Searching from an 8,000 ft mountaintop in the southern Atacama desert, astronomers at the European Southern Observatory telescope La Silla, led by Stéphane Urdy, may have discovered the first Earth-like planet outside of our own solar system. The new planet is the smallest so-called exoplanet yet found. It orbits one of the 100 closest stars to us, Gliese 581. The planet, designated Gl581 c, is estimated to have an average surface temperature of 0-40 degrees Celsius. This is a particularly exciting find: it means liquid water might exist on its surface, a factor that makes it much more likely for the planet to support life.

A key question in planetary and space science is whether we inhabit a ‘rare Earth,’ or a type of planet which is statistically common throughout the billions of stars in our galaxy.

Life on Gl581 c would be in a neighborhood which looks quite a bit different from our solar system, however. The star Gliese 581 is a red dwarf, a hundred times less luminous than our sun and only about 30% of the mass. So far, three planets have been discovered around it. The first is a hot, Neptune-sized planet, which whips around the star in only 5.3 days at a distance of only 4% of that between the sun and Earth. The new, “super-Earth” Gl581 c is next out from the sun. Its radius is 50% greater than Earth’s and its mass about 5 times greater. A “year” to make an orbital revolution lasts a mere 13 Earth days. But because the star it orbits is much fainter than the sun, this places Gl581 c firmly in the habitable zone of this type of star. This is the Mediterranean climate of a solar system—not boiling hot and not freezing cold. Rounding out the system is a planet 7.7 times the mass of the sun, but with an orbital period of 84 days. It is likely a frozen world.

A key question in planetary and space science is whether we inhabit a “rare Earth,” or a type of planet which is statistically common throughout the billions of stars in our galaxy. The search for exoplanets is one of the most rapidly moving arenas of astronomy. Since the first was confirmed in 1995, over 229 planets have been discovered. This new Earth-like world is too faint to image directly and there are many questions about Gl581 c which cannot be answered yet. Is it “locked” to the star—that is, is one face always facing the hot star and the other cold space? Orbital dynamics predict an object this close might be. Does it have an atmosphere? This would help mitigate the effects of being locked, spreading the sun’s warmth to the far side of the planet.

If the planet has any ET-like inhabitants, they are just now getting the television programs from 1987: Teenage Mutant Ninja Turtles, Married with Children, and Star Trek: the Next Generation.

If the planet has any ET-like inhabitants, they are just now getting the television programs from 1987: Teenage Mutant Ninja Turtles, Married with Children, and Star Trek: the Next Generation. In the late 1980s, idea of life elsewhere in the universe was popularized as a subject for scientific pursuit in part due to the efforts of Carl Sagan and the SETI Institute. Within the past decade, the discipline has grown, acquired a name and focused its objectives. Astrobiology is the study of the origin, distribution, and future of life on Earth and the search for life beyond.

The enabling factor has been technologic advances over the past two decades which have allowed us to precision land rovers on Mars, genetically trace the evolution of Earth’s earliest and hardiest microbes, and find the subtle signals of planets around other stars. For example, Gliese 581 was detected based on detecting periodic variations in the velocity of a star due to the gravitational pull of an unseen planet. The particular High Accuracy Radial velocity Planet Searcher (HARPS) instrument used by the La Silla team detected velocity variations corresponding to about 9 km/hr—the speed of a person walking—from 120 trillion miles away. As more exoplanets are discovered, the impetus builds for missions on the planning board for NASA and the European Space Agency (ESA). NASA’s Terrestrial Planet Finder (TPF) mission and ESA’s Darwin mission would launch telescopic instruments which would include a spectrometer, allowing us to image and obtain the chemical composition of atmospheres of Earth-like planets. Are we indeed a “rare Earth”? In the coming decades, we should prepare to find out. 

Bethany Ehlmann is a graduate student in planetary sciences at Brown University