Two MIT planetary scientists, Julien de Wit and Sara Seager, have published research showing how it is possible to determine the weight of an exoplanet using the surrounding starlight. Not only does this represent a way to determine the weight of something that is seemingly impossible to gauge, it will also facilitate the hunt for planets that are most like our own, possibly expediting the discovery of a planet like Earth.
The method works by measuring the starlight that is able to pass through the planet's atmosphere, a change from the current method that is typically used: radial velocity. In particular, this new method works better than radial velocity when it comes to smaller planets and instances where light is faint. The process, which was detailed in Nature today, builds upon a common method for identifying the existence of exoplanets in general.
To identify the existence of an exoplanet, scientists will monitor the light from a star, which will decrease to a certain degree if a planet passes in front of it. This decrease in light not only informs those watching that a planet is nearby, but can also be used to determine the mass of that planet by measuring how much light passes around the planet through its atmosphere.
When light passes through the atmosphere, its spectrum is changed, with the specifics of that change depending on, among other things, temperature, atmospheric pressure, and gravitational pull. The spectrum of the light that passes through the atmosphere as the planet moves past its star can give researchers information about these things.
This method has been demonstrated as effective, not the least of which was by using a planet with a known mass (as determined through radial velocity). Using the starlight spectrum method, the researchers calculated the planet's mass as determined by the method's equations, revealing an accurate final figure the same as that determined by conventional means.