New detections of iron-60 in marine sediments suggest that our planet has been traveling for 33,000 years through a cloud of gas and dust from the explosion of a supernova.
As the Earth revolves around the Sun, our Solar System also drifts through the Milky Way, rotating once every 225 to 250 million years. Obviously, the same goes for the hundreds of billions of other stars that make up the Milky Way.
That said, our galaxy experiences an explosion of stars every fifty years or so. Given its immense size (about 150,000 light-years in diameter), the likelihood of one of these stars exploding in our backyard is very low. A supernova is roughly estimated to occur once every few million years less than 400 light-years from the Sun.
Statistically speaking, during its 4.5 billion year old history , so Earth has "flirted" with several supernovas.
These events then shaped the galactic landscape traversed by our planet. Indeed, if the "interstellar void" appears invisible to us , it actually consists of gas and dust whose particles are incredibly diffuse .
Despite everything, we can measure the density variation of these particles in the interstellar medium. Basically, just take two stars that are supposed to have similar luminosity. If one of them appears darker than the other, then we can deduce that it is seen through a thicker veil of dust gas which absorbs some of its light. This event is called "dust extinguishing “.
By observing the stars closest to Earth, astronomers have seen many of these "dust extinctions". By squaring them, we can then trace the boundaries of a huge cloud of gas and dust slightly denser than the local interstellar medium (0.3 versus 0.05 atoms per cubic centimeter) measuring about thirty light years wide by forty light-years long . And surprise:we are inside.
Several million years ago, ancient bacteria evolving in the ocean floor indeed collected iron particles which they transformed and used to align themselves with the field terrestrial magnetic. Some of these microorganisms then fell on iron 60 , a radioactive isotope of iron created in supernovae.
Thanks to the analysis of the fossilized remains of these bacteria, we know that some used iron 60 about 6 million years ago , then between 1.7 and 3.3 million years . This therefore demonstrates that the Earth was "dusted" with supernova remnants at those times.
In fact, it still seems to be the case today. Indeed, physicists from the Australian National University have recently isolated a few atoms of this isotope of iron deposited in marine sediments for about 33,000 years . Last year, a study published also found the presence of iron-60 in the snows of Antarctica. And this isotope, one could read, would have landed on Earth during the last twenty years .
In other words, for at least 33,000 years, it would seem that our planet has been traveling through the "ashes" of a supernova.
The origin of this debris is not entirely clear, but it could come from a group of stars called the Scorpio-Centaurus Association (Sco-Cen) , positioned 400 light-years from Earth. Their largest representatives are class O and B stars. Much more massive than the Sun, these objects have a very short lifespan (only a few million years) before exploding as a supernova.
We also know from the European Space Agency (ESA), which in 1997 published one of the first comprehensive catalogs of positions and motions of stars in our galaxy, that our system was closer to Sco-Cen 5 to 7 million years ago . Thus, we could imagine that several supernovae in this group of stars are the origin of the interstellar clouds that regularly envelop us.
