Scientists at the European Space Agency (ESA) have discovered what appears to be the remains of a supervolcano on the surface of the planet Mars.
According to reports, the massive caldera measures around 40 by 30 kilometers (25 by 19 miles), with a crater depth of about 1,750 meters (5,741 feet) compared to its surrounding plains. Experts believe the size of the Martian crater is comparable to the supervolcano beneath Yellowstone Park.
The discovery was made as part of the ESA's ongoing Mars Express mission.
Pictures of the crater were taken in November 2014 using a high-resolution camera placed on board the agency's satellite.
The Mars Express was focusing on the Siloe Patera feature located on Mars' Arabia Terra region when the caldera was spotted.
Scientists theorize that Martian craters, such as the one the ESA satellite found, must have been formed around 3 billion years ago after volcanic eruptions spewed large amounts of ash and lava onto the planet's surface.
The area encompassing Siloe Patera consists of two other craters close to the massive caldera photographed by the Mars Express.
"A number of irregularly shaped craters have been detected in the Arabia Terra region that could represent a family of ancient supervolcano calderas," the ESA said.
"Siloe Patera is one such example. It is characterized by two depressions with steep-sided walls, collapse features and low topographic relief."
The two giant craters are believed to have been created by two separate volcanic explosions due to the release of the magma pressure from underneath Mars.
The ESA studied the images to verify if the craters were indeed formed by a supervolcano or massive impacts on the planet's surface.
The agency explained that for a depression to be created by an impact, certain features on the surface must be present. These include a central peak, uplifted crater rims and ejecta blankets.
While some of the smaller craters in the vicinity of Siloe Patera do have these features, experts say the massive depressions do not.
They pointed out that the area beside the large craters seem to cut to the lower left, which they think could have been formed by a lava flow.
However, there is also the likelihood that the cut on one section of the crater could have been created by a meteoroid that impacted Mars' surface on an oblique angle.
The ESA scientists believe more studies are needed to help explain the phenomenon.