Five carbon- and nitrogen-bearing species in a hot giant planet's atmosphere.

The atmospheres of gaseous giant exoplanets orbiting close to their parent stars (hot Jupiters) have been probed for nearly two decades1,2. They allow us to investigate the chemical and physical properties of planetary atmospheres under extreme irradiation conditions3. Previous observations of hot Jupiters as they transit in front of their host stars have revealed the frequent presence of water vapour4 and carbon monoxide5 in their atmospheres; this has been studied in terms of scaled solar composition6 under the usual assumption of chemical equilibrium. Both molecules as well as hydrogen cyanide were found in the atmosphere of HD 209458b5,7,8, a well studied hot Jupiter (with equilibrium temperature around 1,500 kelvin), whereas ammonia was tentatively detected there9 and subsequently refuted10. Here we report observations of HD 209458b that indicate the presence of water (H2O), carbon monoxide (CO), hydrogen cyanide (HCN), methane (CH4), ammonia (NH3) and acetylene (C2H2), with statistical significance of 5.3 to 9.9 standard deviations per molecule. Atmospheric models in radiative and chemical equilibrium that account for the detected species indicate a carbon-rich chemistry with a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55). According to existing models relating the atmospheric chemistry to planet formation and migration scenarios3,11,12, this would suggest that HD 209458b formed far from its present location and subsequently migrated inwards11,13. Other hot Jupiters may also show a richer chemistry than has been previously found, which would bring into question the frequently made assumption that they have solar-like and oxygen-rich compositions.

Nightside condensation of iron in an ultrahot giant exoplanet.

Ultrahot giant exoplanets receive thousands of times Earth's insolation1,2. Their high-temperature atmospheres (greater than 2,000 kelvin) are ideal laboratories for studying extreme planetary climates and chemistry3-5. Daysides are predicted to be cloud-free, dominated by atomic species6 and much hotter than nightsides5,7,8. Atoms are expected to recombine into molecules over the nightside9, resulting in different day and night chemistries. Although metallic elements and a large temperature contrast have been observed10-14, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night ('evening') and night-to-day ('morning') terminators could, however, be revealed as an asymmetric absorption signature during transit4,7,15. Here we report the detection of an asymmetric atmospheric signature in the ultrahot exoplanet WASP-76b. We spectrally and temporally resolve this signature using a combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by -11 ± 0.7 kilometres per second on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside16. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. We conclude that iron must therefore condense during its journey across the nightside.

Rad-hard properties of the optical glass adopted for the PLATO space telescope refractive components.

PLAnetary Transits and Oscillations of stars (PLATO) is a medium sized mission (M3) selected by the European Space Agency (ESA) for launch in 2026. The PLATO payload includes 26 telescopes all based on a six-element refractive optical scheme. Some components will be eventually manufactured by S-FPL51, N-KZFS11 and S-FTM16 glass whose radiation resistance is partially or totally unknown. The radiation-resistance properties of such materials have been investigated by using a 60Co γ-rays source as probe. Each optical component has been characterized by a depth profile curve which describes the transmission loss as a function of the thickness in dependence of the impinging dose. A model to simulate the throughput of the whole instrument has been developed and used to verify the instrument performance considering different stellar spectra.