Transcript Credit: NASA

KEPLER MISSION OVERVIEW
NASA/Ames Research Center/Kepler Mission
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“Is Earth unique, and if not, how many Earth-size planets might there
be in our galaxy, orbiting their parent stars at just the right distances to
have liquid water on their surfaces?”
“What are the distributions in planet size, in planet orbits, and the
types of stars hosting planets”? (modified from NASA, Press Kit/Feb. 2009)
As one mission scientist put forth: “while not
searching for ET, the Kepler Mission may
potentially discover ET’s home”
Kelper Mission Overview (outline)
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Paradigm Changing Mission and Overview
Queries being addressed through Kepler
What the Kepler mission is designed to do
Kepler’s unique features
Kepler’s target
Kepler’s orbit
Kepler’s spacecraft
o Dimensions
o Command and control
o The Kepler instrument – Photometer
o The sunshade
o CCD radiator
o Solar array
o Thruster modules
o High gain antenna
o Data compilation
Kepler Mission Overview (cont.)
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Transit method
o Characteristics of a planetary transit
o Probability of transits
o Why does Kepler need so many (6.5 million) stars
o Disadvantages in method
o Advantages
Follow-up to potential target
Summary
NASA’s 1st mission to identify:
Earth-size and
smaller planets
Credit: NASA
Kepler’s unique features
 Largest Schmidt telescope in space
 170,000 multi-channel photometer
 95 mega-pixel focal plane
 Instrument precision of 10 ppm
 Largest field of view for such an
instrument
While incredibly powerful astronomical instruments,
when compared to the Kepler mission, the Hubble Space
Telescope and other space telescopes are not optimized
for planet reconnaissance. They typically point at many
different areas of the sky, have very small fields of view,
and rarely look continuously at just one star field.
HST
Kepler targeting
Credit: Jon Lomberg
The Kelper
telescope is
detecting exoplanet
candidates by
monitoring the
Cygnus Lyra region
of the Milky Way
galaxy and
measuring the
brightness of more
than 100,000 stars
every 30 minutes,
including Earthsize planets that
can be detected by
the telescope
Kepler’s orbit
 Earth-trailing heliocentric (http://www.youtube.com/watch?v=54fnbJ1hZik)
 Orbital period equaling 371 days
Credit: NASA
Dimensions:
Diameter = ~ 3 m
Height = ~ 5 m
Credit: NASA
The command manager
performs command
processing of both
stored-sequence and
real-time commands.
The command and data
handling system is the
spacecraft’s brain. It can
operate the spacecraft
either with commands
stored in computer
memory or via real-time
commands radioed from
Earth for immediate
execution. In addition, it
handles engineering and
science data destined to
be sent to Earth.
The sole Kepler instrument is a
photometer.
It has a Schmidt telescope with
a 95 cm clear aperture and 140 cm
primary mirror; it has a 105
degrees2 field of view
Credit: NASA
The photometer features a focal plane array with 95 million pixels.
The focal plane array is the largest camera NASA has flown in space.
The Kepler focal plane
consists of 42 science
CCD and 4 fine guidance
CCD. Each science CCD
is 2200 columns by 1024
rows, thinned, backilluminated, anti-reflection
coated, 4-phase devices
manufactured by e2v.
Each CCD has two
outputs with the serial
channel on the long edge.
The pixels are 27 µm2,
corresponding to 3.98
arcsec on the sky
Credit: NASA
Interior perspective of the Kepler Photometer
Credit: NASA
 Bandpass = 430-890 nm
 Dynamic range = 9th to 15th magnitude stars
 Science data storage = ~ 2 months
The Kepler photometer uses a
pointing control system to orient itself
in deep space (i.e., to determine and
control the spacecraft’s attitude).
The two star trackers, which provide
the spacecraft with inertial attitude
data, are part of an attitude
determination and control system. The
system includes fine guidance
sensors, reaction wheels, and coarse
sun sensors.
Credit: NASA
Credit: NASA and Ball Aerospace
The sunshade provides a 55 degree sun avoidance angle for the
photometer, while at the same time allowing for a 16 degree field
of view. The sunshade provides continuous viewing of the star
field in Cygnus throughout the lifetime of the mission.
The CCD array is cooled by heat
pipes connected to an external
radiator.
Kepler’s thermal control system
includes heat pipes, thermally
conductive adhesives, heaters, and
temperature sensors. Propane and
ammonia flowing through pipes
embedded in the spacecraft’s
exterior panels cool the focal plane.
The electrical power system provides
power for all onboard systems, including
the photometer. Power is provided by the
solar arrays and an onboard battery.
The solar array is rigidly mounted on the
spacecraft’s upper deck, providing both
power and a shield for the photometer
from direct solar heating.
The solar array is expected to generate up
to 1,100 Watts of electrical power
Firing of the thrusters removes the
excess momentum from the reaction
wheels. There is enough fuel to last
for ~ 6 years. Once the hydrazine is
exhausted, the reaction wheels are
expected to spin up to rates that
exceed their design capacity.
The high-gain antenna is part of the
telecom subsystem designed to operate
out to a distance of 96 million
kilometers. The system also uses two
receiving low-gain antennas and two
transmitting low-gain antennas. The
system can receive commands from
Earth at speeds ranging from ~7 to
2,000 bits per second, and can transmit
data to Earth from 10 to 4.3 million bits
per second, the highest data rate of
any NASA mission to date.
Data Compilation
The 95 megapixels of data can’t be stored continuously for 30 days,
thus the science team has pre-selected 5% of the total pixels of
interest associated with each star of interest, approximating. These
data are then recompiled, compressed, and stored. The on-board
photometer flight software compiles the science and ancillary pixel
data and stores them in a 16 GigaByte solid-state recorder.
Porter et al., 2012, Ecological and evolutionary informatics 2, 121-129
Method - Transit Method
Credit: NASA
Tiny dims
(“winks”) in star
brightness
(which can last
anywhere from
an hour to half a
day) occur when
a planet passes
in front of a star
(planetary
transit). The
amount the star
dims depends on
the relative sizes
among the star
and planet.
Credit: NASA AMES
Characteristics of a Planetary Transit
 Period of recurrence
of the transit
 Duration of the transit
 Fractional change in
brightness of the star
Credit: NASA
Exoplanets are confirmed by observing several transits that have the
same decrease in star light, time to transit the star, and total amount of
time between successive transits. It takes ~ 1000 people-hours to
confirm an exoplanet
 Transits are only seen when a star’s planetary system is nearly
perfectly aligned with our line of sight.
 The probability of a transit depends on the size of the planet’s orbit
relative to the size of the star.
 For a planet in an Earth-sized orbit, the possibility of it being aligned
to produce a transit is less than 1%.
H-alpha image (view
into the
chromosphere) of
(left) a Jupiter transit
superimposed to scale,
as if viewed from
outside our solar
system, and (right) an
Earth transit to scale.
Credit:NASA
3 or more transits with a consistent period, brightness change, and duration
collectively provide ample evidence that an extra-solar planet has been identified.
Probability of transits
i = inclination of planet’s orbit to the plane of the sky
Ɵ0 = angle of planet’s orbit with respect to the observer (= 90˚ - i)
a = planet’s semi-major axis
Rs = stellar radius
Then, the probability that a planet will transit is given by:
Modified form http://www3.geosc.psu.edu/~ruk15/Transits/Transits.ppt
Probability of detecting Jupiter in the solar system =
700000km (solar radius) /5.2 AU (semi major axis
of 778 million km) = ~0.1%
To find one Jupiter at 5.2 AU from a Sun like star, one
needs to look at ~ 1/(0.1%) ~ 1/(0.1%) ~ 1000 stars
• Beatty, T.G., and Seager, S. (2010) Transit probabilities with stellar inclination constraints.
The Astrophys. Journ. 712, 1433-1442.
• Brown, R.H. (1968) Measurement of stellar diameters. Ann.Rev.AstrA&Astro. 6, 13-38.
• Cassen, P., Guillot, T., and Quirrenbach, A. (2006) Extrasolar Planets. Swiss Soc. For Astr.
&Astr. 31, DOI: 10.1007/978-3-540-31470-7 .
 ~ 6.5 million stars occupy the target region between Cyngnus
and Lyra.
 Why are so many necessary for the Kepler
mission?
 Due to the way in which the Kepler instrument searches for
planets, there has to be planetary systems that are lined up so
that the planet actually passes between the star and Kepler
telescope and its orbit. The probability of that is estimated to be
only 1-10%.
 So of those 6.5 million scattered over the target region, only
about 200,000 our of interest to the Kepler team.
 Of those of interest, the team selects 170,000 or so that are most
suitable to perform reconnaissance for planets.
 The team expects to end up with somewhere between a few
hundred and few thousand signals that are really planets around
the stars that are being looked at.
The transit method makes it possible to:
 determine the size of the planet through the lightcurve (will be
discussed in the coming weeks).
 study the atmosphere of the transiting planet. When the planet
transits the star, light form the star passes through the upper
atmosphere of the planet. By studying the high-resolution stellar
spectrum carefully, one can detect elements present in the planet’s
atmosphere.
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measure the planet’s radiation when the planet is blocked by its
star (secondary eclipse)
The transit method has two major
disadvantages:
1. Planetary transits are only observable for
planets whose orbits are perfectly aligned with
the instrument’s vantage point.
o The probability of a planetary orbital plane
being directly on the line-of-sight to a star is the
ratio of the diameter of the star to the diameter
of the orbit. ~ 10% of planets with small orbits
have such alignment, and the fraction decreases
for planets with larger orbits. For a planet
orbiting a sun-sized star at 1AU, the probability
of a random alignment producing a transit is
0.47%.
Therefore, the method cannot answer the
question of whether any particular star is a
host to planets.
The transmit method has two major disadvantages (cont.)
2. The method results in a high rate of false detections. A transit
detection requires additional confirmation, typically from the radialvelocity method.
Follow-up to a potential target
 Once Kepler’s candidate planetary transit events are
identified, a team of ground-based observers perform
follow-up observations to rule out false positive events that
may mimic a sequence of transits.
 The follow-up observations provide additional information
about the characteristics of the parent stars, their size, mass,
age, etc., and should lead to the detections of other planets
in the systems. If a planet has been detected by the transit
method, for example, the Transit Timing Variation method
(TTV) can be applied based on the variations in the timing
of the transit. The method is capable of detecting additional
planets in the system with sizes potentially as small as
Earth-sized planets (see Holman & Murray (2005) Science).
Results of the Paradigm-changing
Kepler mission will be highlighted in
the coming weeks
Credit: http://orbiterchspacenews.blogspot.com/2010/12/kepler-mission-manager-update.html