Exoplanet Atmospheres: Insights via the Hubble Space Telescope

Exoplanet Atmospheres: Insights via the Hubble Space Telescope

Nicolas Crouzet 1, Drake Deming 2, Peter R. McCullough 1

1 Space Telescope Science Institute2 University of Maryland

May 2, 2013

Hubble Science Briefing

The Solar system

8 planets in the Solar system:Mercury , Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune

Sizes to scaleDistances NOT to scale

Hubble Science Briefing 5/2/132

The first exoplanet: 51 Peg b (Mayor & Queloz 1995)

51 Peg b: Mass ≈ 0.5 Jupiter masses Orbital period = 4.2 days!!

A revolution!!


The radial velocity method

How do we detect exoplanets?

Indicates the mass of the planethttp://media4.obspm.fr/exoplanetes/pages_exopl-methodes/vitesses-radiales.html credit Emmanuel Pécontal


http://media4.obspm.fr/exoplanetes/pages_exopl-methodes/vitesses-radiales.html


























The transit method


Indicates the radius of the planet


The imaging method

Direct detection of exoplanets


HR 8799 (Marois et al. 2008, 2010)


Historical background

The discovery of exoplanets


1995: The first exoplanet around a Sun-like star, 51 Peg b

Mayor & Queloz 1995



1999: The first transiting exoplanet, HD 209458 b

Charbonneau et al. 2000



2008: Direct imaging of Fomalhaut b and HR8799 b

Marois et al. 2008Kalas et al. 2008



Léger et al. 2009

2009: The first transiting super-Earth, CoRoT-7 b



2012: The first Earth-size exoplanets, Kepler 20 e & f

Fressin et al. 2012




The discovery of exoplanets

As of April 30th, 2013:

880 exoplanets:132 in multiple

systems308 transiting


And probably millions more…



Currently only a few exoplanets can be characterized

Detection = Finding planets

Characterization = Studying in detail individual planets, after their detection

Requires a bright host star to maximize the signal

Detection and characterization

Basics


The power of the transit method


Transit spectroscopy with the Hubble Space Telescope

Image of the target star on the detector


HST has several spectrographs on board


Spectrum:

Measure of the light at different wavelengths

Variations reveal absorption by molecules in the atmosphere of the planet

Absorption

WavelengthHubble Science Briefing 5/2/1323

First detection of an exoplanet atmosphere…

HD209458b - HST STIS (Charbonneau et al. 2002)

… that is escaping

HD209458b - HST STIS (Vidal-Madjar et al. 2003, 2004)


Excess absorption


The NICMOS controversy

Methane and water in the atmosphere of HD198733b (Swain et al. 2008)

NICMOS: Near Infrared Camera and Multi-Object Spectrometer onboard Hubble Space Telescope



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)

HD189733b




Need more observations




But NICMOS became unavailable…

New instruments installed on HST, including Wide Field Camera 3 (WFC3)

Installation by a team of astronauts in May, 2009



WFC3 observations of HD 189733:

coming this year…



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-JupitersHubble Science Briefing 5/2/13

30

HD 209458 bRecent observations with HST WFC3 (Deming et al. 2013)

Detection of water vapor in the planet’s atmosphere! (signal: 200 parts per million)

Best precision ever achieved for exoplanet spectroscopy (40 parts per million)



HD 209458 b


Interpretation: Presence of clouds and/or haze in the planet’s atmosphere, that weaken the signal

But water vapor signal is smaller than expected!


HD 209458 b


Interpretation: Presence of clouds and/or haze in the planet’s atmosphere, that weaken the signal

But water vapor signal is smaller than expected!

HST provides clues about HD 209458 b’s atmosphere: water vapor, with clouds and/or haze


GJ 1214 bA 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



GJ 1214 b

The spectrum is flat!!

Bean et al. 2010 - Ground based observations Berta et al. 2012 - HST WFC3



GJ 1214 b


Atmosphere has to be “heavy” (high molecular weight)…

Inconsistent with a cloud-free extended atmosphere

But it might also be a very cloudy atmosphere


GJ 1214 b

Atmosphere has to be “heavy” (high molecular weight)…

But it might also be a very cloudy atmosphere


Inconsistent with a cloud-free extended atmosphere

Still an open question…On-going HST program for more observations


The future

Transiting Exoplanet Survey Satellite (TESS)

NASA Mission for launch in 2017

Discover Transiting Earths and Super-Earths orbitingbright, nearby stars

Principal Investigator: George Ricker (MIT)

Aim:


The James Webb Space Telescope (JWST)

Mirror: 6.5 meters (21 feet) in diameterObservations in the infraredOrbit about 1.5 million km (1 million miles) from the EarthLaunch: goal 2018

JWST… a big thing!!

The future


Predicted performances: Example of carbon dioxide in a habitable SuperEarth

The future

The James Webb Space Telescope (JWST)


Conclusion

These observations bring information about molecules, clouds, and haze in the atmosphere of exoplanets

HST plays a major role in transit spectroscopy

The transit method is the most powerful to characterize exoplanets

The future: TESS and JWST


Thanks!!


Documents

Exoplanet Atmospheres: Insights via the Hubble Space Telescope