Astro Bob blog: Sailing, sailing over the Hellas SeaResearchers discover that a huge Martian crater may once have been a sea.
By: Bob King, Duluth News Tribune
Sailing, sailing over the Hellas Sea
The large blue body of water is the hypothetical sea that may have once filled Mars' largest crater, Hellas, located in the planet's southern hemisphere. Hellas covers an area about the size of Alaska. Illustration: NASA
A new study on the geology of Mars published by research scientist Dr. Leslie Bleamaster at the Planetary Science Institute indicates that Mars' largest crater, the Hellas Basin, was once likely filled with water. Hellas, which means Greece in ancient Greek, is an ancient impact scar punched out by an asteroid over 4 billion years ago. It spans over 1200 miles across and its bottom is 5 miles deep. Based on studies from orbiting space probes of layered, sedimentary rocks along the crater's eastern rim, scientists estimate that a large Martian sea the size of Alaska filled of Hellas between 4.5 and 3.5 billion years ago. Sediments formed from materials that flowed from the highlands beyond the crater rim into Hellas when Mars was a wetter, volcanically active planet.
Hellas as it is today as seen in this photo taken by the Hubble Space Telescope. Credit: NASA/ESA
Because of its size and pale orange color, Hellas is fairly easy to see in a telescope when Mars is favorably placed in its orbit near Earth. This past Mars observing season, the planet's southern hemisphere was in the throes of autumn, and clouds often covered Hellas, making the basin even brighter. Now that it's winter at Hellas, its floor will be frequently covered with frost.
Although a little tricky to see clearly, the light-toned, grainy areas at left are examples of layered sediments in the Hellas Basin. Photo taken by the Mars Reconnaissance Orbiter (MRO). Credit: NASA/JPL/University of Arizona
While the highest point on Mars is the caldera of the (probably) extinct Olympus Mons volcano, the lowest place you'll find is inside the Hellas basin. Low elevation gives the giant crater a more clement climate than other regions of the planet, sort of a Martian version of Death Valley. The average mid-summer air temperature on typically sunny Martian afternoon hovers around thre freezing mark while soil temperatures can climb as high as 75 degrees. Be sure to dress extra warm for the night however as the temp dips to 50 below. Mars' thin air can't hold heat like Earth's beefy atmosphere.
These curious landforms in Hellas were probably sculpted by some sort of thick, slow-moving material. Astronomers suspect they were created by moving ice. Great amounts of ice both beneath the surface as well in the form of rock-covered glaciers has been found with ground-penetrating radar in the basin. Credit: NASA/JPL/University of Arizona
If Hellas' shores once tasted the slap of salty waves, there may have been enough time for primitive life to evolve. Is it now incorporated in those sediments as microfossils? That question will have to wait until we can send a robot to dig, sample and return sediments from along that far eastern shore.
I like to think the ancient Greeks would have been delighted with the news that their country's namesake on Mars would have close ties to their seafaring culture.