Extrasolar Planets

Dr. Jade Carter-Bond(Lillian’s Daughter)

U3A6 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 helpme pay my rent

Dr. Jade Carter-Bond(Lillian’s Daughter)

U3A6 June, 2012

Astronomy RIGHT NOW!

Today Venus is transiting the Sun and we have great visibility from Australia.

Start: 8:16 amEnd: 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 amEnd: 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.auhttp://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 SunBy Mark Anderson

Chasing VenusBy 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 planetsPlanet = 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 Solar-type 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 stars2321 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 H2O 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 planets2321 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.auhttp://venustransit.nasa.gov

The Day the World Discovered the SunBy Mark Anderson

Chasing VenusBy Andrea Wulf

http://www.planethunters.org/