Water cycle at the Gale crater - More than three Martian years of in situ humidity observations by MSL/REMS
Authors: Harri Ari-Matti , Genzer Maria , Gomez-Elvira Javier , Savijärvi Hannu , McConnochie Timothy , Hieta Maria , de la Torre Manuel , Polkko Jouni , Martinez German , Paton Mark , Vazquez Luis 
Published: March 2020

&lt;p&gt;The Mars &amp;#160;Science &amp;#160;laboratory &amp;#160;(MSL) &amp;#160;has been providing in situ Martian observations with excellent quality since &amp;#160;early &amp;#160;August &amp;#160;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 &amp;#160;REMS-H &amp;#160;relative &amp;#160;humidity &amp;#160;device &amp;#160;is &amp;#160;based &amp;#160;on &amp;#160;polymeric &amp;#160;capacitive &amp;#160;humidity &amp;#160;sensors &amp;#160;developed &amp;#160;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.&lt;/p&gt;&lt;p&gt;The &amp;#160;annual &amp;#160;in &amp;#160;situ &amp;#160;water &amp;#160;cycle &amp;#160;based &amp;#160;on &amp;#160;more than three &amp;#160;full &amp;#160;Martian &amp;#160;years &amp;#160;at &amp;#160;the &amp;#160;Gale &amp;#160;crater &amp;#160;will &amp;#160;be &amp;#160;discussed. &amp;#160;We will &amp;#160;utilize &amp;#160;the &amp;#160;REMS-H &amp;#160;instrument&amp;#8217;s &amp;#160;in &amp;#160;situ &amp;#160;observations &amp;#160;accompanied &amp;#160;by &amp;#160;orbital &amp;#160;observations &amp;#160;and &amp;#160;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.&lt;/p&gt;&lt;p&gt;The &amp;#160;strong &amp;#160;diurnal &amp;#160;variation &amp;#160;suggests &amp;#160;there &amp;#160;are &amp;#160;surface-atmosphere &amp;#160;exchange &amp;#160;processes &amp;#160;at &amp;#160;Gale &amp;#160;Crater &amp;#160;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.&lt;/p&gt;&lt;p&gt;Atmospheric humidity shows clear increase during early mornings around the time when Curiosity &amp;#160;started &amp;#160;to &amp;#160;climb &amp;#160;up &amp;#160;Mt. &amp;#160;Sharp. Around that time there was also a major dust storm followed by a moderate storm. The &amp;#160;MSL &amp;#160;MastCam &amp;#160;pictures &amp;#160;from &amp;#160;this &amp;#160;time &amp;#160;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.&amp;#160; 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.&lt;/p&gt;