Huge simulations find some “completely unexpected” results

Galaxy M51

Galaxy M51 is a spiral galaxy, some 30 million light-years away, that is in the process of merging with a smaller galaxy seen in its upper left corner. Credit: X-ray: NASA / CXC / SAO; Optician: Detlef Hartmann; Infrared: NASA / JPL-Caltech

Researchers have discovered that rocky exoplanets that formed early in the life of the galaxy appear to have had a greater chance of developing a plate tectonic and magnetic field than planets that formed later. Since both conditions are considered favorable for the development of life, this means that if life exists in the Galaxy, it could have developed sooner rather than later, and that more recently formed planets may have less chance of developing life.

As chief scientist, planetary researcher Craig O’Neill said: “Plate tectonics is important for habitability, and it seems that the optimal conditions for plate tectonics existed for planets that formed early in the galaxy’s lifespan. , and is unlikely to be easily repeated. For a lifetime, maybe that was as good as it sounds. “

Exoplanets, planets in orbit around distant stars, have been attracting great interest due to the possibility that some of them may harbor life. In presenting the results at the Goldschmidt Geochemistry Conference, Professor Craig O’Neill (Director of the Macquarie Planetary Research Center, Macquarie University) continued:

“Due to the large distances involved, we have a limited amount of information about these exoplanets, but we can understand some factors, such as the position, temperature, and some insight into the geochemistry of the exoplanets. This allows us to model how they develop. “

Using huge simulations involving hundreds of processors in Australia’s National Computing Infrastructure, the team ran the parameters through the ASPECT geodynamic code, which simulates the development of the planets’ interior. O’Neill’s group was able to demonstrate that many of the early planets tended to develop plate tectonics, which is conducive to the development of life.

He commented: “Plate tectonics acts as a kind of thermostat for Earth, creating the conditions that allow life to evolve. Earth has a lot of iron at its core, and we assumed that this would be necessary for tectonic development. However, we found that even low iron planets can develop plate tectonics if the timing is right. This was completely unexpected. “

The development of plate tectonics has an important side effect. “The planets that formed later may not have developed plate tectonics, which means they don’t have this thermostat built in. This not only affects the surface temperature, but means that the core stays warm, inhibiting the development of a magnetic field. If there is no magnetic field, the planet is not protected from solar radiation and will tend to lose its atmosphere. Then life becomes difficult to sustain. A planet must be lucky to have the right position and the right geochemistry at the right time if it is to sustain life, “said Professor O’Neill.

The researchers know that the overall chemical balance of the galaxy has changed over time for various reasons, such as material that fuses into stars and planetary bodies, or that is ejected through a supernova. This means that the interstellar material available to form planets is significantly different from that available in the early galaxy.

“So the planets that formed earlier did so under favorable conditions to allow the development of life,” said Craig O’Neill. “These conditions are increasingly rare in our galaxy.”

Commenting, Professor Sara Russell said:

“In recent years, incredible projects like POT The Kepler mission has located thousands of planets orbiting other stars. However, these exoplanet Observations alone provide very basic information. It is so important to combine observation campaigns with large simulation projects like this that they really tell us something about the geological evolution of planets formed at different stages of galactic evolution. This allows us to build an image of what these strange worlds might be like and how habitable they can be. ”

Sara Russell is a member of the Scientific Committee of the Geochemical Society. She is a professor of Planetary Sciences and leader of the Planetary Materials Group at the Natural History Museum, London. She was not involved in this work, this is an independent comment.

As of June 5, 2020, NASA has confirmed the detection of 4,158 exoplanets in our galaxy. The closest exoplanets that have been found orbit the star Proxima Centuri, which is about 4 light-years from Earth (the most recent data indicates 2 or 3 exoplanets).

The Goldschmidt conference is the world’s leading geochemistry conference, organized by the Geochemical Society and the European Geochemical Association. It is conducted annually and covers materials such as climate change, astrobiology, planetary and stellar development and conditions, the chemistry of Earth’s materials, pollution, the underwater environment, volcanoes, and many other topics.