Illustration of Older Sun-like Star
A study using data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton suggests X-rays emitted by a planet's host star may provide critical clues to how hospitable a star system could be. Researchers looked at the X-ray brightness from 24 stars with masses similar to the Sun or less, each at least one billion years old. The artist's illustration depicts one of these older Sun-like stars with a planet in orbit around it, which researchers found to be relatively calm compared to younger stars. The large dark area is a "coronal hole", a phenomenon associated with low levels of magnetic activity.
(Credit: NASA/CXC/M.Weiss)

Chandra X-ray Image of GJ 176
Since stellar X-rays mirror magnetic activity, X-ray observations can tell astronomers about the high-energy environment around the star. In the study the X-ray data from Chandra and XMM-Newton revealed that stars like the Sun and their less massive cousins calm down surprisingly quickly after a turbulent youth. This X-ray image shows the Chandra data of one of the observed objects, a two billion year old star called GJ 176, located 30 light years from Earth.
(Credit: X-ray: NASA/CXC/Queens Univ. of Belfast/R.Booth, et al.; Illustration: NASA/CXC/M.Weiss)