Surprising discovery about Earth-like planets

19 June 2012

Earth-like planets are much more common in our galaxy than has previously been assumed. New research shows that such planets can form around all types of star, not only around certain stars with a high proportion of heavy elements. The results have been published in the journal Nature. One of the authors of the article is Anders Johansen, a researcher in astronomy at Lund University, Sweden.

Since the mid-1990s researchers have discovered more and more planets outside our own solar system, known as exoplanets. There are two categories of planet in space, terrestrial planets like Earth and gas giants like Jupiter. Until now, it was believed that both types of planet only existed around stars containing a lot of heavy elements.

However, astronomers have now for the first time actually measured the amount of heavy elements in stars with Earth-like planets found with the help of the Kepler satellite. The results indicate that Earth-like planets can form around all types of star, including those stars that do not have a lot of heavy elements.

“The results are surprising and very interesting”, says Anders Johansen at the Department of Astronomy and Theoretical Physics at Lund University.

Planets are formed in the discs of gas and dust that orbit young stars. When the dust particles collide, larger and larger bodies are formed, until a new planet has been created from the dust. Both terrestrial planets and the cores of gas giants are formed from heavy elements, for example iron. It is therefore easy to understand why planets are found around stars with a high proportion of heavy elements that can provide material for the formation of the planets. However, the new research findings show that Earth-like terrestrial planets can form around all types of star.

“The new findings mean that Earth-like planets are much more common in the Milky Way than had previously been believed. It also means that life in the universe could be much more common”, says Anders Johansen.

The American Kepler satellite was launched on 7 March 2009. From its orbit around Earth, the satellite looks for planets around other stars. Anders Johansen does not work on the Kepler satellite; rather, he is a theorist with a focus on planet formation.

“I was invited by the team behind Kepler to help write parts of the article for Nature on how their new observations affect our view of how planets are formed”, says Anders Johansen, whose own research was awarded prestigious funding from the European Research Council last year.

The research findings have been published in the scientific journal Nature.

Text: Lena Björk Blixt