1. Chapter 12.  Extrasolar Systems
UTSC – Lecture 17
Chapter 12.  Extrasolar Systems
Extrasolar planet discovery:
- Pulsar planets
Wobble method (radial velocity)
Transit (occultation, eclipse) method
Examples and statistics

2. HD 1415969 Age ~ 5 Myr, a transitional disk
Observations by Hubble Space Telescope (NICMOS near-IR camera).
Age ~ 5 Myr,
a transitional disk
Gap-opening PLANET ?
So far out?
Only if migrated outward
R_gap~350AdR ~ 0.1 R_gap

3. HD 14169A disk gap confirmed by new observations
(HST/ACS)

4. Alpha Pisces Austrini
(α PsA)
Fomalhaut
A disk of a bright southern star

5. <1 Myr
5 Myr
20 Myr
200 Myr
4567 Myr

6. Planets Orbiting Other Stars
Are there planets orbiting other stars?
Are there planets like Earth?
The evidence so far makes that seem likely
YES
We already have found Earth-mass planets
But we don’t yet know how closely they resemble our planet

7. Extrasolar Planets
A planet orbiting another star is called an extrasolar planet or an exoplanet
Such a planet would be is usually quite faint and difficult to detect close to the glare of its star.
However, there are ways to find these planets.
To see how, all you have to do is imagine walking a dog.

8. Think of someone walking a poorly trained dog on a leash.
Extrasolar Planets
Think of someone walking a poorly trained dog on a leash.
The dog runs around pulling on the leash.
Even if it were an invisible dog, you could plot its path by watching how its owner was jerked back and forth around the
Center of Mass

9. Extrasolar Planets
In the same way, astronomers can detect a planet orbiting another star – by watching how the star moves as the planet tugs on it.

10. How the star moves is revealed by either:
Extrasolar Planets
How the star moves is revealed by either:
It’s sinusoidal motion on a sky (astrometric detection), or
How its light changes frequency due to te Doppler effect (radial velocity detection), or
If it sends pulses as a pulsar, then by the time delay of pulse arrival times
When the star approaches us, we see lower frequency of pulses, or of electromagnetic waves

11. Extrasolar Planets: discovery in 1992
[In 1988, Canadian astronomers Bruce Campbell, G.A.H. Walker, and S. Yang discovered an extrasolar planet orbiting a binary star system, but their discovery was not confirmed until 2002.]
The first 3 confirmed extrasolar planets were discovered around a pulsar by the Polish astronomer Alex Wolszczan (b. 1946)
[read: Volsh-chan] in 1992
He studied & worked in Toruń, the city of Copernicus, but discovered planets with the Arecibo radio telescope in Puerto Rico, with his coworker D. Frail.

12. Extrasolar Planets: discovery
Pulsar’s name is PSR
It formed in a supernova explosion and has 3 ms period of rotation
4 Planets have masses:
0.02, 4.3, 3.9, ME
distances 0.19, 0.36, 0.46, 2.6 AU

13. Chart of three PSR 1257+12 planets & inner solar system planets

14. Extrasolar Planets: 51 Peg
The first planet orbiting a sunlike star was discovered in 1995 around the star 51 Pegasi.
As the planet circles the star, the star wobbles slightly.
The very small motions of the star are detectable as Doppler shifts in the star’s spectrum.
This is the same technique used to study spectroscopic binary stars.
Michel Mayor (b.1942), Switzerland

15. Extrasolar Planets: 51 Peg
From the motion of the star and estimates of the star’s mass, astronomers can deduce that the 51 Peg b planet has half the mass of Jupiter and orbits only 0.05 AU from the star ( << sun-Mercury distance)
Half the mass of Jupiter amounts to 160 Earth masses. A large planet, larger than Saturn.

17. For years, they had assumed that many stars had planets
Extrasolar Planets
Astronomers were not surprised by the announcement that a planet orbits 51 Peg
For years, they had assumed that many stars had planets
Nevertheless, some of them (Canadian David Grey) greeted the discovery with skepticism
That skepticism led to careful tests of the data and further observations that confirmed the discovery

18. Extrasolar Planets
Over 500 planets have been discovered in this way – including at least three planets orbiting the star Upsilon Andromedae, and five orbiting 55 Cancri – true planetary system.
More than 40 such multiple-planet systems have been found.

19. Extrasolar Planets
Another way to search for planets is to look for changes in the brightness of a star when the orbiting planet crosses in front of or behind it.
The decrease in light is
very small, ~Rpl 2
Astronomers have used
this technique to detect
a few 1000s of planets as
they crossed in front of their
stars.

20. Extrasolar Planets
The Spitzer Infrared Space Telescope has detected two planets when they passed behind their stars.
These planets are hot and emit significant infrared radiation.
As they orbit their parent stars, astronomers detect variation in the amount of infrared from the system.
edit
Measurements reveal that they have Jupiter-like diameters as well as masses. So, astronomers conclude they have Jovian densities and compositions.

21. Extrasolar Planets

22. Extrasolar Planets
2012
Planets known so far

23. Extrasolar Systems: the first images, HR 8799
Actually getting an image of a planet orbiting another star is about as easy as photographing a bug crawling on the bulb of a searchlight miles away.
Planets are small and dim and get lost in the glare of the stars they orbit.

24. Beta Pictoris giant planet

25. Extrasolar Planets
In 2007, astronomers discovered what could be low-mass Earth-like planets orbiting a red dwarf star named Gliese 581 located a mere 20.3 light-years away.
In 2011, a team of scientists in France confirmed that at least one of the planets could have an atmosphere and oceans, and support Earth-like life.

26. Extrasolar Planets: Gliese 581

27. Extrasolar Planets: Kepler satellite observatory
The main aim of the Kepler mission is to find Earth like planets in habitable zones around other stars.
For the first time in the history of our search for the worlds that resemble our own, we have the technical capabilities to see small rocky planets.

28. Extrasolar Planets
The sizes of the newly discovered planets range from 1.5 times the size of Earth to large Jupiter-sized worlds.
Spectral analyses of trails of smaller planets show traces of silicates (building blocks of rocks), ice, and water.
The Spitzer infrared telescope, which prior to the Kepler mission discovered numerous large, hot, Jupiter-like planets around their stars, is being used to confirm the Kepler telescope findings.

29. Extrasolar Planets: Kepler 11 system
In the few first months of the mission more than 1200 planet candidates were detected, many of them multiple planetary systems.
One such system is Kepler 11, six tightly packed planets located 2000 light-years from Earth; planets range from 2.5 to 4.5 times Earth’s size.

30. Kepler 11 system

31. 2011

32. Extrasolar Planets
Some unusual arrangements of planets have been discovered by the Kepler mission.
Notably, astronomers were shocked to see two planets sharing an orbit – the planets were arranged in the exact angular distance that theoretically allows for such an arrangement.
Seeing such variety of possibilities allows us to explore and test many hypotheses about our own solar system’s origin and formation.

33. Extrasolar Planets
The discovery of extrasolar planets gives astronomers added confidence in the solar nebula theory.
The theory predicts that
planets are common.
Astronomers are finding them
orbiting many stars.