A distant planet has been weighed with light that passed through its atmosphere 63 years ago. This new mass-measuring technique should allow researchers to determine which distant planets could support life.
To identify a truly Earthlike exoplanet with the potential for life, astronomers need to confirm three essential attributes: an atmosphere that contains life-supporting molecules such as oxygen and water, plus a size and mass similar to Earth’s. The only attribute easy to measure now is size: Telescopes provide good estimates by measuring planets’ shadows when they cross in front of their stars. Soon, detailed observations of exoplanet atmospheres will become possible. With NASA’s James Webb Space Telescope, set for launch in 2018, astronomers will be able to analyze starlight that passed through a planet’s atmosphere, known as a transmission spectrum. That spectrum can reveal what kinds of molecules the planet’s atmosphere holds.