Extrasolar Planets This exoplanet orbiting 51 Pegasi is currently being vaporized by it’s parent star
Exoplanet Exploration: A new field in Astronomy For centuries Astronomers have asked two fundamental questions. 1. Do other worlds exist? 2. Is there life on those other worlds? Over the last 15 years we have been able to answer “YES” to the first question. Other worlds are common in the universe Within the next 15 years we will be able to answer the second question.
Extrasolar Planet (Exoplanet) - A planet that orbits a star outside our solar system. Artists conception of Gliese 581 C - The only terrestrial planet discovered in a stars Habitable Zone (besides Earth). Water on this planet would be in liquid form, like Earth. It is 5 times more massive than Earth and twice the size.
As of April, 2009, over 400 Extrasolar Systems have been discovered. But only 8 terrestrial planets have been found Oceans of lava glow red on the night side of Gliese 876 d. In the distance glow two other planets c and b of Gliese 876. It is 7 times the mass of earth, and has a mean temperature of 642 Kelvin.
287 Extrasolar Systems Discovered so far (April 2008): 6 Terrestrial Planets 182 Gas Giants 77 Hot Jupiters 3 Hot Neptunes (Water Giants) 5 Pulsar Planets
Besides planets, Astronomers have also detected: - 3 Kuiper Belts - 2 Asteroid Belts Artists concept of the asteroid belt and planets around the star HD 69830
Besides planets, Astronomers have also detected: - 14 Forming Solar Systems with newly formed planets Images of planet forming dust disks around stars
Properties of Known Extrasolar Systems Why are most exoplanets gas giants that orbit close to the parent star? Because our current detection methods are biased toward finding gas giants close to the parent star. It is difficult to find small terrestrial planets with our current methods.
The challenges of observing extrasolar planets stem from three basic facts: • Planets don't produce any light of their own, except when young. • They are an enormous distance from us. • They are lost in the blinding glare of their parent stars. . The first planets to be found around nearby stars have never been seen. Instead, astronomers have discovered them indirectly, inferring the existence of an unseen companion through its effects on the star itself.
Exoplanet Detectoion Methods: 5 proven methods - Astrometry & Radial Velocity Method : 235 systems - Transit Method: 46 systems - Microlensing Method: 6 systems - Pulsar Timing Method: 3 systems
1) Astrometric Method Astrometric Method: Astrometry consists of measuring a star's position in the sky and observing the ways in which its position changes over time. If the star has a planet, then the gravitational influence of the planet will cause the star to move in a tiny circle.
Astrometric Method Astrometric displacement of the Sun due to Jupiter as at it would be observed from 10 parsecs, or about 33 light-years.
Astrometric Method Astrometric Method: Pro’s and Con’s Pro’s: 1 telescope can search many stars at a time Con’s: Does not work for far away stars (Can’t see the motion) Difficult to detect Terrestrial planets (not sensitive enough) Process is slow (needs to observe multiple orbits)
2) Radial Velocity Method Doppler Effect Demo # of frames b.t. strikes
Radial Velocity Method Doppler Effect - The change in frequency of a wave as perceived by an observer moving relative to the wave source. If a wave source is moving TOWARD an observer, the waves tend to “pile up”, INCREASING the frequency, or pitch. If a wave source is moving AWAY FROM an observer, the waves tend to “spread out”, DECREASING the frequency, or pitch.
Radial Velocity Method The Doppler effect works for all kinds of waves, including light. Instead of the pitch changing, the color changes. The color change is very slight, and not noticeable to the human eye. However, it can be seen when studying the spectrum. The spectrum appear to be shifted toward the red or blue
Radial Velocity Method Blue Shift - Object is approaching Red Shift - Object is receding
Radial Velocity Method Radial Velocity Method (Doppler Method) - This method measures slight changes in a star's velocity as the star and the planet move about their common center of mass. Astronomers can detect this motion by analyzing the spectrum of starlight due to the Doppler shift in the stars spectrum. The larger the planet and the closer it is to the host star, the faster the star moves about the center of mass, causing a larger color shift in the spectrum of starlight. That's why many of the first planets discovered are Jupiter-class (300 times as massive as Earth), with orbits very close to their parent stars.
Radial Velocity Method Planet: 55 Cancri E – A Hot Terrestrial Planet
Radial Velocity Method Radial Velocity Method: Pro’s and Con’s Pro’s: Can be used on far away stars Con’s: Can only observe 1 star at a time (with high tech spectrographs) Difficult to detect Terrestrial planets (not sensitive enough) Process is slow (needs to observe multiple orbits)
3) Transit Method From the vantage point of the Earth, the planet of HD 209458 moves across the face of its star once every few days. It is so close that it is being vaporized by the star.
Transit Method Transit Method: If a planet passes directly between a star and an observer's line of sight, it blocks out a tiny portion of the star's light, thus reducing its brightness. Sensitive instruments can detect this periodic dip in brightness. From the period and depth of the transits, the orbit and size of the planets can be calculated.
Transit Method Transit Method: Pro’s and Con’s Pro’s: Can be used on far away stars Can detect Terrestrial Planets (Method is sensitive enough) Can determine atmospheric composition Con’s: Can only detect ~1% of all solar systems (angles need to exactly align) Process is slow (needs to observe multiple orbits) Also called Photometric Method
Gravitational Microlensing Method If a planet transits EXACTLY through the center of the parent star, gravity from the planet will bend the starlight Like a lens. The lensed light is magnified, and the star appears to briefly brighten. Telescopes can watch for the breif brightening of a star to detect a planet.
Gravitational Microlensing Method Pro’s: Sensitive enough to detect terrestrial planets Con’s: The chances of a planet microlensing are very rare. Extremely sensitive instruments need to be used.
Pulsar Timing Method Pulsar 1 Pulsar 2 Pulsar 3
Pulsar Timing Method Pulsar- The core of an exploded star that gives off a spinning beam of radiation (like a lighthouse). From earth, it appears to Pulse radiation at a specific rate. Pulsar Timing Method: A planets gravitational influence will disrupt the natural Pulse cycle of a pulsar. Astronomers can measure the disrupted pulses to determine the planets size and orbit.
Pulsar Timing Method Pro’s: Con’s: Only works for Pulsars (Very rare) The original planets would be destroyed in the explosion of the star. The planets they find are formed from the debris after the star exploded. (Some astronomers do not consider these objects to be planets)
Future Space Missions: Kepler Mission – Transit Method
Future Space Missions: Kepler Mission – Transit Method
KEPLER MISSION i. Mission Started in April 2009 ii. The Kepler Mission uses the Transit method to search over 10,000 stars. iii. It will find gas giants as well as Terrestrial planets. iv. Expected to find: between 50 to 650 Terrestrial Planets in Earth like orbits,and 900 Hot Gas Giants.
SIM PlanetQuest Mission • Expected Start -2012 • Will use astrometric method • will search the nearest 250 stars. • Expected to find terrestrial and gas planets
Darwin and TFP • TFP = Terrestrial Planet finder • Expected start: 2015 • Will directly image terrestrial planets using IR (take actual pictures!)
Darwin and TFP Expects to find: • Signs of life in the atmospheres in order to determine if the planet is habitable • If a Terrestrial planet has CO2, H2O, O3 (Ozone) it will be habitable.
Exit Slip • List the 5 types of detection methods used to discover extra solar planets • Describe how we use either the transit method or the doppler effect to discover exoplanets • What is the current mission to find exoplanets, what type of method does it use, and what does it expect to find.
Basic Definitions • Protoplanetary Disk -rotating disk of dense gas surrounding a young newly formed star, • Protostar -a cloud of hot, dense gas and dust that is gravitationally collapsing to form a star • Protoplanets -are moon-sized planets, or larger embryos within protoplanetary discs