The Habitable-Exoplanet Observatory (HabEx) is a candidate flagship mission being studied by NASA and the astrophysics community in preparation of the 2020 Decadal Survey. The first HabEx mission concept that has been studied is a large (~4m) diffraction-limited optical space telescope, providing unprecedented resolution and contrast in the optical, with extensions into the near ulttraviolet and near infrared domains. We report here on our team’s efforts in defining a scientifically compelling HabEx mission that is technologically executable, affordable within NASA’s expected budgetary envelope, and timely for the next decade. We also briefly discuss our plans to explore less ambitious, descoped missions relative to the primary mission architecture discussed here.
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.
Euclid is an ESA Cosmic Vision wide-field space mission concept dedicated to the high-precision study of Dark Energy
and Dark Matter. The mission relies on two primary cosmological probes: Weak gravitational Lensing (WL) and Baryon
Acoustic Oscillations (BAO).
The first probe requires the measurement of the shape and photometric redshifts of distant galaxies. The second probe is
based on the 3-dimensional distribution of galaxies through spectroscopic redshifts. Additional cosmological probes are
also used and include cluster counts, redshift space distortions, the integrated Sachs-Wolfe effect (ISW) and galaxy
clustering, which can all be derived from a combination of imaging and spectroscopy.
Euclid Imaging Channels Instrument of the Euclid mission is designed to study the weak gravitational lensing
cosmological probe. The combined Visible and Near InfraRed imaging channels form the basis of the weak lensing
measurements. The VIS channel provides high-precision galaxy shape measurements for the measurement of weak
lensing shear. The NIP channel provides the deep NIR multi-band photometry necessary to derive the photometric
redshifts and thus a distance estimate for the lensed galaxies.
This paper describes the Imaging Channels design driver requirements to reach the challenging science goals and the
design that has been studied during the Cosmic Vision Assessment Phase.
The NIP is a near infrared imaging photometer that is currently under investigation for the Euclid space mission
in context of ESA's 2015 Cosmic Vision program. Together with the visible camera (VIS) it will form the basis of
the weak lensing measurements for Euclid. The NIP channel will perform photometric imaging in 3 near infrared
bands (Y, J, H) covering a wavelength range from ~ 0.9 to 2 μm over a field of view (FoV) of ~ 0.5 deg<sup>2</sup>. With
the required limiting point source magnitude of 24 mAB (5 sigma) the NIP channel will be used to determine
the photometric redshifts of over 2 billion galaxies collected over a wide survey area of 20 000 deg<sup>2</sup>. In addition
to the photometric measurements, the NIP channel will deliver unique near infrared (NIR) imaging data over
the entire extragalactic sky, enabling a wide variety of ancillary astrophysical and cosmological studies. In this
paper we will present the results of the study carried out by the Euclid Imaging Consortium (EIC) during the
Euclid assessment phase.
Dark matter in a universe dominated by a cosmological constant seeds the formation of structure and is the scaffolding
for galaxy formation. The nature of dark matter remains one of the fundamental unsolved problems in astrophysics and
physics even though it represents 85% of the mass in the universe, and nearly one quarter of its total mass-energy
budget. The mass function of dark matter "substructure" on sub-galactic scales may be enormously sensitive to the mass
and properties of the dark matter particle. On astrophysical scales, especially at cosmological distances, dark matter
substructure may only be detected through its gravitational influence on light from distant varying sources. Specifically,
these are largely active galactic nuclei (AGN), which are accreting super-massive black holes in the centers of galaxies,
some of the most extreme objects ever found. With enough measurements of the flux from AGN at different
wavelengths, and their variability over time, the detailed structure around AGN, and even the mass of the super-massive
black hole can be measured. The Observatory for Multi-Epoch Gravitational Lens Astrophysics (OMEGA) is a mission
concept for a 1.5-m near-UV through near-IR space observatory that will be dedicated to frequent imaging and
spectroscopic monitoring of ~100 multiply-imaged active galactic nuclei over the whole sky. Using wavelength-tailored
dichroics with extremely high transmittance, efficient imaging in six channels will be done simultaneously during each
visit to each target. The separate spectroscopic mode, engaged through a flip-in mirror, uses an image slicer
spectrograph. After a period of many visits to all targets, the resulting multidimensional movies can then be analyzed to
a) measure the mass function of dark matter substructure; b) measure precise masses of the accreting black holes as well
as the structure of their accretion disks and their environments over several decades of physical scale; and c) measure a
combination of Hubble's local expansion constant and cosmological distances to unprecedented precision. We present
the novel OMEGA instrumentation suite, and how its integrated design is ideal for opening the time domain of known
cosmologically-distant variable sources, to achieve the stated scientific goals.
DUNE (Dark Universe Explorer) is a proposed mission to measure parameters of dark energy using weak gravitational
lensing The particular challenges of both optical and infrared focal planes and the DUNE baseline solution is discussed.
The DUNE visible Focal Plane Array (VFP) consists of 36 large format red-sensitive CCDs, arranged in a 9x4 array
together with the associated mechanical support structure and electronics processing chains. Four additional CCDs
dedicated to attitude control measurements are located at the edge of the array. All CCDs are 4096 pixel red-enhanced
e2v CCD203-82 devices with square 12 μm pixels, operating from 550-920nm. Combining four rows of CCDs provides
a total exposure time of 1500s. The VFP will be used in a closed-loop system by the spacecraft, which operates in a drift
scan mode, in order to synchronize the scan and readout rates. The Near Infrared (NIR) FPA consists of a 5 x 12 mosaic
of 60 Hawaii 2RG detector arrays from Teledyne, NIR bandpass filters for the wavelength bands Y, J, and H, the
mechanical support structure, and the detector readout and signal processing electronics. The FPA is operated at a
maximum temperature of 140 K for low dark current of 0.02-/s. Each sensor chip assembly has 2048 x 2048 square
pixels of 18 μm size (0.15 arcsec), sensitive in the 0.8 to 1.7 μm wavelength range. As the spacecraft is scanning the sky,
the image motion on the NIR FPA is stabilized by a de-scanning mirror during the integration time of 300 s per detector.
The total integration time of 1500 seconds is split among the three NIR wavelengths bands. DUNE has been proposed to
ESA's Cosmic Vision program and has been jointly selected with SPACE for an ESA Assessment Phase which has led
to the joint <i>Euclid</i> mission concept.