Mystery Mountain Pops Up in Striking Ceres Photo
There's a mountain on dwarf planet Ceres, but scientists have no idea how it got there.
At first glance, it looks like a pile of excavated material from the crater beside it, much like a trench dug in a child's sandbox. But when you realize the pile of material is actually 3 miles high and on the surface of dwarf planet Ceres, the scene becomes quite mysterious.
Imaged by NASA's Dawn mission that is orbiting Ceres in the Main Asteroid Belt, this is the clearest-yet observation of a feature that mission scientists are having a hard time explaining. Called Ahuna Mons by the team (that was once dubbed "Lonely Mountain"), this mountain is bigger than Washington's Mount Rainier and California's Mount Whitney and from afar looked like a pyramid.
Dawn is now orbiting Ceres at its lowest mapping orbit of only 240 miles and Ahuna Mons' intricate features have snapped into focus. It is no longer a pyramid, it is a dome, but clues as to how it formed and why it took this shape are elusive. This mosaic of high-resolution pictures were captured in December and they show the mountain's steep, smooth sides streaked with bright material.
"No one expected a mountain on Ceres, especially one like Ahuna Mons," said Dawn's principal investigator Chris Russell, of the University of California, Los Angeles. "We still do not have a satisfactory model to explain how it formed."
The now-famous Occator Crater lies some 420 miles northwest of Ahuna Mons, a huge impact crater that is speckled with bizarre white patches that have, so far, also eluded a satisfactory explanation. It's possible that the bright features on the slopes of Ahuna share a common source as Occator's white spots and it is hoped that now Dawn is so close to Ceres' surface, these questions may soon be answered.
"Dawn began mapping Ceres at its lowest altitude in December, but it wasn't until very recently that its orbital path allowed it to view Occator's brightest area," said Marc Rayman, Dawn's chief engineer and mission director at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This dwarf planet is very large and it takes a great many orbital revolutions before all of it comes into view of Dawn's camera and other sensors."
Exactly a year ago, on March 6, 2015, Dawn arrived in Ceres orbit, continuing its historic explorations of the asteroid belt between the orbits of Mars and Jupiter. Having already explored massive asteroid (and protoplanet) Vesta from 2011 to 2012, Dawn slowly powered its way to Ceres, its second orbital objective. The mission has transformed our view of this region of the solar system, revealing the genesis and evolution of planets, highlighting some intriguing mysteries along the way.
"Ceres has defied our expectations and surprised us in many ways, thanks to a year's worth of data from Dawn. We are hard at work on the mysteries the spacecraft has presented to us," said Carol Raymond, deputy principal investigator for the mission also based at JPL.
The mysterious mountain Ahuna Mons is seen in this mosaic of images from NASA's Dawn spacecraft.
After spending eight months at dwarf planet Ceres, the Dawn spacecraft
. What the heck are those bright spots seen from afar? What sort of processes sculpt its airless surface? Scientists will get a better sense of this when the spacecraft moves from its previous orbit of 915 miles (1,470 kilometers) to just 235 miles (380 kilometers). Dawn began its maneuvers on Oct. 23 and will reach the lowest orbit of its mission by mid-December.
The spacecraft is expected to finish its work in mid-2016, and remain in orbit as a small satellite -- an artificial moon -- of Ceres. Meanwhile, in the thousands of pictures beamed back from the mission, scientists are starting to get a sense of what the surface really looks like.
This is actually a picture from February when Dawn was closing in on Ceres, but it gives you a sense of what the dwarf planet is shaped like. Unlike other members of the asteroid belt, Ceres is round -- that's what makes it a dwarf planet. You can also see some white spots on the surface that are still puzzling scientists after months of study.
While scientists were of course interested in what the pictures showed, back then the main purpose of these shots was for "optical navigation", according to the Dawn blog. "Just as when it reached its first deep-space target, the fascinating protoplanet Vesta, mission controllers have to discover the nature of the destination as they proceed,"
. "They bootstrap their way in, measuring many characteristics with increasing accuracy as they go, including its location, its mass and the direction of its rotation axis."
We can easily see that Ceres was
. In this picture, the crater to the left has much sharper edges than the prominent crater to the right, indicating that erosion -- probably erosion from other impacts -- has worn down the older craters.
A more careful look reveals that there are actually craters on TOP of craters as space rocks of various sizes, even down to the size of pebbles or dust, periodically crash into the surface of Ceres.
If you look inside craters such as this one of Dantu -- which is roughly 77 miles (124 kilometers) across --
. The small craters you see inside occurred after the bigger crater was formed. The slumping walls show that erosion has started to occur. There's a bit of white on the surface, perhaps showing something exposed from below, and a small rille in the center.
This is one of the images scientists are using to get a better look at the white spots, which have been speculated to be water ice or indications of a mineral. "Occator is home to the brightest area on Ceres, which tends to appear overexposed in most images,"
about this recent composite image. "This view uses a composite of two images of Occator: one using a short exposure that captures the detail in the bright spots, and one where the background surface is captured at normal exposure."
As observers of Earth's moon know, when you start to look at an object in different lights, different features are visible. When the sun is directly overhead on the moon, the sunlight can wash-out some of the craters' sides. When it is at a steeper angle, the shadows start to show a little bit more detail. So by looking at different angles of Ceres (at different times of the day on Ceres' surface),
, scientists can see a little more of its craters and its detail -- just by using simple geometry.