Geoscientist Online

It’s more Camembert than Wensleydale. The moon appears to have a runny liquid centre. Harriet Jarlett reports.

Geoscientist Online 19 January 2011

Modern computing and analytical techniques have been used to squeeze the last rops of interpretation from data gathered 40 years ago by Apollo astronauts. Researchers say it bolsters the lately rather shaky-looking “Giant Impact Theory”, which holds that the Moon formed in a collision between the early Earth and another body – and was not captured by the Earth’s gravitational field.

In the final Apollo mission, Harrison Schmitt (the first (and so far the only) geologist to go to the moon), collected a pristine and beautiful moon rock sample, Troctolite 7653. Analysis of this sample in 1999 showed evidence of magnetic alignment, and the possibility of a liquid Moon core and magnetic dynamo. It can now be compared with seismic signals collected between 1962 -1977 after Apollo 17 deployed four seismometers onto the lunar surface. However, the rarity of Moonquakes meant data was sparse, while the cracked and broken surface meant signals were masked by noise. Computers of the seventies were as a result unable to decode the signals they received.

Today’s advanced equipment, and new analytical techniques, mean this data can now be reanalysed. Dr Renee Weber, a NASA scientist, used array processing as well as applying a stacking sequence to the 40 year-old data to remove the noise and pick out the strongest signals from 38 deep moonquakes. They found the Moon has a solid inner, iron-rich core 240km in diameter, and a liquid iron outer core, which is still fluid after 4.5 billion years. However our satellite also contains a partially melted section that our own planet is missing, comprising large lumps of solid rock and magma.

Weber understands this new discovery is an integral piece in the jigsaw of lunar origin, "if we have any hope of determining once and for all how the moon formed then we need to understand its structure completely." This new insight proves that the internal moon structure is more Earthlike than previously appreciated, and that the moon originally had a magnetic field of its own. Out of four current hypotheses of Moon creation, this new evidence gives more support to the GIT, which holds that a Mars-sized object collided with the early Earth .

Reference

• Renee C. Weber, Pei-Ying Lin, Edward J. Garnero, Quentin Williams, and Philippe Lognonne Science 1199375Published online 6 January 2011 [DOI:10.1126/science.1199375]