TRAPPIST-1 planets have an Earth-like composition, research suggests

June 8 (UPI) -- An astrophysicist at the University of Oklahoma says several Earth-sized planets in the TRAPPIST-1 system are Earth-like in other ways.

According to new analysis by Billy Quarles, at least six of the seven exoplanets boast an Earth-like consistency and are likely composed mostly of dense rock.

One of the alien worlds, however, features a mass much smaller than Earth despite being roughly the same size. This exoplanet, TRAPPIST-1f, is 25 percent water.

The findings -- detailed in the Astrophysical Journal Letters -- suggest TRAPPIST-1e may be the most Earth-like and best target for astronomers looking for evidence of life.

"The goal of exoplanetary astronomy is to find planets that are similar to Earth in composition and potentially habitable," Quarles said in a news release. "For thousands of years, astronomers have sought other worlds capable of sustaining life."

In February, NASA announced the discovery of seven Earth-sized planets surrounding a single star -- three of which are entirely within the planetary system's habitable zone.

"This is the most exciting discovery we've had yet with the Sptizer Telescope," Sean Carey, manager of the Spitzer Science Center, said during the press conference.

In the months since, astronomers have been trying to learn more about the unique system.

By watching the planets in the TRAPPIST-1 system as they transit their host star, scientists can estimate each world's radius. Their synchronized orbits allow researchers to gauge their mass. And by comparing each exoplanet's mass and radius, Quarles was able to calculate density.

A planet's density reveals its likely composition. Those with densities similar to Earth are likely to made up mostly of rock. Finding planets with compositions similar to Earth is essential to the search for alien life.