The Mars Atmosphere
The Mars Atmosphere
The space vehicle Insight of NASA sent us an interesting picture from Mars. If only we knew what they wanna tell us! Maybe it’s a welcome ceremony!
Recurring slope lineae (RSL) are seasonal features on Mars that leave behind gullies similar to those left by running water on Earth. Their discovery a few years ago has prompted many experiments at Martian conditions to determine how these features form. At Martian surface pressures and temperatures, it’s not unusual for water to boil. And that boiling, as some experiments have shown, introduces opportunities for new transport mechanisms.
Researchers found that water in “warm” (T = 288 K) sand boils vigorously, ejecting sand particles and creating larger pellets of saturated sand. Water continues boiling out of the pellets once they form, creating a layer of vapor that helps levitate them as they flow downslope. The effect is similar to the Leidenfrost effect with drops of water sliding on a hot skillet; there’s little friction between the pellet and the surface, allowing it to travel farther.
The mechanism is quite efficient in experiments under Earth gravity and would be even more so under Mars’ lower gravity. It also requires less water than alternative explanations. The pellets that form are too small to be seen by the satellites we have imaging Mars, but the tracks they leave behind are similar to the RSL seen above. (Image credit: NASA; research credit: J. Raack et al., 1, 2; via R. Anderson; submitted by jpshoer)
The size of Mars compared to Earth and Moon
The Martian atmosphere is scant compared to Earth’s, but its winds still sculpt and change the surface regularly. The average atmospheric pressure on Mars is only 0.6% of Earth’s, and the density is similarly low at 1.7% of Earth’s. Despite this thinness, Martian winds are still substantial enough to shift sands on a daily basis, as shown above. These two images were taken one Martian day apart, showing how sand ripples moved and how the Curiosity rover’s tracks can be quickly obscured. Part of the reason Mars’ scant atmosphere is still so good at moving sand is that Martian gravity is roughly one-third of ours; if the sand is lighter, it doesn’t take as much force to move! (Image credit: NASA/JPL-CALTECH/MSSS)
It may look like grainy, black and white static from a 20th-century television, but this animation shows what may be the first view of gravity waves seen from the ground on another planet. The animation was stitched together from photos taken by the Mars Curiosity rover’s navigation camera, and it shows a line of clouds approaching the rover’s position.
Gravity waves are common on Earth, appearing where disturbances in a fluid propagate like ripples on a pond. In the atmosphere, this can take the form of stripe-like wave clouds downstream of mountains; internal waves under the ocean are another variety of gravity wave. If these are, in fact, Martian gravity waves, they are likely the result of wind moving up and over topography, much like their Terran counterparts. (Image credit: NASA/JPL-Caltech/York University; research credit: J. Kloos and J. Moores, pdf; via Science; h/t Cocktail Party Physics)