Steamy “super Earth” Has Sauna Potential

This artist’s impression shows the super-Earth exoplanet GJ 1214b passing in front of its faint red parent star 40 light years from Earth. Starlight passing through the planet's atmosphere revealed the signature of water vapor. Credit: ESO/L.Calcada

An extrasolar planet named GJ 1214b, discovered last year with the 147-inch telescope at the European Southern Observatory, appears to have a watery atmosphere. The planet orbits a dim star in the constellation Ophiuchus and has a diameter about 2 1/2 times that of Earth and density 6 1/2 times greater. It’s probably composed of rocky materials, unlike the majority of the 504 extrasolar planets thus far discovered, which are Jupiter-sized and orbit very close to their parent stars. These primarily gaseous worlds go by the nickname “hot Jupiters.”  Based on its more Earth-like diameter and composition, astronomers classify GJ 1214b as a “super Earth”, a more massive, somewhat larger version of our own planet.

The planet GJ 1214b appears to be surrounded by an atmosphere that is either dominated by steam or blanketed by thick clouds or hazes. The planet appears as a large crescent in the foreground with its red parent star in the distance. Credit: L. Calcada

What makes this planet especially exciting is that its atmosphere has substantial amounts of water vapor either in the form of steam or perhaps as dense clouds or hazes. Astronomers have analyzed several other hot Jupiters’ atmospheres and detected familiar compounds like methane, carbon dioxide and water, but this is the first time water has been found in the skies of a “super Earth.”

GJ 1214 b lies 40 light years from Earth and is relatively large compared to the star it orbits, making it easy to study. Unlike Earth, which is 93 million miles from the sun and takes a year to complete an orbit, GJ 1214b is only 1 1/4 million miles from its sun and cycles round in just 38 hours. To study the atmosphere, the team observed the light coming from the star as the planet passed in front of it. Some of the starlight passes through the planet’s atmosphere and, depending on the chemical composition and weather on the planet, specific wavelengths or colors of light are absorbed. The team then compared their measurements with what they would expect to see for several possible atmospheric compositions. Water vapor, like other molecules and elements, has a characteristic “signature” it imprints on light rays. Astronomers detected that signature in the airy envelope surrounding G 1214b thanks to the fortuitous alignment of Earth-planet-star.

Orion and the Milky Way hang above the four main VLT telescopes. Notice Orion's upside down. That's because the VLT is in Chile in the southern hemisphere. Credit: ESO

What about liquid water? Of that there’s probably precious little. G 1214b orbits so close to its parent sun, its surface temperature is estimated to be nearly 400 degrees, too hot for oceans but perhaps tempting for hardy Finns and others who love a good sauna.

A while back, I thought I might be around long enough for the first extrasolar planets to be discovered, but never imagined that so many would be found so quickly. Even more amazing, given the right circumstances, we can now probe their atmospheres. Not that it’s an easy to do. The international discovery team used the Very Large Telescope (VLT), an array of four 323-inch telescopes and four 71-inch auxiliary telescopes, equipped with a sensitive spectrograph, an instrument that spreads out starlight so astronomers study it in detail. The light from the VLT’s multiple telescope array can be combined to create, in effect, one gigantic telescope with enough resolving power to unveil the finest of details.

If you’d like to read more about the discovery, check out the ESO release. When Galileo first pointed his telescope at Jupiter in the fall of 1609, he discovered it wasn’t just a bright “star” but a world of its own, a brother to Earth. Likewise for Mars, Saturn and all the planets. As we peel away exoplanets from the glaring light of their parent stars, the revolution in our understanding of our place in the universe that began with Galileo, continues to this very day.