12 February 2019
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Simulations show how planetary systems born in massive star formation regions makes them much drier. Image: Roger Thibaut
Without these radioactive elements, Earth could have become an uninhabitable ocean world covered in ice
A new simulation suggests that radioactive elements injected by a massive star into the early Solar System may have helped create the solid surface and moderate climate on Earth.
In the absence of these radioactive elements, Earth could have turned into an uninhabitable ocean world covered in global ice sheets, the scientists behind the simulation suggest.
The new study was carried out by Tim Lichtenberg, a postdoctoral fellow at the University of Oxford, along with peers from the universities of Bern, Bayreuth, and Michigan. The researchers created new computer models to simulate how small planetesimals merge to form large planets.
Planetesimals are said to be the building blocks of planets. These rocky-icy bodies are formed in a disk of gas and dust around the young star, and could be dozens of kilometres in size.
In their work, the scientists simulated the formation of thousands of planets. They also investigated what kind of planets will be formed from different planetesimals and how much water content they are likely to have.
The results indicated the existence of two different types of planetary systems. The first type is similar to our solar system, where planets have little water content. Such systems are created in the presence of a massive star around them.
The second type includes those systems where planets are primarily ocean worlds. Such systems typically form in the absence of a massive star around them.
According to the researchers, when the Solar System was taking shape, a supernova (the death of a massive star) occurred nearby, which injected radioactive elements, including Aluminium-26 (Al-26), into the nascent Solar System. The heat generated by these radionuclide rapidly dehydrated the planetesimals before their accretion onto larger protoplanets. This possibly helped form an Earth with much less water content.
According to the scientists, significantly greater water content on Earth would have prevented geochemical processes, such as the carbon cycle on Earth, that help stabilise the climate on the planet and create surface conditions conducive to life.
While these results might help solve some mysteries, they also raise other questions.
"It is great to know that radioactive elements can help make a wet system drier and to have an explanation as to why planets within the same system would share similar properties," says University of Michigan astronomer Michael Meyer.
"But radioactive heating may not be enough. How can we explain our Earth, which is very dry, indeed, compared to planets formed in our models? Perhaps having Jupiter where it is was also important in keeping most icy bodies out of the inner solar system."
The researchers believe the new results could help future space telescopes to improve the predicted implications of the Al-26 dehydration mechanism.
The findings of the study are published in the journal Nature Astronomy.
