From the report: "We can start to see that Mars didn't just have one wet period early in its history and then dried out," study lead author Edwin Kite, an assistant professor of geophysical sciences at the University of Chicago, told Space.com. "It's more complicated than that; there were multiple wet periods." The team's work suggests that Martian rivers flowed intermittently but intensely over much of the planet's 4.5-billion-year history, driven by precipitation-fed runoff. The rivers' impressive width -- in many cases, more than twice that of comparable Earth catchments -- is a testament to that intensity.

It's unclear how much water Martian rivers carried, because their depth is hard to estimate. Determining depth generally requires up-close analysis of riverbed rocks and pebbles, Kite said, and such work has only been done in a few locations on Mars, such as Gale Crater, which NASA's Curiosity rover has been exploring since 2012. The ancient Mars rivers didn't flow in just a few favored spots; rather, they were distributed widely around the planet, Kite and his colleagues found.

Comments

Re:No rain?

[Dunbal]

It had a magnetosphere. Then the core cooled and stopped rotating, causing the loss of the magnetic field. The magnetic field of a planet is not some innate property of planetary material - it's caused by movement, rotation, eddies, and whirlpools of liquid iron. The massive volcanoes on Mars point to a past where Mars did have a liquid layer. However the planet has since cooled down, unlike Earth which being much bigger will take more time to cool.

Re:They need to dig more

[mjwx]

An assault rifle is a select fire automatic rifle with a detachable box magazine using a round shorter than most WWII and previous era bolt action rifles and longer than pistol rounds. It was named so by the Germans who first invented it, the Sturmgewehr 44 which means "assault rifle" in German as the rifle was designed for infantry assault and breakout. The name stuck because that's pretty much what the weapon is designed for.

You gun nuts really need to learn your history. Next thing you'll be asking is why is it called a revolver is called a "revolver".

Yours Sarcastically,
Capt. F Obvious.

Re:No rain?

[RockDoctor]

The atmospheric pressure of Mars obviously varies with altitude (distance from the planet centre). The "zero" for altitude, since there is no sea level to work from, is taken as the point where it has a pressure of 600 Pa (kg/m^2), which is near the middle of the range. That is 0.006 of the atmosphere of Earth. This pressure is below the triple point of water and water ice would directly sublime to the vapour without going through a liquid phase. In the deeper basins of Mars (equivalent to the Dead Sea, Caspian Sea, and Death Valley, but several kilometres deeper) you might be able to get liquid water to be stable, but you'd have to heat it to around 10degC (70 or 80 deg hotter than the general surface) and seal it into a plastic bag to actually get the water to condense again, as the ppH2O (Partial Pressure of water) would be in the bag along with a significant amount of CO2, which would dilute the water vapour, making it harder for "rain" to form.

it'd rain "earlier" than it would in equivalent conditions on Earth.

It'd rain later. Sorry, but Kim Stanley Robinson knew he was playing fast and loose with the gas laws in his fiction, even if some people (Elon Musk, I'm looking at you!) have taken the fiction as fact.