Some of the most remarkable images of Curiosity released so far have come not from the seventeen cameras onboard the rover but from one traveling 300 kilometers overhead.
The HiRISE camera - part of the Mars Reconnaissance Orbiter (MRO) - has been in orbit around Mars since 2006, snapping incredible photographs of gullies, sand dunes, and layered outcrops in unprecedented detail. HiRISE's latest gig has been as martian spy satellite, photographing MSL in the act of landing, and documenting the post-mortem. First there was the descent photograph, the intricately coordinated image of MSL's unfurled parachute trailing behind the aeroshell. Then came the crime scene photograph, showing every piece of landing-stage debris splayed out on the martian surface: the skycrane, the parachute, and, of course, the rover itself.
HiRISE and other instruments aboard MRO have been integrated into every step of MSL preparation and operation, providing mission planners with an unprecedented level of detailed knowledge about what to expect on the ground. According to Sarah Milkovich, HiRISE's representative at JPL and an MSL science team member, it started with the landing site selection process. "HiRISE can acquire stereo images," Milkovich says, "which can give you a better sense of depth and give you the feeling that you're actually standing on the surface."
When integrated with data from MRO's CRISM instrument, the distinct layers of Gale Crater's central mound showed signs of phyllosilicate and sulfate minerals, which point to the influence of liquid water at some point in the planet's past. "Initially, Gale Crater wasn't on the shortlist of landing sites," recalls Milkovich, "but it was the data from MRO that started moving Gale to the top of the list."
Now that Curiosity is on the ground, HiRISE acts as the rover's personal satellite navigation service. "The details of how we drive are determined by instruments on the rover," says Milkovich, "but the big picture of how we drive is determined by HiRISE." With a resolution of 30 centimeters per pixel, the camera is able to spot potential hazards and potential scientific targets long before the rover arrives. "We can look at the places we're going to drive in advance, to start thinking about the science we want to do when we get there," explains Milkovich.
With the ability to image the same location at multiple time points into the foreseeable future, HiRISE can also facilitate scientific studies that wouldn't otherwise be possible. The camera can check back on places Curiosity will leave wheel tracks and determine how quickly they are covered by the pervasive martian dust. Similar investigations have been conducted with the Mars Exploration Rovers, and as the data set grows, scientists will get a better sense of dust transport and accumulation patterns across the planet's surface.
Rover support from orbit is nothing new, but the full integration of such high-resolution imagery from site selection to landing analysis to mission planning represents a new era in Mars exploration. MRO's eyes in the sky can examine potential hazards and preview scientific targets weeks or months ahead of time, making for a more efficient and productive mission.