What The Oceans Do For Us

Deep sea sediments gives insight into plutonium-244 origin

We can learn a lot about the history of our planet from ocean exploration.  As it turns out, we can also learn about processes beyond our solar system.  Supernova (star) explosions are large, violent processes.  Current theory suggest that supernovae distribute elements essential to life, such as potassium and iron, and heavy elements, such as the radioactive element plutonium-244, throughout space, with some eventually settling on the sea floor.  However, research recently published in Nature Communications suggests that recent heavy element production may not originate from standard supernovae.

Dr Anton Wallner, senior fellow at the Research School of Physics and Engineering, Australian National University  and researchers analysed 25 million years of accretion from deep sea sediments collected from a stable area of the Pacific Ocean and 10 centimetre-thick samples of the Earth’s crust.  Plutonium-244 does not occur naturally on Earth.  With a half-life of 81 million years, any plutonium-244 discovered on Earth now must have been created within the last few hundred million years.  The team discovered far less plutonium-244 than they would expect if it was, as current theory suggests, produced from standard supernovae.  This suggests that over the past few hundred million years, plutonium-244 production comes from rarer events, such as the merging of two neutron stars.

The paper is open access so if you fancy a read you can access it here http://dx.doi.org/10.1038/ncomms6956

Image: NASA/ESA/JHU/R.Sankrit & W.Blair.
“X-ray, Optical & Infrared Composite of Kepler’s Supernova Remnant “On October 9, 1604, sky watchers — including astronomer Johannes Kepler, spotted a “new star” in the western sky, rivalling the brilliance of nearby planets.  “Kepler’s supernova” was the last exploding supernova seen in our Milky Way galaxy. Observers used only their eyes to study it, because the telescope had not yet been invented. Now, astronomers have utilized NASA’s three Great Observatories to analyze the supernova remnant in infrared, optical and X-ray light.” [1] Colour Code (Energy): Blue: X-ray (4-6 keV), Chandra X-ray Observatory, The higher-energy X-rays come primarily from the regions directly behind the shock front. Green: X-ray (0.3-1.4 keV), Chandra X-ray Observatory; Lower-energy X-rays mark the location of the hot remains of the exploded star. Yellow: Optical, Hubble Space Telescope; The optical image reveals 10,000 degrees Celsius gas where the supernova shock wave is slamming into the densest regions of surrounding gas. Red: Infrared, Spitzer space telescope; the infrared image highlights microscopic dust particles swept up and heated by the supernova shock wave.”

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