The conclusion that the rocks of Meridiani Planum, where Opportunity landed on January 25, were once underwater follows three weeks of meticulous experiments. “We’ve been attacking it with every piece of our hardware and the puzzle pieces have been falling into place,” Dr Squyres said.
Four separate pieces of evidence have combined to build a compelling picture. The alpha particle X-ray spectrometer has found high concentrations of sulphate salts, which have to be dissolved in water to accumulate. The Mossbauer spectrometer has also found a mineral called jarosite, which is formed in the presence of water.
Physical features of the rock have provided important clues. Round particles known as “spherules”, which Dr Squyres likened to “blueberries in a muffin”, appear to have been formed by dissolved minerals. Holes known as “vugs” have been left by crystals of salt, laid down in briny water.
Some of the key discoveries came from analysis of a rock nicknamed El Capitan, after a rock formation in Yosemite National Park in California.
“Put the story together, and it is hard to avoid the conclusion that this stuff was deposited in liquid water,” Dr Squyres said.
Ed Weiler, NASA’s associate administrator for space science, said, “Opportunity has landed in an area of Mars where liquid water once drenched the surface. This area would have been a good, habitable environment.”
Scientists will have to wait, however, to find out whether this environment actually supported life. Neither Opportunity nor her sister rover, Spirit, carries the instruments needed to search for traces of living organisms. Britain’s Beagle 2 Mars probe, which was lost last year, did carry two experiments that would have been able to detect life.
The old theory about Canals on Mars was based on an optical illusion. Mark Henderson reported:
The question of whether water and life ever existed on Mars dates from the 17th century, when the Dutch astronomer Christiaan Huygens first identified light patches at the poles that appeared to be ice caps.
The notion, however, did not capture the public imagination until the 1890s, with the publication of three books by the American Percival Lowell.
Inspired by the work of the Italian astronomer Giovanni Schiaparelli, who in 1877 had seen a criss-cross network of straight channels, or canali, on the Martian surface, Lowell built an observatory in Flagstaff, Arizona, from which to examine the planet more closely.
Having mistranslated canali as “canals”, Lowell concluded that the lines were evidence of a vast irrigation system built by an intelligent civilization. By 1910, his theory was complete: Mars was drying out and dying through lack of water, accounting for its red hue and necessitating the irrigations.
The hypothesis eventually foundered on the discovery that Schiaparelli’s canali did not exist: they were optical illusions produced by the telescopes of the period. But the idea that Mars could be wet and inhabited stuck, inspiring hundreds of science fiction novels and films.
In the 1960s and 1970s, a series of Martian flypasts by NASA’s Mariner Spacecraft dispelled any possibility that Mars was at all Earth-like, showing that carbon dioxide, rather than water and oxygen, was the main component of its atmosphere and ice caps. The Viking landings of 1976went further, finding no conclusive evidence of either water or life, although some investigators still contend that the results of one of the spacecraft’s experiments turned up positive for the existence of micro-organisms.
The result was a 20-year hiatus in Mars exploration as space scientists, largely convinced that the planet was barren, turned their attention and dollars elsewhere.
All that changed, however, on August 6, 1996, with the discovery of the Martian meteorite ALH84001, which contained mineral deposits that some scientists interpreted as fossilised microbes.
Interest in Mars was revived overnight.
Martian space race
On 5 February 2004 The Times Science Correspondent reported:
Europe intends to go head-to-head with the United States in a race to bring a piece of Mars back to Earth in the next chapter of the search for life on the Red Planet.
A European mission to scoop up half a kilogram of Martian rocks and carry them home for analysis will blast off in 2011, European Space Agency (ESA) officials announced yesterday.
The project, which will involve British companies and scientists, is the most ambitious element of the ESA’s Aurora programme, a “road map” for exploring Mars that aims to land European astronauts on the planet by 2033. It will also put the agency in direct competition with NASA, which is planning its own sample return mission at the same time.
The Aurora programme is offering the first serious challenge to the US lead in civilian space flight since the Soviet successes of the 1950s and 1960s. While the two space agencies prefer to be seen as partners rather than adversaries, their increasing emphasis on Mars exploration – as shown by President Bush’s recent pledge of a manned mission to the planet – is inevitably lending an edge of rivalry to their efforts.
As the orbits of Earth and Mars make missions practical only every two years or so, each forthcoming “window” will see a flotilla of similar European and American craft being launched for the Red Planet. Last year the ESA’s Mars Express and Beagle 2 probes blasted off just a couple of weeks before NASA’s Spirit and Opportunity rovers and such races will soon become commonplace.
In 2007 NASA is sending a lander named Phoenix and the ESA is considering a plan to refly Beagle 2, possibly as a pack of four or five landers to ensure maximum chances of success.
Two years afterwards, both agencies want to send large rover missions to the planet – NASA’s Mars Science Laboratory and the ESA’s ExoMars which would seek signs of life and test for hazards to future human pioneers.
The agencies are following identical timetables for sample return: in 2011, a “return vehicle” would be launched and parked in orbit around Mars waiting for a second mission in 2014. This would land on the planet, then blast off into orbit to dock with the waiting orbiter and return home.
Both agencies see manned missions to the Moon as essential precursors to sending astronauts to Mars: the ESA envisages a human Moon mission in about 2024 while NASA wants to establish a permanent lunar base at the same time. The earliest likely date for a manned mission to Mars is 2030. The European “road map” was presented by Franco Ongaro, the Aurora mission’s project manager at a London conference held to consider Britain’s contribution.
The Government is likely to support the project, even though it does not yet back manned spaceflight. Aurora is structured to allow countries to opt in for five years at a time, so Britain would be able to drop out when the manned phase begins. The initial five year budget has been set at €900 million (£615 million) and British scientists want the Government to contribute £30 million a year. It spends about £180 million annually on civilian space exploration.
Dr Ongaro played down the notion that the ESA and NASA were embarking on a fresh space race, but insisted that Europe was just as well placed as the US to lead worthwhile missions to Mars.
He said that the Aurora budget was comparable to NASA’s expenditure on long-term Mars exploration and that both would have to overcome similar technical challenges. “Neither us nor the Americans know at the moment how a mission to the Moon or to Mars can be done,” he said. “For the next five years both NASA and ourselves are going to be working on exactly the same thing: how to do it. We intend to have a programme of the same type and scale as theirs.”