Ahuna Mons sticks out like a sore thumb. While most of Ceres’ features dig into the surface, this mountain rises about 13,000 feet into the sky.
What could cause a mountain to form on a small world made up of salts, muddy rocks and water ice? Scientists point to a common force. Volcanism. But in Ahuna Mons’ case, “an unusual type of volcanism, involving salty water and mud,” says NASA’s Ottaviano Ruesch.
Volcanism was thrown around by scientists before. Now, a new study says volcanism is the likely culprit. And it could change how scientists view even the smallest worlds.
Scientists knew just by looking at Ahuna Mons that something was going on. But how did they settle on volcanism as the source for how it formed?
After all, mountains can form in a variety of ways. Crustal plate interaction and asteroid impacts are two other common ways mountains form throughout the solar system.
You know the saying ‘what you see is what you get.’ It works for mountains too. Crustal plate interaction creates long mountain chains, not a single mountain. Mountains created by asteroid impacts have a central peak.
Ahuna Mons, especially the shape of the domed top, remind scientists of features seen elsewhere in the solar system. Mountains on Mars and Earth are seen with similar peaks.
Armed with images and 3-D terrain maps, the scientists kept finding features that strengthened the case for a volcanic dome. Cracks at Ahuna Mons’ summit are often seen in other volcanic domes and occur when they expand. Other surface features look eerily similar to those found on Earth.
Ceres on the Left. Earth on the Right.
Ahuna Mons isn’t the first evidence of cryovolcanism. Plumes on Enceladus and Triton point to volcanic activity. As do mountains on Titan.
Two things surprise scientists about Ahuna Mons. Location and age. And both are connected. Volcanic activity in the solar system isn’t a surprise. But it happening on Ceres? That is.
Why? Because Ceres doesn’t have the gravitational interactions that can generate heat like Enceladus does. Fountains of water-ice stream from Enceladus because of heat generated from the gravitational tug of war with the much larger Saturn. Ceres is in the middle of the asteroid belt. It doesn’t have the luxury of another large planet nearby to generate heat.
Plus, scientists believe Ahuna Mons is young. Anywhere between a few hundred million years to one billion years old.
“Ahuna Mons is telling us that Ceres still had enough heat to produce a relatively recent cryovolcano,” Ruesch said.
A small body like Ceres should lose its heat pretty quickly after forming. But it didn’t. At least, in this one area.
NASA’s Lucy McFadden called the mountain a one-of-a-kind feature. “There is nothing quite like Ahuna Mons in the solar system,” said McFadden. “It’s the first cryovolcano we’ve seen that was produced by a brine and clay mix.” Every other volcano we know about was created by either mostly rock or ice.
The study of Ahuna Mons and the rest of Ceres continues. Scientists want to train Dawn’s visible and infrared mapping spectrometer at the mountain to figure out its exact surface composition. They will continue looking for signs of anything special at Ahuna Mons. And, if there is any link between the bright features on the mountain and Ceres’ infamous bright spots.
Dawn rises above Ceres
For more than eight months, the Dawn spacecraft has skimmed just 240 miles above Ceres’ surface. With the primary mission completed, Dawn’s missions team is looking for other observations.
Starting tomorrow (Sept. 2), Dawn will begin transitioning to an orbit 910 miles above Ceres. And it will view the surface from a different angle.
“Most spacecraft wouldn’t be able to change their orbital altitude so easily. But thanks to Dawn’s uniquely capable ion propulsion system, we can maneuver the ship to get the greatest scientific return from the mission,” said Marc Rayman, chief engineer and mission director of Dawn.
The higher orbit also helps extend the spacecraft’s limited supply of hydrazine propellant. It won’t need to use as much to fight Ceres’ gravitational pull at the higher altitude.
Regardless, Dawn won’t hit Ceres for at least 50 years as part of a requirement from the NASA Planetary Protection Office.
Right now, the mission team is busy developing an extended mission plan to submit to NASA next month.