Abstract
Mid-infrared detector arrays operating from 2.8 to 20 μm are baselined in the design of the Origins Space Telescope Mid-Infrared Spectrometer Instrument. This instrument is designed to detect and measure the spectral signatures of gases of biogenic origin in the atmospheres of exoplanets as they transit their host stars. In order to make these detections, the detector array’s pixels need to have high-signal stability when exposed to a constant flux in multiple time-series integration over a typical transit time of a few hours. With the use of a densified pupil spectrometer design, pointing effects can be mitigated because pointing variations do not displace spectra on the detector and each wavelength of light is averaged over a large number of pixels, giving good spectrophotometric stabilities. The current state-of-the-art detector arrays do not achieve these stabilities, although with a feasible development program this level of performance should be achievable. Three detector technologies are under consideration for this development, HgCdTe arrays, Si:As impurity band conduction arrays, and transition edge superconductor bolometer arrays. We primarily treat the HgCdTe technology development, but also introduce the paths forward for the other two technologies. After a few years-long investigative programs, a down-select will be undertaken to select the flight technology.
Highlights
The Origins Space Telescope (Origins) traces our cosmic history, from the formation of the first galaxies and the rise of metals to the development of habitable worlds and present-day life
Transit spectroscopy has proven to be an essential tool for characterizing the atmospheres of exoplanets and the mid-infrared transit spectrometer instrument (MISC-T) on Origins will employ a densified pupil optical design,[1] which, limited in use for a wide range of astronomical investigations, is optimized for the removal of
Mid-IR detector stability was recently added to the NASA Science Missions Directorate Astrophysics Division “Technology Gap List” in recognition of the importance of exoplanet characterization and the power of the mid-IR to trace important molecules in the atmospheres of exoplanets discovered through transit observations.[18]
Summary
The Origins Space Telescope (Origins) traces our cosmic history, from the formation of the first galaxies and the rise of metals to the development of habitable worlds and present-day life Origins does this through exquisite sensitivity to infrared radiation from ions, atoms, molecules, dust, water vapor and ice, and observations of extra-solar planetary atmospheres, protoplanetary disks, and large-area extragalactic fields. The James Webb Space Telescope (JWST) mid-infrared instrument (MIRI) uses the same detector technology as Spitzer/infrared array camera (IRAC) channels 3 and 4 [Fig. 1(a)], which have been able to achieve ∼60 ppm precision on timescales of several hours, including the phenomological calibration of on-orbit drifts. The biosignature case for Origins requires a mid-IR detector stability of down to ∼5 ppm, depending on the wavelength, over several hours (Table 1) This stability requirement in the performance is an order of magnitude beyond the state-of-the-art that has been achieved on-orbit and may require new development beyond existing technology. This paper primarily treats the HgCdTe technology development, and introduces and compares the paths forward for the other two technologies
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