Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Greenhouse Effect in the Atmosphere of an Earthlike Planet Orbiting an M-Dwarf Star

Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject to high levels of galactic cosmic rays (GCRs) which produce nitrogen oxides in earthlike atmospheres. We investigate to what extent this NOx may modify biomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well as related compounds such as water (H2O) (essential for life) and methane (CH4) (which has both abiotic and biotic sources) . Our model results suggest that such signals are robust, changing in the M-star world atmospheric column by up to 20% due to the GCR NOx effects compared to an M-star run without GCR effects and can therefore survive at least the effects of galactic cosmic rays. We have not however investigated stellar cosmic rays here. CH4 levels are about 10 times higher than on the Earth related to a lowering in hydroxyl (OH) in response to changes in UV. The increase is less than reported in previous studies. This difference arose partly because we used different biogenic input. For example, we employed 23% lower CH4 fluxes compared to those studies. Unlike on the Earth, relatively modest changes in these fluxes can lead to larger changes in the concentrations of biomarker and related species on the M-star world. We calculate a CH4 greenhouse heating effect of up to 4K. O3 photochemistry in terms of the smog mechanism and the catalytic loss cycles on the M-star world differs considerably compared with the Earth

An ultrahot Neptune in the Neptune desert

About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. Such lack of planets of intermediate size (the ‘hot Neptune desert’) has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here we report the discovery of an ultrashort-period planet with a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet’s mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0^(+2.7)_(−2.9)% of the total mass. With an equilibrium temperature around 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope. Follow-up observations of the planet’s atmosphere to better understand its origin and physical nature will be facilitated by the star’s brightness (V_(mag) = 9.8)

Auf der Suche nach Planeten um andere Sonnen

Seit der ersten zweifelsfreien Entdeckung eines extrasolaren Planeten hat sich dieser Zweig der Astronomie stürmisch entwickelt. Mit verschiedenen Methoden sucht man weltweit nach Exoplaneten, jetzt wird mit COROT ein Satellit gestartet, der dieser Aufgabe gewidmet ist. Er soll bei insgesamt 60000 Sternen mit Hilfe der Transitmethode nach Planeten suchen. Mit ihm könnte der erste Gesteinsplanet von der Größe der Erde gefunden werden

CHEOPS

CHEOPS (CHaracterising ExOPlanet Satellite) is the first S-class mission from ESA, which will be launched in December 2019. CHEOPS’ payload is a telescope of 32 cm aperture. It will perform photometric observation from low Earth orbit to measure transits of already known host stars further characterize already known planetary systems. The mission goals are - to search for shallow transits on stars already known to host planets obtaining a transit signal-to-noise ratio of 5 for an Earth-size planet with a period of 50 days on G5 dwarf stars with V- magnitude brighter than 9th. - to provide precision radii for a number of hot Neptune planets orbiting stars brighter than 12th V magnitude and to search for co-aligned smaller mass planets - to measure the phase modulation due to the different contribution of the dayside of hot Jupiter planets and in some cases to measure the secondary eclipse

Planetary Transits and Oscillations of Stars: PLATO

Up to now, no Earth-like planet in the habitable zone around a sun-like star has been found. The majority of the detected exoplanets lack the full set of bulk parameters as radius, mass, stellar type and age. That is what PLATO is designed for: to find terrestrial planets in the habitable zone and determine their bulk densities with a precision never reached before. PLATO is a M-class mission in ESAs Cosmic Vision Programme 2015-2025. The international PLATO Consortium is lead by DLR (Prof. Heike Rauer). It will be launched in 2026 with an Ariane-6 rocket from Kourou, French Guyana. The mission duration is 4 years, an extension up to 6 years is possible. There are consumables for 8 years