So far, NASA has identified several possible locations. Other than Mars, where the curved nature of some of the rock formations clearly points to the process of water erosion in the past, the agency also thinks that there are liquid oceans under a layer of ice on Europa, one of Jupiter’s satellites. And on spacecraft flybys of Enceladus, one of Saturn’s moons, scientists have witnessed colossal geysers spewing water out into the atmosphere.
“If we find life on other planets, that could give us an indication as to whether our kind of life is common — is everything based on DNA and carbon?” Elachi says. “Other kinds of life might be based on a different kind of structure. So that would give us insight into our own biological evolution.
“And then beyond our solar system the key objective is to find out whether life on other planets exists,” he adds. “One the one hand you would say, of course, since there are so many stars and the laws of physics and chemistry are just the same. And therefore planets should exist that are similar to our planet.”
Right now, Curiosity is searching out suitable locations to drill for more samples at a site called Yellowknife Bay. And after that, it will take on its primary target, an attempt to climb up Mount Sharp, or Aeolis Mons — no mean feat, considering that the mountain is not that much shorter than Kilimanjaro. But Elachi and the JPL team are already hard at work preparing for new missions. In 2020, NASA is planning to send another rover to Mars to capitalise on Curiosity’s success, and perhaps store samples so that they can be returned to Earth in future.
The big question, of course, is that of manned missions. Although there isn’t a specific programme for sending humans to Mars, tentative plans are being outlined. Given that the best window for a mission, or when the planets are closest together, is every eighteen years, the next target date is obvious.
“We are thinking that by about 2036 we will probably send a human,” says Elachi. “That is a big challenge, because it takes nine months to get there and nine months to get back. Just imagine you are sending three or four people for eight months, think how much food, garbage and water they will require, and so on. So it’s a big engineering challenge, but it’s feasible.”
When it comes to human exploration further afield, however, Elachi says that the restraints of modern technology are such that manned missions will have to wait.
“Anything in our solar system you can get to,” he says. “When we look at neighbouring stars, what we will be able to do with our telescopes in future is to take images of planets around them, and by taking those pictures we will be able to determine if they actually have an atmosphere — whether that might be oxygen or methane, for example — and what sort of temperatures are there.
“Actual travel, I would say, is unlikely in the near future unless there is a major breakthrough in technology, and that would take many, many years,” he adds. “In this business, you have to be patient.”
That’s not to say that JPL is not working hard to change all that. According to Elachi, the current method of powering spacecraft, chemical propulsion, has just about reached its limit. Instead, the agency is testing electric propulsion — which involves taking gases like xenon, ionizing them, and then placing them in an electric field, allowing atoms to move at extremely high speeds — on a spacecraft called Dawn’s mission to the asteroid Vesta and the dwarf planet Ceres. Other methods that are being explored include solar sails, which have been tested by the Russians and the Japanese, as well as NASA.