Lujendra Ojha

Volcanic Exhalation of Sulfur on Mars


We know from in situ bulk chemical and mineralogical analyses, remote sensing data, and geochemical models that the Martian crust is sulfur(S)-rich, exceeding the S content of terrestrial basalts by almost an order of magnitude. Ultimately, S is delivered to the crust by volcanic exhalation of SO2 and H2S gases. On Earth, volcanic ash, spewed along with other gases, can adsorb up to 30 % of the exhaled S gas species with subsequent deposition. The above maps show the concentration of S and Cl on Mars (from Gamma Ray Spectrometer (GRS) on Mars Odyssey). A large sedimentary deposit of likely pyroclastic origin on Mars called the Medusae Fossae Formation (MFF) has the highest concentration of S and Cl. In our recent work, we estimated how much sulfur would have been released to the Martian atmosphere by explosive volcanism. Based on reasonable terrestrial analog estimates that the MFF adsorbed, at maximum, 30% of the exhaled S gas species, we find that a significant amount of S (>10^17 kg) would have been delivered to the atmosphere over the time it took for the MFF to be deposited on Mars. S-gases are greenhouse gases, thus, if the MFF was deposited on a short time scale, then climatic conditions enabling the existence of liquid water may have been maintained by this amount of exhaled S gases. (Link to the paper).

Hidden Reservoirs of Water-Ice On Mars


Recently, along with a few coauthors, I used the Martian gravity and topography data to find the density of the north polar cap of Mars (pictured above). The north polar cap of Mars consists of thick sheets of extremely pure ice called the north polar layered deposits (white unit in the image above) and the sand-rich basal unit. Radar data has been able to provide information on the composition of the north polar layered deposits, however, the composition of the basal unit is not entirely clear. In this study, I used gravity data of Mars to estimate the density of the basal unit. We found relatively low density for the BU which suggests that it may contain more than 50 % ice. Thus, our study suggests that the basal unit may one of the largest sources of water ice on Mars. Paper coming out soon.


Explosive Volcanism on Mars?


The image above shows a tiny section of the Medusae Fossae Formation (MFF), which is one of the largest sedimentary deposits on Mars. The origin of the MFF is a fascinating mystery. The area covered by the MFF is equivalent to 20% of the size of the continental USA. If one were to distribute the MFF globally on Mars it will make a ~9 meter thick layer. A variety of formation mechanisms have been proposed to explain the depositional history of the MFF including glacial activity emplacing paleo-polar deposits which incorporated eolian sediments, direct atmospheric deposition of suspended eolian sediment, coarse-grained ignimbrite deposits from pyroclastic density currents, fine-grained distal ashfall from volcanic eruptions, and water-ice.

Recently, I and Kevin Lewis used the Martian gravity data to constrain the density of the MFF (Link). We find that the MFF is a relatively porous unit with a bulk density of 1,765 ± 105 kg m^−3. Along with Suniti Karunatillake, Mariek Schmidt, and Kevin Lewis, I was able to also constrain the chemistry of the MFF using the Gamma Ray Spectrometer (GRS) data. Turns out, the MFF has the highest concentration of sulfur and chlorine on Mars. We published that work in Nature-Communication recently (Link) . The relatively low density of the MFF along with the enrichment of major volcanic gases such as S and Cl suggest that the origin of the MFF may be tied to explosive volcanism on Mars.

Lots of work to follow on this topic in the future.