There are a small number of isotopes that offer clues regarding ancient supernova that helped form the Earth and the rest of the Solar System . Of these , the one astronomers and wandering scientist turn to most often is iron-60 , so what create it so useful ?
Most of the component that make up the Earth are form in ruinous explosions , eithersupernovae or kilonovae . ground on this fact alone we know that at least one , and probably several , such explosions occur somewhere in our part of the galaxy before the Sun formed .
These explosions dispersed elements into the cloud of gas from which the Solar System condensed . Although the vast majority of that swarm was atomic number 1 and helium , various processes led to those two elements beingrare on Earth , while concentrating most of the others .
The origins of iron
These initial elements consisted of a commixture of unchanging andradioactive isotopes . In the case of smoothing iron , for example , the Earth inherited a great deal of iron-56 ( that is atoms with 26 protons and 30 neutrons ) . Much smaller amounts of iron-54 and 57 ( still with 26 proton , or it would n’t be iron , but 28 and 31 neutron ) and a tiny amount of iron-58 were also present . All of these are not radioactive , so the Earth has as much today as it ever did , allowing for some deliveries from meteorite .
However , the supernovae that seed the cloud from which we take shape would also have make some iron-55 , 59 , and 60 , all of which are radioactive . However , these isotopes took a very different path .
Iron-59 has ahalf - lifeof 44.6 days . A year after the explosion in which these atoms were take form , less than 1 percentage survived . If any make it the journey from the set off star to the Sun ’s protoplanetary disc , it was gone by the time there was an real planet . Iron-55 has a half - living of 2.7 years , but that ’s still far too curt for perceptible quantities to be left from before the Earth ’s organization , or even from nearby explosions that have go on since .
Why Iron-60 is special
However , iron-60 is a unlike matter . Its half - life is 2.6 million years – long enough to create a persistent bequest , but forgetful enough that we can differentiate it from isotope that last forever . We can even discover the presence of iron-60 after it is gone . Beta decomposition turns iron-60 to cobalt-60 , which then turns relatively quick into nickel-60 . The distribution of iron-60 in the early Solar System has been investigated by looking for the abundance of nickel-60 .
Meanwhile , sea sediments give away several spikes in iron-60 over the last few tens of jillion of years . The Earth has no way of make this isotope ( at least until humans built nuclear reactors ) , nor a process for concentrating it . Instead , these increases argue something off - satellite must have showered Earth with iron-60 atoms . The same process would have also spray plenty of other isotopes over us .
However , as with the iron associated with Earth ’s organisation , those isotopes with substantially shorter half - life are long snuff it . Those that are stable are so abundant on the major planet already that a little extra from blank space is not obtrusive .
We have even confirmed the extraterrestrial nature of these iron-60 spikes by finding matching oneson the Moon .
However , while we may have a universal idea that upsurges in iron-60 occurred3.4 - 1.7 millionand8 millionyears ago , identify the source is trickier . Supernovae are suppose to be the most rough-cut source of iron-60 , butkilonovaecan bring forth batch as well . The distance of time of the most recent iron-60 spike has been assign by some uranologist to two supernovae happening close enough together in clock time that their height overlap , but by others toa kilonova instead . Telling the difference is not gentle .
There ’s even a third selection , albeit an unlikely one . So - called asymptotic giant subdivision ( AGB ) stars can make many of the threatening element once thought to be the preserve of exploding stars alone . They not only make a flock of iron-60 , but shedit into space , along with aluminum-26 .
As far as we know , AGB champion do n’t disperse these element anything like as widely as supernovae . Nevertheless , a stuffy confrontation with an AGB star could produce a ear in copiousness , although the chances of such a close encounter late are considered small .
A further inquiry is whether all this iron-60 matters . Although it is radioactive , iron-60 decay so tardily that it is quite secure in the volumes detected . However , the observed spike coincide withperiods of planetary cooling system . The iron-60 itself would not be responsible for for that , but it is potential , although still very speculative , that follow cosmic ray from the same explosion could have sparked increase cloud concealment thataffected the spheric mood .
