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- Title
On the transit Ly-α signatures of terrestrial planets in the habitable zones of M dwarfs.
- Authors
Kislyakova, Kristina; Holmström, Mats; Odert, Petra; Lammer, Helmut; Erkaev, Nikolay; Khodachenko, Maxim; Shaikhislamov, Ildar
- Abstract
We model the transit signatures in the Lyman-alpha (Lyα) line of an Earth-sized planetorbiting in the habitable zone of the M dwarf GJ 436. We estimate the transit depth in thisline for an exo-Earth with three types of atmospheres: a hydrogen-dominated atmosphere, anitrogen-dominated atmosphere, and a nitrogen-dominated atmosphere with anamount of hydrogen equal to that of the Earth. For all types of atmospheres, wecalculate the in-transit absorption a planetary transit would produce in the stellarLyα line. We use a Direct Simulation Monte Carlo (DSMC) code to model theplanetary exospheres and corresponding absorption. The code allows to includeseveral species and traces neutral particles and ions. It includes several ionizationmechanisms, such as charge exchange with the stellar wind, photo- and electron impactionization, and allows to trace particles collisions. At the lower boundary of theDSMC model we assume an atmosphere density, temperature, and velocity obtainedwith a hydrodynamic model for the lower atmosphere. We show that for a smallrocky Earth-like planet orbiting in the HZ of GJ 436 only the hydrogen-dominatedatmosphere is detectable with the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST). Neither a pure nitrogen atmosphere nora nitrogen-dominated atmosphere with an Earth-like hydrogen concentration inthe upper atmosphere are detectable. In this case, the main source of atmospherichydrogen is charge exchange with the stellar wind. Our results indicate that Earth-liketerrestrial planets with hydrogen-dominated atmospheres can be observed in the Lyαline if they orbit very nearby stars, or if several observational visits are available.
- Subjects
HUBBLE Space Telescope (Spacecraft); HABITABLE planets; INNER planets; CHARGE exchange; UPPER atmosphere; ATMOSPHERIC boundary layer; MONTE Carlo method
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article