The southern highlands of Mars are dissected by hundreds of ancient valley networks (3.9-3.5 billion years old), which are evidence that water once sculpted the Martian surface. According to new research, these valley networks were carved by water melting beneath glacial ice, not by free-flowing rivers as previously thought.
Fig: A view of Mars showing the planet’s northern polar ice cap. Image credit: ISRO / ISSDC / Emily Lakdawalla.
The similarity between many Martian valleys and the subglacial channels on Devon Island in the Canadian Arctic motivated Dr. Grau Galofre and colleagues to conduct this new study.
Fig: A glacial valley network on Mars. Image credit: Grau Galofre et al.
In the study, the scientists analyzed 10,276 Martian valley segments, using a novel algorithm to infer their underlying erosion processes.
They used data from the Mars Orbiter Laser Altimeter (MOLA) instrument on NASA’s Mars Global Surveyor spacecraft and the High Resolution Stereo Camera (HRSC) on ESA’s Mars Express orbiter.
These results are the first evidence for extensive subglacial erosion driven by channelized meltwater drainage beneath an ancient ice sheet on Mars. The findings demonstrated that only a fraction of valley networks match patterns typical of surface water erosion, which is in marked contrast to the conventional view.
Using the geomorphology of the Martian surface to rigorously reconstruct the character and evolution of the planet in a statistically meaningful way is, frankly, revolutionary.
Fig: Distribution of Martian valley networks (purple) and those analyzed (white) by Grau Galofre et al. Image credit: Grau Galofre et al, doi: 10.1038/s41561-020-0618-x.
The team’s theory also helps explain how the Martian valleys would have formed 3.8 billion years ago on a planet that is further away from the Sun than Earth, during a time when the Sun was less intense.
Climate modeling predicts that Mars’ ancient climate was much cooler during the time of valley network formation. They tried to put everything together and came up with a hypothesis that hadn’t really been considered: that channels and valleys networks can form under ice sheets, as part of the drainage system that forms naturally under an ice sheet when there’s water accumulated at the base.
These environments would also support better survival conditions for possible ancient life on Mars.
A sheet of ice would lend more protection and stability of underlying water, as well as providing shelter from solar radiation in the absence of a magnetic field — something Mars once had, but which disappeared billions of years ago.
References: Anna Grau Galofre, A. Mark Jellinek & Gordon R. Osinski, “Valley formation on early Mars by subglacial and fluvial erosion”, Nature Geoscience, published online August 3, 2020; doi: 10.1038/s41561-020-0618-x ; Link: https://www.nature.com/articles/s41561-020-0618-x