New Delhi, Sept. 24: A guest instrument on the Chandrayaan-1 spacecraft detected signatures of water molecules on the moon, resolving a four-decades-old mystery, several months before the premature end of India’s first lunar mission.

The discovery, made earlier this year but announced today by American and Indian scientists, has altered existing ideas of a bone dry moon and kindled fresh hopes that humans might some day be able to harvest water from the lunar soil.

The Nasa instrument, the Moon Mineralogy Mapper (M3), developed by Brown University and the Jet Propulsion Laboratory in the US, observed characteristic signatures of water molecules in sunlight reflected from the lunar surface. M3 was among six foreign lunar observation payloads that piggybacked on Chandrayaan-1, which carried four Indian-made instruments.

Two other Nasa spacecraft — Cassini and Deep Impact — have corroborated the findings made by M3 through an analysis of archived data and fresh observations of the lunar surface in June this year. The results from all three missions will appear in the journal Science on Friday.

The studies indicate that the water molecules are present in tiny quantities in the top few millimetres of soil and rocks on the lunar surface. “We haven’t found water either in its liquid or ice form. We have detected only water molecules in extremely minute quantities in surface soil,” an Isro scientist said.

The mission scientists estimate that about 1,000kg of soil will yield about a litre of water. “This is fantastic. We’ve found something we never thought we would see,” said Lawrence Taylor, director of the Planetary Geosciences Institute at the University of Tennessee and member of the M3 team, who has studied hundreds of moon rocks brought back by the Apollo missions from 1969 to 1972.

Traces of water found in one set of the Apollo boxes were, Taylor said, attributed to contamination from Earth because the seals on the boxes had been broken. The alleged absence of water on the moon had remained an enduring mystery. “This is like finding a renewable resource on the moon,” Taylor told The Telegraph.

The observations suggest that the solar wind — a stream of electrons and hydrogen ions ejected from the surface of the sun — helps produce water on the moon daily.

The entire lunar surface is hydrated during at least some parts of the lunar day, according to a team led by Jessica Sunshine, senior scientist at the University of Maryland, who is a member of the M3 and Deep Impact missions. Nasa’s Deep Impact is on a mission to explore comets.

But scientists believe the intense solar heat also destroys the water molecules. “The concept is — the solar wind from the sun creates the molecules and the heat from the sun destroys them,” said Jitendra Goswami, director of India’s Physical Research Laboratory, who, along with S. Kumar from the National Remote Sensing Agency, had helped interpret some of the M3 data.

Isro’s Chandrayaan-1 spacecraft, launched in October 2008, had experienced instrument failures earlier this year, leading to loss of communication with the spacecraft and prompting the agency to end the mission in August.

The M3 results are among the most significant to emerge from the mission, but scientists have said data from its other instruments continue to be analysed.There has been no direct observation of water on the moon so far.

But a team at Brown University in the US had in July last year reported indirect evidence for water in the interior of the moon by examining pebble-like glasses returned to the Earth by the Apollo missions.

Scientists say future research would be aimed at trying to understand better the water formation process and to determine whether the water molecules can accumulate near the poles where it is colder than at lower latitudes.

“Harvesting water from the moon could significantly reduce the costs of long-term human activities on the moon. It takes $50,000 to carry a litre of water to the moon on a rocket,” Taylor said.

The action of the solar wind appears to be dominant in the mornings and evenings, said Tony Farnham, an astronomer at the University of Maryland who is a member of team that observed the moon using Deep Impact. “The heat from the sun either destroys the water molecules or ejects them into space from where they may fall back. The molecules that fall near the poles are more likely to survive and accumulate,” Farnham told The Telegraph.