Steven F. Sholes

NASA's Jet Propulsion Laboratory · Planetary Geosciences

The existence of possible early oceans in the northern hemisphere of Mars has been researched and debated for decades. The nature of the early martian climate is still somewhat mysterious, but evidence for one or more early oceans implies long-lasting periods of habitability. The primary evidence supporting early oceans is a set of proposed remnant...

The existence of possible early oceans in the northern hemisphere of Mars has been researched and debated for decades. The nature of the early martian climate is still somewhat mysterious, but evidence for one or more early oceans implies long-lasting periods of habitability. The primary evidence supporting early oceans is a set of proposed remnant...

The Perseverance rover landed on the floor of Jezero crater on 18 February 2021. The landing site, named “Octavia E. Butler” is located ~2.2 km from the SE-facing erosional scarp of the western fan deposits, which are of strong interest for the mission [1-2]. Images obtained using the Mastcam-Z camera and the Remote Micro-Imager (RMI) of the SuperC...

Orbital and rover observations of relict geomorphic features and stratigraphic architectures indicate Mars once had a warmer, wetter climate. Constraining the character, relative timing and persistence of ancient aqueous activity on Mars is possible through detailed interrogation of the stratal geometry of aqueously deposited sedimentary bodies. Su...

Proposed ocean paleoshorelines on Mars have faced criticism over their genetic interpretation and because they deviate significantly from an expected equipotential surface (by many kilometers). Multiple geophysical deformation models have been proposed to explain this large topographic range and deviation including true polar wander and direct Thar...

Perseverance images of a delta on Mars The Perseverance rover landed in Jezero crater, Mars, in February 2021. Earlier orbital images showed that the crater contains an ancient river delta that was deposited by water flowing into a lake billions of years ago. Mangold et al . analyzed rover images taken shortly after landing that show distant cliff...

Mars’ controversial hypothesized ocean shorelines have been found to deviate significantly from an expected equipotential surface. While multiple deformation models have been proposed to explain the wide range of elevations, here we show that the historical locations used in the literature and in these models vary widely. We find that the most comm...

Mars today has no active volcanism and its atmosphere is oxidizing, dominated by the photochemistry of CO2 and H2O. Using a one-dimensional photochemical model, we consider whether plausible volcanic gas fluxes could have switched the redox-state of the past martian atmosphere to reducing conditions. In our model, the total quantity and proportions...

Whether extant life exists in the martian subsurface is an open question. High concentrations of photochemically produced CO and H2 in the otherwise oxidizing martian atmosphere represent untapped sources of biologically useful free energy. These out-of-equilibrium species diffuse into the regolith, so subsurface microbes could use them as a source...

Primary support for ancient Martian oceans has relied on qualitative interpretations of hypothesized shorelines on relatively low‐resolution images and data. We present a toolkit for quantitatively identifying paleoshorelines using topographic, morphological, and spectroscopic evaluations. In particular, we apply the validated topographic expressio...

Whether extant life exists in the martian subsurface is an open question. High concentrations of photochemically produced CO and H2 in the otherwise oxidizing martian atmosphere represent untapped sources of biologically useful free energy. These out-of-equilibrium species diffuse into the regolith, so subsurface microbes could use them as a source...

Mars today has no active volcanism and its atmosphere is oxidizing, dominated by the photochemistry of CO2 and H2O. Mars experienced widespread volcanism in the past and volcanic emissions should have included reducing gases, such as H2 and CO, as well as sulfur-bearing gases. Using a one-dimensional photochemical model, we consider whether plausib...

Geological activity is thought to be important for the origin of life and for maintaining planetary habitability. We show that transient sulfate aerosols could be a signature of exoplanet volcanism, and therefore a geologically active world. A detection of transient aerosols, if linked to volcanism, could thus aid in habitability evaluations of the...

The residual south polar cap (RSPC) of Mars has been subject to competing processes during recent Mars years of high resolution image coverage: continuing erosion of scarps while the maximum extent grows as well as shrinks (Piqueux, S., Christensen, P.R. [2008]. J. Geophys. Res. (Planets) 113, 2006; James, P.B., Thomas, P.C., Malin, M.C. [2010]. Ic...

Method validity of object-based image analysis with respect to the study of surface geomorphology of the martian south polar cap.