ASU USGS project: THEMIS Development of sharpest map of Mars' surface properties

A small impact crater on Mars named Gratteri, 4.3 miles (6.9 km) wide, lies at the center of large dark streaks. 

Unlike an ordinary daytime photo, this nighttime image shows how warm various surface areas are. 

Brighter tones mean warmer temperatures, which indicate areas with rockier surface materials. 

Darker areas indicate cooler and dustier terrain. For example, the bright narrow rings scattered across the image show where rocks are exposed on the uplifted rims of impact craters. 

Broad, bright areas show expanses of bare rock and durable crust. Fine-grain materials, such as dust and sand, show up as dark areas, most notably in the streaky rays made of fine material flung away in the aftermath of the meteorite's impact. 

Image courtesy NASA/JPL-Caltech/Arizona State University.

A heat-sensing camera designed at Arizona State University has provided data to create the most detailed global map yet made of Martian surface properties.

The map uses data from the Thermal Emission Imaging System (THEMIS), a nine-band visual and infrared camera on NASA's Mars Odyssey orbiter.

A version of the map optimized for scientific researchers is available at the U.S. Geological Survey (USGS).

The new Mars map was developed by the Geological Survey's Robin Fergason at the USGS Astrogeology Science Center in Flagstaff, Arizona, in collaboration with researchers at ASU's Mars Space Flight Facility.

The work reflects the close ties between space exploration efforts at Arizona universities and the U.S. Geological Survey.

"We used more than 20,000 THEMIS nighttime temperature images to generate the highest resolution surface property map of Mars ever created," says Fergason, who earned her doctorate at ASU in 2006.

"Now these data are freely available to researchers and the public alike."

Surface properties tell geologists about the physical nature of a planet or moon's surface.

• Is a particular area coated with dust, and if so, how thick is it likely to be?
• Where are the outcrops of bedrock? 
• How loose are the sediments that fill this crater or that valley? 

A map of surface properties lets scientists begin to answer questions such as these.

Darker means cooler and dustier
The new map uses nighttime temperature images to derive the "thermal inertia" for areas of Mars, each the size of a football field.

Thermal inertia is a calculated value that represents how fast a surface heats up and cools off.

As day and night alternate on Mars, loose, fine-grain materials such as sand and dust change temperature quickly and thus have low values of thermal inertia.

Bedrock represents the other end of the thermal inertia range: because it cools off slowly at night and warms up slowly by day, it has a high thermal inertia.

"Darker areas in the map are cooler at night, have a lower thermal inertia and likely contain fine particles, such as dust, silt or fine sand," Ferguson says.

The brighter regions are warmer, she explains, and have surfaces with higher thermal inertia. These consist perhaps of coarser sand, surface crusts, rock fragments, bedrock or combinations of these materials.

The designer and principal investigator for the THEMIS camera is Philip Christensen, Regents' Professor of Geological Sciences in the School of Earth and Space Exploration, part of the College of Liberal Arts and Sciences on the Tempe campus.

NB: Four years ago, Christensen and ASU researchers used daytime THEMIS images to create a global Mars map depicting the planet's landforms, such as craters, volcanoes, outflow channels, landslides, lava flows and other features.


"A tremendous amount of effort has gone into this great global product, which will serve engineers, scientists and the public for many years to come," Christensen says.

"This map provides data not previously available, and it will enable regional and global studies of surface properties. I'm eager to use it to discover new insights into the recent surface history of Mars."

As Fergason notes, the map has an important practical side. "NASA used THEMIS images to find safe landing sites for the Mars Exploration Rovers in 2004, and for Curiosity, the Mars Science Laboratory rover, in 2012," she says.

"THEMIS images are now helping NASA select a landing site for its next Mars rover in 2020."

Mars ASU THEMIS camera to get new views of Red Planet

ASU's Thermal Emission Imaging System (THEMIS) is taking regular temperature measurements of the ground as the orbit of NASA's Mars Odyssey spacecraft drifts toward a time of day that will give THEMIS views of Mars around sunrise and sunset. 

This will be the first systematic observations of these times of day in more than a generation. 

Here, THEMIS is imaging the floor of Gale Crater, using its visual wavebands to create a color view of the area where Mars rover Curiosity (too small to be imaged) is exploring for ancient habitable environments. 

Image courtesy NASA /JPL-Caltech /Arizona State University.

For the first time since the Viking Mars mission of the 1970s, which ended more than a generation ago, scientists will soon begin systematic observations of Mars from orbit at times of day around local sunrise and sunset.

The instrument they will use is the Thermal Emission Imaging System (THEMIS) camera, designed at Arizona State University.

Mars Odyssey carries three main science instruments: The Gamma Ray Spectrometer (GRS), the Thermal Emission Imaging System (THEMIS), and the Mars Radiation Environment Experiment (MARIE).

The spacecraft has been drifting toward the new orbit for more than a year, and a small engine burn on Feb. 11 accelerated the drift so it can finalize the orbit in November of 2015.

During the transition, THEMIS will continue observations as the orbital time of day changes.

Philip Christensen

"We don't know exactly what we'll find when we get to an orbit where we see Mars just after sunrise," says Philip Christensen, designer and principal investigator for THEMIS.

He is a Regents' Professor of Geological Sciences in ASU's School of Earth and Space Exploration on the Tempe campus. Christensen developed the post-orbit change observing plan.

THEMIS is a multi-band camera that images Mars in nine infrared (heat-sensitive) "colours" and five visible ones. It was launched on Mars Odyssey in April 2001 and reached the Red Planet in October that year.

The spacecraft spent several months dipping into the Martian atmosphere to regularize its orbit, and THEMIS began science imaging in February 2002.

With more than 12 years elapsed since arrival, Mars Odyssey is the longest-working Mars spacecraft of any nation.


Morning and evening on Mars
Besides revealing landscapes in sharp relief, thanks to the low sun angle, the new orbital time of day for THEMIS promises to let scientists explore frosts, ground fogs, early morning clouds and hazes, and other transient atmosphere-related features that usually vanish as the Martian day goes on.

"We know that in places, carbon dioxide frost forms overnight," says Christensen. "And then it sublimates immediately after sunrise."

"What would this process look like in action? How would it behave? We've never observed this kind of phenomenon directly."

He notes that the Martian atmosphere is more variable than scientists have appreciated in the past.

"We can look for seasonal differences," says Christensen. "Are fogs more common in winter or spring? Do they vary from day to day? From one part of the year to another? From year to year? We'll check it out."

In addition, THEMIS will measure surface temperatures at thousands of locations. These observations can yield insight about materials in the ground and about temperature-driven processes.

These include warm-season flows of water or brine seen on some slopes, and gas-and-sand geysers fed by spring thawing of carbon dioxide ice near Mars' south pole.

Jeffrey Plaut

"We're teaching an old spacecraft new tricks," says Odyssey project scientist Jeffrey Plaut at NASA's Jet Propulsion Laboratory in Pasadena, California.

"We will be in position to do something that has never been done systematically: to watch how morning fog, clouds and surface frost develop at different times of year."

After Mars Odyssey reaches its intended orbit of 6:45 a.m. and p.m. (local time) in November 2015, mission engineers expect Odyssey will have enough propellant for nine to 10 more years of operation, an important matter for ongoing Mars exploration.

Besides conducting its own observations, Odyssey also serves as a crucial communications relay to Earth for the two active rovers, Curiosity and Opportunity, operating on the Martian surface.

"Mars is a dynamic world," says Christensen. "And for a generation, we've not been positioned to explore this part of it so thoroughly."