Sounds swell!

Area where all the discoveries have been made.

Credits - NASA/JPL

Pegasi - 51b - First Blood!

• 1995 - First planet found to orbit a star
• Called a hot Jupiter (Jovian) planet. (?)
• First discovery using wobbling method.

Staring into the heavens!

• Kepler first came online in 2009 and focused itself to view a patch of about 150,000 stars.
• Waiting to catch any dips in light coming from individual stars (Transit method). Went offline in 2013.
• ~2000 planets sifted through 4 years data and is still revealing new planets!
• Spitzer for I.R.

The modern era of exoplanet discovery

Seeing is believing!

• The Direct Imaging method.
• H.S.T. discovered ~40 planets.
• Direct imaging helps characterizing the planets. Detection + characterization in one go!
• J.W.S.T. and W.F.I.R.S.T. - frontiers of modern technology.

• Direct imaging allows astronomers to understand a planet's orbit, the composition of its atmosphere and the probability it has clouds and other elements.

Challenges

Closest discovered exoplanet at least a dozen light year away

Greater the distance, bigger your telescopes need to be. (T.M.T).

Next to an annoyingly bright star

Methods used

Radial velocity method or Wobbling

• A star's wobble can tell us if it has planets and if so how many and of what sizes!
• Utilizes doppler effect (as star moves back and forth w.r.t. Earth's frame of reference, light waves are compressed and elongated. (redshift)

Transits and eclipses

• Most successful method yet.
• Sit and detect dips in the light coming off the start (dip in apparent brightness).
• Phases give scattering phase functions.

• Planet blocks off a part of star's light proportional to planet to star's cross-sectional area ratio.
• Eg:- A dip of 1% in overall brightness indicates radius of planet is about 1/10 the radius of the star.
• By inferring radius of star using separate astrometry methods, one can calculate volume of the planet.
• Mass calculated using Doppler spectroscopy.

Bright planet Far from star

Direct Imaging - Reflection and Emission

1. Reflection (usual seeing)

Coronagraphs, Adaptive optics etc. are used.

• Fomalhaut - b - First extrasolar planet detected by direct imaging without coronagraphs! (Exceptionally bright cases).
• Direct imaging provides with a lot of information - eg. absorption spectra.
• Is there a way to not get blinded by star light without any blocking?

Seeing in Infrared (I.R. imaging) - Emission

• Planets orbiting young stars are still hot and give off I.R.
• In the visible range the reflected light from the planets would be swallowed up by the brilliance of the star, the independent heat of the planets stands out far more clearly in the infrared range!
• Emission spectoscopy gives most amount of information - even about atmosphere and seasons.
• Since thermal radiation given off depends on the the vertical temperature profile of the planet, star-planet distance (hotter when close).

Other methods

• Gravitational microlensing (49)
• Astrometry (1)

Opportunities

• Landmass distribution (continents and oceans).
• Atmospheric composition
• Oceanic heat transport
• Seasons
• Geology