Science Cases
Discovery of Nearby Earth-like Worlds
iLocater will achieve unprecedented long-term RV precision at infrared wavelengths. By measuring the Doppler reflex motion induced by orbiting planets, such observations will address:
- Which of the nearest stars host terrestrial planets with mass comparable to the Earth?
- Which nearby planets are located in the “habitable zone?”
The TESS Space Mission
NASA’s recently approved Transiting Exoplanet Survey Satellite (TESS) will discover terrestrial planets from space (Ricker et al. 2010). Scheduled for launch in 2018, TESS will detect rocky worlds at distances of only 10-100 light-years, providing a list of several hundred new transiting planets including 500 super-Earths. TESS is powerful but only measures planet radii, not masses. iLocater will come on-line at the LBT observatory in 2017 and:
- Provide TESS with high-priority targets for follow-up observations.
- Perform crucial follow-up measurements for TESS discoveries to determine planet masses and densities, thus creating the first substantive library of physical properties for Earth-like worlds.
The First Systematic Study of Planets in Binaries
Binary stars constitute 50% of all stellar systems, yet our understanding of planet formation and evolution is currently based on single stars alone. Due to a selection bias, seeing-limited spectrometers cannot spatially separate the light from two nearby stars. A diffraction-limited spectrometer can circumvent this issue by using adaptive optics to prevent spectral contamination. iLocater will enable the first systematic study of planets in close-separation binary systems to address the following questions:
- How does the occurrence rate of planets change as a function of binary star separation?
- How does the occurrence rate of planets change as a function of binary star mass ratio?
- How does the eccentricity distribution of planets in binaries differ from that of single stars?
The First Terrestrial Planet Spin-Orbit Angles
Unlike our solar system, many planets found orbiting other stars have orbits that are “tilted” relative to the spin axis of their parent star. In fact, several planets even have retrograde orbits: they move counter to the direction of stellar rotation. This confounding result is currently an unsolved mystery in planet formation theory. Thus far, spin-orbit measurements have only been obtained for gas giant planets. iLocater will be the first instrument to measure spin-orbit angles for terrestrial worlds.
- Are the orbits of small planets like the Earth aligned with the spin axis of their parent star?
The Youngest Exoplanets
Star-spots induce spurious Doppler signals that currently preclude the detection of planets around young stars. iLocater is optimized for a wavelength range where the effects of star-spots are minimized. By targeting the youngest stars our instrument will address the following:
- What is the timescale for planet migration through a circumstellar disk?
- What is the mass and density of giant planets found transiting the youngest stars?
Characterizing the Atmospheres of Super-Earths
When a planet transits a small fraction of starlight passes directly through the planet's atmosphere leaving a measureable imprint of its chemical composition. iLocater will acquire the first low/moderate resolution spectra of “mini-Neptunes” and “super-Earths.”