Bringing us one step closer to discovering an Earth-like planet in a distant solar system, a team of European scientists recently found the smallest extrasolar planet orbiting a main-sequence star yet.
The planet, Gliese 436c, has about five times Earth's mass and orbits the red dwarf star Gliese 436 in the constellation Leo.
The team, led by Ignasi Ribas of the Institut de Ci??ncies de l'Espai in Spain, analyzed perturbations in the orbit of a previously known, Neptune-like planet that circles the same star.
They found that these perturbations could be explained by the presence of a smaller planet whose orbit is outside that of the known planet - Gliese 436c.
More than 280 planets have been discovered orbiting other stars, but the majority of these are more similar to Jupiter and Neptune than to Earth and Mars. Much larger than Earth and gaseous, these exoplanets are unlikely to have surface liquid water or be able to sustain life.
Gliese 436c is one of a group of exoplanets known as super-Earths. Super-Earths have 10 times Earth's mass or less and have a similar rocky composition.
Gliese 436, like the Sun, is a main sequence star at the midpoint of its life span. It is about 30 light years, or 180 trillion miles, away from Earth.
As a cool red dwarf star, its average surface temperature is less than 3,600 degrees Celsius. In comparison, the Sun has a surface temperature of about 5,800 degrees Celsius.
Despite being similar in size and composition to Earth and orbiting a similar star, Gliese 436c probably does not contain surface liquid water.
Like most other rocky exoplanets previously discovered, it orbits so closely to its star that the planet's surface temperatures would be too high for liquid water to exist.
Gliese 436c completes an orbit once every five Earth days - one year on this planet is only five Earth days long, while one of its days is 22 Earth days long.
However, as scientists develop better and better techniques for sensing extrasolar planets, the discovery of an Earth-massed planet should not be far in the future.
Extrasolar planets are much more common than once thought, with an estimated ten percent of main sequence stars having planet systems.
The discovery of an Earth-like, rocky planet that is far away enough from its star to allow for liquid water, and the possibility of life, is foreseeable within the next decade.
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