The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance (1008.0031v2)

Abstract: The all sky surveys done by the Palomar Observatory Schmidt, the European Southern Observatory Schmidt, and the United Kingdom Schmidt, the InfraRed Astronomical Satellite and the 2 Micron All Sky Survey have proven to be extremely useful tools for astronomy with value that lasts for decades. The Wide-field Infrared Survey Explorer is mapping the whole sky following its launch on 14 December 2009. WISE began surveying the sky on 14 Jan 2010 and completed its first full coverage of the sky on July 17. The survey will continue to cover the sky a second time until the cryogen is exhausted (anticipated in November 2010). WISE is achieving 5 sigma point source sensitivities better than 0.08, 0.11, 1 and 6 mJy in unconfused regions on the ecliptic in bands centered at wavelengths of 3.4, 4.6, 12 and 22 microns. Sensitivity improves toward the ecliptic poles due to denser coverage and lower zodiacal background. The angular resolution is 6.1, 6.4, 6.5 and 12.0 arc-seconds at 3.4, 4.6, 12 and 22 microns, and the astrometric precision for high SNR sources is better than 0.15 arc-seconds.

• The paper presents the innovative mission design, detailing the use of cryogenically-cooled detectors and sky scanning in a Sun-synchronous orbit to achieve high sensitivity.
• The paper highlights on-orbit performance with point source sensitivities reaching 0.08 to 6 mJy across four mid-infrared bands, ensuring extensive all-sky coverage.
• The paper demonstrates significant scientific outcomes, including breakthroughs in brown dwarf detection, studies of ULIRGs, and precise asteroid characterization.

The Wide-field Infrared Survey Explorer (WISE): Analysis of Mission Implementation and Scientific Outcomes

The paper "The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance" provides a detailed examination of the design, operational capabilities, and preliminary scientific results from the WISE mission. Launched on December 14, 2009, WISE embarked on a mission to map the entire sky in four mid-infrared wavelengths with unprecedented sensitivity and resolution compared to its predecessors, IRAS and AKARI.

Mission Design and Implementation

WISE is a NASA-funded medium-class Explorer mission designed to provide an all-sky survey in the mid-infrared spectrum. The spacecraft operates in a Sun-synchronous low Earth orbit, utilizing a 40 cm diameter telescope within a solid-hydrogen-cooled cryostat to achieve optimal sensitivity across four infrared bands (3.4, 4.6, 12, and 22 μm). The primary survey strategy was sky scanning with great circles centered on the Sun, maximizing usable observing time while minimizing solar interference. Throughout its operational period, WISE achieved angular resolutions of 6.1 to 12.0 arcseconds across its four bands, surpassing the sensitivity limits of previous infrared missions.

On-orbit Performance and Data Acquisition

WISE's infrared detectors, a combination of HgCdTe and Si:As BIB arrays, demonstrated exceptional sensitivity. Achieving better than 5-sigma point source sensitivities of 0.08, 0.11, 1, and 6 mJy across the bands, the mission completed initial sky coverage by July 17, 2010. The spacecraft experienced extended observational capability, continuing operations beyond the expected cryogen depletion date, which allowed for more comprehensive data collection.

The WISE mission design facilitated redundancy in sky coverage, ensuring that over 99% of the sky was observed in at least eight frames, with many regions gaining even higher coverage densities. This extensive sky mapping was processed by the Infrared Processing and Analysis Center (IPAC), producing a highly detailed image atlas and extracted source catalog for public scientific use.

Scientific Outcomes and Implications

The scientific scope of WISE includes key contributions to several domains:

1. Brown Dwarf Stars: With its heightened sensitivity, particularly in the 4.6 μm band, WISE is capable of detecting cool brown dwarfs down to significantly lower temperatures than optical surveys, improving our understanding of the local substellar population.
2. Ultra-Luminous Infrared Galaxies (ULIRGs): WISE's ability to identify high-redshift ULIRGs and AGN will aid in exploring the evolution of massive galaxies and the role of mergers in AGN activation across cosmic time scales.
3. Asteroids and Comets: The mission's infrared sensitivity substantially enhances the measurement of asteroid sizes and albedos, critical for accurate characterization of Near-Earth Objects and main asteroid belt residents.
4. Galactic and Extragalactic Structure: By mapping stars and galaxies with high angular resolution and sensitivity, WISE provides invaluable insights into galactic morphology, star formation regions, and the large-scale distribution of matter in the universe.

Future Developments and Continued Impact

The vast dataset and catalog generated by WISE have propelled significant advancements in infrared astronomy, providing a robust baseline for future space-based infrared observatories, including JWST. The survey data continues to enable diverse research, from the local solar neighborhood to the furthest reaches of observable galaxies. Future research can anticipate further leveraging the deep integration of WISE data with optical and other wavelength surveys, enhancing multi-wavelength analysis of astrophysical phenomena.

In conclusion, the WISE mission represents a significant advancement in infrared astronomical surveys. Its comprehensive, high-sensitivity sky mapping has opened new avenues in various fields of research, from planetary science to the cosmological inquiry, setting a foundational reference for subsequent observational strategies and scientific inquiries.