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Characterising exoplanet atmospheres, magnetospheres and stellar winds from energetic neutral atom observations Mats Holmstrm Swedish Institute of Space Physics Exoplanets in Lund Lund, May 8, 2015 12:10-12:30 matsh@irf.se

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Characterising exoplanet atmospheres, magnetospheres and stellar winds from energetic neutral atom observations

Mats Holmström Swedish Institute of Space Physics

Exoplanets in Lund Lund, May 8, 2015 12:10-12:30 matsh@irf.se www.irf.se/~matsh/ www.irf.se/program/sspt/

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Overview

Energetic neutral atom (ENA) imaging
Basic principles
ENAs from the solar wind interaction with
Mars
Venus
Earth
The Moon
Exoplanet ENAs
Observations
Models

SLIDE 3

Energetic Neutral Atoms (ENA)

Here we focus on the energy range: 1 eV - 10 keV

[Wurz, 2000]

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ENA Properties

Straight line trajectories

Unaffected by electromagnetic fields, or gravity

Can be imaged by a detector
Produced by
Charge exchange
Sputtering

SLIDE 5

Solar wind interactions

[Kivelson and Russel]

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Planetary ENA Experiments (outside Earth)

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Earth Ring current ENAs

SLIDE 8

ENA Production at Mars

Generated by
Solar wind-exosphere charge

exchange

Atmospheric sputtering and backscatter

(of precipitating ions and ENAs)

Planetary ions-exosphere charge exchange
Three-dimensional emissions

SLIDE 9

ENA Imaging of Non-Magnetized Planets

[C:son Brandt]

SLIDE 10

[Futaana, 2004]

Mars Express ENA imager Field of View

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Mars

[Galli et al., JGR, 2008]

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Subsolar ENA jet at Mars observed by ASPERA-3

[Futaana et al., JGR, 2006]

Dynamics: Effect of an interplanetary shock

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Magnetosheet ENAs at Earth

IBEX observations [Fuselier et al., GRL, 2010]

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Observation MHD Model [Galli at al., JGR, 2008]

Venus

ASPERA-4 on Venus Express

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ENA Production at the moon

Generated by sputtering from
Micro meteoroid impact vaporization
Photon desorption
Precipitating
Magnetospheric ions
Solar wind ions
Significant contribution only from

precipitating solar wind ions

wo-dimensional emissions

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SARA on Chandrayaan-1 [Futaana et al., 2004]

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The Moon reflects the solar wind

Observation by SARA on Chandrayaan-1: ~20% of the solar wind protons are reflected by the Moon as neutral H. [Wieser et al., PSS, 2009]

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Reflected spectrum

[Wieser et al., PSS, 2009]

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First direct

bservation of a

mini-magnetosphere

Hydrogen Energetic Neutral Atoms (ENAs) from precipitating solar wind protons

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Exoplanet ENAs?

Transit Lyman-alpha observations
Direct observation of hot hydrogen
Local observation of the exoplanet environment

[Vidal-Madjar et al., Nature, 422, 2003]

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Model of Hot Jupiter ENA Production

[Holmström et al., Nature, 2008]

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Comparison with observation

[Ekenbäck, ApJ, 2010] Using typical solar wind parameters, and published atmospheric parameters

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Recent HD 209458b model

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Conclusions

Energetic neutral atoms (ENAs) have been observed

throughout the solar system

They should be produced also in other planetary

systems from the interaction between exoplanets and stellar winds

Lyman-alpha observations give us the possibility to
bserve these ENAs
Energetic Neutral Atoms (ENAs) contribute to the
bserved Lyman α absorption
Stellar wind, atmospheric, and magnetospheric

properties could be inferred from Lyman α

bservations through ENAs
Plasma processes should be considered in exoplanet