HiRISE: 45,000 Mars Orbits and Counting
Ten years ago on March 24, the UA-built camera began taking the most detailed images of the Martian surface to date. Since then, the camera has become the world's eye on Mars, bringing us detailed vistas of landscapes ranging from strangely alien to earthly familiar.
True to its purpose, NASA's Mars Reconnaissance Orbiter, or MRO, the spacecraft that began orbiting Mars a decade ago, has delivered huge advances in knowledge about the Red Planet.
According to NASA's Jet Propulsion Laboratory, MRO has revealed in unprecedented detail a planet that held diverse wet environments billions of years ago and remains dynamic today. MRO carries, among other instruments, the High Resolution Imaging Science Experiment, or HiRISE, camera, designed and operated by the Lunar and Planetary Lab at the University of Arizona.
One example of the orbiter's major discoveries was published last year, about the possibility of liquid water being present seasonally on present-day Mars. It drew on three key capabilities researchers gained from this mission: telescopic camera resolution, to find features narrower than a sidewalk; spacecraft longevity, to track seasonal changes over several Martian years; and imaging spectroscopy, to map surface composition.
"Our views of both ancient and modern Mars have changed dramatically in the past decade," says Alfred McEwen, principal investigator of HiRISE. "Now we know that hydrated minerals are common in ancient bedrock, many sand dunes are active, that carbon dioxide frost rather than water is carving gullies, and there is water in other seasonal flows."
Other discoveries have resulted from additional capabilities of the orbiter. These include identifying underground geologic structures, scanning atmospheric layers and observing the entire planet's weather daily. All six of the orbiter's science instruments remain productive in an extended mission more than seven years after completion of the mission's originally planned primary science phase.
The Arrival at Mars
On March 10, 2006, the spacecraft fired its six largest rocket engines for about 27 minutes, slowing it down enough for the gravity of Mars to catch it into orbit. Those engines had been used only once before, for 15 seconds during the first trajectory adjustment in the seven-month flight from Earth to Mars.
For its first three weeks at Mars, the spacecraft flew elongated, 35-hour orbits ranging as far as 27,000 miles from the Red Planet. During the next six months, a process called aerobraking used hundreds of carefully calculated dips into the top of the Martian atmosphere to gradually adjust the size of the orbit. Since September 2006, the craft has been flying nearly circular orbits lasting about two hours, at altitudes from 155 to 196 miles.
The spacecraft's two large solar panels give MRO a wingspan the length of a school bus. That surface area helped with atmospheric drag during aerobraking and still cranks out about 2,000 watts of electricity when the panels face the sun. Generous power enables the spacecraft to transmit a torrent of data through its main antenna, a dish 10 feet in diameter. The total science data sent to Earth from MRO — 264 terabits — is more than all other interplanetary missions combined, past and present.
"The HiRISE team at the UA developed routines to automatically process the raw data into beautiful images, within hours of when the data is returned," McEwen says.
Lockheed Martin Space Systems of Denver built the spacecraft with the capability to transmit copious data to suit the science goals of revealing Mars in great detail.
For example, the HiRISE camera has returned images that show features as small as a desk anywhere in observations that now have covered about 2.4 percent of the Martian surface, an area equivalent to two Alaskas, with many locations imaged repeatedly. The Context Camera, or CTX, managed by Malin Space Systems of San Diego, has imaged more than 85 percent of Mars, with resolution showing features smaller than a tennis court. The Compact Reconnaissance Imaging Spectrometer, or CRISM, built and operated by Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, also has imaged nearly 80 percent of the planet in multiple visual-light and infrared wavelengths, providing composition information at scales of 100 to 200 yards per pixel.
Data from MRO has improved knowledge about three distinct periods on Mars. Observations of the oldest surfaces on the planet show that diverse types of watery environments existed, some more favorable for life than others. More recently, water cycled as a gas between polar ice deposits and lower-latitude deposits of ice and snow, generating patterns of layering linked to cyclical changes similar to ice ages on Earth.
Watching Mars Change
Dynamic activity on today's Mars includes impact events, avalanches, dust storms, seasonal freezing and thawing of carbon dioxide sheets, gully formation, sand migration and summertime seeps of brine.
"This mission has helped us appreciate how much Mars — a planet that has changed greatly over time — continues to change today," said MRO project scientist Rich Zurek of JPL in Pasadena, California, which manages the mission.
MRO provides three types of crucial support for rover and stationary lander missions to Mars. Its observations enable careful evaluation of potential landing sites. They also help rover teams choose routes and destinations. Together with NASA's Mars Odyssey, which has been orbiting Mars since 2001, MRO relays data from robots on Mars' surface to NASA Deep Space Network antennas on Earth, multiplying the productivity of the surface missions.
Recently, the mission has begun investigating areas proposed as landing sites for future human missions in NASA's Journey to Mars.
"The Mars Reconnaissance Orbiter remains a powerful asset for studying the Red Planet, with its six instruments all continuing capably a decade after orbit insertion," Zurek said. "All this and the valuable infrastructure support that it provides for other Mars missions, present and future, make MRO a keystone of the current Mars Exploration Program."
Just this week, another orbiter blasted off the Earth, slated to join MRO in orbit around Mars by mid-October: The ExoMars Trace Gas Orbiter, or TGO, a collaboration project of the European Space Agency, or ESA, and Russia's Roscosmos State Space Corporation. The UA's HiRISE team is supporting the Colour and Stereo Surface Imaging System, or CaSSIS, for science planning software development, data processing and science analysis.
NASA's Jet Propulsion Laboratory contributed to this story.
Click here for a gallery featuring some of HiRISE's most stunning shots, revealing the surprisingly active face of the Red Planet.
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University of Arizona in the News