Curiosity Mastcam Left image taken on Sol 2283, January 7, 2019.
Credit: NASA/JPL-Caltech/MSSS

 

NASA’s Curiosity Mars rover is wrapping up Sol 2293 duties.

The robot’s last day at Rock Hall saw scientists gathering last data at this location.

Curiosity Front Hazcam Left A photo taken on Sol 2293, January 18, 2019.
Credit: NASA/JPL-Caltech

Reports Brittney Cooper, an atmospheric scientist at York University, Toronto, Ontario, Canada and Claire Newman, also an atmospheric scientist at Aeolis Research in Pasadena, California: Scientists had a 2.5 hour science block filled with Mastcam change detection imaging of the Rock Hall drill fines and alternating Chemistry and Camera (ChemCam) Remote Micro-Imager (RMI) and Laser-Induced Breakdown Spectrometer (LIBS) observations of the Rock Hall dump pile, drill tailings, and target “St.Cyrus 2.”

Curiosity Navcam Left A image acquired on Sol 2293, January 18, 2019.
Credit: NASA/JPL-Caltech

Regional dust storm

“Gale Crater has become a lot dustier in recent sols due to a regional dust storm in the southern hemisphere that was spotted by the Mars Climate Sounder team, so we added several extra environmental observations to see how this is affecting the atmosphere,” Cooper and Newman explain. These included extra measurements of the amount of dust above us (with the observation known as the “Mastcam tau”) and of visibility across the crater (with the “Navcam Line of Sight” and “Mastcam Crater Rim Extinction” observations), they add.

Also added were more Rover Environmental Monitoring Station (REMS) one-hour measurements to better capture the diurnal cycles of pressure and temperature.

Curiosity Navcam Right A image taken on Sol 2293, January 18, 2019.
Credit: NASA/JPL-Caltech

 

Daily pressure cycle

“When the regional or global dust loading increases, it changes how the atmosphere expands and contracts in response to solar insolation, which affects how air moves around and alters the large-scale patterns of surface pressure (since pressure is caused by the mass of air in a column over the surface). We monitor this by seeing how the shape of the daily pressure cycle changes from sol to sol,” Newman and Cooper explain.

More atmospheric dust also means more of the incoming solar radiation is absorbed before it reaches the rover, the atmospheric specialists point out, so daytime near-surface and ground temperatures decrease compared to normal. At night, however, the warmer overlying atmosphere emits more thermal radiation, keeping the temperature of the surface and near-surface warmer than usual. More dust heating also means that near-surface and surface temperatures are more strongly coupled, resulting in a reduced surface-to-air temperature contrast, all of which REMS measurements are starting to show.

Curiosity Rear Hazcam Right A photo acquired on Sol 2293, January 18, 2019.
Credit: NASA/JPL-Caltech

Dust devil searches

“Another effect of increased dustiness is therefore that we expect to observe fewer convective vortices and dust devils (dusty vortices), because a smaller surface-to-air temperature difference means less heat is pumped into the atmosphere to drive convection,” Cooper and Newman say. “So tosol we also included three types of Navcam dust devil searches, to see if the dust activity produces a decrease in the number or size of dust devils. We’d normally expect to see a lot of dust devils in the current season (local summer).”

Curiosity Navcam Left A image acquired on Sol 2293, January 18, 2019.
Credit: NASA/JPL-Caltech

In fact, the atmospheric researchers note, one dust devil passed right over Curiosity just as a movie was being taken a few sols before the dust began to increase!

Vortex pressure drop

In investigating frames of the movie, there was a slight reduction in visibility as this happened; at the same time, the dust devil’s low-pressure core produced the largest vortex pressure drop ever measured on Mars (over 7 pascal) which is about 1% of the total surface pressure). A pascal (Pa) is a metric measurement unit of pressure.

“Although we can’t ‘see’ the dust devil in the images, we can tell the rover was inside one because of the decrease in visibility combined with the dramatic decrease in pressure,” Newman and Cooper conclude.

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