The extrasolar planet census recently passed a major milestone, with 5500 confirmed candidates in 4,243 solar systems. With so many exoplanets available for study, astronomers have learned a great deal about the types of planets that exist in our galaxy and have been rethinking several preconceived notions. These include the notion of “habitability” and whether Earth is the standard by which this should be measured – i.e., could there be “super habitable” exoplanets out there? – and the very concept of the circumsolar habitable zone (CHZ).
Traditionally, astronomers have defined habitable zones based on the type of star and the orbital distance where a planet would be warm enough to maintain liquid water on its surface. But in recent years, other factors have been considered, including the presence of planetary magnetic fields and whether they get enough ultraviolet light. In a recent study, a team from Rice University extended the definition of a CHZ to include a star’s magnetic field. Their findings could have significant implications in the search for life on other planets (aka. astrobiology).
The research team consisted of Anthony S. Atkinson, a graduate student with the Department of Physics and Astronomy at Rice University, Professor David Alexander, the director of the Rice Space Institute and member of the Texas Aerospace Research and Space Economy Consortium, and Alison O. Farrish, a NASA Postdoctoral Program Fellow at NASA’s Goddard Space Flight Center. The paper describing their findings, “Exploring the Effects of Stellar Magnetism on the Potential Habitability of Exoplanets,” appeared on July 9th in The Astrophysical Journal.
Artist’s impression of exoplanets orbiting different types of stars. Credit: NASA/W. Stenzel
On Earth, the presence of an intrinsic magnetic field has been vital to the emergence and evolution of life as we know it. Without it, our atmosphere would have been stripped away long ago by energetic particles emanating from the Sun – which was the case with Mars. In addition to Earth’s atmosphere, our planet’s magnetic field ensures that a limited amount of solar radiation and cosmic rays reach the surface. For this reason, astrobiologists consider a planetary magnetic field essential for determining whether or not an exoplanet is habitable.
