Water cycle at the Gale crater - More than three Martian years of in situ humidity observations by MSL/REMS

The Mars  Science  laboratory  (MSL)  has been providing in situ Martian observations with excellent quality since  early  August  2012. MSL carries onboard the REMS-instrument, which has provided extremely valuable atmospheric observations of atmospheric pressure, temperature of the air, ground temperature, wind speed and direction, relative humidity (REMS-H), and UV measurements. The  REMS-H  relative  humidity  device  is  based  on  polymeric  capacitive  humidity  sensors  developed  by Vaisala Inc. and it makes use of three (3) humidity sensor heads. The humidity device is mounted on the REMS boom providing ventilation with the ambient atmosphere through a filter protecting the device from airborne dust.

The  annual  in  situ  water  cycle  based  on  more than three  full  Martian  years  at  the  Gale  crater  will  be  discussed.  We will  utilize  the  REMS-H  instrument’s  in  situ  observations  accompanied  by  orbital  observations  and  modeling efforts. We will infer the hourly atmospheric VMR from the REMS-H observations and compare these VMR measurements with predictions of VMR given by our 1D column Martian atmospheric/regolith model to investigate the local water cycle, exchange processes and the local climate in Gale Crater.

The  strong  diurnal  variation  suggests  there  are  surface-atmosphere  exchange  processes  at  Gale  Crater  during all seasons, which deplete moisture to the ground in the evening and nighttime and release the moisture back to the atmosphere during the daytime. Our modeling results presumably indicate that adsorption processes take place during the nighttime and desorption during the daytime. Other processes, e.g. convective turbulence play a significant role in the daytime in conveying the moisture into the atmosphere.

Atmospheric humidity shows clear increase during early mornings around the time when Curiosity  started  to  climb  up  Mt.  Sharp. Around that time there was also a major dust storm followed by a moderate storm. The  MSL  MastCam  pictures  from  this  time  show exposed bedrock scenery with sparse and thin layers of wind-blown dust. Our simulations indicate that a plausible explanation for the increase of the atmospheric humidity during early mornings could be the Mt Sharp bedrock material having a relatively high inertia and low porosity.  Overall, we will discuss the water cycle at gale crater during the period of more than three Martian years with specific focus on the effects of increased airborne dust and underlying changing terrain during the latter part of the current MSL mission.