Speaker
Description
As our Earth moves through space, it traps particles originating from
within our Solar System and from the surrounding interstellar medium.
Each year, about 30.000 tons of interplanetary dust accumulate on Earth. A
large fraction can be found as micrometeorites on the Earth's surface -
submillimetre-sized particles liberated from larger bodies such as
asteroids and comets. Additionally, interstellar dust signatures from
supernovae were observed in deep-sea archives, indicating recent nearby
stellar explosions.
We analysed sediment samples from a depth of 4200 m below the sea surface
originating from the Indian Ocean for their $^{60}$Fe content. This long-lived
radionuclide, with a half-life of 2.6 million years, is produced and
ejected by exploding stars. Using accelerator mass spectrometry (AMS) at
ANU, Canberra, we detected an excess of $^{60}$Fe corresponding to a time
period of 2-3 million years ago. Dating of the samples was achieved with
AMS measurements (HZDR, Dresden, and VERA, Vienna) of cosmogenic $^{10}$Be and
$^{26}$Al - both are long-lived radionuclides produced in the Earth's
atmosphere.
Micrometeorites contribute to a continuous extraterrestrial influx of
$^{10}$Be, $^{26}$Al, and possibly $^{60}$Fe. These cosmogenic radionuclides accumulate
within the microparticles as they are irradiated by cosmic rays in space.
Measuring the concentrations of $^{10}$Be, $^{26}$Al, and $^{60}$Fe within a single
micrometeorite yields information on its cosmic ray exposure duration and
its origin within our Solar System.
