Orange stars live longer than the sun and are less violent than red dwarf stars, making the planets around them good candidates for hosting life (Illustration: ESO)

The universe’s best real estate for life may be around stars a little less massive than the sun, called orange dwarfs, according to a new analysis. These stars live much longer than sun-like stars, and have safer habitable zones – where liquid water can exist – than those of lighter red dwarf stars.

Stars similar in mass to the sun, categorised as a yellow dwarf, have received the most attention from planet hunters. But recent research suggests orange dwarfs may provide an even better hunting ground for life-bearing planets.

Edward Guinan of Villanova University in Pennsylvania, leads a team that has been studying how the properties of stars vary with mass. The team is using observations from a variety of sources, such as archival measurements from the ROSAT X-ray satellite, and more recent measurements from ground-based telescopes.

Long lifetimes

The results confirm that red dwarf stars, which weigh between 10 and 50% as much as the sun, are far more prone to unleashing powerful flares that can deliver deadly radiation to nearby planets. This activity declines as the red dwarfs age, and scientists have not ruled out red dwarf planets as potential abodes for life, but any such life would certainly face some big challenges.


Orange dwarfs, on the other hand, with masses between 50 and 80% that of the sun, have only a little bit more flare activity than sun-like stars. They would also provide a haven for life for a much longer time – roughly double the 10-billion-year lifetime of a sun-like star.

Moreover, they change very little in brightness compared to sun-like stars. Our own sun has brightened by about 30% since the solar system began, and will likely make Earth too hot for life in about 1 billion years, even though the sun will still have about 5 billion years of fuel left to burn.

Good targets

The odds of intelligent life arising may be better on planets around orange dwarfs than sun-like stars, given the extra time available for it to evolve.

That makes orange dwarfs not only good targets for habitable planet searches, but for the search for extraterrestrial intelligence (SETI) as well, Guinan says. “There are old ones around – some are 8 to 9 billion years old, and could have planets that are more evolved,” he told New Scientist.

Orange dwarfs are about three to four times as abundant as sun-like stars, making planet searches easier. Indeed, some planets have already been found around orange dwarfs, though outside the stars’ habitable zones.

But Gregory Laughlin of the University of California, Santa Cruz, says it should be possible with current technology to find Earth-mass planets in the habitable zones of nearby orange dwarfs. “They do seem to be a sweet spot for prospects of actually detecting habitable planets,” he told New Scientist.

Guinan discussed his research this week at an astrobiology conference in Baltimore, Maryland.