Figure 1:
Very high velocity precision is needed to measure the mass of low mass
planets through the subtle motion, the “wobble”, that a planet induces
in its host star. The extreme precision radial velocity spectrometer
(EPDS) destined for Kitt Peak will measure stellar motions with a
precision of 0.1 - 0.5 m/s (or 0.2 - 1 mph), velocities comparable to
the running speed of a desert tortoise or gila monster. With such high
precision, the spectrometer will be able to detect and characterize
Jupiter- and Neptune-sized gas giant planets as well as super-Earth and
Earth-sized rocky planets.
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.
Media Contact:
Dr. Joan Najita
National Optical Astronomy Observatory
950 N Cherry Ave
Tucson AZ 85719 USA
+1 520-318-8416
E-mail: najita@noao.edu
