Extrasolar PlanetsInstructor: Calvin K. Prothro; P.G., CPG

(John Rusho)

Section 003: F343, T Th 11:00 p.m. to 12:15 p.m.

Section 004: F381, T Th 12:30 p.m. to 1:45 p.m

OCC - Onondaga Community College

How Do We Find These Things? Current Progress

• To date (January 2006) 176 planets in more than 153 systems have been discovered using a variety of methods

• Fun Facts– Largest semimajor

axis: 5.9 AU– Lowest mass planet:

0.02 MJ

– Largest Number of Planets: 4

• At around five times the mass of Earth, the newest planet, designated OGLE–2005-BLG-390Lb, is the lowest-mass planet ever detected outside the solar system.

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How Do We Find These Things?

• • To date there have been 5 methods successfully used to detect extrasolar planets:

• Pulsar Timing• Transit Photometry• Gravitational Microlensing• Direct Detection• Doppler Spectroscopy

Pulsar timing• The first method used to discover extra-solar planets.

• This method observes the anomalies in the regularity of pulses from a pulsar. This led to the 'discovery' of the first planet with the orbital period of one year.

• It also led to the discovery of the PSR B1620-26c a planet orbiting a primary (a pulsar) and secondary (White Dwarf) in a circumbinary orbit . This planet is the only known planet to orbit two stars.

Transit method • The Transmit method

detects a planet's shadow when it transits in front of its host star.

• This method only works for the small percentage of planets whose orbits happen to be perfectly in line with the astronomers' vantage point.

• This method can be used on very distant stars.

Gravitational Microlensing • The gravitational microlensing effect occurs when

the gravitational field of a planet and its parent star act to magnify the light of a distant background star.

• For the effect to work the planet and star must pass almost directly between the observer and the distant star.

• Since such events are rare, a very large number of distant stars must be continuously monitored in order to detect planets at a reasonable rate.

• This method is most fruitful for planets between earth and the center of the galaxy, as the galactic center provides a large number of background stars.

Gravitational Microlensing

This graphic illustrates the principle of gravitational microlensing. The observatory on Earth sees the source (more distant) star appear to brighten dramatically when the lens (closer) star passes between them. The planet orbiting the lens star causes a variation in that brightening.

Direct Detection

This is an infrared image of the star GQ Lupi (A). It is 400 light years from our Solar System and is approximately 70% of our Sun's mass.

It is orbited by a planet (b) at a distance of approximately 20 times the distance between Jupiter and our Sun.

It is unclear what the mass of the planet is, but it is estimated to be between 1 and 42 times the mass of Jupiter.

European Southern Observatory

Direct Detection

• The best way to gain information on the composition of the greatest number of stars is through direct detection.

• This is made quite difficult because of the 109 and 1010 contrast ratio in the reflected light of Jupiterlike and Earthlike planets respectively.

• For young extrasolar planets we could look to the planet’s thermal emission whose contrast ratio is much more favorable, perhaps by as many as four orders of magnitude at 5-10 microns.

Direct observation

• In March 2005 it was announced that scientists using the Spitzer Space Telescope were able to detect infrared radiation emitted from two extrasolar planets.

Extra Solar Planet Detection by the Doppler Detection method

• Dr. Jaquin’s Powerpoint on Extrasolar Planets is located on his website in Unit 2 Supplemental Material # 6.

• GOOD LUCK!

Doppler Wobble

• As the star moves toward the Earth, the light waves coming from it are compressed and shifted toward the blue (shorter-wavelength) end of the spectrum.

• As the star moves away from us, the light waves are stretched out

toward the red (longer-wavelength) end of the spectrum.

Summary of Steps in the Doppler Detection method

1. Many separate measurements of a star’s velocity are made over a long period of time.

2. If the star “wobbles” then it has an unseen companion causing the wobble. It may be a planet or a low-mass star.

3. The period P of the wobble equals the orbital period of the unseen companion.

4. Using Kepler’s 3’rd law the semi-major axis r of the unseen companion’s orbit can be calculated from the period of its orbit.

5. Using the equation for the orbital velocity, the unseen companion’s orbital velocity v PL can be calculated from its orbital semi-major axis.

6. Using the conservation of momentum principle, the mass of the unseen companion MPL can be estimated from the planet’s orbital velocity, the mass of the star and the star’s observed maximum velocity, K

7. The estimated mass is only a lower limit for the mass because the orbital inclination i is unknown and cannot be determined from the Earth. The planet’s mass may be larger.

EXAMPLE: 47 Ursae Majoris

• Type of Star: Yellow Dwarf

• Spectral Class: G1V

• Distance: 46 Lightyears

• Luminosity: 1,82 L

• Mass: 1,03 Solar Masses

• Surface Temperature: 5800 K

NOTE: The planet orbiting 47 Ursae Majoris is close enough to its sun for liquid water to exist on any of its moons.

47 Ursae Majoris

51 Pegasi

Jupiter doppler effect intensity

• 55 Cancri is one of the most interesting planetary systems discovered so far. It holds the record for number of planets, most distant Jovian planet and least massive planet

The Coolest So Far

The End…

or maybe just the beginning ?