Astronomy Now Home
Home Magazine Sky Chart Resources Store

On Sale Now!

The August 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). The Astronomy Now iPad/iPhone editions are now available worldwide on the App Store.

Top Stories

Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...

Ice found at Moon’s
north pole

Posted: 3 March 2010

Bookmark and Share

Radar data analysed from India’s Chandrayaan-1 spacecraft reveals ice deposits in craters dotted around the Moon’s north pole that could contain as much as 600 million tons of ice.

NASA's Mini-SAR instrument detected more than 40 small craters containing water ice. The craters range in size from 2 to 15 kilometres in diameter and lie in permanent shadow, preventing the ice from evaporating into space. Although the Moon is drier than any desert on Earth, the north polar craters could contain as much as 600 million tons of ice.

Craters showing normal radar reflection patterns are circled in red. Those circled in green are in permanent shadow and likely harbour large reservoirs of frozen water ice. Image: NASA.

Mini-SAR uses the polarization properties of reflected radio waves to characterise surface properties. The instrument sends out pulses that are left-circular polarized; typical planetary surfaces reverse the polarization so that “normal” echoes are right-circular polarized. The ratio of received power in the same sense transmitted (left circular) to the opposite sense (right circular) is called the circular polarization ratio (CPR). Most of the Moon has a low CPR, but regions displaying high CPR values include rough terrain associated with ejected material from fresh craters. Ice, although transparent to radio energy scatters the pulses, thus giving an enhancement in same sense – left circular – reflections and an elevated CPR value.

Many craters have high CPR values inside and outside of their crater rims, which is typical of the rough surfaces associated with relatively fresh, young craters. But a number of the north polar craters corresponding to sites of permanent shadow have high CPR values inside their rims but not outside. In these cases, the high CPR value cannot be associated with surface roughness and must be caused by a material that is restricted to the interiors of the basin.

"After analysing the data, our science team determined a strong indication of water ice, a finding which will give future missions a new target to further explore and exploit," says Jason Crusan, program executive for the Mini-RF Program for NASA's Space Operations Mission Directorate. The science team estimate that, depending on the size of the crater, the ice deposits could be several metres thick.

A faint plume of ejecta containing water vapour was created as the LCROSS probe impacted a lunar south pole crater last year. Image: NASA.

The water inventory at the north pole is derived from two processes: by delivery from comet impacts billions of years ago, and through a recently confirmed process that suggests water molecules are being produced all over the Moon's surface every day. During the daytime the solar wind, which includes hydrogen ions, interacts with oxygen in the lunar soil to form and accumulate hydroxyl and water molecules. Water is lost at noon when it is hotter, but when it cools down in the evening it can accumulate water again, and over time the water molecules naturally migrate to the poles. Confirmation of this process came from three different missions: Chandrayaan-1, Deep Impact and Cassini, and was announced six months ago.

Around the same time NASA's Lunar Reconnaissance Orbiter (LRO) also found evidence for widespread hydrogen all over the Moon, and not just at permanently shadowed polar locations. Then, the Lunar Crater Observation and Sensing Satellite (LCROSS) that plummeted into a south pole lunar crater in October, threw up a plume of debris that contained the signature of water.

"The emerging picture from the multiple measurements and resulting data of the instruments on lunar missions indicates that water creation, migration, deposition and retention are occurring on the Moon," says Paul Spudis, principal investigator of the Mini-SAR experiment. "The new discoveries show the Moon is an even more interesting and attractive scientific, exploration and operational destination than people had previously thought."

Related Stories

20 Oct 09: LCROSS captures all phases of Centaur impact

15 Oct 09: The water-generating Moon

09 Oct 09: LCROSS mission concludes but science continues

24 Sept 09: Scientists announce evidence of water on Moon

18 Sept 09: LRO hints at water on Moon

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


© 2014 Pole Star Publications Ltd.