Does life exist on worlds orbiting other stars? You can help us find out.
Where should we look for life outside our solar system? A good place to start is with planets that have masses similar to Earth, and orbit in their stars' not-too-hot, not-too-cold habitable zones. One way astronomers look for these exoplanets is the radial velocity method. A planets tugs on its star as it orbits, giving the star a slight wobble. These wobbles can be detected with a spectrograph, which splits starlight into its component wavelengths. As a star wobbles, its spectrum shifts. By recording these shifts over time, astronomers can infer that a planet is present.
ESO / L. Calçada
Watching a star wobble
A star's wobble shifts its spectrum due to the doppler effect.
Even the highest-resolution spectrographs are limited in the size of planets they can detect. A big, Jupiter-like planet might cause a star to wobble by several meters per second. But a small, Earth-like planet might only wobble its star by ten centimeters per second. Such small shifts are hard to tease out of star spectra, and are easily masked by variations in the way the starlight is captured at the telescope. To make matters more difficult, the star of an exoplanet with an Earth-like orbital period needs to be measured for years to confirm the planet's existence.
Therefore, it's important to carefully calibrate the spectrographs used to record these shifts—astronomers must ensure it's the planet's spectra that's changing over time, not the telescope. And that's where The Planetary Society comes in, with our newest sponsored project, Exoplanets Laser.
Exoplanets Laser uses a system of lasers to generate an artificial spectrum that is imprinted alongside the star spectrum. The artificial spectrum consists of evenly spaced, well-defined lines that can be used as a baseline to calibrate long-term star observations.
A sample laser frequency comb spectrum
In this laser frequency comb, colorized for illustrative purposes, the solid lines are the star spectrum and the dots are the artificial laser spectrum. The dark gaps in the star spectrum represent different chemical elements in the starlight. Long-term star observations can be calibrated using the artificial spectrum to reveal if the star is wobbling due to the presence of an exoplanet.
The project is led by Dr. Debra Fischer, a professor of astronomy at Yale University, along with postdoc Tyler McCracken. We’ve supported Fischer’s exoplanet work before. In 2009, we raised $45,000 to help her team build a fiber-optic system used to reduce the errors in spectrograph data. Versions of this system, which we called FINDS (Fiber-optic Improved Next generation Doppler Search) Exo-Earths, are now used by exoplanet hunters around the world.
Fischer’s team has already built an Exoplanets Laser prototype in their Yale lab. Now, they need to upgrade to a professional-grade laser, which will cost $65,000. The new system will eventually be installed at the 4.3-meter Discovery Channel Telescope, southeast of Flagstaff, Arizona. The DCT will be home to EXPRES, the Extreme Precision Spectrograph, which is also being built by Fischer's group. EXPRES and Exoplanets Laser will be used in support of Yale's 100 Earths project, a quest to find and characterize 100 Earth-like exoplanets. We believe Exoplanets Laser can greatly advance the field of exoplanet astronomy. Please consider donating to the project, which supports The Planetary Society's mission to find and understand planets outside of our solar system.
Interested in learning more about exoplanets? Check out our free introductory astronomy course on the subject, taught by Dr. Bruce Betts, our director of projects. Betts interviews Debra Fischer in the video.