Kepler: a search for a habitable planet

1
Kepler a search for a habitable planet

• Teresa Wong
• Northwestern University
• Earth 438

2
Overview

• Mission explore the structure and diversity of
  planetary systems
• Launched March 2009

3
Scientific goals

• Determine the percentage of terrestrial and
  larger planets there are in or near the habitable
  zone of a wide variety of stars
• Determine the distribution of sizes and shapes of
  the orbits of these planets
• Estimate how many planets there are in
  multiple-star systems
• Determine the variety of orbit sizes and planet
  reflectivities, sizes, masses and densities of
  short-period giant planets
• Identify additional members of each discovered
  planetary system using other techniques
• Determine the properties of those stars that
  harbor planetary systems

4
Habitable planet

• Mass between about ½ - 10 Earth masses, or radii
  about 0.8 2.2 Earth radii

5
Where to look for?
Kasting, Whitmire, and Reynolds, (1993)
6
Detection of extrasolar planets Transition method

• Transit a planet crossing in front of its star
  as viewed by an observer
• Transits produce a small change in a star's
  brightness of about 1/10000, lasting for 2 to 16
  hours

7
Detection of extrasolar planets Transition method

• Orbital size and mass of the planet calculated
  from Keplers 3rd law
• The fractional change inbrightness/transit depth
  the ratio of the area of the planet to the area
  of the star
• Duration of transit
• From orbital size and temperature, the planets
  characteristic temperature can be calculated

8
Detection of extrasolar planets Photometer

• Continuously point at a single star field in
  Cygnus-Lyra region except during Ka-band
  downlink.
• Monitor 100,000 main-sequence stars for planets
• Mission lifetime of 3.5 years extendible to at
  least 6 years

9
(No Transcript)
10
Kepler spacecraft
11
Kepler spacecraft and photometer

• 0.95m diameter telescope
• Reduce noice from photon counting statistics, so
  that it can measure Earth-like transit
• 105 square degrees of view
• Detectors 95 mega pixels (42 CCDs with 2200x1024
  pixels)
• Photometric One-Sigma Noise Performance
• Total noise with solar-like stellar variability
  and photonshot noise for an mv12 star lt 2x10-5
• Flight segment and instrument mass 1071 kg,
  maximum expected (10/06)
• Flight segment and instrument power 771 W,
  maximum expected (10/06)

12

• As of July 2008
• the photometer is integrated with the spacecraft
  bus
• Solar array and reaction wheel assemblies
  installed
• Complete flight segment comprehensive performance
  test done,as well as acoustics, vibration, and
  pyro-shock tests

Photometer Being Lowered onto Spacecraft
13
Geometric probability
14
Signal-to-noise dependence
SNR vs transition duration for various stellar
variabilities
15
Simulated transit events
16
Simulated events
17
Expected results

• From transits of terrestrial planets in one year
  orbits
• About 50 planets if most are the same size as
  Earth (R1.0 Re) and none larger
• About 185 planets if most have a size of R1.3 Re
• About 640 planets if most have a size of R2.2 Re
• About 12 with two or more planets per system

18
References

• http//kepler.nasa.gov/
• http//www.ballaerospace.com/gallery/kepler/