How to find an exoplanet
A presentation for Science Week 2013
Sheffield College (Norton Campus)
Ken Crow
Presentation Outline
1. What is an exoplanet?
2. Why look for exoplanets?
3. How many exoplanets have been found?
4. A (very short) history of exoplanet detection.
5. Exoplanet detection techniques (the 3 main ones).
6. What does the future hold?
What is an exoplanet?
The term exoplanet is used by
astronomers.
It is shorthand for :
Extra Solar Planet
This means a planet around another star
(a star that is not our sun).
Stars are vast distances away.
The nearest star is 40 trillion kms away.
Why look for exoplanets?
• Are we alone in the universe?
• Is Earth in a special place?
• Is there a special place for life in the galaxy?
• Is sentient life unique to humanity?
• Is simple life common in the cosmos?
• What type of planetary system supports life?
• What kind of chemistry supports life?
How many exoplanets?
New instruments and technologies.
Currently to date: (April 2013)
3315 potential planets
882 confirmed planets
(A very short) history of exoplanet detection.
•
1992
•
Alex Wolszczan and Daile Frail detect first exoplanet.
•
Detected by measuring timings of a Pulsar (Neutron star).
•
Planets orbiting a dying stellar remnant.
•
1995
•
Michel Mayor and Didier Queloz detect planet around 51 Pegasi.
•
Ordinary main sequence star.
•
Since the first 2 confirmed exoplanets, detection has increased rapidly.
Images of instruments used for detecting.
Hubble space telescope launched 1990
Kepler launched 2009
Exoplanet observation methods
• Radial velocity
• Watching the spectral nature of a star change over time.
• Transiting light curves
• Watching a star dim as a planet passes in front of it.
• Gravitational micro-lensing
• Detecting objects as they disrupt the light from a distant star.
Radial Velocity
Common ‘centre of mass’ (CoM)
Both star and planet orbit ‘CoM’
Star would seem to ‘wobble’
Spectra observed of starlight
Absorption lines move back and
forth
Radial velocity
Advantages
Disadvantages
•
Highly repeatable measurements
•
Biased toward high mass close orbit
•
Ground based measurements
•
Each additional planet confuses
results
Transiting light curves
Orbital plane in line of sight
Small chance of success
Planet passes in front of star
Starlight dims
Space based mission
Mass, atmospheric conditions, temp.
Transiting light curves
Advantages
Disadvantages
•
Lot of planetary information gained
•
Biased toward high mass
•
A lot of stars monitored at once
•
Space based mission required
•
Small chance of alignment
Gravitational Microlensing
3 star systems line up
Very small chance of detection
Gravity magnifies distant light light
Planetary system causes ‘blip’
Small planets far orbits possible
Gravitational Microlensing
Advantages
•
Small planets at far orbits detected
•
A lot of stars monitored at on
•
Many stars monitored at once
Disadvantages
•
Chance alignments with very small
probability
•
Planetary deviations easily missed
•
Deviations will not repeat
The future?
NASA & ESA agree on joint instrument
Launched in 2017
Transiting Exoplanet Survey Satellite (TESS)
All sky survey
Any questions?
Thanks for listening