THE MISSION TO MARS

The success of the Mars Rover mission furthers the enduring quest for life on the Red Planet and increases the possibility of sending a manned mission there.

THE Mars Exploration Rover (MER) mission of the National Aeronautics and Space Administration (NASA) has so far been quite remarkable. Given the failure-ridden four-decade history of missions to Mars, with nearly two-thirds of the 30-odd probes having failed, this nested Matriushka doll-like spacecraft has performed flawlessly in its over-480-million-km and nearly seven-month-long journey from the earth to Mars right up to its landing. Indeed, in the orbiter-cum-lander Mars mission of the European Space Agency (ESA), communication with the United Kingdom-built lander, Beagle 2, which separated from the mother spacecraft Mars Express on December 19 and landed on Mars on December 25, has been completely lost and efforts to establish contact are still on. Similarly, the Japanese orbiter Nozomi, which was expected to enter into a Mars orbit in December, managed to achieve only a fly-by. This ill-fated spacecraft, launched in July 1998 and planned to be injected into a Mars orbit in October 1999, suffered a series of setbacks and has been in an orbit around the sun since. But after the failure, the Mars project has now been abandoned and the spacecraft will continue to orbit the sun.

The NASA lander, on the other hand, hit the bull's eye, with the touchdown spot being only 6 km away from the target in the vast and bleak 150-km wide flat expanse of Gusev Crater which, the scientists believe, is the remnant of a lakebed of a warm and wet planet that Mars was aeons ago. Spirit has landed in a region of Gusev that has been swept by the Martian tornadoes, known as dust devils, blowing the fine-grained soil away and exposing the denser material below. "We hit the sweet spot," Steve Squyres, the Spirit's principal investigator, has been quoted as saying. "What we wanted was some place where the wind has cleaned off the rocks for us and this is it." The region around Spirit's landing site, as captured by the currently orbiting NASA's Mars orbiter Odyssey, seems to be criss-crossed by the tracks of dust devils that have carried away dust and left the gravel behind. This is good, according to scientists, because they are easier for the Rover's geology instruments to penetrate and analyse.

THE goal of the Rover mission is to determine when and how water, if it was really there, disappeared. Since water is crucial for life, the mission will also search for traces of life to determine whether there was enough time for life to evolve. So over the next three months Spirit will explore the Martian surface as it treks around, searching the rocks and soil for clues to Mars water, and may be Martian life. Already Spirit, whose separation from the lander and rolling out into the Martian landscape on its own is still a few days away, has returned the sharpest images of the Martian surface ever from its Panoramic Camera or PanCam.

The mission team is ecstatic. "These pictures are the highest-resolution, highest-detail pictures of Mars ever obtained. They are absolutely spectacular. You're getting a glimpse into the kind of detail that we're seeing at just this one part of the landing site. We're looking at one little wedge in front of the rover. We've still got the entire terrain all the way around to build up around us at this kind of resolution," Jim Bell of Cornell University, the chief designer of the camera, was quoted as saying. "This is just the tip of the iceberg in terms of what you're about to see in the way of images," Squyres has said. "This is something like one-eighth of a single PanCam panorama and this isn't stereo. We're going to have stereo PanCam come down fairly soon, too, and that's going to be just stunning. So this is just a tiny taste of what's to come."

The success of the MER mission has come as a shot in the arm for the beleaguered NASA in the wake of the Columbia shuttle disaster in February last. "We are back! And we are on Mars," NASA administrator Sean O'Keefe said after the successful landing of Spirit. O'Keefe has also announced plans to name the landing site of Spirit as Columbia Memorial Station, in honour of the astronauts who died in the tragedy. In fact, Spirit carries a six-inch diameter aluminium memorial plaque mounted on the back of its high-gain antenna in memory of the astronauts and the fateful STS-107 mission.

THE `Red Planet' Mars, whose average distance from the sun is about 230 million km (1.5 times farther compared to the earth), is 6,780 km in diameter and is about the half the size of the earth but has the same land area as the earth. Its mass is one-tenth of the earth's and its gravity 38 per cent of that of the earth. A Mars year is about twice that of the earth (687 earth days) and its rotation period (a Mars day or `Sol') is 24 hours 39 minutes 35 seconds (1.027 earth days). The landscape has the appearance of a rocky desert. Its average density is 3.9 times that of water compared to the earth's 5.5 times. Its atmosphere is composed chiefly of CO2 (95.3 per cent), nitrogen (2.7 per cent) and argon (1.6 per cent). Its atmospheric pressure is less than 0.01 times that of the earth. Surface temperature varies between -1280C during polar night to 270C at equator during midday at the closest point in its solar orbit. So Mars, a much more complex body than the earth, is a cold, nearly airless planet bombarded by hostile radiation both from the sun and deep space. But is it lifeless too and has it always been so? This is one of the key questions that Mars explorations have sought to answer besides understanding its geology, chemistry and climate.

Coming in the wake of the recent closest passage of Mars and the earth - which indeed is one of the reasons for the timing of the various missions - the present mission seems to have also kindled the public interest greatly. While the notion of an inhabited Mars has caught the public imagination since the early 20th century, scientific evidence of that has been lacking despite four decades of probing the planet in a variety of ways. Indeed, the very first successful probe, Mariner 4's fly-by in 1965, revealed large impact craters, much like those on the barren and lifeless moon and so did the later Mariners 6 and 7 in 1969 and Mariner 9 in 1971. The hopes of finding Martian life were further dashed when NASA's two Viking landers in 1976 did not detect any sign of biological activity. But since then, an analysis of pictures from the Viking orbiters seems to suggest some intriguing possibilities of a more hospitable Martian past.

Scientists have detected potential signs of an ancient coastline from these pictures. More recently, the current orbiters - Mars Global Surveyor (MGS), launched in November 1996, and 2001 Mars Odyssey, launched in April 2001 - have revealed many features that seem to suggest strongly of Mars having been shaped by running water that has since disappeared. Images from Odyssey's camera suggest large amounts of ice mixed with Mars surface materials at high latitudes, as well as potential evidence of ancient snowpacks. These have led to the conjecture that water may still be there buried as layers of ice just under the Mars surface. There is definitely no evidence of the existence of complex organisms in recent times at least on what appears to be a hostile planet. But scientists have speculated that life in some form, perhaps very simple microbes, may have arisen in historic times when Mars may have been wetter and warmer. A promising way to answer this is to look at the diverse clues that water could have left on the planet.

THE MER project is a part of the newly restructured long-term Mars Exploration Programme (MEP) of NASA, a fundamentally science-driven programme with a focus on understanding Mars as a dynamic system and addressing whether life is, or ever was, part of that system. The basic strategy of this programme is "Follow the Water". This, according to James Garvin and Orlando Figueroa of the Office Space Sciences, NASA, "serves to connect the fundamental programme goals pertaining to biological potential, climate, the evolution of the solid planet and preparations for eventual human exploration". Explorations of extreme environments on the earth have shown that wherever there is liquid water below the boiling point, evidence of life has been seen. Hence the strategy on Mars.

The NASA programme has been conceived on a "seek, in-situ, sample" approach; that is, progressively narrowing down the cycles of "seeking" Mars - first from orbit, then on the surface, followed by collection of well selected samples for return to the earth. "No other single strategy can answer as many questions about Martian chemistry, geology, climatology, and the presence of or potential for life, past or present," observed a report of the United States National Academies' expert committee.

MGS and Odyssey constituted the first level of seeking, the MER the next. It is actually a twin rovers mission. The objective is to deliver two mobile laboratories for geological investigations on Mars. Spirit, which was launched on June 10 and parachuted into Gusev Crater on January 4, is the first of the two golf cart-sized rovers. It will be followed by the landing of the companion rover called Opportunity, which was launched on July 7 and is scheduled to land on January 25 at another similar site called Meridiani Planum near the Martian equator halfway around the planet from Gusev. The rovers, which carry an identical suit of cameras and instruments, can sense and get around obstacles as they target spots on the Mars surface selected by scientists by analysis of images sent by the rovers.

"Think of them as robotic field geologists," Squyres said. The rovers will look around with a stereo colour camera and with an infrared instrument that can classify rock types from a distance. They will go to the rocks that seem most interesting and reach out with a robotic arm that has a handful of tools, a microscope, two instruments for identifying what the rock is made of and a grinder for getting to a fresh unweathered surface inside the rock. Thus, they will be able to carry out the first ever detailed geological studies on Mars. They will also enable "ground truth" characterisation for the calibration of observations from instruments aboard the orbiters.

THE spacecraft carrying the MERs is like a nested Russian doll. The rover is tucked inside a folded-up lander wrapped in airbags. The lander is, in turn, covered by a protective aeroshell. Both Spirit and Opportunity, which are identical, are larger, more mobile and better equipped than the 1997 Mars Pathfinder rover called Sojourner. Each rover has a mass of nearly 180 kg and is expected to travel about 40 metres per Martian day. Surface operations have been planned for 90 Sols or 92 the earth days for each rover extending up to April but could continue longer depending on the status of the vehicles.

Launched by the Delta rocket, the MERs use the same airbag-cushioned landing scheme that successfully delivered the Mars Pathfinder rover for entry, descent and landing. A parachute is deployed to slow the spacecraft and airbags inflate to cushion the landing. Upon reaching the surface, the spacecraft will bounce at least a dozen times - Spirit is said to have bounced 32 times - with heights reaching as high as 15m, and roll a kilometre or more before coming to a stop. When it stops, the airbags deflate, retract and the spacecraft's petals open up, bringing the lander to an upright position and exposing the rover. Unlike the Pathfinder mission, wherein the instruments were divided between the lander and the small rover, Spirit and Opportunity carry all the instruments. Soon after landing, the rovers begin reconnaissance of its landing site by taking 3600 images in visible colour and infrared using the PanCam. In the case of Spirit this operation is what yielded those spectacular images.

Each rover carries five scientific instruments and a rock abrasion tool (RAT): a PanCam provided by the Jet Propulsion Laboratory (JPL) of NASA; a miniature thermal emission spectrometer from Arizona State University; a Mossabauer spectrometer from the Johannes Gutenberg University, Mainz, Germany; an Alpha-particle X-ray spectrometer from the Max Planck Institute for Chemistry, Germany; and a microscopic imager from JPL. RAT has been provided by Honeybee Robotics, New York. The payload also includes magnetic targets provided by Niels Bohr Institute, Copenhagen, Denmark. The spectrometers, microscopic imager and RAT are deployed on a robotic arm.

A minor hitch in Spirit's airbag retraction has delayed some operations a bit and has also resulted in a change in the sequence of operations. The retraction system seems to have hit a block or the airbags have got stuck somewhere so that this operation has been postponed for a while. Even without retraction, the lander has been brought to the upright position and its petals opened up. However, because of the airbag problem, the rover cannot exit straight out as planned. Some other manoeuvre will have to performed for the rover to exit in a different - perhaps in a perpendicular direction.

The strategy of following the water trail has essentially dictated the final choice of the landing sites for the rovers. But it required more than two years of study by over 100 scientists and engineers to evaluate potential sites using information from the two orbiters. Candidate sites had to be near Mars' equator, not too rugged, not too rocky, not too dusty and low enough in elevation so that the lander would pass through enough atmosphere to slow down sufficiently for landing. In all, 155 sites met the criteria. The two that made the final grade in addition showed powerful evidence of past liquid water (though some researchers recently have challenged this evidence).

Scientists believe that Spirit's landing site, Gusev Crater, named after a Russian astronomer Matvei Gusev, may have held a lake a long time ago. Gusev is at 150 South and is in a transition zone between the highlands in the southern part of the planet and the smoother plains in the north. The valley, called Ma'adim Vallis, runs about 900 km from the highlands to Gusev. The speculation is that water flowing down the valley would have pooled in Gusev. The one-time Gusev lake may have deposited sediments in the floor of the crater that preserve records of the lake environment. If Spirit can find and approach sedimentary samples, several physical traits that the panaromic camera and the microscopic imager as well as the grinder pick up might testify to the long-lost environment. On the other hand, scientific interest in Opportunity's landing site, Meridiani Planum, a smooth plain, arises not from the shape of the terrain, as at Gusev, but from an unusual mineral deposit - grey hematite which is rich in iron oxide, usually formed in association with water - found by MGS using its on-board instrument called the thermal emission spectrometer (TES).

The high-resolution images of Gusev have already thrown up some complexity. The crater is a surprisingly rolling, rock-strewn landscape and totally unlike the relatively smooth, wind-swept lakebed that the initial, low-resolution images had indicated. According to the mission scientist Ray Arvidson, deputy principal investigator for the MER project, lakebed deposits may well be present, but they may be more difficult to find than originally thought. "This is not your typical lakebed, if it's a lakebed," he has said. "A lakebed is typically flat with very fine-grain sediments. That's not what we're looking at. We're looking at a surface that's rock-strewn, a surface that probably has a number of secondary craters that have excavated rocks. So it's not a primary depositional surface of a lakebed. If there are lake sediments there, they've been chewed up and rocks have been brought in, either from the bottom or laterally by some set of processes." Even if life never developed on Mars, scientific exploration may yield clues about the pre-biotic chemistry that led to life on the earth. "Mars as a fossil graveyard of the chemical conditions that fostered life on the earth is an intriguing possibility," observes a NASA document. At both sites, surprises are only to be expected given that there is so much unknown about the Red Planet. Mars has held surprises for every mission sent so far.

As part of NASA's MEP, the MER project will be followed up by missions up to 2009, beginning with Mars Reconnaissance Orbiter in 2005, Phoenix Mars Scout in 2007, Mars Science Laboratory in 2009 and Mars Telecommunication Orbiter in 2009. In the next decade there will be a transition from "following the water" to a search for "building blocks of life". Even as that is planned, a manned mission to Mars may well take shape. Indeed, the successful landing of Spirit has rekindled White House's interest in manned mission to Mars and President Bush is apparently favourable to the idea. According to reports, Bush may well announce it as part of the new long-term space policy for NASA. The Russians too have already announced their plan for a manned mission to Mars as an international programme. Mars may well be the destination for international deep space missions by 2020.