Image credit: NASA Ames/SETI Institute/JPL-Caltech
Each time a new star is born, so too are its planets. The points of light that we see in the constellations of the night sky each represent a distinct location, a specific address in the galaxy, where orbiting planets perform a rhythmic dance around their parent stars. Thanks to incredible recent discoveries from NASA's Kepler space mission, we now know the statistics of exoplanets. Other solar systems are common, and rocky worlds resembling the Earth may be innumerable.
The Milky Way is teeming with terrestrial planets having conditions that might be conducive to the emergence of life. Which of the stars nearest to Earth are host to planets with temperate climates? What are their physical properties? Do they have an atmosphere with compositions that we might recognize?
At the University of Notre Dame, we are building a new instrument named "iLocater" to answer these very questions.
Dr. Jonathan Crass and PhD student Andrew Bechter install the enclosure of the iLocater demonstration system in the lab at Notre Dame.
What is iLocater?
iLocater is an ultra-precise planet-finding spectrometer that operates at infrared wavelengths. It will be one of the world's first diffraction-limited Doppler radial velocity instrument. Currently being designed and built in the Department of Physics at the University of Notre Dame, iLocater will be installed at the Large Binocular Telescope (LBT), AZ and will support observations and discoveries from NASA's TESS space mission.
iLocater has been approved for construction by the LBT science steering committee, board, and observatory director.
iLocater was also featured as part of the Notre Dame What Would You Fight For? series. The video below aired on NBC during halftime of the Sept. 6, 2014 Notre Dame vs. Michigan football game.
The following animation, courtesy of the European Southern Observatory (ESO) / L. Calçada, shows how spectrographs are used to identify exoplanets:
The orbiting planet's gravitational pull causes its parent star to "wobble," i.e. change its radial velocity in a periodic fashion. This movement creates a tiny Doppler shift in the star's spectrum that can be detected using a spectrograph.
Working at the Diffraction Limit
iLocater will receive a well-corrected beam of starlight from the LBT Interferometer (LBTI). With input images that achieve ~30 times higher spatial resolution than “seeing-limited” designs (i.e., all radial velocity predecessors), iLocater will simultaneously enable high spectral resolution (R=150,000-240,000) and a compact optical design at low cost. Compared to present-day Doppler instruments, a diffraction-limited spectrometer will:
- be significantly easier to stabilize (temperature, pressure), thus leading to higher radial velocity precision;
- receive two orders of magnitude less background contamination from sky-emission and the moon;
- identify neighboring stars through adaptive optics imaging;
- and employ a single-mode optical fiber to eliminate "modal noise" entirely, an effect known to induce spurious Doppler shifts;
Further, iLocater will have the unique ability to monitor and ameliorate internal systematic errors by using two separate telescope dishes simultaneously, enabling the first RV measurement precisions well below 1 m/s at near-infrared wavelengths.
Lab demonstration of the elimination of modal noise using a single-mode fiber (left). Multimode fibers (right) alter the illumination pattern of light as it enters the spectrograph limiting the precision of stellar velocity measurements. All existing spectrometers use multimode fibers; iLocater will become the first to circumvent this noise source.