1. PHYS 2070 Tetyana Dyachyshyn
EXTRASOLAR PLANETS
PHYS 2070
Tetyana Dyachyshyn
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2. 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.

3. 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.

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

5. Observations of thousands of extrasolar planets
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1990s:
Theories of formation of planetary systems concentrated on our own solar system
Present:
Observations of thousands of extrasolar planets

6. Exoplanet Properties Hot Jupiters Super Earths
Hundred times closer to their host stars so the amount of sunlight they get is times larger
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Super Earths
Rocky planets upto 10 times as massive as Earth
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7. 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

8. 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.

9. 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

10. 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

11. 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

12. 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 Observations were discontinued due to electronic failures. The satellite was stopped in June 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

13. 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.

14. 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 days
Sensitive to planets at long orbital period

15. 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 km

16. 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

17. 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

18. 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)

19. 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

20. 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

21. 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.