This simulated view of Ahuna Mons (Mt. Ahuna) was made using stereo photos NASA’s Dawn spacecraft acquired from its low mapping orbit in August shows one of the asteroid Ceres most remarkable features. Ahuna Mons is likely a cryovolcano or “cold volcano”, formed when salty mud rose up from underground in a growing, dome-like features similar to volcanic domes seen on both the moon and Earth.
The difference between a cryovolcano and a regular one is that instead of molten rock, molten ice laced with minerals erupts and spills over the landscape. Repeated eruptions of watery mud enriched with salt built Ahuna Mons. Unlike a classic eruptive volcano, lavas spread more gently from a vent at the surface and accumulated layer-by-layer to create a volcanic dome. On Ceres, which has no atmosphere to speak of, the water would have quickly vaporized into space, leaving clay minerals and salt-streaked slopes behind.
Ceres’ volcano is geologically young, probably between 50 and 240 million years, a drop in the bucket given Ceres formation age of 4.6 billion years ago. Based on its size and altitude, it took somewhere between a few hundred to a few hundred thousand years for the volcano to build up to its present form. That’s one of the reasons it looks so fresh compared to the cratered landscape that surrounds it. The summit stands 13,000 feet (4,000 meters) high, and the mountain is 11 miles (17 km) across its base.
The streaks were created by rockfalls down the steep slopes slanted some 35° and must be made of finer stuff below the resolution limit of the camera to appear so smooth. Take a look at the summit, which has cracks like those seen in volcanic domes when they expand. It’s hard to say what formed the dome in the first place. Did an impact rupture the crust, creating a vent for the muddy mix to reach the surface?
On the opposite hemisphere from the mountain, a large crater created by an huge impact may have focused seismic energy at the mountain’s location, causing the surface to rupture. We know that Ceres contains a lot of water — at least 25% — with even higher amounts in its crust. Either leftover heat in the interior or some impact-related event warmed the ice-water-salt mix enough to mobilize it until it rose to the surface.
The foreground crater is coincidentally 11 miles (17 km) across. From the lowest point in this crater to the top of the volcano is 24,800 feet (7,560 meters) vertically across a horizontal distance of only 9 miles (15 km). With 2.7 % of Earth’s gravity, the hike from crater bottom to dome top would not be as rigorous as you might think. At 175-pound person would only weigh 2.25 pounds on Ceres. You could hop your way up to the top in no time.