Stellar wind induced soft X-ray emission from close-in exoplanets

Author(s)

K. G Kislyakova, Luca Fossati, Colin Johnstone, Mats Holmström, V. V. Zaitsev, Helmut Lammer

Abstract

In this Letter, we estimate the X-ray emission from close-in exoplanets. We show that the Solar/Stellar Wind Charge Exchange Mechanism (SWCX), which produces soft X-ray emission, is very effective for hot Jupiters. In this mechanism, X-ray photons are emitted as a result of the charge exchange between heavy ions in the solar wind and the atmospheric neutral particles. In the solar system, comets produce X-rays mostly through the SWCX mechanism, but it has also been shown to operate in the heliosphere, in the terrestrial magnetosheath, and on Mars, Venus, and the Moon. Since the number of emitted photons is proportional to the solar wind mass flux, this mechanism is not very effective for the solar system giants. Here we present a simple estimate of the X-ray emission intensity that can be produced by close-in extrasolar giant planets due to charge exchange with the heavy ions of the stellar wind. Using the example of HD 209458b, we show that this mechanism alone can be responsible for an X-ray emission of ≈10

²² erg s

^-1, which is 10

⁶ times stronger than the emission from the Jovian aurora. We discuss also the possibility of observing the predicted soft X-ray flux of hot Jupiters and show that despite high emission intensities they are unobservable with current facilities.

Organisation(s)

Department of Astrophysics

External organisation(s)

Swedish Institute of Space Physics, Russian Academy of Sciences, Österreichische Akademie der Wissenschaften (ÖAW), Open University

Journal

The Astrophysical journal Letters

Volume

799

No. of pages

5

ISSN

2041-8205

DOI

https://doi.org/10.1088/2041-8205/799/2/L15

Publication date

2015

Peer reviewed

Yes

Austrian Fields of Science 2012

103003 Astronomy, 103004 Astrophysics

Keywords

ASJC Scopus subject areas

Astronomy and Astrophysics, Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/fc87ea90-5671-4542-80ed-9823d129a546