I. What is an Exoplanet? EXOPLANETS III. Established Detection Techniques • What is a Planet? II. Finding Exoplanets: Not So Easy A. Radial Velocity B. Pulsar Timing C. Transit Method International Astronomical Union (IAU) definition: A “planet” is a celestial body A star with a planet moves in its own A pulsar is a rotating neutron star: a small Planet crossing (or transiting) in that It is difficult to detect the outer planets in our solar system itself! small orbit due to the planet's gravitational and highly dense remnant of an exploded front of its parent star decreases the 1. is in orbit around the Sun, This is because: force. star (supernova). observed light from the star. 2. has sufficient mass for its self-gravity to overcome rigid body forces so 1. The outer planets are very faint due to their distance This results in variations in the speed with Pulsars emit beams of electromagnetic The amount the star dims is that it assumes a hydrostatic equilibrium (nearly round) shape, and from the sun. which the star moves toward or away from radiation which we detect as extremely dependent on the relative sizes of the 3. has cleared the neighbourhood around its orbit. 2. Again, due to their distance from the sun, they move Earth (i.e. the star’s radial velocity). regular pulses as they rotate star and the planet. Eight planets : Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. very slowly. The variations in radial velocity lead to Since the rotation of a pulsar is very • What is an Exoplanet? Exoplanets are, of course, even more difficult to detect since variations in the frequency of light from the regular, slight changes in the timing of its 1. They are extremely far away and are very faint star (Doppler effect) observed pulses can be used to track the The radial-velocity method of exoplanet pulsar's motion. IAU has proposed a working definition according to which an exoplanet compared to stars. Imagine trying to detect a dot as TRANSIT METHOD thick as a strand of spider web from a distance of 100 detection involves measuring these Thus, variations in the timing of the pulses 1. has a mass below the limiting mass for thermonuclear fusion of km, just using the light from a 10 W bulb 1 m away from variations in the frequency of light from the can reveal the movements of the pulsar due F. Orbital Phase Reflected deuterium (≈ 13 Jupiter masses for solar metallicity), the strand. star in order to confirm the presence of the to orbiting planets. Light Variation 2. has mass above the mass required for a planet in our Solar System, planet. 2. Since telescopes are never perfect, there will always be and some blurring. The blurring of the image of the star, E. Direct Imaging Short period giant planets in close 3. is in orbit around a star or a stellar remnant orbits around their stars will undergo extremely bright compared to the planet, can wash out D. Gravitational Planets are extremely faint light sources the image of the planet. reflected light variations. Microlensing compared to stars and what little light This is because, like our Moon, they comes from them tends to be lost in the Gravitational microlensing takes place also go through phases from full to glare from their parent star. new and back again. IV. Early Milestones in Exoplanets Exploration: V. Exoplanets Statistics: when the gravitational field of one star acts It is very difficult to detect them directly. It like a lens and magnifies the light of a Since telescopes cannot resolve the is easier to obtain images when the planet is planet from the star, they see only the First Published Discovery to The First Ever Declaration of Most Distant: 21500 light years distant background star. especially large (considerably larger than Receive Subsequent Confirmation: Detection (False Alarm): Such an effect occurs only when the two combined light. Least Distant: 4.37 light years (around Alpha-Centauri) Jupiter), widely separated from its parent The brightness of the host star will stars are almost exactly aligned. star, and hot so that it emits intense infrared Least Massive: 0.02 MEarth seem to change over each orbit in a Published: 1988 Confirmed: 2003 Year: 1991 Retraction: 1992 If the lens star has a planet orbiting it, the radiation. Largest Radius: 22.4 REarth periodic manner. Scientists: Campbell, Walker and Yang gravitational field of the planet may cause The images have then been made at Scientists: M. Bailes, Andrew Lyne Smallest Radius: 0.57 REarth With high photometric precision, it Telescope: Canada-France-Hawaii Longest Year: 876 yrs small variations in the observed lensing infrared where the planet is brighter than it 3.6 m Telescope, Hawaii and S.L. Shemar effect. is possible to detect a planet in transit Shortest Year: 5.7768 hrs is at visible wavelengths. across its star. Discovery: Planet around Gamma Telescope: Lovell Telescope, England Most Eccentric Orbit: 0.9349 Coronagraphs are used to block light from Such Jupiter-sized planets are Cephei, a binary star system 45 light Claim: Discovery of a planet in orbit Least Eccentric Orbit: 0.001 the star while leaving the planet visible. years away around the pulsar PSR 1829-10. detectable by space telescopes such as Longest Orbit : ~2740 light min the Kepler space observatory (see Smallest Orbit: ~0.05 light min section VII). First Definitive Detection First planet to be discovered 3 Least Dense: 80-180 kg/m It is expected that in the long run, (around a pulsar [see III B]): around a normal (sun-like) star: 3 Most Dense: 23000 kg/m this method may find the most planets that will be discovered by the Kepler Year: 1992 Confirmation: 1994 Year: 1995 Confirmation: 1995 DIRECT IMAGING DIRECT IMAGING mission. Scientists: Aleksander Wolszczan Scientists: M. Mayor and D. Queloz Sizes of Kepler Exoplanet Candidates and Dale Frail Telescope: Haute-Provence (see section VII for Kepler Mission) Telescope: Arecibo Observatory, Observatory, France No of Planetary Systems Detected: 676 VIII. Habitability: Can Exoplanets Sustain Life ??? Puerto Rico Discovery: Jupiter-mass planet Total no of confirmed Exoplanets: 859 Discovery: Two Earth-Mass planets around the sun-like star 51 Pegasi, in Most No. of Confirmed Exoplanets around one star: 7 NASA ‘s suggested criteria: i) extended regions of liquid water, ii) conditions orbiting the pulsar PSRB 1257+12 an orbit smaller than that of Mercury favourable for the assembly of complex organic molecules and, iii) energy sources to sustain metabolism. VI. Some Programs & Telescopes VII. Kepler Space Mission Habitable Zone (HZ): The region around a star where the temperature is such that a 10th mission in NASA’s Discovery Program. planet could have water in liquid state on its surface. HST Objective: Search for Earth-size habitable exoplanets. Suitable Planets: HabPlanet (Kepler has found 54 Suitable Stars [HabStars]: 1. Kepler Space Mission (see section VII) Advantage: Avoids atmospheric effects, hence, provides exos that may be in HZ) 2. CoRoT Space Mission precise measurements (see graph of light curves below). (We have known 17000 of them from the Hipparcos Mission) Terrestrial i.e. rocky 3. Hubble Space Telescope( HST) Orbit: Earth-like, around sun with a period of 372 days Spectral Class: early F, G, Mid K (Sun : G) Mass: Sufficient gravity to retain thick 4. EPICS for Very Large Telescope (VLT), ESO, Chile (1.8m) Launched on March 9, 2009. Duration of the mission is Photospheric Temp: 4000-7000K (Sun: 5777K) atmosphere and atmospheric pressure (liquid water) 5. European Extremely Large Telescope (EELT)(39.2m, 4.2m) expected to be about 7 to 8 years Life : Few billion years (Life can evolve) Radius: Sufficiently small surface to volume ratio to 6. PRL Advanced Radial-velocity All-sky Search (PARAS), Mt. Abu Surveying our neighbourhood in Milky way Low Variability in temperature and luminosity sustain geological activity and have a magnetic field 7. Gemini Planet Imager for Gemini Space Telescope, Hawaii & Chile(8.1m) As per Jan. 2013, it has found 2740 likely candidates High Metallicity : High proportion of element Geochemistry and Metallicity: Rich in C, H, O, N and 8. Subaru Telescope, Mt. Kea, Hawaii(Japan)(8.2m) 105 of them have been confirmed by further studies other then H and He as it reflects in planets other elements thought to be necessary for life 9. Palomar Observatory, Next space mission: Gaia. To be launched in August Orbit : Small eccentricity (small temperature fluctuations) i. Hale Telescope(5.1m) 2013 Rotation: Tilted axis- moderate seasons, low precession ii. 48-inch Samuel Oschin Telescope Kepler Telescope Day-night cycle should not be too slow iii. The 60-inch Telescope Kepler Orbit 48’’ S-O Hale An earth like satellite of a Jupiter like exoplanet in HZ is also Subaru EELT VLT PARAS Gemini considered as a potential candidate .