Rocky planets like Earth may be much more common in the Universe than previously thought. An international group of scientists came to this conclusion. According to new data, the formation of dry, rocky planets may be a natural consequence of supernova explosions near young star systems. The work was published in the journal Science Advances.
It is believed that Earth and other terrestrial planets were formed from so-called planetesimals – objects composed of a mixture of ice and rock. For future planets to become “dry” and rocky, they will have to lose a significant portion of their water very early on. An important role in this process is played by the heating caused by the decay of short-lived radioactive isotopes, especially aluminum-26. Its presence in the early solar system was confirmed by analysis of ancient meteorites.
Until now, scientists assumed that such isotopes entered the protoplanetary disk only from a nearby supernova. However, the calculations showed a contradiction: to provide the necessary amount of radioactive material, the explosion must have occurred too close and simply destroyed the disk where the planets were formed.
Researchers led by Ryo Sawada from the University of Tokyo have proposed a new explanation – the so-called “soaking mechanism”. According to the model, the supernova exploded at a safe distance of about 3.2 light-years from the young Solar System. The shock wave accelerates the charged particles, turning them into a stream of cosmic rays.
Radioactive elements, as calculations have shown, entered the protoplanetary disk in two ways. Some isotopes, such as iron-60, are introduced directly as dust. The remainder, including aluminum-26, is formed inside the disk when cosmic rays collide with stable atoms and cause nuclear reactions. Taken together, this mechanism accurately reproduces the composition of radioactive elements present in meteorites.
According to the authors, such a situation can occur quite often. They estimate that about 10 to 50 percent of stars similar to the Sun could form in environments with similar levels of radioactive isotopes. This means that dry, rocky planets with limited water – potentially habitable – could be common in our galaxy.
