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DEPARTMENT OF PHYSICS AND ASTRONOMY
3677 Life in the Universe:
Extra-solar planets
Dr. Matt Burleigh
www.star.le.ac.uk/mrb1/lectures.html
Course 3677 Life in Universe 2013/2014 Academic Year
Course Given by Prof. Mark Sims and Dr. Matt Burleigh
Topics: Life in Universe and Extra-Solar Planets
Lecture Dates and Lecturer
Actual
Lecture
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Lecture by
Topic
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Time
Date
Nominal Course
Order 2013/14
M.R. Sims
M. Burleigh
M. Burleigh
M. Burleigh
M. Burleigh
M.R. Sims
M.R. Sims
M.R. Sims
M.R. Sims
M.R. Sims
M.R. Sims
M. Burleigh
Both
Life in Universe
Extra-Solar Planets
Extra-Solar Planets
Extra-Solar Planets
Extra-Solar Planets
Life In Universe
Life In Universe
Life In Universe
Life In Universe
Life In Universe
Life In Universe
Extra-Solar Planets
Continuous
Assessment Answers
Revision Lectures
Phys A
KE LT2
Phys A
Phys A
KE LT2
Phys A
Phys A
KE LT2
Phys B
KE LT2
Phys B
KE LT2
Phys B
1300
1300
1300
0900
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0900
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1100
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1100
5/11
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12/11
13/11
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4/12
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8
9
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11
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6
7
12
13
R1
R2
M. Burleigh
M.R. Sims
Phys D
Phys B
0900
0900
7/5/14
15/5/14
Please note course is not in nominal order due to availability of Lecturers
Course has been extensively revised from previous years as Prof. Raine is no longer teaching part of
the course, consequently exam format has changed to 4 questions two short (20 marks each), two
long (30 marks each) all compulsory.
Dr. Matt Burleigh
3677: Life in the Universe
Course outline
• 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:
secondary eclipses & transmission spectroscopy
– Transit timing variations
Dr. Matt Burleigh
3677: Life in the Universe
Course outline
• Lecture 3
–
–
–
–
Microlensing
Direct Imaging
Other methods: astrometry, eclipse timing
Planets around evolved stars
• Lecture 4
– Statistics: mass and orbital distributions, incidence of solar
systems, etc.
– Hot Jupiters
– Super-Earths
– Planetary formation
– Planetary atmospheres
– The host stars
Dr. Matt Burleigh
3677: Life in the Universe
Course outline
• Lecture 5
– The quest for an Earth-like planet
– Habitable zones
– Results from the Kepler mission
• How common are rocky planets?
• Amazing solar systems
– Biomarkers
– Future telescopes and space missions
Dr. Matt Burleigh
3677: Life in the Universe
Useful web sites
• Extra-solar planets encyclopaedia: exoplanets.eu
• Exoplanet Data Explorer (California Planet Survey):
exoplanets.org
• NASA exoplanet archive:
exoplanetarchive.ipac.caltech.edu
• Planet hunters (Zooniverse): www.planethunters.org
• Kepler mission: kepler.nasa.gov
• Next Generation Transit Survey: www.ngtransits.org
Dr. Matt Burleigh
3677: Life in the Universe
Useful books
• Extrasolar planets & Astrobiology: Caleb A.
Scharf
• Extrasolar planets: the search for new worlds:
Stuart Clark
• Transiting Exoplanets: Carole A. Haswell
• The Exoplanet Handbook: Michael Perryman
• An Introduction to Astrobiology: Iain Gilmore &
Mark Sephton
• Life in the Universe: Bennett & Shostak
Dr. Matt Burleigh
3677: Life in the Universe
Useful numbers
•
•
•
•
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
Dr. Matt Burleigh
3677: Life in the Universe
What is a planet?
• International Astronomical Union
definition –
– An object orbiting a star
– Too small for dueterium fusion to
occur
• Less than 13 times the mass of Jupiter
– Formation mechanism?
• Forms from a circumstellar disk of dust
and gas around a young star
– Lower mass limit – IAU decided
that Pluto should be downgraded!
Dr. Matt Burleigh
3677: Life in the Universe
What is a planet?
Above, left to right: limb of Sun, late M
(red) dwarf, L brown dwarf, T brown
dwarf, Jupiter.
The coolest stars, old brown dwarfs and
gas giant planets have the same radii!
Dr. Matt Burleigh
3677: Life in the Universe
A brief history of extra-solar planets
• 16th century: the Italian philosopher Giordano
Bruno said that the fixed stars are really suns like
our own, with planets going round them
• 19th Century: astronomers believed orbital
anomalies in the binary star 70 Oph could be
explained by an unseen planet, but later
disproved
• 1950s & 60s: Peter van de Kamp concluded that
irregularities in the high proper motion of nearby
Barnard’s Star were caused by a planet. Sadly,
this too turned out to be erroneous.
• late 1980s: Canadian Gordon Walker found
tentative evidence for exoplanets using radial
velocity method: but not confirmed until 2000s!
• 1991: Andrew Lyne & Setnam Shemar at Jodrell
Bank claimed to have discovered a pulsar planet
in orbit around PSR 1829-10, using pulsar timing
variations. They withdrew the claim later that
year due to an error in their calculations.
New York Times
16th April 1963
Dr. Matt Burleigh
3677: Life in the Universe
A brief history of extra-solar planets
• 1991 Radio astronomers Alex Wolszczan & Dale
Frail discovered planets around a pulsar
PSR1257+12
– Variations in arrival times of pulses suggests
presence of three or more planets
– Planets probably formed from debris left after
supernova explosion
• 1995 Planet found around nearby Sun-like star 51
Peg by Swiss astronomers Michel Mayor & Didier
Queloz using the “Doppler Wobble” method
– Most successful detection method by far, but other
methods like transits are now very successful
• >1000 exoplanets confirmed to date by all
methods
– >100 found since I gave this lecture last year
– Kepler has several thousand more candidates
Dr. Matt Burleigh
3677: Life in the Universe
Blue: radial velocity, Green: transiting, Red: microlensing,
Orange: direct imaging, Yellow: pulsar timing
Dr. Matt Burleigh
3677: Life in the Universe
Dr. Matt Burleigh
3677: Life in the Universe
Dr. Matt Burleigh
3677: Life in the Universe
Pulsar planets
• Pulsars are neutron stars that emit radio pulses every ~second as they
spin
– More stable and accurate than an atomic clock
• If a planet accompanies the pulsar, then the pulsar will orbit the centre
of mass of the system
– The pulses will then arrive earlier or later than expected
• Radio observations have found a dozen or so such “pulsar planets”
– Wolszczan & Frail’s discovery of PSR1257+12’s planets in 1991 at Arecibo
in Puerto Rico were the first confirmed exoplanets
– PSR1257+12’s planets are all ~Earth mass or smaller
Dr. Matt Burleigh
3677: Life in the Universe
Pulsar planets
• Pulsars are created when
a massive star (>8Msun)
explodes as a supernova
– Their original planetary
systems will not survive
– Radio-detected planets
thought to have formed
from supernova debris
– Planets will be bathed in
high energy radiation
from pulsar – no chance
of life!
Dr. Matt Burleigh
3677: Life in the Universe
Planet Hunting: The Radial Velocity Technique
(“Doppler Wobble”)
• Star + planet orbit
common centre of gravity
• As star moves towards
observer, wavelength of
light shortens (blue-shifted)
• Light red-shifted as star
moves away
873 planets detected by Doppler
Wobble inc. 142 multiple systems
Dr. Matt Burleigh
3677: Life in the Universe
Measuring Stellar Doppler shifts
• Method:
– Observe star’s spectrum through a cell of iodine gas
– Iodine superimposes many lines on star’s spectrum
– Measure wavelength (or velocity) of star’s lines relative to the
iodine
• Measure:
 Dl / le = (l0-le) / le = vr / c
Dr. Matt Burleigh
lo=observed wavelength, le=emitted wavelength
3677: Life in the Universe
M* from spectral type
Dr. Matt Burleigh
3677: Life in the Universe
Doppler Wobble Method
• Since measure K (= v* sin i), not v* directly, only know
mass in terms of the orbital inclination i
• Therefore only know the planet’s minimum mass, M sin i
– If i=90o (eclipsing or transiting) then know mass exactly
Orbital
plane
i=900
Orbital
plane
i0
Dr. Matt Burleigh
3677: Life in the Universe
Example: 51 Peg
• P= 4.15days =
4.15x86400s =
3.5856x105s
• G5V star, M*=1.11Msun
= 1.11x1.989x1030kg
= 2.21x1030kg
• Find r = 0.052AU,
vpl=1.37x105ms-1
Mpl sin i = 0.45Mjup
Dr. Matt Burleigh
3677: Life in the Universe
Above: eccentric orbit
(e=0.93)
Top right: 55 Cancri
multiple-planet system (4,
maybe 5 planets)
Bottom right: 3 planet
HD37124 system
Dr. Matt Burleigh
3677: Life in the Universe
HARPS radial velocity spectrograph
• Built by Geneva Observatory
• First installed on ESO 3.6m at La
Silla, Chile in 2002/3
• Has found over 130 planets
• Precision 30cm/s – 1m/s
• Simultaneously observes star and a
reference Thorium lamp through two
separate fibres
• Highly stable optical bench, housed
in sealed, thermally stable room
• Second HARPS installed on Italain
Galileo telescope on la Palma 2012
Dr. Matt Burleigh
3677: Life in the Universe
Doppler Wobble Method
• Precision of current surveys routinely <1m/s
– Jupiter causes Sun’s velocity to vary by 12.5m/s
– All nearby, bright Sun-like stars are good targets
• Lots of lines in spectra, relatively inactive
– Smallest planet found by this method is ~1Mearth:
Alpha Cen Bb – nearest star system to us!
– Most are Neptune size and larger
• Length of surveys limits distances planets
have been found from stars
– Earliest surveys started 1988
– Jupiter (5AU from Sun) takes 12 yrs to orbit Sun
– Saturn takes 30 years
• Would be strongly hinted at but not yet completed
one orbit since surveys began
– Do not see planet directly
Dr. Matt Burleigh
3677: Life in the Universe
Alpha Cen Bb
• Alpha Cen system is the
nearest star system to us
• Alpha Cen B has been
monitored by radial velocity
method
• Very recent discovery of a
rocky planet:
• Minimum mass 1.1xEarth
• Period 3.2 days
•
• Dumusque et al. 2012, Nature
Thought: if Alpha Cen B has a rocky
planet, do most stars have rocky
planets?
Dr. Matt Burleigh
3677: Life in the Universe