New findings from NASA’s Mars Reconnaissance Orbiter (MRO) provide the strongest evidence yet that liquid water flows intermittently on present-day Mars.
Using an imaging spectrometer on MRO, researchers detected signatures of hydrated minerals on slopes where mysterious streaks are seen on the Red Planet. These darkish streaks appear to ebb and flow over time. They darken and appear to flow down steep slopes during warm seasons, and then fade in cooler seasons. They appear in several locations on Mars when temperatures are above minus 10 degrees Fahrenheit (minus 23 Celsius), and disappear at colder times.
These downhill flows, known as recurring slope lineae (RSL), often have been described as possibly related to liquid water. The new findings of hydrated salts on the slopes point to what that relationship may be to these dark features. The hydrated salts would lower the freezing point of a liquid brine, just as salt on roads here on Earth causes ice and snow to melt more rapidly. Scientists say it’s likely a shallow subsurface flow, with enough water wicking to the surface to explain the darkening.
Lujendra Ojha of the Georgia Institute of Technology (Georgia Tech) in Atlanta, first noticed these puzzling features as a University of Arizona undergraduate student in 2010, using images from the MRO’s High Resolution Imaging Science Experiment (HiRISE).
HiRISE observations now have documented RSL at dozens of sites on Mars. The new study pairs HiRISE observations with mineral mapping by MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).
The spectrometer observations show signatures of hydrated salts at multiple RSL locations, but only when the dark features were relatively wide. When the researchers looked at the same locations and RSL weren’t as extensive, they detected no hydrated salt.
Scientists interpret the spectral signatures as caused by hydrated minerals called perchlorates. The hydrated salts most consistent with the chemical signatures are likely a mixture of magnesium perchlorate, magnesium chlorate and sodium perchlorate. Some perchlorates have been shown to keep liquids from freezing even when conditions are as cold as minus 94 degrees Fahrenheit (minus 70 Celsius). On Earth, naturally produced perchlorates are concentrated in deserts, and some types of perchlorates can be used as rocket propellant.
Perchlorates have previously been seen on Mars. NASA’s Phoenix lander and Curiosity rover both found them in the planet’s soil, and some scientists believe that the Viking missions in the 1970s measured signatures of these salts. However, this study of RSL detected perchlorates, now in hydrated form, in different areas than those explored by the landers. This also is the first time perchlorates have been identified from orbit.
The discovery is the latest of many breakthroughs by NASA’s Mars missions. Liquid water is considered one of the essential ingredients for life, and its presence raises the question of whether Mars, which appears so dry and barren, could possess niches of habitability for microbial Martians.
NASA’s Mars Reconnaissance Orbiter:
NASA’s Mars Reconnaissance Orbiter blasted off from Cape Canaveral in 2005, on a search for evidence that water persisted on the surface of Mars for a long period of time. While other Mars missions have shown that water flowed across the surface in Mars’ history, it remains a mystery whether water was ever around long enough to provide a habitat for life.
The spacecraft carries six instruments, three engineering instruments, and two more science-facility experiments experiments:
- HiRISE (High Resolution Imaging Science Experiment): This visible camera reveals small-scale objects in the debris blankets of mysterious gullies and details of geologic structure of canyons, craters, and layered deposits.
- CTX (Context Camera): This camera provides wide-area views to help provide a context for high-resolution analysis of key spots on Mars provided by HiRISE and CRISM.
- MARCI (Mars Color Imager): This weather camera monitors clouds and dust storms.
- CRISM (Compact Reconnaissance Imaging Spectrometer for Mars): This instrument splits visible and near-infrared light in its images into hundreds of “colors” that identify minerals, especially those likely formed in the presence of water, in surface areas on Mars not much bigger than a football field.
- MCS (Mars Climate Sounder): This atmospheric profiler detects vertical variations in temperature, dust, and water vapor concentrations in the Martian atmosphere.
- SHARAD (Shallow Radar): This sounding radar probes beneath the Martian surface to see if water ice is present at depths greater than one meter (3.3 feet).
Engineering Instruments
Mars Reconnaissance Orbiter carries three instruments that assist with spacecraft navigation and communications.
- Electra UHF Communications and Navigation Package: Electra allows the spacecraft to act as a communications relay between the Earth and landed crafts on Mars that may not have sufficient radio power to communicate directly with Earth by themselves.
- Optical Navigation Camera: This camera was tested for improved navigation capability for future missions. Similar cameras on orbiters of the future will serve as high-precision interplanetary “eyes” to guide incoming spacecraft as they near Mars.
- Ka-band Telecommunications Experiment Package: During the cruise phase of the mission, Mars Reconnaissance Orbiter demonstrated the use of a radio frequency called the Ka-band to enhance communications using significantly less power.
Science Facility Experiments
Two additional science investigations rely on engineering data.
- Gravity Field Investigation Package: By tracking the orbiter during the primary science phase, team members have been mapping the gravity field of Mars to understand the geology of the surface and near-surface and the geophysical processes that produced these land features. For example, analysis may reveal how the planet’s mass is redistributed as the Martian polar caps form and dissipate seasonally.
- Atmospheric Structure Investigation Accelerometers: Data collected from accelerometers during aerobraking is helping scientists understand the structure of the Martian atmosphere.