Shrinking moon may explain lunar quakes

The moon has shrunk in the past billion years, and may still be shrinking today, triggering moonquakes and making the moon a more active body than previously thought.

The shrinkage has wrinkled parts of the moon's surface like a raisin, creating pinched formations called lobate scarps.

Apollo astronauts imaged some of these wrinkles near the moon's equator 40 years ago. Now, new images from NASA's Lunar Reconnaissance Orbiter (LRO) have revealed 14 more. Some of these lie near the poles, showing that the scarps occur all over the moon's surface.

Thomas Watters of the Smithsonian Institution in Washington, DC, and colleagues say the wrinkles likely formed as the moon cooled and contracted.

The features are surprisingly recent, having formed no more than 1 billion years ago. That estimate is based on the fact that they partly destroyed some pre-existing small craters that seem to be no more than 1 billion years old. "The moon may still be geologically and tectonically active and still shrinking today," Watters said in a teleconference with reporters on Thursday.

Growing pains

If so, the wrinkles might still be growing, and the contraction might have triggered some of the moonquakes recorded by seismometers placed on the moon in the 1970s by NASA astronauts, he said.

He and his colleagues are planning to see if the wrinkles have grown in the past few decades by comparing LRO images with those taken by Apollo astronauts.

The team calculates that the moon's diameter has shrunk by just 200 metres in the last billion years, suggesting the amount of recent cooling has been relatively small, he says. Mercury also has wrinkles, but they are "humungous", suggesting it has experienced much more cooling in its lifetime than the moon, he said.

The moon's rate of cooling is affected by its interior structure and composition, so the new data might teach us something about the moon's innards, said Patrick McGovern of the Lunar and Planetary Institute in Houston, Texas, who was not involved in the study.

Journal reference: Science, DOI: 10.1126/science.1189590

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The Earth and Moon formed later than previously thought

The Earth and Moon were created as the result of a giant collision between two planets the size of Mars and Venus. Until now it was thought to have happened when the solar system was 30 million years old or approx. 4,537 million years ago. But new research from the Niels Bohr Institute shows that the Earth and Moon must have formed much later – perhaps up to 150 million years after the formation of the solar system. The research results have been published in the scientific journal, Earth and Planetary Science Letters.

"We have determined the ages of the Earth and the Moon using tungsten isotopes, which can reveal whether the iron cores and their stone surfaces have been mixed together during the collision”, explains Tais W. Dahl, who did the research as his thesis project in geophysics at the Niels Bohr Institute at the University of Copenhagen in collaboration with professor David J. Stevenson from the California Institute of Technology (Caltech).

Turbulent collisions



The planets in the solar system were created by collisions between small dwarf planets orbiting the newborn sun. In the collisions the small planets melted together and formed larger and larger planets. The Earth and Moon are the result of a gigantic collision between two planets the size of Mars and Venus. The two planets collided at a time when both had a core of metal (iron) and a surrounding mantle of silicates (rock). But when did it happen and how did it happen? The collision took place in less than 24 hours and the temperature of the Earth was so high (7000º C), that both rock and metal must have melted in the turbulent collision. But were the stone mass and iron mass also mixed together?

Until recently it was believed that the rock and iron mixed completely during the planet formation and so the conclusion was that the Moon was formed when the solar system was 30 million years old or approximately 4,537 million years ago. But new research shows something completely different.

Dating with radioactive elements

The age of the Earth and Moon can be dated by examining the presence of certain elements in the Earth’s mantle. Hafnium-182 is a radioactive substance, which decays and is converted into the isotope tungsten-182. The two elements have markedly different chemical properties and while the tungsten isotopes prefer to bond with metal, hafnium prefers to bond to silicates, i.e. rock.

It takes 50-60 million years for all hafnium to decay and be converted into tungsten, and during the Moon forming collision nearly all the metal sank into the Earth’s core. But did all the tungsten go into the core?

"We have studied to what degree metal and rock mix together during the planet forming collisions. Using dynamic model calculations of the turbulent mixing of the liquid rock and iron masses we have found that tungsten isotopes from the Earth’s early formation remain in the rocky mantle”, explains Tais W. Dahl, Niels Bohr Institute at the University of Copenhagen.

The new studies imply that the moon forming collision occurred after all of the hafnium had decayed completely into tungsten.

"Our results show that metal core and rock are unable to emulsify in these collisions between planets that are greater than 10 kilometres in diameter and therefore that most of the Earth’s iron core (80-99 %) did not remove tungsten from the rocky material in the mantle during formation", explains Tais W. Dahl.

The result of the research means that the Earth and the Moon must have been formed much later than previously thought – that is to say not 30 million years after the formation of the solar system 4,567 million years ago but perhaps up to 150 million years after the formation of the solar system.

Source <http://insciences.org>

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LCROSS Impact Data Indicates Water on Moon

The argument that the moon is a dry, desolate place no longer holds water.

Secrets the moon has been holding, for perhaps billions of years, are now being revealed to the delight of scientists and space enthusiasts alike.

NASA today opened a new chapter in our understanding of the moon. Preliminary data from the Lunar CRater Observation and Sensing Satellite, or LCROSS, indicates that the mission successfully uncovered water during the Oct. 9, 2009 impacts into the permanently shadowed region of Cabeus cater near the moon’s south pole.

The impact created by the LCROSS Centaur upper stage rocket created a two-part plume of material from the bottom of the crater. The first part was a high angle plume of vapor and fine dust and the second a lower angle ejecta curtain of heavier material. This material has not seen sunlight in billions of years.

"We're unlocking the mysteries of our nearest neighbor and by extension the solar system. It turns out the moon harbors many secrets, and LCROSS has added a new layer to our understanding," said Michael Wargo, chief lunar scientist at NASA Headquarters in Washington.

Scientists have long speculated about the source of vast quantities of hydrogen that have been observed at the lunar poles. The LCROSS findings are shedding new light on the question of water, which could be more widespread and in greater quantity than previously suspected.

Full story here

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Golden spacecrafts landed on the Moon?

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