September Sky Notes
Written by John Stapleton
Image Credit: A Collins (TAS Member)
Water, water everywhere! Nor yet a drop to drink!
The recent successful landing on the Moon by the Indian Chandrayaan probe is the latest in the search for water on the moon. This water is believed to be contained in ice sheltered in the deeper, darker craters at the lunar poles, particularly the South Pole. This search has been going on for some 70 years ever since researchers at Caltech in the USA suggested that deep, shadow-filled craters may contain ice in 1961. Trace amounts of water were found in some rock samples brought back from the Moon by Apollo astronauts, but these were put down to the almost inevitable contamination on the journey to Earth.
Soviet scientists working with samples returned by the Luna 24 probe in 1976 claimed that they had definitively found water at about 0.1% by mass (10 times the expected value but still minuscule.
In 1994 the U.S. Military probe “Clementine” orbited the poles of the Moon with some of the most sophisticated camera and detection equipment available at the time. It revealed radio echoes consistent with an icy, rather than a rocky surface in certain areas of the Moon’s South Pole. However these results were inconclusive and have been discredited.
The Lunar Prospector probe launched in 1998 examined both Lunar poles for concentrations of Hydrogen (one of the constituent elements of water) and found it abundant to 50 parts per million, but this could equally be due to the Hydroxyl radical (OH) which is chemically bound to other atoms to form the rocky compounds in the Lunar surface. Based on these observations NASA scientists calculated that, if water is present, it could amount to 1-3 cubic kilometres. At the end of its mission Lunar Prospector was deliberately crashed into the Shoemaker Crater at the Lunar South Pole in the hope that detectable quantities of water would be liberated. Earth based observers detected no water at all.
NASA’s Cassini-Huygens and Deep Impact missions made fly-by studies of the Lunar poles on their way to Saturn and Comet Tempel-Tuttle respectively, but only succeeded in producing more conflicting and confusing results.
Japan’s Kaguya lunar mapping probe failed to detect any water on the Moon but made the first detailed optical observations of the permanently shadowed Shackleton crater, a favourite site for the possible Lunar ice to exist. China’s Chang’e took the first detailed photographs of these areas of the Moon. Both of these missions took place in 2007.
In 2008, India’s Chandrayaan 1 detected water in the thin atmosphere above the Lunar South Pole in 650 mass spectra readings. This thin atmosphere had first been detected by Kaguya which showed that it was created when Oxygen from the Earth’s atmosphere was transported to the Moon via magnetospheric ions (ions travelling along magnetic field lines between the Earth and the Moon).
The Pragyan Rover aboard the Chandrayaan mission will look for further evidence of water during the month that it is expected to operate on the Moon. There is still a long way to go to confirm the existence of readily available water at the Lunar poles. The importance of these explorations is paramount, as water on the Moon would mean that gallons of the life-preserving liquid would not have to be carried aboard manned spacecraft destined for the Moon and the possibility of maintaining a permanent Lunar Base would become more realistic.