  Volcanic activity on Mars peaked during the Noachian and Hesperian periods
but has continued since then in isolated locales. Elysium Planitia hosts
numerous young, fissure-fed flood lavas with ages ranging from approximately
500 to 2.5 million years (Ma). We present evidence for what may be the youngest
volcanic deposit yet documented on Mars: a low albedo, high thermal inertia,
high-calcium pyroxene-rich deposit distributed symmetrically around a segment
of the Cerberus Fossae fissure system in Elysium Planitia. This deposit is
similar to features interpreted as pyroclastic deposits on the Moon and
Mercury. However, unlike previously documented lava flows in Elysium Planitia,
this feature is morphologically consistent with a fissure-fed pyroclastic
deposit, mantling the surrounding lava flows with a thickness on the order of
tens of cm over most of the deposit and a volume of 1.1-2.8E7 cubic meters.
Thickness and volume estimates are consistent with tephra fall deposits on
Earth. Stratigraphic relationships indicate a relative age younger than the
surrounding volcanic plains and the Zunil impact crater (~0.1-1 Ma), with
crater counting suggesting an absolute model age of 53 to 210 ka. This young
age implies that if this deposit is of volcanic origin then the Cerberus Fossae
region may not be extinct and Mars may still be volcanically active today. This
interpretation is consistent with the identification of seismicity in this
region by the Interior Exploration using Seismic Investigations, Geodesy, and
Heat Transport (InSight) lander, and has additional implications for
astrobiology and the source of transient atmospheric methane.
