A group of astronomers measured the masses of small and rocky exoplanet and found that our solar system is not that unique at all. Their study likewise revealed that these planets are likely made up of similar materials found on Earth allowing the researchers to come up with a "recipe" on how to "bake" an Earth-like planet.

For the study presented at the American Astronomical Society meeting on Jan. 5, Courtney Dressing, from the Harvard-Smithsonian Center for Astrophysics (CfA), and colleagues used the High-Accuracy Radial velocity Planet Searcher (HARPS) North instrument to determine the mass of Kepler-93b, a planet 1.5 times bigger than the size of the Earth that orbits around its star.

Located on a 3.6-meter telescope in the Canary Islands, HARPS-N can measure the masses of small and Earth-sized planets helping scientists determine the densities and compositions of these extraterrestrial worlds. The instrument is also being used to confirm and follow-up the exoplanets discovered by NASA's Kepler Mission.

Using the HARPS-North, the team was able to nail the mass of Kepler-93b to 4.02 times the mass of the Earth, which means that the exoplanet has a rocky composition. The astronomers then measured the densities of the ten known exoplanets that have a diameter 2.7 times less than the Earth's.

The researchers found that five of these planets with diameters 1.6 times less than that of the Earth exhibited a strong association between size and mass. Interestingly, Venus and Earth also fit into the same correlation.

Earth has a rocky composition and is known to have an iron core. Venus is also believed to have the same characteristics indicating that these small exoplanets may also have similar rock-iron compositions and some very Earth-like characteristics. With these, the researchers were able to come up with a detailed recipe on how to make another Earth-like world.

"Our solar system is not as unique as we might have thought," Dressing said. "It looks like rocky exoplanets use the same basic ingredients."

The researchers likewise found that the densities of larger and more massive exoplanets are significantly lower indicating that these are largely composed of water and other volatiles. These bigger exoplanets also have more diverse compositions.

Dressing and colleagues pointed out that not all of the planets that are six times less massive than the Earth are rocky but noted that average close-in small planets are more likely to have Earth-like compositions.