Venus On The Move: Its Transit To Aid Search For Exoplanets

Tuesday's transit of Venus will be an exciting event for casual star enthusiasts and dedicated astronomers alike. Scientists plan to use this rare celestial event -- during which Venus passes between the sun and the Earth, showing up as a small silhouette on the solar disc -- to aid their search for planets outside of our solar system.

It's this observational model with which we can compare observations of other stars that may have planets around them, explained Mark Giampapa of the National Solar Observatory.

By aiming their instruments at the transit, astronomers can see if they are able to detect clues about Venus' atmosphere using methods that could be applied to observations of far-flung worlds.

NASA's Kepler mission, which is surveying our corner of the Milky Way to try and detect Earth-size exoplanets, is likely to benefit from the transit of Venus as well, albeit indirectly.

The Kepler observatory's single instrument is a very sensitive photometer -- a big light bucket, as NASA researcher Martin Still describes it -- that would be overwhelmed by the light of the sun.

If we tried to point Kepler at the sun, it would fry, said Still.

NASA will be keeping an eye on the transit via the Hubble Space Telescope, but even this instrument can't handle the full blazing light. Instead, Hubble will aim its cameras at the moon to catch the light from the sun bouncing off of it as Venus passes by.

Once Hubble captures the transit, its instruments will split the light into its component wavelengths, which can be used to ascertain the chemical components of Venus' atmosphere. Certain atoms or molecules absorb certain wavelengths of light, so when scientists look at the data captured by Hubble, they'll see patterns of absorption indicating what kinds of chemicals are in the mix.

Of course, we already know what sorts of gases are brewing on Venus -- mostly carbon dioxide -- thanks to space probes, but observing the transit of a well-known planet will allow scientists to work on methods for observing the transits of unknown planets.

It's a forerunner to what future space missions will be doing to planets orbiting distant stars using far more precise instruments, Still said.

The NSO will also be looking to see if their telescopes can detect signs of linear light polarization, a distinctive pattern of light scattering caused by the presence of an atmosphere.

The transit is a unique opportunity in terms of being able to gain insight into the methods and interpretations that we can apply to stars and exoplanets, Giampapa said.

(The transit of Venus is forecasted to start on Tuesday at around 6 p.m. Eastern time. If the weather in your area is cloudy or rainy, you can watch the transit live on the websites of NASA or the NSO. Or alternatively, you can hope to live long enough to catch the next transit in 2117.)