Definition of a planet a little history

Lecture 1

• Lecture 1

• Definition of a planet
• A little history
• Pulsar planets
• Doppler “wobble” (radial velocity) technique

• Lecture 2

• Transiting planets
• Transit search projects
• Detecting the atmospheres of transiting planets

Lecture 3

• Lecture 3

• Microlensing
• Direct Imaging
• Planets around evolved stars

• Lecture 4

• Statistics: mass and orbital distributions, incidence of solar systems, etc.
• Hot Jupiters
• Super-Earths
• Planetary formation
• The host stars

Lecture 5

• Lecture 5

• The quest for an Earth-like planet
• Results from the Kepler mission
• Habitable zones
• Biomarkers
• Future telescopes and space missions

RSun = 6.995x108m

• RSun = 6.995x108m

• Rjup = 6.9961x107m ~ 0.1RSun

• Rnep = 2.4622x107m ~ 4Rearth

• Rearth = 6.371x106m ~ 0.1Rjup ~ 0.01RSun

• MSun= 1.989x1030kg

• Mjup= 1.898x1027kg ~ 0.001MSun = 317.8Mearth

• Mnep= 1.02x1026kg ~ 5x10-5MSun ~ 0.05Mjup = 17.15Mearth

• Mearth= 5.97x1024kg = 3x10-6MSun = 3.14x10-3Mjup

• 1AU = 1.496x1011m

• 1 day = 86400s

Habitable zone defined as where liquid water exists

• Habitable zone defined as where liquid water exists

• Changes in extent and distance from star according to star’s spectral type (ie temperature)

Searching for Earths by transit method

• Searching for Earths by transit method

• Launched 2009 by NASA

• 0.95m schmidt telescope, FOV ~ 105 square deg.

• 150,000 MS stars, with V=10 - >14 mag

• Aim: find an Earth around a Sun-like star in a one year orbit

• Need three transits

• So mission lasts at least three years…

Kepler observes probable transit events

• Kepler observes probable transit events

• “Validates” these

• with 3 transits
• tries to rule out background binaries/triple star systems
• Statistical likelihood planet is “real”

• But transit only gives radius

• To confirm it’s a planet, need mass, and hence density

• Confirm structure: gas giant or terrestrial
• Although we don’t know where boundary lies: ”Super-Earths”

Mass comes from two sources

• Mass comes from two sources

• Radial velocity observations
• But most Kepler stars are too faint for Doppler Wobble measurements with current telescopes
• Transit timing variations

• Kepler & media confuse planet status

• “Earth-sized”?
• “Earth-like”?
• “Earth-mass”?

“Astronomers Find First Habitable Earth-Like Planet”

• “Astronomers Find First Habitable Earth-Like Planet”

• Science Daily, 24 April 2007

• “Gliese 581g: the most Earth like planet yet discovered”

• Daily Telegraph, 29 Sep 2010

• “Super-earth exoplanet found that could support life”

• The Guardian, 13 Sep 2011

Kepler has observed 3 transits

• Kepler has observed 3 transits

• Lies within its star’s habitable zone

• 290 day orbit

• The radius is 2.4x Earth

• NO mass measurement

• Upper limit of 38x Earth
• Could be rocky, or gaseous
• Host star too faint (>11th) for RV

Multiple system of 6 planets

• Multiple system of 6 planets

• Masses measured through transit timing variations

• Effect of gravity on time of centre of successive transits

So we find a planet with the same mass as Earth, and in the habitable zone:

• So we find a planet with the same mass as Earth, and in the habitable zone:

• How can we tell it harbours life?

• Search for biomarkers

• Water
• Ozone
• Albedo