The European Space Agency’s Mars Express has snapped some incredible images of the area known as Tantalus Fossae, a series of tectonic faults that extend for 2,400 kilometers (1,500 miles). They did not form in a catastrophic event (like other bits of Mars) but through the formation of a large volcano, Alba Mons.
Today, Mars is a frigid desert world, but eons past it had water on its surface and active volcanism. The signs of this past activity have been observed on the ground and from orbit, and tell of a complex geological history.
Alba Mons, formerly known as Alba Patera, is an impressive volcano. It is not the highest, with a top altitude of 6.8 kilometers (4.2 miles). A sizable mountain for Earth’s standard, but a tiny one compared to Mars’ own Olympus Mons which reaches over three times as high with a 26 kilometer (16 mile) altitude. But what is impressive about Alba Mons is its surface area, which makes it the biggest volcano on Mars and as wide as the United States north-to-south.
The formation of this gargantuan volcano cracked the surrounding area, creating the long streaks seen from orbit in exquisite detail by Mars Express, which has been around the Red Planet for almost 20 years. These formations are known as graben and are created when two parallel faults form and the rock between them sinks down in the resulting void, given the appearance of a scratched surface. They are up to 10 kilometers (6 miles) in width and 350 meters (1,148 feet) in depth.
The volcano was active for less (geological time) than Olympus Mons. According to previous studies, the volcanic deposits around Alba Mons are between 3.6 and 3.2 billion years old. The age estimate is done statistically, by looking at the number of craters in a region. Younger surfaces tend to have fewer craters.
In fact, the image shows quite a prominent large impact crater, the fault lines cross its bottom which means it had already been created by space rock before Alba Mons formed. But other craters across the region, smaller in size, are more recent, interrupting the fault lines with their basins and their rims. There are also older valleys that criss-cross the grabens. These must also have formed before Alba Mons rose from the ground.
The name Tantalus comes from the Greek mythological figure, the son of the nymph Plouto and Zeus who was punished in the afterlife by standing in a pool of water beneath a fruit tree with low branches. The moment he tried to reach for fruit, the branches would move out of reach. If he wanted to quench his thirst and drink from the pool, the water would recede. That’s where the word tantalizing comes from in English.