Hubble Science Briefing
Exoplanet Atmospheres:
Insights via the Hubble Space Telescope
Nicolas Crouzet 1, Drake Deming 2, Peter R. McCullough 1
1 Space
Telescope Science Institute
2 University of Maryland
May 2, 2013
The Solar system
Sizes to scale
Distances NOT to scale
8 planets in the Solar system:
Mercury , Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune
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A revolution!!
The first exoplanet: 51 Peg b
(Mayor & Queloz 1995)
51 Peg b:
Mass ≈ 0.5 Jupiter masses
Orbital period = 4.2 days!!
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How do we detect exoplanets?
The radial velocity method
Indicates the mass of the planet
http://media4.obspm.fr/exoplanetes/pages_exopl-methodes/vitesses-radiales.html
Hubble Science Briefing
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credit Emmanuel Pécontal
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How do we detect exoplanets?
The radial velocity method
Indicates the mass of the planet
http://media4.obspm.fr/exoplanetes/pages_exopl-methodes/vitesses-radiales.html
Hubble Science Briefing
5/2/13
credit Emmanuel Pécontal
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How do we detect exoplanets?
The radial velocity method
Indicates the mass of the planet
http://media4.obspm.fr/exoplanetes/pages_exopl-methodes/vitesses-radiales.html
Hubble Science Briefing
5/2/13
credit Emmanuel Pécontal
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How do we detect exoplanets?
The radial velocity method
Indicates the mass of the planet
http://media4.obspm.fr/exoplanetes/pages_exopl-methodes/vitesses-radiales.html
Hubble Science Briefing
5/2/13
credit Emmanuel Pécontal
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How do we detect exoplanets?
The radial velocity method
Indicates the mass of the planet
http://media4.obspm.fr/exoplanetes/pages_exopl-methodes/vitesses-radiales.html
Hubble Science Briefing
5/2/13
credit Emmanuel Pécontal
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How do we detect exoplanets?
The radial velocity method
Indicates the mass of the planet
http://media4.obspm.fr/exoplanetes/pages_exopl-methodes/vitesses-radiales.html
Hubble Science Briefing
5/2/13
credit Emmanuel Pécontal
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How do we detect exoplanets?
The transit method
Indicates the radius of the planet
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How do we detect exoplanets?
The imaging method
HR 8799 (Marois et al. 2008, 2010)
Direct detection of exoplanets
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Historical background
The discovery of exoplanets
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Historical background
1995: The first exoplanet around a Sun-like star, 51 Peg b
Mayor & Queloz 1995
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Historical background
1999: The first transiting exoplanet, HD 209458 b
Charbonneau et al. 2000
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Historical background
2008: Direct imaging of Fomalhaut b and HR8799 b
Kalas et al. 2008
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Marois et al. 2008
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Historical background
2009: The first transiting super-Earth, CoRoT-7 b
Léger et al. 2009
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Historical background
2012: The first Earth-size exoplanets, Kepler 20 e & f
Fressin et al. 2012
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Historical background
The discovery of exoplanets
As of April 30th, 2013:
880 exoplanets:
132 in multiple systems
308 transiting
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Historical background
And probably millions more…
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Detection and characterization
Basics
Detection = Finding planets
Characterization = Studying in detail individual planets, after their detection
Requires a bright host star to maximize the signal
Currently only a few exoplanets can be characterized
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The power of the transit method
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Transit spectroscopy with the Hubble Space Telescope
Image of the target star on the detector
HST has several spectrographs on board
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Transit spectroscopy with the Hubble Space Telescope
Spectrum:
Measure of the light at different wavelengths
Variations reveal absorption by molecules in the atmosphere of the planet
Absorption
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Wavelength
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Transit spectroscopy with the Hubble Space Telescope
First detection of an exoplanet atmosphere…
HD209458b - HST STIS
… that is escaping
HD209458b - HST STIS
(Charbonneau et al. 2002)
(Vidal-Madjar et al. 2003, 2004)
Excess absorption
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Transit spectroscopy with the Hubble Space Telescope
The NICMOS controversy
NICMOS: Near Infrared Camera and Multi-Object Spectrometer onboard Hubble Space Telescope
Methane and water in the atmosphere of HD198733b (Swain et al. 2008)
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Transit spectroscopy with the Hubble Space Telescope
The NICMOS controversy
HD189733b
A new look at NICMOS transmission spectroscopy
of HD 189733, GJ-436 and XO-1
“No conclusive evidence for molecular features”
(Gibson et al. 2011)
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Transit spectroscopy with the Hubble Space Telescope
The NICMOS controversy
Need more observations
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Transit spectroscopy with the Hubble Space Telescope
But NICMOS became unavailable…
New instruments installed on HST, including Wide Field Camera 3 (WFC3)
Installation by a team of astronauts in May, 2009
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Transit spectroscopy with the Hubble Space Telescope
WFC3 observations of HD 189733:
coming this year…
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Transit spectroscopy with the Hubble Space Telescope
HD 209458 b
Sodium in an escaping atmosphere, detected by HST
Why is sodium important?
A key to distinguish between 2 classes of hot-Jupiters as proposed by theoretical models
(Fortney 2008, 2010)
- Strongly irradiated hot-Jupiters:
- planet is very hot (~ 2000 to 5000°F)
- large day-night temperature contrast
- do not show sodium in their atmosphere
- Less irradiated hot-Jupiters:
- planet is cooler (less than 2000°F)
- more redistribution of heat around the planet
- show sodium in their atmosphere
Sodium helps to understand the general characteristics of hot-Jupiters
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Transit spectroscopy with the Hubble Space Telescope
HD 209458 b
Recent observations with HST WFC3 (Deming et al. 2013)
Best precision ever achieved for exoplanet
spectroscopy (40 parts per million)
Detection of water vapor in the planet’s
atmosphere! (signal: 200 parts per million)
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Transit spectroscopy with the Hubble Space Telescope
HD 209458 b
But water vapor signal is smaller than expected!
Interpretation:
Presence of clouds and/or haze in the
planet’s atmosphere, that weaken the signal
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Transit spectroscopy with the Hubble Space Telescope
HD 209458 b
But water vapor signal is smaller than expected!
Interpretation:
Presence of clouds and/or haze in the
planet’s atmosphere, that weaken the signal
HST provides clues about HD 209458 b’s atmosphere:
water vapor, with clouds and/or haze
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Transit spectroscopy with the Hubble Space Telescope
GJ 1214 b
A transiting super-Earth or mini-Neptune (Charbonneau et al. 2009)
Radius = 2.7 RE
Mass = 6.6 ME
Density = 1.9 g/cm3 (Earth: 5.5 g/cm3)
Marcy 2009
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Transit spectroscopy with the Hubble Space Telescope
GJ 1214 b
Bean et al. 2010 - Ground based observations
Berta et al. 2012 - HST WFC3
The spectrum is flat!!
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Transit spectroscopy with the Hubble Space Telescope
GJ 1214 b
Inconsistent with a cloud-free extended atmosphere
Atmosphere has to be “heavy” (high molecular
weight)…
But it might also be a very cloudy atmosphere
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Transit spectroscopy with the Hubble Space Telescope
GJ 1214 b
Inconsistent with a cloud-free extended atmosphere
Atmosphere has to be “heavy” (high molecular
weight)…
But it might also be a very cloudy atmosphere
Still an open question…
On-going HST program for more observations
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The future
Transiting Exoplanet Survey Satellite (TESS)
NASA Mission for launch in 2017
Principal Investigator: George Ricker (MIT)
Aim:
Discover Transiting Earths
and Super-Earths orbiting
bright, nearby stars
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The future
The James Webb Space Telescope (JWST)
JWST… a big thing!!
Mirror: 6.5 meters (21 feet) in diameter
Observations in the infrared
Orbit about 1.5 million km (1 million miles) from the Earth
Launch: goal 2018
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The future
The James Webb Space Telescope (JWST)
Predicted performances: Example of
carbon dioxide in a habitable SuperEarth
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Conclusion
The transit method is the most powerful to characterize exoplanets
HST plays a major role in transit spectroscopy
These observations bring information about molecules, clouds,
and haze in the atmosphere of exoplanets
The future: TESS and JWST
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Thanks!!
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