Living on Martian Time
Postdoc Kevin Lewis says he feels like he’s living with perpetual jet lag. Some of his days begin in the early morning; others don’t start until night, long after the cafeteria has stopped offering anything besides a cooler of ice cream. Regardless of what time it is in California, Lewis starts work when the clock strikes 2 p.m. on a planet 16 minutes away -- for someone traveling at the speed of light. As a member of the scientific team working with the Curiosity rover exploring the surface of Mars, Lewis is living on Martian time.
The Curiosity rover, which landed on Mars in August, is the centerpiece of NASA’s Mars Science Laboratory mission. For the next two years of the primary mission, Curiosity will be exploring the geology of Gale Crater, located just south of the Martian equator. So far, the rover has travelled about 400 meters across the crater floor toward Mt. Sharp, which rises 5 kilometers high in the crater’s center. This mission target was chosen because of the layered materials that make up the floor of the crater and the mountain, as well as the numerous channels cutting into the mountain which allows access to the layers for study.
The 300 scientists working on the project at NASA’s Jet Propulsion Laboratory in Pasadena have a strict schedule, dictated by the orbits of the Mars Odyssey and Mars Reconnaissance satellites which relay communication between Earth and Curiosity. The satellites are in sun-synchronous orbits and thus pass over the rover at about 2pm and 2am every Martian day. Since a Martian day is about 40 minutes longer than an Earth day, the scientists’ days are constantly shifting relative to Earth time.
A workday for Lewis typically starts about half an hour before the 2 p.m. download time, when the various scientific and engineering teams gather to wait for Curiosity’s report on its previous day’s work. Once the data arrives, they have about two hours to analyze it and decide on a plan for the next day. A flurry of activity begins, as images are projected, data is analyzed on laptops, and small groups cluster to discuss and coordinate priorities. Once a course of action is determined, engineers turn the mission instructions into the code that will guide the rover. And this must all be done by the next morning on Mars.
At the beginning of Curiosity’s journey, Lewis says, the priorities were for general examination and testing of the rover and of its instruments. Now, as more instruments come online, more and more science is being done, but the scientists must always balance their priorities for data collection with engineering concerns like power constraints, data volume, feasibility, and the capabilities of the rover.
The team can direct the rover’s course of action via code, but there is no real-time interactive component. Once Curiosity receives its instructions for the day, it is effectively on its own, relying on hazard avoidance cameras and other devices to protect itself. Lewis notes that the first concern is always for the health and safety of the rover.
Lewis’ focus is on the geology of Gale Crater and he has plenty of questions. What makes up the layers? What is the stratigraphy? What is their chemistry? Did the materials form during a special, relatively short period in Martian history, or did they develop over a long time period? How important was water? But he is in a good position to start finding some answers.
“I’m still always a little shocked that an observation that I request actually makes it to the rover and it does what I want it to do,” he said. An example of this was his involvement in the decision to examine the feature called Glenelg; its name is appropriately palindromatic since Rover had to take a 180° detour to get there. Glenelg is in an area where three terrains intersect, allowing Curiosity to do its first real field geology as it documents Martian stratigraphy. On its way to Glenelg, Curiosity has sent back images of rock layers with abundant rounded pebbles up to 4 cm in size, too large to have been transported by wind. Resembling conglomerates found in stream deposits on earth, this is intriguing evidence that flowing water was at one time present on the surface of Mars.
The next few weeks will see the first chemical analyses of Martian soil by Curiosity’s X-ray diffractometer, mass spectrometer, gas chromatograph, and laser spectrometer. Lewis is excited about the data to be collected, but notes that the process is a complicated one. The rover must find an area with sand-sized particles, trench it with a wheel track to confirm the feasibility of scooping, scoop up a sample, put it on a sample tray, image the sample, and then sieve it to appropriate size for the analytical instruments. The first few times the process occurs, the rover will dump the sample before actual analysis in order to scrub and expose fresh metal surfaces on the processing equipment, to minimize any terrestrial contamination. “We want to be sure we are measuring Mars, not Earth,” he says. The process means it will still be a few weeks before scientists receive the first analytical information.
For now, Lewis and most of the 300 members of the science team are in Pasadena. In another month, they will return home and continue the process remotely via teleconference. Lewis says he expects to be in his Guyot Hall office at variously-shifting hours of the day and night. He will still live for a while on Martian time.