What lies beneath

Once created, these valleys continue to transform. As shown clearly in the generated bird’s-eye view, the valley floors are relatively smooth, marked by gently weaving lines reminiscent of a flowing river. Rather than water, these valleys have been filled by a slow, viscous flow of ice-rich rock, a lot like the rock glaciers we see here on Earth.

Rock glaciers are very sensitive to changes in climate, and so act as good markers for how a planet’s environment has changed over time. Here, they indicate that this region of Mars has experienced alternating periods of cool and warm, freeze and thaw.

These temperature fluctuations are driven by the tilt of Mars’s rotational axis; unlike Earth, which sticks at a reasonably steady and moderate tilt due to the stabilising influence of our large Moon, Mars’s tilt varies dramatically over time. This leads to alternating warm spells and ice ages, periodically letting ice creep near to the planet’s equator before shrinking back to its poles.

While Earth and Mars both experience tilt fluctuations in this way, the variations are far bigger on Mars. Mars’s tilt has swung between 15 and 45 degrees in the last 10 million years, while Earth’s has varied between 22 and 24.5 degrees. These regular shifts – known as Milankovitch cycles – play an important role in our planet’s climate, but their effects are more subtle than those on Mars.