Extraterrestrial dust on the deep ocean floors of Earth could significantly change our present understanding of cosmic supernovae, researchers say in the report of a new study.
The scientists have analyzed dust from exploding stars from far outside our solar system, which has traveled through space to be deposited on Earth.
"Small amounts of debris from these distant explosions fall on the earth as it travels through the galaxy," says lead researcher Anton Wallner of the Research School of Physics and Engineering at the Australian National University.
The researchers looked at the dust to determine the amount of heavy elements believed to be created by the massive cosmic explosions, but what they found was at odds with current supernova theory, they said.
"We've analyzed galactic dust from the last 25 million years that has settled on the ocean and found there is much less of the heavy elements such as plutonium and uranium than we expected," Wallner says.
Current theory holds that materials that are essential for human life, such as iron, iodine and potassium, are created by supernovae and spread through space.
They also create heavy radioactive elements like uranium and plutonium, as well as gold, silver and lead.
The researchers analyzed samples of sea bottom representing 25 million years of sediment accretion.
They looked for plutonium-244, which can be used as a radioactive clock by the known nature of its decay, which gives a half-life of 81 million years.
Any plutonium present when the earth first formed would have long since decayed, "So any plutonium-244 that we find on earth must have been created in explosive events that have occurred more recently, in the last few hundred million years," Wallner says.
What the researcher found -- or more to the point, what they didn't find -- surprised them.
"We found 100 times less plutonium-244 than we expected," Wallner says.
That suggests the formation process for the heaviest elements in a supernova is something different that current astrophysical theory posits, the researchers say, since the levels found in the oceans is less than expected even though it is known there have been supernova exploding in our cosmic neighborhood.
"It seems that these heaviest elements may not be formed in standard supernovae after all," Wallner says. "It may require rarer and more explosive events such as the merging of two neutron stars to make them."
The study has been published in Nature Communications.
