Kitt Peak National Observatory is the future home of a state-of-the-art instrument that will be used to detect and characterize other worlds. The new instrument, an extreme precision radial velocity spectrometer, will measure the subtle motion of stars produced by their orbiting planets.

The spectrometer, funded by NASA, will be deployed on an existing telescope at Kitt Peak, the 3.5-meter WIYN telescope. The National Optical Astronomy Observatory (NOAO), which is funded by NSF, is a partner in the telescope and operates Kitt Peak.

The spectrometer is the cornerstone of a newly established partnership between NSF and NASA focused on exoplanet research (NASA-NSF Exoplanet Observational Research; NN-EXPLORE), which aims to advance exoplanet science through the use of the NOAO share of the WIYN telescope.

As an initial step in the partnership, NASA announced on 2015 January 22 a request for proposals to build an Extreme Precision Doppler Spectrometer (EPDS) for use by the astronomical community. The spectrometer will measure stellar radial velocities with a precision sufficient to characterize Jupiter- and Neptune-sized gas giant planets as well as super-Earth and Earth-sized rocky planets.

The new spectrometer will be a world-class precision radial velocity instrument, with a minimum velocity precision of better than 0.5 m/s (1 mph) and a goal of 0.1 m/s (0.2 mph). For context, the leisurely speed of 0.2 mph is close to the top speed of a desert tortoise; and 1 mph is similar to the sprint speed of a gila monster.

Such extreme precision is needed to measure the mass of an orbiting planet through the slight motion that the planet induces in the star. As a planet orbits a star, it causes the star to move, or "wobble", as both objects orbit their gravitational center of mass. Lower mass planets induce subtler motions in the star, and correspondingly higher velocity precision is needed to characterize them.

Jupiter causes a 13 m/s (29 mph) amplitude wobble in the Sun, whereas the Earth induces a much smaller wobble (about 0.1 m/s). As a result, extreme precision is needed to characterize rocky Earth-sized planets.

The new spectrometer is expected to play a critical role in characterizing high-priority exoplanet targets identified by current and future NASA missions, in particular Kepler, K2, and TESS. The Kepler mission has found more than 1000 confirmed exoplanets and more than 3000 unconfirmed planet candidates to date.

K2, Kepler's extended mission survey of selected fields in the ecliptic plane, is currently underway. The future Transiting Exoplanet Survey Satellite (TESS) will conduct an all-sky survey of transiting exoplanet systems around relatively bright and nearby stars.

Achieving the scientific potential of these missions requires supporting ground-based observations. High-resolution imaging and spectroscopy are used to rule out astronomical false positives. Precise radial velocity measurements are needed to confirm the planetary nature of the companions and to measure their masses.

As Kitt Peak Director Lori Allen explains, "Once we measure a planet's mass, we can use what we know about the planet's size, as measured by Kepler and TESS, to infer whether the planet is rocky like the Earth or gaseous like Jupiter."

NASA has established an aggressive development schedule for the new spectrometer in order to make the instrument available for use by the astronomical community on a timescale relevant to the availability of data from the TESS mission (mid-FY18).

"NASA and the NSF are excited to team up to advance humankind's understanding of planets around other stars," said Doug Hudgins, Program Scientist for NASA's Exoplanet Exploration Program. "The new EPDS spectrometer will give the US science community access to a world-class instrument for years to come."

Although the new spectrometer is its cornerstone, the NSF-NASA partnership will be launched much in advance of its arrival. Beginning this year, the partnership will establish an exoplanet-related Guest Observer research program on the WIYN telescope using existing WIYN instrumentation. The new spectrometer will be included in the Guest Observer program beginning in 2018.

The National Optical Astronomy Observatory is operated by Association of Universities for Research in Astronomy Inc. under a cooperative agreement with the National Science Foundation.