All posts for the month November, 2019

The birth of El Niño. This animation shows anomalies, or departures from normal, in Sea Surface Temperature (SST) over the past year. As spring became summer in 1997, a Kelvin Wave of warm water crossed the Pacific and accumulated off the coast of South America, shown here in red. From
Map of atmospheric temperature and changes in temperature from Komacek & Showman (2019).
Brightness map and changes in brightness from Komacek & Showman (2019).
Variations in the brightness of the hot Jupiter Kepler-76b. From Jackson et al. (2019).
Martian dunes west of the giant Hellas impact basin and observed by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter. From

Mars is a dry, dusty place, with globe-girdling sand seas, mile-wide dust devils, and frequent world-wide dust storms.

In spite of the ubiquity of dust on Mars, though, the physics of dust-lifting and transport remain mysterious. For instance, the seasonal appearance of dark streaks on slopes across the surface of Mars, called recurring slope lineae, were thought to result from flow of brine. Recently, though, we’ve found they are more likely granular flow, but what exactly drives their seasonality is unknown.

Warm-season features originally thought to be evidence of salty liquid water active on Mars today. More recent studies show they are very probably granular flow. From

Experiments conducted by the aeolian physics group at University of Duisburg-Essen has brought a little clarity to the mystery of martian dust.

One of the biggest challenges for experiments exploring martian dust transport is replicating Mars’ low gravity (40% of Earth’s) and air pressure (10% of Earth’s). Since gravity and pressure help determine how winds move dust, accurate experiments must somehow create winds in a low-gravity environment under near vacuum.

To make a little pocket of Mars on Earth, Maximilian Kruss and colleagues took a small vacuum chamber centrifuge onto a “vomit comet” and conducted parabolic flights to create short periods of microgravity.

Kruss and colleagues’ low-pressure, microgravity chamber. From Kruss et al. (2019).

They filled the chamber with martian-like dust grains and turned up the fan to figure out when the winds were strong enough to start blowing the dust. By imaging the grain bed and tracking the grains, they estimated this threshold wind velocity, which is key to understanding when and where Mars can blow dust around.

Video of grains blowing across a chamber bed. From

Kruss and colleagues found, reassuringly, that theoretical models about dust transport were accurate. These results help us understand aeolian processes on a wide range of bodies, not only on Mars but any body with a low-pressure atmosphere.

Dunes (left) and wind streaks (right) on the surface of the comet 67P as seen by the Rosetta Mission. From

Indeed, even comets play host to aeolian processes. When the Rosetta Mission flew past comet 67P, it saw features on the comet’s surface that looked for all the world like wind streaks and dune fields.

Kruss and colleagues suggest dust transport may be important on some exoplanets, where gravities and atmospheric pressures span an even wider range than in our solar system. And so, these results, taken from a tiny vacuum chamber, may bear on processes on worlds across the whole galaxy.