Astronomers have just moved closer to understanding how the raw ingredients for life may have arisen on Earth as well as on planets light-years beyond the solar system.
One team, using the Hubble Space Telescope, has for the first time detected an organic molecule in the atmosphere of a planet orbiting another star. Although the orb can’t support life, the discovery bodes well for finding organic material on more habitable exoplanets. Another team found that space rocks delivered a bigger helping of amino acids—the building blocks of proteins—to the early Earth than previously suspected.
To learn more about the composition of an alien planet, Mark Swain of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and his colleagues set their sights on a Jupiter-like body tightly orbiting the star HD 189733, which is 63 light-years from Earth. The planet, along with some 35 of the more than 270 exoplanets now known, has a special feature: As seen from Earth, it periodically passes in front of its parent star. During each of these mini-eclipses, some of the starlight filters through the planet’s atmosphere and is absorbed by its atoms and molecules. The amount of starlight and the specific wavelengths absorbed reveal the composition of the planet’s atmosphere.
Swain and his colleagues confirm previous suggestions that water vapor exists in the planet’s atmosphere and also identify methane—the first time any carbon-bearing compound has been detected in the atmosphere of an exoplanet. The team reports the findings in the March 20 Nature.
“We’re starting to probe the chemistry of the atmospheres of planets beyond the solar system,” says Swain.
Methane is a compound that may have played a role in getting life started on the early Earth. However, the massive, searingly hot planet circling HD 189733 orbits the star at less than one-tenth Mercury’s distance from the sun and therefore “cannot support life as we know it,” Swain emphasizes.
Over the next few years, however, astronomers hope to record more subtle mini-eclipses, created by smaller planets dubbed superEarths, that are farther from their parent stars and lie in the zone where water might remain liquid. “The detection of methane in [those cases] would be a very big deal” and may require the power of Hubble’s proposed successor, the James Webb Space Telescope, says David Charbonneau of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
In a study closer to home, a team led by Zita Martins of Imperial College London reports finding the highest known concentration of amino acids—between 180 and 249 parts per million—ever uncovered in ancient space rocks. The two rocks, found in Antarctica during the 1990s, belong to a rare type of meteorite called CR chondrites. This class of asteroid fragments is thought to contain the oldest and best preserved record of organic materials that have fallen to Earth.
Martins’ team, including Conel Alexander of the Carnegie Institution of Washington (D.C.), determined that the amino acids were carried in the rocks before the meteorites landed on Earth, the researchers report in an upcoming Meteoritics & Planetary Science.
During the era known as the late heavy bombardment, from 3.8 billion to 4.5 billion years ago, comets and asteroids peppered Earth and delivered extraterrestrial organic materials, including tons of carbon each year. The new data suggest that meteorites delivered much higher abundances of amino acids to the early Earth than previously suspected. “The higher the contents of key molecules in primitive extraterrestrial materials, the more likely it is that exogenous material played a role in the origin of life,” says Alexander.
“These new meteorites will get us closer to understanding the origin of the amino acids,” he adds.
