Volcanism often goes hand in hand with tectonic shifts in the rock crust on all terrestrial planets and the Moon. Magma bubbles rise up from the planet's interior, making room as they ascend and pour their molten rock over the planet's surface in the form of lava. The emptied magma chambers create cavities, which can cause the rigid masses of rock of the crust to sag and shift. Depending on their nature, these tectonic movements on the planet's surface can be defined as thrust faults, in the case of contractions, and as extensional faults, in the case of stretching. The latter is the most common form of tectonics on Mars. The Cerberus Fossae are two parallel extensional faults that run almost 1000 kilometres across a young volcanic plain in the Elysium Planitia region. The High Resolution Stereo Camera (HRSC) system, developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and operated on board the ESA Mars Express spacecraft, photographed these striking rifts in January 2018.
Systematic processing of the camera data was carried out at the DLR Institute of Planetary Research in Berlin-Adlershof. The Cerberus Fossae – Latin for 'Rifts of Cerberus', the multi-headed 'hellhound', who guards the gates of the underworld in Greek mythology – are particularly striking tectonic fissures. The two trenches run almost exactly parallel to one another and stretch from northwest to southeast. They are extremely steep-sided throughout and in some places cut almost vertically down through the layers of lava. This is an indication that the trenches are still very young, as over time erosion causes rock to break off from steep slopes and edges, so that the gradient of the slopes become increasingly shallow.
One of the youngest geological structures on Mars
The few impact craters on the volcanic plain also indicate that the landscape here cannot be very old. The age of the lava flows can be determined quite by counting all of the craters and measuring their various diameters, and comparing this with other areas of Mars. This method of determining the age of geological surfaces can be applied to all bodies in the Solar System that have a solid surface. Scientists therefore assume that parts of this plain were flooded with low viscosity lava in the recent geological past, possibly even less than 100 million years ago. Lava also rose to the surface out of the Cerberus Fossae (and later presumably so did groundwater).
This makes the near-Equator region of the Cerberus Fossae one of the youngest geological structures on Mars. Although neither Mars Express nor the numerous space probes that have observed the planet from orbit have discovered any signs of volcanic activity, scientists believe that tectonic movements are occurring within the Martian crust. The Seismic Experiment for Interior Structure (SEIS) developed by the French Space Agency (CNES) was launched aboard the NASA InSight space probe on 6 May 2018 for the purpose of recording Marsquakes. InSight will land a few hundred kilometres to the west – still on the Elysium Plain – on 26 November 2018, and will start recording Marsquakes around the turn of the year. The aim is to investigate the state and structure of the Martian interior. Also on board InSight is the HP3 (Heat Flow and Physical Properties Package), an experiment developed by DLR, designed to measure the flow of heat from the core and mantle to the surface of Mars, in order to draw conclusions about the state and development of Mars’ metallic core.
Cerberus and Athabasca Valles: parts of the vast Elysium volcanic region
The Cerberus Fossae are tectonic features originating most likely from dilational faulting or from subsidence due to dike emplacement. Rounded collapse pits observed in the northern Cerberus Fossae indicate an early stage of graben subsidence, and are particularly evident in the northern part of the Cerberus Fossae. Besides, numerous volcanic dikes formed in the Martian past in the north-western volcanic region of Elysium, which is home to the 12.5 kilometre-high volcano Elysium Mons. Dike emplacement induces deformation and can lead to the formation of fissures and graben at the surface above the dike.
The outflow channel system Athabasca Valles (see image 6), which rises in the Cerberus Fossae can bee seen to the west of the image shown here. Presumably, the Cerberus Fossae fissures have ruptured the Martian crust millions of years ago to a certain depth, to be able to discharge lava from a volcanic source as well as groundwater. The dark material within the Cerberus Fossae and on the floor of the unnamed impact crater were carried here by winds and formed dunes made of dark sand. Dark dunes are very common on the surface of Mars and consist of old volcanic ash.