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Eugene N. Parker predicted the existence of solar wind in 1958. The NASA spacecraft is the first named for a living person.
I LOVE space documentaries!!
After years of tantalising hints, scientists have finally found direct evidence of water ice tucked away at the bottom of craters near the moon's poles.
"A long time ago people thought 'Oh, we've solved this problem', but not many people realise we do not have any definitive evidence," said Shuai Li, a planetary scientist at the University of Hawaii.
His team's findings, published today in the Proceedings of the National Academy of Sciences, boosts the moon's potential as a habitable destination and stepping stone for future space missions.
Back in the early 1960s, scientists proposed that water ice could exist in permanently shaded parts of bodies such as the moon, Mercury and the dwarf planet Ceres.
In the past decade, hydrogen-rich areas have been detected at the poles by NASA's Lunar Reconnaissance Orbiter (LRO) and the Indian spacecraft Chandrayaan-1.
Hydrogen is a fundamental component of water — so evidence of hydrogen has been interpreted to indicate the presence of water near the poles. But that data can be misleading, Dr Li said.
"It could be hydrogen, it could be hydroxl, it could be water, or could be anything else with hydrogen. The data can not distinguish which is which," he said.
Hydrogen is also a component of the solar wind — a constant stream of high energy particles from the sun that whips across the surface of the moon.
To pin down the source of the hydrogen, Dr Li and his colleagues analysed data from the Moon Mineralogy Mapper on the Chandrayaan-1 spacecraft, which measures the wavelength of molecules reflecting off the surface.
"Ice is very unique on the lunar surface," Dr Li said.
"As it goes to longer wavelengths the reflections are lower. This is opposite to the lunar surface material."
Craig O'Neill, a planetary scientist at Macquarie University, said the data provided definitive evidence of water ice.
"I buy this evidence more or less on face value," said Dr O'Neill, who was not involved in the research.
"While most people had assumed what we were seeing was water on the moon, or certainly supporting evidence for water on the moon, this is really a smoking gun."
The data shows tiny patches of exposed ice water at the bottom of a small number of craters on both the north and south poles.
"The reason we see more on the south is the south pole has more cold spots than the north pole," Dr Li said.
Here in the darkest and coldest parts of the moon, temperatures can plummet to minus 238 degrees Celsius — the coldest in the solar system.
But this pattern is very different to ice deposits at the poles of Mercury and Ceres, both of which also experience freezing temperatures at the poles.
"On Mercury and Ceres it's a continuous, large area of ice, but on the moon it's just spots like salt and pepper," Dr Li said.
The moon formed as a hot, molten chunk of rock jettisoned from Earth following an impact with another large body around 4.5 billion years ago.
Unlike Mercury or Ceres, the moon's orbit only stabilised in the past 2-3 billion years, said Dr O'Neill.
"It would mean that the water we're seeing here wasn't delivered to the moon 4 billion years ago, really early in its history.
"It's probably been delivered over time by cometary impacts, and only been able to survive in those south pole craters since they've actually been in the shade."
The rate of cometary impacts also dropped significantly around the 2-3 billion-year mark.
But the meteorites that did continue to rain on the surface could have ploughed up the shaded areas throwing water vapour into the air.
Dr Li and his colleagues propose this process — known as impact gardening — may explain why the ice cover is patchy.
"A vapour plume could be either lost into space or can condense back to the surface," Dr Li explained.
Once considered a dry, hostile place, confirmation that there is water ice on the moon's surface makes it a favourable place for space exploration, Dr O'Neill said.
"What that means for us from an engineering point of view, and a practical point of view we know now the moon definitely has these resources.
"We actually have water there, so we don't have to bring it with us, which cuts down launch costs immensely.
"It makes the moon a lot more feasible in terms of human colonisation or just using it as a mission base for the rest of the solar system as well."
Dr Li said their research provided a clear map of where to find water ice in the polar regions.
But for now, he said, we still have a large knowledge gap about these dark, freezing regions.
"We've been studying the moon since before the Apollo era ... but we've barely touched the polar parts of the moon," he said.
"In the future, I think it's worth sending a mission that focuses on the polar regions to look at those dark regions to see what's going on there."
The only mission to come close in the near future will be the Korean Pathfinder Orbiter.
Due to launch in 2020, it will be kitted out with a NASA-built camera known as ShadowCam.
The camera is designed to peer inside permanently shaded craters near the poles, but its cameras will not operate at wavelengths to detect water ice, Dr Li said.
I wonder if this is the morality cell...