The Habitable Exoplanet (HabEx) Imaging Mission: preliminary science drivers and technical requirements

HabEx is one of four candidate flagship missions being studied in detail by NASA, to be submitted for consideration to the 2020 Decadal Survey in Astronomy and Astrophysics for possible launch in the 2030s. It will be optimized for direct imaging and spectroscopy of potentially habitable exoplanets, and will also enable a wide range of general astrophysics science. HabEx aims to fully characterize planetary systems around nearby solar-type stars for the first time, including rocky planets, possible water worlds, gas giants, ice giants, and faint circumstellar debris disks. In particular, it will explore our nearest neighbors and search for signs of habitability and biosignatures in the atmospheres of rocky planets in the habitable zones of their parent stars. Such high spatial resolution, high contrast observations require a large (roughly greater than 3.5m), stable, and diffraction-limited optical space telescope. Such a telescope also opens up unique capabilities for studying the formation and evolution of stars and galaxies. We present some preliminary science objectives identified for HabEx by our Science and Technology Definition Team (STDT), together with a first look at the key challenges and design trades ahead

Interférométrie spatiale dédiée à la recherche de planètes extrasolaires : Simulations des propriétés d'imagerie et de spectroscopie

Parmi les différentes techniques envisagées pour détecter et caractériser des planètes extrasolaires orbitant autour d'étoiles proches, l'interférométrie spatiale infrarouge est la seule qui permette une détection directe de planètes telluriques et le sondage de leur atmosphère par spectroscopie. Nous nous intéressons ici exclusivement à la pupille d'entrée d'un tel interféromètre, et à l'optimisation de ses propriétés d'imagerie et de spectroscopie. Apres avoir passé en revue les contraintes imposées par les principales sources de bruit astrophysique, nous proposons une configuration à 5 télescopes, répartis sur une base d'environ 50m sur 25m. Avec un tel réseau interférométrique, un temps d'intégration de 30h permettrait de reconstruire une "image" d'un système planétaire situé à 10pc et analogue au notre. La spectroscopie des planètes ainsi détectées pourrait révéler la présence de vapeur d'eau, de dioxyde de carbone, et d'ozone en quelques semaines d'intégration

Reflected spectroscopy of small exoplanets III: probing the UV band to measure biosignature gasses

Direct-imaging observations of terrestrial exoplanets will enable their atmospheric characterization and habitability assessment. Considering the Earth, the key atmospheric signatures for the biosphere is O$_2$ and the photochemical product O$_3$. However, this O$_2$-O$_3$ biosignature is not detectable in the visible wavelengths for most of the time after the emergence of oxygenic photosynthesis life (i.e., the Proterozoic Earth). Here we demonstrate spectroscopic observations in the ultraviolet wavelengths for detecting and characterizing O$_2$ and O$_3$ in Proterozoic Earth-like planets, using ExoReL$^\Re$. For an O$_2$ mixing ratio 2 to 3 orders of magnitude less than the present-day Earth, and an O$_3$ mixing ratio of $10^{-7}-10^{-6}$, we find that O$_3$ can be detected and its mixing ratio can be measured precisely (within $~1$ order of magnitude) in the ultraviolet ($0.25-0.4\ \mu$m) in addition to visible-wavelength spectroscopy. With modest spectral resolution ($R=7$) and S/N ($\sim10$) in the ultraviolet, the O$_3$ detection is robust against other potential gases absorbing in the ultraviolet (e.g., H$_2$S and SO$_2$), as well as the short-wavelength cutoff between 0.2 and 0.25 $\mu$m. While the O$_3$ detection does not rely on the near-infrared spectra, extending the wavelength coverage to the near-infrared ($1-1.8\ \mu$m) would provide essential information to interpret the O$_3$ biosignature, including the mixing ratio of H$_2$O, the cloud pressure, as well as the determination of the dominant gas of the atmosphere. The ultraviolet and near-infrared capabilities should thus be evaluated as critical components for future missions aiming at imaging and characterizing terrestrial exoplanets, such as the Habitable Worlds Observatory.Comment: 13 pages, 8 figures, 3 tables, accepted for publication in A

Ring-apodized vortex coronagraphs for obscured telescopes. I. Transmissive ring apodizers

The vortex coronagraph (VC) is a new generation small inner working angle (IWA) coronagraph currently offered on various 8-meter class ground-based telescopes. On these observing platforms, the current level of performance is not limited by the intrinsic properties of actual vortex devices, but by wavefront control residuals and incoherent background (e.g. thermal emission of the sky) or the light diffracted by the imprint of the secondary mirror and support structures on the telescope pupil. In the particular case of unfriendly apertures (mainly large central obscuration) when very high contrast is needed (e.g. direct imaging of older exoplanets with extremely large telescopes or space- based coronagraphs), a simple VC, as most coronagraphs, can not deliver its nominal performance because of the contamination due to the diffraction from the obscured part of the pupil. Here we propose a novel yet simple concept that circumvents this problem. We combine a vortex phase mask in the image plane of a high-contrast instrument with a single pupil-based amplitude ring apodizer, tailor designed to exploit the unique convolution properties of the VC at the Lyot-stop plane. We show that such a ring-apodized vortex coronagraph (RAVC) restores the perfect attenuation property of the VC regardless of the size of the central obscuration, and for any (even) topological charge of the vortex. More importantly the RAVC maintains the IWA and conserves a fairly high throughput, which are signature properties of the VC.Comment: 10 pages, 6 figure

White-Light Nulling Interferometers for Detecting Planets

A report proposes the development of a white-light nulling interferometer to be used in conjunction with a singleaperture astronomical telescope that would be operated in outer space. When such a telescope is aimed at a given star, the interferometer would suppress the light of that star while passing enough light from planets (if any) orbiting the star, to enable imaging or spectroscopic examination of the planets. In a nulling interferometer, according to the proposal, scattered light would be suppressed by spatial filtering in an array of single-mode optical fibers rather than by requiring optical surfaces to be accurate within 1/4,000 wavelength as in a coronagraph or an apodized telescope. As a result, angstrom-level precision would be needed in only the small nulling combiner, and not in large, meter-sized optics. The nulling interferometer could work as an independent instrument in space or in conjunction with a coronagraphic system to detect planets outside our solar system

The Habitable Exoplanet (HabEx) Imaging Mission: preliminary science drivers and technical requirements

HabEx is one of four candidate flagship missions being studied in detail by NASA, to be submitted for consideration to the 2020 Decadal Survey in Astronomy and Astrophysics for possible launch in the 2030s. It will be optimized for direct imaging and spectroscopy of potentially habitable exoplanets, and will also enable a wide range of general astrophysics science. HabEx aims to fully characterize planetary systems around nearby solar-type stars for the first time, including rocky planets, possible water worlds, gas giants, ice giants, and faint circumstellar debris disks. In particular, it will explore our nearest neighbors and search for signs of habitability and biosignatures in the atmospheres of rocky planets in the habitable zones of their parent stars. Such high spatial resolution, high contrast observations require a large (roughly greater than 3.5m), stable, and diffraction-limited optical space telescope. Such a telescope also opens up unique capabilities for studying the formation and evolution of stars and galaxies. We present some preliminary science objectives identified for HabEx by our Science and Technology Definition Team (STDT), together with a first look at the key challenges and design trades ahead