Dr. John M. Grunsfeld, Associate Administrator
Science Mission Directorate
National Aeronautics and Space Administration
Committee on Science, Space, and Technology Subcommittee on Space
U.S. House of Representatives
Mr. Chairman and Members of the Committee, thank you for the opportunity to appear
today to discuss the topic of extrasolar planets, or simply exoplanets, which are defined
as planets that orbit a star other than our own Sun.
NASA thrives on the synergy created by a critical mass of brilliant scientific and
engineering talent, supported by a broad range of expert professionals. We work, as an
Agency, to send humans to an asteroid and on to orbit Mars. We work, as an Agency, to
understand the universe from the beginning of time to the future of Earth's climate.
NASA's budget request for 2014 fully funds the James Webb Space Telescope for launch
in 2018, and supports a Mars lander for launch in 2020. The request supports
development of critical human exploration capabilities, and space technology to enable
our future in space. With the 2014 request NASA is planning a first-ever mission to
identify, capture, and redirect an asteroid into orbit around the Moon. This mission
represents an unprecedented technological challenge -- raising the bar for human
exploration and discovery, while helping protect our home planet and bringing us closer
to a human mission to Mars in the 2030s. The President's budget request for NASA
advances a strategic plan for the future that builds on U.S. preeminence in science and
technology, improves life on Earth, and protects our home planet.
Within the broader agency mission, NASA's Exoplanet Exploration Program focuses on
answers to fundamental questions that are likely as old as humankind itself: 1) Are there
other planets in the universe? 2) Are there other planets just like Earth out there? and 3)
Are we alone? While these questions have been the subject of speculation since
humankind first gazed to the heavens and wondered what was out there, the scientific study of these intriguing objects is relatively new; the first confirmed discoveries of
exoplanets did not occur until the 1990s. In the intervening years, scientists have
discovered over 850 exoplanets, with new ones being discovered almost daily. In just the
last 4 years, NASA's Kepler mission has contributed 122 confirmed exoplanets and more
than 2,700 exoplanet candidates, and scientists expect that a large fraction of those
candidates will ultimately be confirmed as exoplanets. Confirmed exoplanets are planets
that astronomers have proven to a high degree of confidence, using multiple observations
and, sometimes, two or more different instruments. This is an exciting time for exoplanet
exploration, and the next few years will permit major leaps forward in our understanding
of how many there are, how they formed, and whether they might have conditions that
are hospitable to life as we know it - a condition that is called habitability.
Thanks to the Kepler mission, we now know that when you go outside and look up at the
night sky, virtually every star you see has at least one planet around it. Based on the
latest Kepler results, scientists estimate that at least 17 percent of all the stars out there
have rocky planets orbiting them. Of even greater interest, the results suggest that 15
percent of M stars -- the smallest, coolest class of stars, but also by far the most common
type of star in the galaxy -- have rocky planets in the habitable zone. This number tells
us that the nearest potentially habitable planet could be only 15 light-years away.
Moreover, if that trend holds for other classes of stars, it would mean that there are
approximately 50 billion potentially habitable rocky planets spread throughout our own
NASA's Exoplanet Exploration Program is leading the quest to discover and characterize
exoplanets and search for life in the universe. There are several key exoplanet detection
techniques in use today, with the most prolific being the radial velocity and the transit
techniques. The radial velocity technique uses Doppler shifts in the light of a star to
detect the tiny wobble caused by a planet orbiting around it. This technique is employed
by astronomers to detect exoplanets using large ground-based telescopes around the
world including by NASA-funded scientists at the Keck telescopes in Hawaii. The transit
technique measures the tiny decrease in the brightness of a star that occurs when an
orbiting planet passes in front of it. The transit technique is the method used by NASA's
Kepler mission to detect exoplanets. NASA's Spitzer and Hubble Space Telescopes
(HST) have also used the transit technique for characterization of exoplanet atmospheres,
as will NASA's James Webb Space Telescope (JWST) when it launches in 2018. Other
techniques for exoplanet detection and characterization include direct imaging and
gravitational microlensing. Direct imaging uses a coronagraph or occulting mask to
block light from the central star so the much fainter planet nearby can be discerned. The
Keck telescopes, HST, and, when launched, JWST are all capable of direct imaging.
Microlensing uses Einstein's gravitational bending of light to find planets orbiting distant
stars or isolated planets free floating in interstellar space. NASA is studying a wide-field
infrared survey telescope, the highest priority large-scale space-based activity of the
National Academy of Sciences' most recent decadal survey in astronomy and
astrophysics, which will use this technique to detect exoplanets, and may employ other
technology to characterize exoplanets.
Current State of Exoplanet Exploration
NASA's Kepler mission is revolutionizing the search for extrasolar planets. Launched in
March 2009, NASA's Kepler Space Telescope searches for exoplanet candidates by
continuously measuring the brightness of more than 150,000 stars. When a planet
candidate passes, or transits, in front of the star from the spacecraft's vantage point, light
from the star is blocked. Different sized planets block different amounts of starlight. The
amount of starlight blocked by a planet reveals its size relative to its star. Kepler's
primary goals are to determine how abundant planets are in our galaxy, what the
distribution of sizes and orbits of those planets are, and, ultimately what fraction of stars
might harbor potentially habitable, Earth-sized planets.
As of January 2013, Kepler has identified over 2,700 planet candidates, of which over
350 are nearly the same size as the Earth. In addition, there are 816 "Super Earth"-sized
planets, planets intermediate in size between the Earth and the planet Neptune--as well
as 1,290 Neptune-sized planets; 202 Jupiter-sized planets, and 81 "Super-Jupiter"-sized
planets. More than 50 of Kepler's planet candidates orbit in the habitable zone of their
host star-- the range of distances from a star where the surface temperature of an orbiting
planet might be suitable for liquid water.
NASA's most recent discovery, announced just a few weeks ago, is two new planetary
systems that include three super Earth-size planets in the "habitable zone" of their stars.
The first system, known as Kepler-62, has five known planets: 62b, 62c, 62d, 62e, and
62f. The second system, Kepler-69, system has two known planets: 69b and 69c.
Kepler-62e, 62f, and 69c are the super Earth-sized planets, with diameters just 1.6x, 1.4x,
and 1.7x that of the Earth, respectively. The host star of the Kepler-69 system belongs to
the same class of stars as our sun, called G-type. It is 93 percent the size of the Sun and
80 percent as luminous and is located approximately 2,700 light-years from Earth in the
constellation Cygnus. The host star of the Kepler 62 system is a smaller, cooler K-type
star, just 2/3 the size of the Sun and only 1/5 as bright. These exciting discoveries
illustrate that we are another step closer to finding a world similar to Earth around a star
like our Sun.
Kepler is teaching us that the galaxy is teeming with planetary systems, and giving us
hints that nature makes small planets efficiently. Having completed its prime mission,
and now some 5 months into its extended mission, the Kepler spacecraft is starting to
show its age. We do not know how much longer it will be able to maintain the very
precise pointing required for its exoplanet mission, but we do know that Kepler's legacy
is secure. It has been a pioneer in expanding our understanding of exoplanets and stellar
seismology and its rich legacy will serve as a solid foundation upon which future
missions will build.
Along with Kepler, NASA's Hubble and Spitzer Space Telescopes have also successfully
detected the feeble signature of an exoplanet in the overwhelming glare of its host star.
Specifically, scientists have used the Hubble Space Telescope to measure the absorption
of hydrogen, carbon, oxygen, carbon dioxide, and water vapor in the boil-off from the atmosphere of two transiting Hot Jupiter exoplanets. These large, gaseous giant planets
are easier to detect due to their size and very short orbital periods. Also, scientists have
used the Spitzer Space Telescope to measure the infrared light from a Hot Jupiter
exoplanet and used that to make a temperature map of the planet's atmosphere and
determine that the planet is whipped by ferocious winds.
Future Exoplanet Exploration Missions
Moving forward from the current exoplanet missions in operation and development,
NASA recently selected a new mission, the Transiting Exoplanet Survey Satellite (TESS),
as part of its Explorer Program. Planned to launch in 2017, TESS will undertake a twoyear,
all-sky search for transiting exoplanets around the nearest and brightest 500,000
stars. While Kepler has taught us about the abundance of planets of all sizes in one
particular region of our galaxy, TESS will reveal the exoplanets that are nearest to our
Solar System. TESS is expected to discover thousands of new planets - including Earthsized,
rocky planets - and those systems will be ideal candidates for characterization by
future missions such as JWST and a wide-field infrared survey telescope.
Building on the pioneering observations of the Hubble and Spitzer Space Telescopes and
the exoplanet surveys of Kepler and TESS, JWST will use transit spectroscopy to
determine atmospheric and physical properties of planets ranging in size from Jupiters to
super Earths; it will be able to study the composition, chemistry, and physical conditions
of exoplanet atmospheres. Additionally, JWST will use direct imaging to find and study
young (i.e., still warm) Jupiters and Saturns as well as rings of dust, and icy/rocky
planetessimals (asteroid and Kuiper Belts) in many exoplanet systems.
Beyond JWST, a wide-field infrared survey telescope would complement Kepler's
exoplanet census by finding thousands of planets down to Earth-size that orbit either in or
outside of the habitable zone of their star. NASA is studying such a mission. As part of
that study, NASA is also studying the use of an existing large space telescope system and
the addition of a coronagraph capable of studying the atmospheres of exoplanets around
other stars through direct imaging. By providing the first opportunity for in-space
operations of a high-contrast coronagraph, such a mission would lead the way toward a
future telescope capable of characterizing in detail Earth-like planets around other stars
and searching for evidence of life beyond our Solar System.
NASA is aware that exoplanets are of great interest to the entire science community and
the general public. The science of exoplanets brings together many scientific disciplines.
That is one reason why all of the data from NASA's space telescopes, including Kepler,
Hubble, and Spitzer, is made openly available for analysis by scientists other than the
members of the science teams for those telescopes. This has resulted in an explosion of
discoveries about exoplanets, including some of the discoveries already mentioned. For
citizen scientists, PlanetHunters.org offers a web site where anyone can search through
Kepler data and discover exoplanets. So far, over 18 million observations have been
analyzed, and 34 candidate planets had been found. In October 2012 it was announced
that two volunteers from the Planet Hunters initiative had discovered a novel Neptune-sized planet which is part of a four star double binary system. This is the first planet
discovered to have a stable orbit in such a complex stellar environment.
Exoplanet Technology Development Infrastructure
To make the exoplanet discoveries possible, and to reduce both the risk and cost of future
exoplanet exploration missions, NASA is investing in exoplanet detection technology.
NASA has developed high contrast imaging testbeds, an advanced visible nulling testbed,
deformable mirrors for ultraprecise wavefront control, and a vacuum surface gauge for
surface characterization and deformable mirror calibration. Moreover, NASA has
computational models and software including coronagraph modeling tools, integrated
thermo-optical-mechanic modeling tools, and generalized error-budgeting tools to design
space-based telescopes and instruments capable of detecting and studying exoplanets.
NASA has in place a comprehensive program to detect and characterize exoplanets.
With the progress we have already made, I am confident that it is not a question of
whether or not we will find an Earth-like exoplanet, but when. With our programs, the
active participation of a rapidly growing scientific community, and our partners, we will
continue to make major strides forward in our understanding of the science of exoplanets.
It is programs like Kepler that capture the imagination of everyday people, including our
students of today who will be the scientists and engineers of tomorrow. NASA has
exciting missions such as JWST, TESS, and the wide field infrared survey telescope after
Kepler to reach even farther back in time, to explore other regions of the universe, and to
start characterizing and analyzing the atmospheres of exoplanets. The future of exoplanet
research is bright, and NASA will continue to play a leadership role in that future. I look
forward to answering any questions you may have.