PHYS 2070 Tetyana Dyachyshyn EXTRASOLAR PLANETS PHYS 2070 Tetyana Dyachyshyn Google Images

What Are Extrasolar Planets? Planets orbiting stars other than the Sun 2013: 900 – official exoplanets; 2500 – “candidates” 02/2015 – 715 planets discovered in our own galaxy The detection of planets orbiting other stars has been a long- standing goal of generations of astronomers.

Today, discoveries of planets orbiting other stars are flooding in at an unprecedented rate, giving us unexpected new examples of planetary systems in action and posing fundamental challenges to our understanding of planet formation.

The study of Exoplanets offers information on: Parent star Interactions between stars and planets Processes that led to their formation

Observations of thousands of extrasolar planets http://www.eso.org/public/archives/releases/sciencepapers/eso1517/eso1517a.pdf Google Images 1990s: Theories of formation of planetary systems concentrated on our own solar system Present: Observations of thousands of extrasolar planets

Exoplanet Properties Hot Jupiters Super Earths Hundred times closer to their host stars so the amount of sunlight they get is 10000 times larger Google Images Super Earths Rocky planets upto 10 times as massive as Earth Google Images

Does Life Exist Elsewhere? Habitable Zone Sufficient distance from host star: not too hot and not too cold Elements for life: liquid water – energy that can support life Environmental conditions have to be just right to sustain life: the right energy, such as heat, and organic materials, such as Carbon Kepler Mission estimates tens of billions planets could exist

Press Release: First Detection of Reflected Visible Light from 51 Pegasi b ESO ESO The first exoplanet discovered around a normal star. Spectroscopic detection of visible light reflected off an exoplanet.

51 Pegasi b Characteristics Mass: half that of Jupiter’s Orbit: inclination of about 9° Diameter: larger than Jupiter Reflectivity: highly reflective Discovery: 1995 APOD 51 Pegasi b displays typical properties for a hot Jupiter that is very close to its parent star and exposed to intense sunlight. ESO

Techniques Developed to Observe 51 Pegasi b Transmission spectroscopy – observing the host star’s spectrum as it is filtered by a planet atmosphere during a transit Occultation photometry and spectroscopy – measuring the occultation (secondary eclipse) depth of the star + planet light curve at different wavelengths to derive the planet’s thermal and reflected signatures Emission spectra – also possible through high- resolution spectroscopy

Article #1 CoRoT Pictures Transiting Exoplanets In this article, the authors review the findings of the CoRoT mission in its search for exoplanets. Searching for exoplanets with the transit method requires both very good photometric precision and a very large number of observed stars. CoRoT – Convection Rotation and planetary Transits

The CoRoT Satellite CoRot – transit method Launched on December 26, 2006 by a Soyuz rocket from Baikonur, the CoRoT satellite has provided astronomical data from February 2007 to November 2012. Observations were discontinued due to electronic failures. The satellite was stopped in June 2014 after programming its slow decay to Earth. A space-based mission allows to detect transiting planets of smaller size and or of longer orbital period

When CoRoT was then launched in 2006, there were 15 known transiting exoplanets; all were giant, gaseous planets, whose transits (2-3 hour long) were easily detected from ground-based telescopes of small size (typically 1m). In total, 163,664 stars were observed during the lifetime of CoRoT.

Methods of Detecting Exoplanets Radial Velocity Direct Imaging Transit Searching for a slight dimming of the star’s light that would be due to the crossing of a planet on the stellar disk Works for planets whose orbit is perfectly aligned with the line of sight between the observer and the parent star Observing for a long time a very large number of stars Biased towards Detecting short-period planets Wobbling due to a gravitational pull by an invisible planet The first detected Jupiter-like exoplanet 51 Pegasi b, orbiting a solar-type star – orbital period 4.5 days Can detect systems at short orbital period High contrast and high resolution imaging The first detected brown dwarf companion Gl 229 B (about 50 MJup) – orbital period 10000 days Sensitive to planets at long orbital period

CoRoT Main Discoveries More diverse planets’ parametres when compared to planets in the Solar System Large planets Gases (H, He, no core) CoRoT 9b Orbital period 95 days Small planets Heavy elements, probably condensed in a central core CoRoT 7b – Super Earth Density 6.61g/cm**3; radius 10000 km

Limitations Solutions Challenging to observe planets with their faint host stars. Solutions TESS and PLATO launches. Unveiling the low-mass planets in the habitable zones of their stars (cool stars for TESS, solar-type stars for PLATO) Surveying bright stars

Article #2 Three WASP-South Transiting Exoplanets: WASP-74b, WASP-83b & WASP-89b 0.95 Mjup 1.5 Rjup Hot Jupiter F9 star WASP-89b 6 Mjup 1.0 Rjup K3 star Massive WASP-83b 0.3 Mjup 1.0 Rjup Saturn-like G8 star

Observations WASP – Wide Angle Search for Planets Euler/CORALIE Spectrograph TRAPPIST Photometer Discovery of transiting exoplanets around stars of V=9- 13 in the Southern Hemisphere 1 in 12 candidates turns out to be a planet (others binaries)

WASP 89 Parametres 12.5 Gyr → older than Galactic disk → “radius anomaly” in those planets that show magnetic activity because it has been proposed that this is due to the reduction in the efficiency of energy transport by convection Magnetic activity in the form of a rotational modulation & through star-spots during transit Transit lightcurves – TRAPPIST

WASP-89 is the first known K star hosting a massive planet in a short-period eccentric orbit The magnetic activity of WASP-89 could be related to the hosting of a massive, short-period planet, since magnetic activity might be enhanced in hot Jupiter hosts Eccentric short period orbits → dynamics of giant planets atmospheres because moved inwards by a “process of high eccentricity migration”, followed by circularisation

Surprises The next step after identifying and characterizing other terrestrial worlds in the solar neighborhood will be to explore their atmospheric properties, in particular in a quest for bio signatures.