How the search for water in space can help to find and preserve the water on Earth
20 March 2000
ESA scientists at the UNESCO forum in The Hague: 'Water, a fragile gift fromStars to planets'The water that we drink and that fills the world's oceans comes from thestars, as the detection of huge amounts of water in many regions of theuniverse by ESA's infrared space telescope, ISO, has recently proved.This fact opened the one-day session on 'Water and Space' organised byESA and UNESCO at a World Water Forum being held in The Hague (NL).Scientists reviewed latest results on the search for water in the Moon and long-standing problems such as what is the precise origin of the water on Earth. Water-related technologies being developed for planetary exploration were also found to be very useful on Earth: for instance machines to extract water directly from minerals and radars to detect underground water at a depth of several kilometres. Participants asked the space agencies to make satellite images of the Earth freely available on the Internet.
UNESCO has declared Wednesday 22 March as 'World Water Day'.The Earth is presently the only 'wet' planet in the Solar System, and that is, after all, the reason why we humans are not Martians - liquid water is considered essential for life. But the blue planet owes its colour to a pure astronomical chance: had the Earth been slightly closer to the Sun it would be like Venus; had it been slightly farther away, it would probably be as dry as Mars is today. This is, scientists say, a sign of the fragility of the system, and also a 'warning': Mars and Venus could reflect the future of our planet.
"Water is a gift from the stars. We have been very lucky, but we must be careful if we don't want to make our planet uninhabitable. Both Mars and Venus had plenty of water in the past. Venus became too hot due to an extreme green-house effect, and water evaporated. We are following the same path by raising the emissions of green-house effect gasses", explained Marcello Coradini, ESA's coordinator on Solar System exploration and chairman of the session at the UNESCO forum.
The wealth of water on Earth is also the source of many questions. For instance, where does it come from? The ultimate answer is that it comes from the stars. Oxygen is produced in the stars' cores and then released into the stars' environment, where it combines with hydrogen under the appropriate conditions, for example during the violent stages of starbirth, when the star spews out gas at high speed and generates a shock wave that heats and compresses the hydrogen and oxygen present in the environment. Water has been detected by ESA's infrared space telescope ISO in many regions: around new-born and dying stars, in the space amid the stars, towards the centre of our galaxy and even in other galaxies, as well as in our own solar system - in the upper atmosphere of the giants planets and Saturn's moon Titan, in the Martian atmosphere and in comets.
"In the Orion nebula, where many new stars are being born, ISO detected enough water to fill the Earth's oceans 60 times a day", said Alberto Salama, an ESA astronomer on the ISO team. "ISO has allowed us to prove that there's a true 'cycle' of water in the universe".
The origin of the ocean's water
It is clear then that water was present in the cloud of material out of which the Solar System formed about five thousand million years ago. But is that the same water we find in the oceans today? And, if so, how exactly did it arrive on the planet? To find out, scientists turn to the other 'watery bodies' of the Solar System: the comets. Current theories suggest that water on Earth was also brought by icy comets that bombed our planet in the past, but astronomers still lack the data to prove this. They need to study the precise chemical composition of the water in comets and compare it with that of the oceans. More precisely, they will measure the relative amount of a form of hydrogen, the 'heavy hydrogen' or deuterium, as compared to the most common form of this element.
"Comets are made of the same material as the Sun and the planets. Logic says that the deuterium/hydrogen ratio should be the same for the Sun, for the comets and for the planets. If there's a different ratio in the planets, we have to find an external phenomena that has modified the ratio. And external could also mean extrasolar origin, a source different from the comets", explained Gerhard Schewhm, project scientist for ESA's Rosetta mission.
Rosetta will probably solve this problem very soon, by becoming the first spacecraft that lands on a comet. In 2003 Rosetta will be launched to Rosetta encounter (in 2011) comet Wirtanen - a small comet about 1.5 kilometres in diameter, orbit very close to its surface for almost two years and finally land on the icy traveller and drill its surface. The data Rosetta will gather about chemical composition will help to write the past history not only of the Earth, but of the whole Solar System.
Water in the Moon... and how to use it
Although the existence of water-ice in the Moon has not been proved yet, scientists and engineers are already thinking seriously about how to use it. Space Agencies have established an International Lunar Exploration Working Group (ILEWG) to coordinate the current and next missions to the moon... and also to discuss far-future 'science fiction' scenarios:
"There are proposals for landers to try to measure the depth and composition of the ices in the craters close to the south pole of the Moon. And people are already thinking about Lunar 'robotic villages' to be used for lunar exploration and utilisation. One may develop 'gas stations' where future spacecraft could take on supplies of fuel (the detected hydrogen in the Moon and abundant oxygen) or water.These stations could even be placed in a precise point between the Moon and the Earth. Considering that putting just one kilogram into a Low Earth Orbit costs 10 000 Euros, all these ideas would lower considerably the cost of future human expansion projects in the solar system, and even of space tourism, for instance", says ESA's Bernard Foing, chairman of the ILEWG and project scientist for the first ESA mission to the Moon, SMART-1.
The 'water-on-the-Moon' story was revived back in 1995 with a confirmation of shadowed polar areas and radar tentative detection by the US DoD spacecraft Clementine. In 1998 another NASA spacecraft, Lunar Prospector, again announced indirect evidence of the presence of water-ice in the Moon. Prospector had detected high levels of hydrogen in shadowed craters near the Moon's south and north poles, and that hydrogen, mission scientists said, could be forming water ice. It was in fact estimated that up to six billion metric tonnes of water ice could be buried in the craters. But an attempt to find direct evidence of water by 'crashing' the Lunar Prospector spacecraft into a crater near the south pole of the Moon, last July, produced no observable signature of water.
"The issue is open. Recent analyses of the Lunar Prospector data fully confirm the presence of high amounts of hydrogen in the poles", says Foing. "Now we have to find out whether the hydrogen is forming water-ice or if it's mixed in the soil. My bet is that it will be probably in both forms".
But according to the scientists the detection of the excess of hydrogen is already good news, since it could be artificially combined with oxygen to produce water. Oxygen represents about 45% of the Lunar surface, although it is of course combined with other elements. But devices to extract water from minerals are already being developed.
ESA's mission SMART-1, to be launched in 2002, will be the next step in the exploration of the Moon. Although it is mostly a technology mission - to develop more efficient space electric propulsion systems and new instruments - SMART-1 will carry a very sensitive spectrometer to clarify once and for all what's inside the shadowed craters in Moon.
Spin-off of space water-related technology
"Space agencies should be more active in bringing their spin-off technology to the public", said Coradini in The Hague. "Sessions like this help us to be aware of the needs of society". He was replying to questions from the public: if machines to extract water from solid minerals are already being developed for planetary exploration, could they be used on Earth? "Indeed", Coradini said. "When the machine is ready you could use it in the middle of the desert. There's a prototype already".
Another likely example of useful space technology is the radar being developed for the next ESA mission to Mars, Mars Express, aimed at the search for underground water. Its on-board radar will be able to detect water kilometres below the surface. Scientists say that, if used on Earth, it could 'see' even deeper.
Participants at the ESA/UNESCO session raised the issues of free availability of satellite images of the Earth, a useful resource for the search of water in our planet. Although ESA already guarantees some access to these resources for developing countries, researchers and universities still have to pay.
The ESA/UNESCO session at the World Water Conference also covered anthropological link between water and space. Italian anthropologist Paola Antolini gave a wonderful lecture about how the people from the desert learnt to build and preserve oases. "Their technologies come from the past, but they might also be useful for future planetary exploration. The Earth is, after all, our oasis in the cosmos", said architect Pietro Laureano, from the Italian Research Centre for Local and Traditional Knowledge.
