Chapter 12.  Extrasolar Systems ASTA01 @ UTSC – Lecture 17 Chapter 12.  Extrasolar Systems Extrasolar planet discovery: - Pulsar planets Wobble method (radial velocity) Transit (occultation, eclipse) method Examples and statistics

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

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

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

<1 Myr 5 Myr 20 Myr 200 Myr 4567 Myr

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

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.

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

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.

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

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.

Extrasolar Planets: discovery Pulsar’s name is PSR 1257+12 It formed in a supernova explosion and has 3 ms period of rotation 4 Planets have masses: 0.02, 4.3, 3.9, 0.0004 ME distances 0.19, 0.36, 0.46, 2.6 AU

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

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

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.

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

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.

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.

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.

Extrasolar Planets

Extrasolar Planets 2012 Planets known so far

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.

Beta Pictoris giant planet

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.

Extrasolar Planets: Gliese 581

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.

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.

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.

Kepler 11 system

2011

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.

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.