Tomorrow, NASA's latest mars probe, the Mars Science Laboratory rover "Curiosity," will land on the Red Planet. It is the largest, heaviest and most ambitious rover ever to head off to Mars. If successful, Curiosity is likely to change much about the way we look at Mars. Long-term geological processes, especially those involving the copious amounts of water now known to exist as ice all over Mars, will be examined. Weather patterns and the likelihood of microbial life (or at least organic compounds) will also be explored.
But what has brought us to this watershed moment? How did Mars evolve from a red smudge in the lenses of giant telescopes to a planet we know better than any save Earth?
Let's take a look back at our discoveries about Mars and the many missions of NASA and others that have brought us to this amazing time in history.
Rod Pyle is the author of Destination Mars: New Explorations of the Red Planet (Prometheus Books, 2012).
While Mars had long captivated the imagination due to its red color and un-starlike motions in the night sky (planets move at a different rate than the background of stars), the advent of the telescope brought the planet far greater notoriety. In the late 1800's, Giovanni Schiaparelli drew elegant (and imaginative) maps of Mars which incorporated features which he termed "<em>canali</em>," Italian for "channels." Later, men like Percival Lowell in the US interpreted this to mean "canals," as in intelligently-designed waterways, and the quasi-scientific search for life on Mars was underway. By the early 1900's, Lowell's books, which included "Mars and its Canals" and "Mars as the Abode of Life" had popularized his theories about massive canals created by sentient Martians. Unfortunately, so far as we can tell, Schiaparelli and Lowell and others were probably mapping the reflections of their own retinas in the telescopic eyepieces. Here is ercival Lowell's 1905 map of Mars, crisscrossed by the many canals he thought he saw.
In 1965, NASA's Jet Propulsion Laboratory, in conjunction with the California Institute of Technology (both in Pasadena, CA), flew the first successful probe past Mars. In a single moment, Lowell's empire was smashed into dust- literally. Mars was a cold, dry dust-bowl. While most in astronomical circles had long abandoned notions of life, intelligent or otherwise, a few die-hards conjectured that at the very least vast plant growths might exist. But the 22 grainy, low-resolution images sent back by Mariner 4 as it whizzed past Mars told another story: the planet was a cold, dry, almost airless desert, scarred by countless craters. It was a dead world very much like our own moon. While scientists cheered the romantics wept. Mars, as a living world, was gone. The 22 images returned from Mariner 4's low-resolution TV camera showed a far different Mars than had been hoped for by the romantics: a cold, dry and dead world.
Mariners 6 and 7 were flyby missions like Mariner 4, and Mariners 8 and 9 were to orbit the planet. Mariner 8 suffered a malfunction shortly after launch, but Mariner 9 proceeded as planned and made a brilliant rendezvous with Mars in November of 1971. What greeted it was, however, not as ideal: Mars was covered in an opaque global sandstorm. Mariner waited almost three months for the dust to settle, but the results were well worth it. In about year of operations it imaged the entire planet and sent back dazzling images of huge volcanoes, immense canyons and- perhaps most importantly- features that were clearly formed by flowing water. Mars was not so dead as it had appeared. Mariner 9 returned stunning, and provocative, images of Mars. This area, known as <em>Noctis Labyrinthis</em>, shows what are clearly some complex interactions between soil, wind and- to everyone's surprise - water.
America was on a roll. NASA has succeeded in reaching the moon, and Mariner 9 had been a boon to the Mars program. Now it was time for the next big step: landing on Mars. In this case, the Soviet Union, long a challenger in space exploration, had reached Mars first with their Mars 3 lander, but it failed upon reaching the surface. The Viking lander was a far more ambitious affair, with a long sampling arm, stereo cameras and a mini life-science lab onboard. Two Viking landers reached mars in 1976, and two orbiters circled the planet. The mission was an unqualified success. Hundreds of thousands of images were returned, the soil was intensively studied and weather and Martian seismology were both recorded. The largest question of all, however, remained open, as the life science results were confusing and inconclusive. Nonetheless, for the next twenty years, Viking stood tall as NASA's most successful robotic exploration of Mars. This spectacular view of <em>Chryse Planitia, </em>or the Golden Plain, was returned from the Viking 1 lander, partially seen in the foreground. The round object at top center is the radio dish for communicating with Earth. The Viking 1 lander was the most long-lived of the program, operating on the surface for almost 6-and-a-half years.
The surface of Mars was undisturbed by foreign machines until the Mars Pathfinder spacecraft reached it on July 4, 1997. Twenty years had passed, and this lander, though small and inexpensive as such things go, carried with it huge expectations. The tiny craft plummeted into the Martian atmosphere and landed with a unique arrangement of inflated bags (looking much like a cluster of beachballs) which cushioned the blow. A day later the tiny rover Sojourner, the first to successfully reach Mars, began its explorations. Though it never traveled more than 35 feet from the lander, Sojourner returned over 550 images and investigated numerous rocks with a small spectrometer attached to a robotic arm. For the first time, planetary scientists knew the basic recipe of Martian rocks, and the stage was set for more ambitious explorations to come. The tiny Mars Pathfinder rover, Sojourner, is seen "sniffing" a rock not far from its landing site. The rover was smaller than a microwave oven but an immense success. Active for almost three months, Pathfinder set the stage for the far more ambitious Mars Exploration Rovers.
Since the Viking orbiters there had been a paucity of good imagery coming back from Mars. JPL's Mars Observer had been sent off in 1992 but failed shortly before arrival at the Red Planet. As a result the stakes were high when the Mars Global Surveyor spacecraft braked into Martian orbit in 1996. But the concerns were for naught. Despite a few tense moments when a strut holding a solar panel jammed, the craft sailed into Martian orbit and operated flawlessly for almost a decade. It was one for the record books, and returned stunning high-resolution images of the surface below, slowly revealing some of Mars' many secrets... including the biggest one of all, where all the water was hiding. The Mars Global Surveyor captured thousands of spectacular images, this picture of <em>Sirenum Terra</em>, among them. In addition to the photo, MGS found long swaths of magnetic terrain, evidence of plate tectonics very early in Martian history. The channels on the slope of the hill also strongly suggested a one-time presence of flowing water.
JPL did not rest on its laurels after the success of Mars Global Surveyor. The MGS mission spawned as many questions as it answered, and higher-quality instrumentation around Mars was called for. The Mars Odyssey mission answered that need. A modestly budgeted mission, M.O. entered Martian orbit in late 2001. Pursuing JPL's mantra of "follow the water," M.O. used its new and highly sensitive instrumentation to do just that, by measuring chemical and mineralogical compositions across the Martian globe. The Mars Odyssey orbiter made high-resolution measurements that allowed NASA's powerful computers to create unparalleled ground-level images. This image is of <em>Candor Chasma</em>, a huge canyon associated with the hemisphere-girdling <em>Valles Marineris</em> feature. Mars Odyssey is now officially the longest-operating spacecraft orbiting Mars with a lifespan of over ten years.
Over the years the Soviet Union endeavored to match US accomplishments in space. They lost the moon, and they lost Mars (not one of their Mars missions succeeded fully). But the European Space Administration, or ESA, partnered with Russia in 2003 to finally send a non-American spacecraft to Mars, and it was a marvel. Mars Express (which also carried the British lander Beagle, which failed) arrived at Mars in late December 2003 after departing Earth on a Russian rocket. It continues to collect data from the Red Planet and has made numerous discoveries. Besides further confirmation that copious amounts of water are locked up in ice all over the planet, Mars Express noted one more thing, something potentially wonderful. It sensed methane in the atmosphere, more than had any right to be there, since the gas is rapidly removed via natural processes. Is its replenishment a result of metabolization by Martian life forms? The answer awaits future missions. This Mars Express shows an area known as <em>Echus Chasma.</em> Despite the impact crater nearby, it is thought that this may have been formed by what would have been one of the largest water sources on Mars.
Following the brilliant, but short lived, success of Mars Pathfinder, the Mars exploration Rovers were of a similar though greatly evolved design. Launched as a pair, as NASA's Mars missions historically were in the 1960's/1970's, the two spacecraft arrived at Mars in 2004, in the same fashion as Pathfinder- bouncing to their destinations. The first to arrive, Spirit, had a shorter lifespan due to the fact that it was operating in a less welcoming environment and developed drive-motor problems. It eventually ended its life stuck in ruddy sand after just over six years of operation. The second rover, Opportunity, has had a better run of luck and after nine cold, dusty years continues to operate. Between the two they explored countless geological formations, discovered the now-famous "blueberries" (hematite spherules indicative of a watery past) and helped to identify the history of water flow- and disappearance- on Mars. This image of the Mars Exploration Rover Opportunity is an artist's rendition, using a real surface photo and a computer-generated rover. Still, it is an accurate representation of the terrain which the rovers traversed during their years-long careers and also shows a scattering of the "blueberries" they discovered.
After four decades of viewing Mars in slowly-increasing detail, it was time for a quantum-leap in fidelity and definition. The Mars Reconnaissance Orbiter was created to fill that need. With a record-holding radio dish measuring nearly ten feet across, the spacecraft arrived in the vicinity of Mars in 2006. Since then, this one machine has sent back more data than all previous planetary missions combined (not just Mars missions)- and that's a lot of data. The camera aboard MRO can discern items less than three feet wide and is far, far more powerful than previous imagers. And the other instruments on the spacecraft are similarly powerful. MRO has found new, huge deposits of frozen water ice, spotted other NASA spacecraft either already on Mars, of in the case of Phoenix, during its landing phase, and even tracked the progress of the Mars rovers. As spring approaches the northern latitudes of Mars, much of the carbon dioxide ice begins to vaporize. When this occurs, some of the rocks and dirt being supported by the ice can start moving. This appeared to be the case here as the MRO spacecraft photographed a Martian avalanche in progress.
The polar regions of Mars had long been of interest to planetary scientists, as it was thought that water might reside on or near the surface as ice. In 1999, the Mars Polar Lander crashed attempting to land near the north pole of that planet. This failure occurred around the same time that the Mars Climate Orbiter also crashed into Mars. Understandably, NASA was a bit gun-shy about another polar landing attempt. But bolstered by the immense successes of the MER and MRO programs, the decision was made to try for the pole again. This mission was chosen with great care to be safe, foolproof and inexpensive, and it was called, appropriately, Mars Phoenix. It was a marvel of economy: built from recycled spacecraft parts, using repurposed software and operating out of the University of Arizona (with grad students filling many key roles). Mars Phoenix landed in the northern polar regions of Mars in 2008. It's primary mission: to investigate the ice near the poles for water content. And despite some false starts, in this it was successful. During the 155-day mission, water, albeit in frozen form, was detected first-hand on Mars. A NASA artist's concept of Mars Phoenix in operation near the end of its service life. The mission was by design a short one; few thought the craft could possibly survive the severe Martian polar winter. But during its 4-month mission, Mars Phoenix made many discoveries and observations. Paramount among them was the confirmation that water ice does exist on the surface near the Martian poles.
2012 is the benchmark year, the Big Event. No, we're not talking about the Mayan calendar, but the landing of NASA/JPL's next big thing, the Mars Science Laboratory rover, named Curiosity. Bigger, heavier, and far more capable than any which have gone before, Curiosity will touch down inside Gale Crater on August 5th. The one-ton machine is the size of a Mini Cooper, capable of overcoming yard-high obstacles and has a nuclear power plant good for many years of full-time operations. Its ability to analyze rocks, search for water (past and present) and even perform limited searches for life on Mars is unprecedented. But to do all these, it must first land. Because of its weight, it cannot bounce to the surface as the MER and Pathfinder rovers did, but instead uses a complex system called "Skycrane," which combines supersonically-deployed parachutes, rocket motors, and a multiple-cable winching system to lower Curiosity to the ground from a hovering rocket-pack. Engineers have, with good reason, termed this portion of the flight "seven minutes of terror." But if all goes well, by late on the evening of August 5th, JPL (Pacific) time, there will be a new face on Mars... one that could change everything. Stay tuned. This artist's concept of the upcoming Mars Science Laboratory rover, named Curiosity, shows just one of its advanced technologies in use. Instead of having to drive up and sample every desired rock with its manipulator arm and drill, it can fire a powerful laser and analyze the burnt gases with a spectrometer from a distance.