A supernova sprayed the Earth and Moon with a radioactive isotope of iron sometime in the last couple million years. The authors conclude that the supernova was only about 300 light years away! Unfortunately I can’t find the full article (without paying for it) so I don’t know how they arrived at that surprising conclusion.
Update: aha, I found a good paper (http://arxiv.org/pdf/1604.00958.pdf) that details how to determine distance for the radioactive iron reaching the Earth. It’s hard to understand, but I think they are combining 1) the amount of Fe^60 discovered on the Earth, and 2) a calculation of how the material dissipates as it reaches the Earth. This yields a “fluence” value (a new term to me) which is the amount of iron atoms per square centimeter arriving at the planet. Then, they compare to some supernova models that predict an amount of Fe^60 emitted from the explosion and use inverse square law to derive a distance.
If that understanding is correct, then that technique sure seems like it could have a lot of systematic errors in it, especially in the assumption of Fe^60 production of the supernova. But it’s not my specialty so who am I to question?
Originally shared by Ciro Villa
Fantastic find! Scientists discover evidence of the presence of Interstellar Iron Isotope 60 (60Fe) on the Moon’s surface, this is Supernovae material!
“Approximately two million years ago a star exploded in a supernova close to our solar system: Its traces can still be found today in the form of an iron isotope found on the ocean floor. Now scientists at the Technical University of Munich (TUM), together with colleagues from the US, have found increased concentrations of this supernova-iron in lunar samples as well. They believe both discoveries to originate from the same stellar explosion.
A dying star ends its life in a cataclysmic explosion, shooting the majority of the star’s material, primarily new chemical elements created during the explosion, out into space.
One or more such supernovae appear to have occurred close to our solar system approximately two million years ago. Evidence of the fact has been found on the earth in the form of increased concentrations of the iron isotope 60Fe detected in Pacific ocean deep-sea crusts and in ocean-floor sediment samples.
This evidence is highly compelling: The radioactive 60Fe isotope is created almost exclusively in supernova explosions. And with a half-life of 2.62 million years, relatively short compared to the age of our solar system, any radioactive 60Fe 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.”
Read more at: http://phys.org/news/2016-04-supernova-iron-moon.html
The study: L. Fimiani et al. Interstellar on the Surface of the Moon , Physical Review Letters (2016). http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.151104
Image: This is a composite image of the lunar nearside taken by the Lunar Reconnaissance Orbiter in June 2009, note the presence of dark areas of maria on this side of the moon. Credit: NASA
#space #astronomy #moon #supernova