At a fundamental level, Mars is a volcanic planet. Its surface is home to the Solar System’s largest extinct volcano, Olympus Mons, and another trio of well-known volcanoes at Tharsis Montes. And those are just the highlights: there are many other volcanoes on the surface. Though that volcanic activity ceased long ago, the planet’s surface tells the tale of a world disrupted and shaped by powerful volcanic eruptions.
It’s difficult to imagine what Mars would’ve been like when Olympus Mons was active. The same goes for the Tharsis Montes trio. We may never know, but thanks to HiRISE, we can try to piece together some of the volcanic events that shaped Mars.
Olympus Mons and Tharsis Montes were the headliners in Mars’ ancient volcanic drama, and we learned of their existence first, thanks largely to NASA’s Mariner 9 spacecraft. In fact, they were spotted by ground observers long before that because they were visible when they protruded above global dust storms. But the surface of Mars is also dotted with other evidence of volcanism.
This Mariner 9 image of Ascraeus Mons is one of the first images to show that Mars has large volcanoes. Image Credit: By NASA/JPL – JPL Photojournal, Public Domain, https://commons.wikimedia.org/w/index.php?curid=17133292
There are massive lava flows and extensive lava plains on the planet. In fact, about half of Mars’ surface is covered in volcanic material, though much of it has been further shaped by other processes over time. Most scientists think that the volcanic activity ended about 500 million years ago, while some think the planet may still be somewhat active.
Earth and Mars are both differentiated bodies, meaning they’re made up of different layers of material with different densities. The more dense material has sunk to the cores. We know a lot more, however, about Earth’s interior than we do about Mars’. NASA’s InSight lander is on Mars right now, probing the planet’s interior to learn more. Image Credit: Earth, left: By Kelvinsong – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=23966175. Mars, right: NASA
The difference lies in what happens after an eruption of magma or a lava flow. Earth has large lava formations that have flowed over the surface, called Large Igneous Provinces (LIPs). Earth’s atmosphere and biosphere hide the evidence of these LIPs after a period of time. But on Mars, ancient formations are still visible. Due to the planet’s inactivity, the evidence is kind of locked in place.
Another view of the crater and the lava breach. Image Credit: NASA/JPL/UofA
Both water and lava flowed over the Martian surface in the past. Both are gone now, but the evidence has been preserved. Eventually, scientists may be able to piece together Mars’ history more completely, but for now, it’s one crater at a time.