Researchers say they've developed a new technique for determining the mass of planets outside our solar system that could help identify potentially habitable worlds.

The new technique uses only a planet's transit signal, or the dip in light that happens when the planet passes in front of its host star. In the past, this information has been used to measure a planet's size and atmospheric properties. Writing in the journal Science, researchers from Massachusetts Institute of Technology say they've found a way to repurpose this signal to determine the planet's mass, too.

"With this method, we realized the planetary mass - a key parameter that, if missing, could have prevented us from assessing the habitability of the first potentially habitable Earth-sized planet in the next decade - will actually be accessible, together with its atmospheric properties," said Julien de Wit, a graduate student in MIT's Department of Earth, Atmospheric and Planetary Sciences.

Knowing a planet's mass is necessary for gaining a clear understanding of the planet's surface and internal activity, the scientists note.

"The mass affects everything on a planetary level, such as any plate tectonics, its internal cooling and convection, how it generates magnetic fields, and whether gas escapes from its atmosphere," de Wit said. "If you don't get it, there is a large part of the planet's properties that remains undetermined."

De Wit was able to put the method to the test on a recently discovered exoplanet located 63 light years away known as 189733b. After calculating the mass, he compared his results to others obtained using a more traditional technique known as radial velocity. The answers matched.

Radial velocity includes deriving the planet-to-star mass ratio by measuring tiny wobbles in a star's orbit as the planet moves around it, its gravitational field causing it to budge ever so slightly. This system works when measuring the mass of planets that are either massive or located in tight orbits around bright stars. Anything else, however, tends to be outside the method's reach.

"Knowing the mass is a very important piece of the puzzle," said Mark Swain, a researcher from NASA's Jet Propulsion Laboratory who was not involved in the research.

"If you found the composition of the planet was almost certainly solid, that required a significant amount of water mixed in with a silicate core, and you knew it had habitable zone-type temperatures, you might make a good case for in-depth studies of that world, because it has what seems like the ingredients for a habitable planet."