Scientists have made a startling discovery while exploring the ocean floor that could change how we understand supernovae. Researchers now believe that exploding stars, often far beyond the confines of our solar system, have deposited extraterrestrial dust at the bottom of the oceans, and that could give us better insights into the composition of far off galaxies.
Researchers have now analyzed these dusts thought to be from supernovae to determine the amount of heavy elements created by this massive explosions.
"Small amounts of debris from these distant explosions fall on the earth as it travels through the galaxy," lead researcher of the study from the Research School of Physics and Engineering at The Australian National University (ANU), Anton Wallner says. "We've analysed 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."
These findings differ from current theories of supernovae, in which some of the materials essential for human life, such as iron, potassium, and iodine are created and distributed throughout space. Supernovae also create other elements such as lead, silver, gold, and heavier radioactive elements like uranium and plutonium.
Wallner's team studied plutonium-244, which serves as a radioactive clock by the nature of its radioactive decay, with a half-life of 81 million years.
"Any plutonium-244 that existed when the earth formed from intergalactic gas and dust over four billion years ago has long since decayed," Wallner says. "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."
The team analyzed a 10 centimeter sample of the Earth's crust, which represented 25 million years of accretion. In addition, they researchers examined deep-sea sediments collected from a stable area at the bottom of the Pacific Ocean.
"We found 100 times less plutonium-244 than we expected," Wallner says. "It seems that these heaviest elements may not be formed in standard supernovae after all. It may require rarer and more explosive events such as the merging of two neutron stars to make them."
Wallner believes that the fact that elements such as plutonium were present, and uranium and thorium are still here on Earth, that an explosive event must have happened close to the Earth around the time it formed.
"Radioactive elements in our planet such as uranium and thorium provide much of the heat that drives continental movement, perhaps other planets don't have the same heat engine inside them."
