An international team of researchers, led by Dr. Gunther Korschinek from the Technical University of Munich, has detected radioactive iron-60 in samples of lunar soil returned to Earth by the Apollo astronauts.
This is a mosaic image, one of the largest ever taken by Hubble of the Crab Nebula, a 6-light-year-wide expanding remnant of a star’s supernova explosion. Japanese and Chinese astronomers recorded this violent event nearly 1,000 years ago in 1054, as did, almost certainly, Native Americans. Image credit: NASA / ESA / J. Hester / A. Loll, Arizona State University.
“The radioactive iron-60 isotope is created almost exclusively in supernova explosions,” Dr. Korschinek explained.
“And with a half-life of 2.62 million years, relatively short compared to the age of our Solar System, any radioactive iron-60 originating from the time of the Solar System’s birth should have long ago decayed into stable elements and thus should no longer be found on the Earth.”
Earlier this year, a team of scientists led by Dr. Anton Wallner of the Australian National University found radioactive iron-60 in sediment and crust samples from the Pacific, Atlantic and Indian Oceans, tracing its source to supernovae occurring about 325 light-years from Earth.
In a study published in the journal Physical Review Letters, Dr. Korschinek and co-authors report on the detection of iron-60 in lunar samples.
The samples were gathered between 1969 and 1972 during Apollo lunar missions 12, 15 and 16, which brought the lunar material back to Earth.
“We assume that iron-60 found in both terrestrial and lunar samples has the same source,” Dr. Korschinek said.
“These deposits are newly created stellar matter, produced in one or more supernovae.”
Since the Moon generally provides a better cosmic record than the Earth, the team was also able to specify for the first time an upper limit for the flow of iron-60 that must have reached the Moon.
Among other things this also makes it possible for scientists to infer the distance to the supernova event.
“The measured iron-60 flow corresponds to a supernova at a distance of about 300 light-years,” Dr. Korschinek said.
“This value is in good agreement with recent theoretical estimations.”
_____
L. Fimiani et al. 2016. Interstellar Fe60 on the Surface of the Moon. Phys. Rev. Lett. 116, 151104; doi: 10.1103/PhysRevLett.116.151104
