Deposits of radioactive isotopes of iron were examined in two new studies to learn more about what happens when a supernova explodes near our planet.

When a star is moving toward the end of its life, it will turn into a supernova and in that moment, various types of materials will spread into space. If this stellar explosion occurs close enough, radioactive debris can reach Earth.

These residues can give us clues about the part of the cosmos in which we find ourselves. Thus, two research teams studied the deposits of the radioactive isotope iron-60, which can be called cosmic bread crumbs.

One team built a model with the data obtained in order to figure out where and when two supernovae took place. The aim of this study is to manage to unravel the mysteries of the Local Bubble, a mass of hot gas that enshrouds our solar system.

This mass of hot gas was discovered several decades ago, but what caused its appearance has remained a mystery for a long time. Scientists have speculated that a supernova produced this big bubble of gas.

Astrophysicist Dieter Breitschwerdt from the Berlin Institute of Technology, led the research team who identified two supernova that could contribute to the gas bubble. One occurred 1.5 million years ago and the other 2.3 million years ago.

They were part of a cluster of stars that passed by Earth at a distance of 300 light years, when the two stars identified in the study exploded.

The team led by Dr. Breitschwerdt modeled the trajectory of the cluster to see if it’s direction matches the moment when deposits of iron-60 were created on Earth. They then confronted the results with the data they had from the Local Bubble. After going back in time and observing the trajectory of the cluster of stars, they observed that the data was a match.

If the phenomenon had occurred closer to Earth, the effects could have been devastating for the planet, even leading to mass extinctions. But if it happened further away, the amounts of iron-60 would have been much lower. Thus, the path of the cluster fits very well with the available data.

Iron-60 is not found naturally on Earth, and this means that it came from elsewhere. Some meteorites that hit Earth can contain small amounts of iron-60, but a supernova is a larger source, according to Dr. Wallner.

After analyzing over 100 samples from the ocean floor, researchers have found evidence of a another supernova, that happened between 6.5 and 8 million years ago.

The impact of a supernova on Earth

Now, what impact could a supernova have on our planet? Besides the fact that it led to the creation of the Local Bubble, a supernova can affect the normal functioning of Earth, depending on how close it occurs.

There is a range of action of a supernova: 30 light years. If our planet is under this range, then it will be bombarded by radiation so powerful that it can destroy the ozone layer, and nothing would stop radiation from reaching the planet’s surface. Thus, a mass extinction is virtually inevitable.

But if it’s further than 300 light years, this does not mean that it will have no impact. When a star explodes, the particles could contribute to creating cloud formations that could lead to the cooling of the planet, perhaps even starting an ice age. Perhaps the most recent supernova identified in these studies contributed to the most recent ice age that occurred on Earth.

Should we expect a catastrophe in the near future?

There are always supernovas happening and in our corner of the universe, one might take place one to three times within one billion years, says Dr. Gehrels. Dr. Wallner adds that “there are no candidates for stars which could have a serious impact.” 

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