As of December, 2014 there were 1781 confirmed exoplanets. Another 4,175 possible exoplanets are waiting to be confirmed and new planets are being found on a regular basis. As more powerful telescopes come online over the next few years, the pace of exoplanet discovery will only accelerate.

This creates a situation where the discovery of new exoplanets isn’t all that remarkable and researchers have to ask which planets to focus on. Now a team of researchers led by Courtney Dressing of the Harvard-Smithsonian Center for Astrophysics (CfA) believe that they have an answer.

The researchers believe that the same recipe that led to life on Earth could lead to habitable planets elsewhere.

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

Using the High-Accuracy Radial velocity Planet Searcher (HARPS)-North instrument on the Telescopio Nazionale Galileo in the Canary Islands the team looked for planets similar in composition to Earth. The HARPS instrument is designed to determine the masses of Earth-sized planets. The mass of the world is then used to determine the density and the density is used to determine the composition of the planet.

“Our strategy for using HARPS-North over the past year has been to focus on planets less than two times the diameter of Earth and to study a few planets really well,” said astronomer David Charbonneau of Harvard, who currently heads the HARPS-North Science Team.

The tongue-in-cheek “recipe” included in their statement the team, who presented in a a meeting of the American Astronomical Society this week included the following:

“Ingredients: 1 cup magnesium, 1 cup silicon, 2 cups iron, 2 cups oxygen, 1/2 teaspoon aluminum, 1/2 teaspoon nickel, 1/2 teaspoon calcium, 1/4 teaspoon sulfur, dash of water delivered by asteroids; Blend well in a large bowl, shape into a round ball with your hands and place it neatly in a habitable zone area around a young star. Do not over mix. Heat until mixture becomes a white hot glowing ball. Bake for a few million years. Cool until color changes from white to yellow to red and a golden-brown crust forms. It should not give off light anymore. Season with a dash of water and organic compounds. It will shrink a bit as steam escapes and clouds and oceans form. Stand back and wait a few more million years to see what happens. If you are lucky, a thin frosting of life may appear on the surface of your new world.”

Kepler-93b has been the teams most recent subject of study. The planet is in a tight 4.7 day orbit around its star and is roughly 1.5 times the size of Earth. Harps-North revealed that the world has a mass 4.02 times that of Earth which means it has a rocky composition.

The team compared the 10 known exoplanets with a diameter of less than 2.7 times that of Earth and measured their masses. According to the researchers the five planets less than 1.6 times the size of Earth had a strong relationship between their mass and size. That relationship is also reflected, in our solar system, in Earth and Venus. This suggests that all of these planets have similar rock to iron compositions.

The larger, more massive exoplanets proved to have lower densities which indicates that that they contain a large amount of water, hydrogen or helium. They also showed more diverse compounds, as opposed to the tight relationship demonstrated by the smaller, rocky planets.

“To find a truly Earth-like world, we should focus on planets less than 1.6 times the size of Earth, because those are the rocky worlds,” said Dressing.

The fact that a planet is similar to Earth does not mean that it is inhabited or habitable. Venus, which is Earth-like, has a poisonous atmosphere and surface temperatures in excess of 1 thousand degrees Fahrenheit.

It is also possible that planets that are not Earth-like could have life. Many scientists think that Saturn’s moon Titan or Jupiter’s moon Europa could support life. However, as the number of known exoplanets grows and researchers have to narrow their focus, knowing which planets are the most like our own will save a great deal of time and energy.

The research by Dressing and associates has been accepted for publication in the Astrophysics Journal.