Transcript Extrasolar Planets - University of New South Wales

Extrasolar Planets
Dr. Jade Carter-Bond
(Lillian’s Daughter)
U3A
6 June, 2012
Extrasolar Planets:
What they are, what we know about
them, why we should care, where ET
lives (just kidding!) what I’ve been doing
for the last 12 years and why your tax
dollars should continue to help
me pay my rent
Dr. Jade Carter-Bond
(Lillian’s Daughter)
U3A
6 June, 2012
Astronomy RIGHT NOW!
Today Venus is transiting the Sun and we have great
visibility from Australia.
Start: 8:16 am
End: 2:44 pm
Transits occur 8 years apart and then not for over a
century.
Next transit: 2117
Astronomy RIGHT NOW!
Today Venus is transiting the Sun and we have great
visibility from Australia.
Start: 8:16 am
End: 2:44 pm
Watch either with a telescope with a solar filter (don’t
look at the Sun directly) or online:
http://www.transitofvenus.com.au
http://venustransit.nasa.gov
Astronomy RIGHT NOW!
1639: First transit of Venus observed. Helped to really
cement the heliocentric model of Nicolaus Copernicus.
1716: Edmund Halley suggested observations could help
determine the distance to the Sun
1761: Observations attempted, failed.
Side note: Charles Mason and Jeremiah Dixon were sent to
observe the transit in Sumatra, only reached Cape Town.
They then went on to survey the border between
Pennsylvania & Maryland – the Mason-Dixon line
Astronomy RIGHT NOW!
1769: Highly observed transit.
Side note: Lieutenant James Cook was sent to Tahiti to
observe the transit & was successful. Then opened his
sealed orders, instructing him to look for “Terra
Australis Incognita” . . .
And here we are!
Astronomy RIGHT NOW!
For further reading, have a look at:
The Day the World Discovered the Sun
By Mark Anderson
Chasing Venus
By Andrea Wulf
Jargon
Extrasolar planet:
Planet orbiting a star other than our own sun.
Most extrasolar planets are gas giants (Jupiter,
Saturn, Neptune)
1 Jupiter mass = 318 Earth masses
The first planets
Planet = wandering star
Plato: “the Sun and Moon and five other stars, which
are called the planets” (360 BC) (Mercury, Venus, Mars,
Jupiter & Saturn)
1781: William Herschel discovered Uranus
1846: Neptune discovered
1930: Pluto discovered (we can argue about definitions
later)
Is that it?
1930 – 1963: Several claims for extrasolar planets,
never confirmed
1963: Jupiter-mass planet orbiting “Barnard’s Star”
(second closest star to the Sun)
1973: Proven false, due to equipment installed at the
telescope
JACKPOT!
1994: The first discovery of a planet orbiting a Solartype star, 51 Pegasi (confirmed 1995)
Planet Rush
1990: 0 extrasolar planets
1995: 1 extrasolar planet
2002: 77 extrasolar planets
5 June, 2012:
767 planets orbiting 613 stars
2321 planet candidates
orbiting 1790 stars
What are they like?
Most planets have masses similar to that of Jupiter:
So most extrasolar planets are gas giants.
What are they like?
Most planets orbit closer to their star than Earth does
to the Sun:
But that’s a selection effect/technique bias.
What are they like?
Of the few we can study, they have unusual
compositions.
We have detected:
CH4
CO2
H2
K
TiO
CO
H
H 2O
Na
VO
What are they like?
Extrasolar host stars tend to be metal rich:
We’re not yet sure exactly what that means for planets.
How do we find them?
We very rarely just “see” the planets!
How do we find them?
We very rarely just “see” the planets!
Two main methods are used:
1. Radial velocity shift surveys
2. Transit surveys
Radial Velocity
Basically look for stellar “jiggles”. Does not directly find
a planet.
No planetary companion: random variations
Planetary companion: systematic variations due to
orbits
Radial Velocity
What does a spectrum look like?
Radial Velocity
No planetary companion: random variations
Planetary companion: systematic variations due to
orbits
Radial Velocity
Very successful – found or confirmed more than 700 of
the 767 known planets
But it has issues!
- The effect is greatest for large mass planet in
very close in orbits
- Requires us to observe for at least one full orbit
(Jupiter = 12 years)
- Requires high precision, placing lower limits on
the size of the signal we can detect
Transit Surveys
Transit surveys look for the dimming of a star as a
planet passes in front of it.
Example: the transit of Venus!
Transit Surveys
Transit Surveys
The reduction in light is tiny: often less than 1%
Jupiter: 1%
Earth: <0.01%
The depth of the dip gives
us the size of the planet;
the width gives us how
long it takes to pass across
the star → orbit size
Transit Surveys
Again, this method has issues:
- It requires the system to be aligned “just right”
- It requires high precision and little interference
One solution: Do it from space!
Kepler Mission
Kepler launched March 6, 2009, to “stare” at stars and
look for light dips.
Possible to find Earth mass planets in orbits similar to
that of the Earth.
Wildly successful!
61 confirmed planets
2321 planet candidates
Kepler Mission
Wanna help?
You too can be a planet hunter!
http://www.planethunters.org/
Anyone can look at public Kepler data and identify
transit dips.
Successful – two papers already published with
possible planets
Why?
Why?
1. To understand our own Solar System – how it
formed and why it is the way that it is.
2. Are we alone?
Why?
Carl Sagan said it best with his introduction to “Pale
Blue Dot”
Photo taken by Voyager 1 (launched 1977) in 1990 from
6 billion km away from Earth. Earth is just 0.12 pixel in
size.
Thank you!
Any questions?
http://www.transitofvenus.com.au
http://venustransit.nasa.gov
The Day the World Discovered the Sun
By Mark Anderson
Chasing Venus
By Andrea Wulf
http://www.planethunters.org/