03/07/2024
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A fascinating feature takes center stage in this new image from ESA’s Mars Express: a dark, uneven scar that rests on the marble ground at the foot of a giant volcano.
A wider view of Aganippe Fossa
This scar, known as the Aganippe Fossa, is a roughly 600km-long jagged feature known as a “graben”: a ditch-like furrow with steep walls on either side.
Aganippe Fossa cuts the underside of one of Mars’ largest volcanoes, Arsia Mons. Mars Express regularly observes Arsia Mons and its nearby companions in the Tharsis region, home to some of Mars’ giant volcanoes. This includes Olympus Mons, the tallest volcano in the Solar System (visible on the context map associated with this new image, such as Arsia Mons).
Arsia Mons itself has a diameter of 435 km and rises more than 9 km above the surrounding plains. For context, the tallest dormant volcano on Earth, Ojos del Salado on the Argentina-Chile border, reaches 7 km.
Penetrating lava
We’re still unsure how and when the Aganippe Fossa formed, but it appears to have formed as magma rising beneath the colossal mass of Tharsis volcanoes caused the Martian crust to stretch and crack.
A snake scar on Mars. Click on the image to enlarge and explore in more detail.
In this view, Mars Express’s High Resolution Stereo Camera (HRSC) captures two different types of terrain: so-called hummocky terrain, which includes many irregularly shaped mounds and valleys all clustered together, and terrain with lobate, which is formed by gently sloping rocks and rock debris.
Topography of Aganippe Fossa
These terrains are characteristic of the ring-shaped ‘halo’ of Arsia Mons, a 100,000 square kilometer disc around the base of the volcano, possibly associated with ancient glaciations. Intriguingly, this halo only built on the northwest flank of the volcano, likely due to the prevailing winds from the opposite direction controlling where the ice settled over time.
Windblown dust and sand have also shaped this part of Mars, creating interesting zebra-like patterns on the right of the frame, while darker material is deposited on lighter soil (or vice versa!). The surface here also shows evidence of lava flows, dating from when the volcano was active.
Exploring Mars
Mars Express has been orbiting the Red Planet since 2003. It is imaging the surface of Mars, mapping its minerals, identifying the composition and circulation of its tenuous atmosphere, probing beneath its crust and exploring how different phenomena interact in the Martian environment.
The HRSC spacecraft responsible for these images has discovered much about the varied surface of Mars in the past 20 years. His images show everything from wind-sculpted ridges and pits to pits in the flanks of colossal volcanoes to impact craters, tectonic faults, river channels and ancient lava basins. The mission has been extremely productive during its lifetime, creating a far more complete and accurate understanding of our planetary neighbor than ever before.
Agannippe Fossa in 3D
The Mars Express High Resolution Stereo Camera (HRSC) was developed and operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).