MRO Radar Maps Extensive Subsurface Martian Ice


Sure, it’s big news the Moon has water ice on the north pole, but Mars is loaded! A new extensive radar mapping of the middle-latitude region of northern Mars shows that thick masses of buried ice are quite common beneath the surface. The Mars Reconnaissance Orbiter’s Shallow Radar instrument has detected subsurface ice deposits that extend for hundreds of kilometers in the rugged region called Deuteronilus Mensae, about halfway from the equator to the Martian north pole. “We have mapped the whole area with a high density of coverage,” said Jeffrey Plaut from JPL. “These are not isolated features. In this area, the radar is detecting thick subsurface ice in many locations.”

The Shallow Radar instrument has been charting the locations of these hidden glaciers and ice-filled valleys, finding that the most common locations are around the bases of mesas and scarps, and confined within valleys or craters. After obtaining more than 250 observations of the study area, which is about the size of California, the science team is beginning to understand how these deposits may have been left as remnants when regional ice sheets retreated.

“The hypothesis is the whole area was covered with an ice sheet during a different climate period, and when the climate dried out,” Plaut said, “these deposits remained only where they had been covered by a layer of debris protecting the ice from the atmosphere.”

These buried masses of ice are a significant fraction of the known non-polar ice on Mars. The ice could contain a record of environmental conditions at the time of its deposition and flow, making the ice masses an intriguing possible target for a future mission with digging capability.

MRO will continue mapping the area to provide more insight into the buried ice.

Source: JPL

New Images Suggest More Recent Lakes on Mars

Image of a channel between putative lakes from the Context Camera (CTX) onboard NASA’s Mars Reconnaissance Orbiter (MRO).

Modern Mars is frigid and dry, but new evidence suggests that in some locations on the equator there may have been lakes as recently as 3 billion years ago.

Researchers from Imperial College London and University College London studied images from the context camera (CTX) on NASA’s Mars Reconnaissance Orbiter (MRO) of several flat-floored depressions in Ares Vallis, near the martian equator.

Previously these depressions were thought to be due to the collapse of the surface as ground ice sublimated directly to gas, but CTX images reveal small channels connecting the depressions, suggesting that water flowed between them. Similar features can be found in “thermokarst” landscapes in Alaska and elsewhere, where permafrost is melting to create lakes and streams.

To determine the age of the features, the scientists counted more than 35,000 craters in the area. Assuming that the current surface was continuously exposed to impacts from space since it was emplaced, the density of craters points to an age of roughly three billion years.

Previously, it was thought that Mars dried up between 4 and 3.8 billion years ago, but if the cratering age from this study is correct, these new results suggest at least brief periods later in martian history when lakes could exist.

The lead author, Dr Nicholas Warner, from the Department of Earth Science and Engineering at Imperial College London, said: “Most of the research on Mars has focused on its early history and the recent past. Scientists had largely overlooked the Hesperian Epoch as it was thought that Mars was then a frozen wasteland. Excitingly, our study now shows that this middle period in Mars’ history was much more dynamic than we previously thought.”

It is not clear how long-lived the lakes were, but Warner and colleagues suggest that they may have served as oases for life in an otherwise inhospitable world. They also suggest that these lakes would be an interesting landing site for future robotic missions.

What’s the next step? The researchers plan to study other equatorial areas, including the mouth of Ares Vallis and Chryse Planitia to see how widespread the putative lakes were.

Large Ocean, Extensive River Network, Rainfall on Ancient Mars

Did Mars once have a vast network of river valleys – “canals” if you will – and an ocean that covered most of the planet’s northern hemisphere? A new computer-generated map of the Red Planet provides a more detailed look at the valley networks on Mars, and indicates the networks are more than twice as extensive as had been previously depicted in the only other planet-wide map of the valleys. “All the evidence gathered by analyzing the valley network on the new map points to a particular climate scenario on early Mars,” said Wei Luo, from Northern Illinois University (NIU). “It would have included rainfall and the existence of an ocean covering most of the northern hemisphere, or about one-third of the planet’s surface.”

This is a global map depicting the dissection density of valley networks on Mars, in relation to the hypothesized northern ocean.  Credit: NIU, LPI
This is a global map depicting the dissection density of valley networks on Mars, in relation to the hypothesized northern ocean. Credit: NIU, LPI

NIU and the Lunar and Planetary Institute in Houston used an innovative computer program to produce the new map that shows regions dissected by the valley networks roughly form a belt around the planet between the equator and mid-southern latitudes, consistent with a past climate scenario that included precipitation and the presence of an ocean covering a large portion of Mars’ northern hemisphere.

Scientists have previously hypothesized that a single ocean existed on ancient Mars, but the issue has been hotly debated.

Luo and Tomasz Stepinski, a staff scientist at the Lunar and Planetary Institute, publish their findings in the current issue of the Journal of Geophysical Research — Planets.

“The presence of more valleys indicates that it most likely rained on ancient Mars, while the global pattern showing this belt of valleys could be explained if there was a big northern ocean,” Stepinski said.

The researchers created an updated planet-wide map of the valley networks by using a computer algorithm that uses topographic data from NASA satellites and recognizes valleys by their U-shaped topographic signature. “The basic idea behind our method is to flag landforms having a U-shaped structure that is characteristic of the valleys,” Stepinski added. “The valleys are mapped only where they are seen by the algorithm.”

Valley networks on Mars exhibit some resemblance to river systems on Earth, suggesting the Red Planet was once warmer and wetter than present.

The networks were discovered in 1971 by the Mariner 9 spacecraft, but scientists have debated whether they were created by erosion from surface water, which would point to a climate with rainfall, or through a process of erosion known as groundwater sapping. Groundwater sapping can occur in cold, dry conditions.

The large disparity between river-network densities on Mars and Earth had provided a major argument against the idea that runoff erosion formed the valley networks. But the new mapping study reduces the disparity, indicating some regions of Mars had valley network densities more comparable to those found on Earth.

A zoomed-in area comparing the old map of valley networks and the new one. (Left) A satellite image, with color indicating elevation; (center) the old map of valley networks; (right) the new map of valley networks.  Credit: Wei Luo, Northern Illinois University
A zoomed-in area comparing the old map of valley networks and the new one. (Left) A satellite image, with color indicating elevation; (center) the old map of valley networks; (right) the new map of valley networks. Credit: Wei Luo, Northern Illinois University

“It is now difficult to argue against runoff erosion as the major mechanism of Martian valley network formation,” Luo said. “When you look at the entire planet, the density of valley dissection on Mars is significantly lower than on Earth,” he said. “However, the most densely dissected regions of Mars have densities comparable to terrestrial values. The relatively high values over extended regions indicate the valleys originated by means of precipitation-fed runoff erosion—the same process that is responsible for formation of the bulk of valleys on our planet.”

“The only other global map of the valley networks was produced in the 1990s by looking at images and drawing on top of them, so it was fairly incomplete and it was not correctly registered with current datum,” Stepinski said. “Our map was created semi-automatically, with the computer algorithm working from topographical data to extract the valley networks. It is more complete, and shows many more valley networks.”

The Martian surface is characterized by lowlands located mostly in the northern hemisphere and highlands located mostly in the southern hemisphere. Given this topography, water would accumulate in the northern hemisphere, where surface elevations are lower than the rest of the planet, thus forming an ocean, the researchers said.

“Such a single-ocean planet would have an arid continental-type climate over most of its land surfaces,” Luo said.

The northern-ocean scenario meshes with a number of other characteristics of the valley networks.

“A single ocean in the northern hemisphere would explain why there is a southern limit to the presence of valley networks,” Luo added. “The southernmost regions of Mars, located farthest from the water reservoir, would get little rainfall and would develop no valleys. This would also explain why the valleys become shallower as you go from north to south, which is the case.

“Rain would be mostly restricted to the area over the ocean and to the land surfaces in the immediate vicinity, which correlates with the belt-like pattern of valley dissection seen in our new map,” Luo said.

Source: EurekAlert