Abstract
The near- to mid-infrared wavelength range contains a wealth of astrophysical information and is crucial for studying cool stars, galaxy evolution, and small bodies in the Solar System. To overcome the limitations imposed by Earth’s atmosphere, such as absorption, scattering, and thermal noise, space-based infrared survey missions have become indispensable. Since the first all-sky infrared survey mission, Infrared Astronomical Satellite (IRAS), subsequent missions such as AKARI and Wide-field Infrared Survey Explorer (WISE) have accumulated massive datasets through wide-field observations, leading to breakthroughs in areas including brown dwarf census studies, active galactic nucleus identification, and measurements of asteroid physical properties. The recently launched Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) will carry out the first all-sky near-infrared spectroscopic survey and is expected to provide new insights into the large-scale structure of the Universe, the formation history of the Milky Way and external galaxies, the distribution of interstellar ices, as well as Solar System small bodies and exoplanetary systems. This article provides a systematic review of the development of near- to mid-infrared space surveys, with a particular focus on the scientific goals, achievements, and technical characteristics of the WISE and SPHEREx missions, and offers an outlook on future advances in this field.
Keywords
0 Introduction
For astronomical observation, the near-mid-infrared band contains a wealth of information. This band not only contains abundant molecular spectral lines, but also the radiation peaks of cold stars and circumstellar dust, the spectral lines emitted by dust in star-forming regions, and some high-redshift galaxies and quasars all fall within this range. Therefore, conducting astronomical observations in this band is of great significance for studying the composition and elements of cold stars and circumstellar dust, as well as the evolution of galaxies and the early universe.
However, due to the influence of Earth's atmospheric infrared radiation and atmospheric absorption window, ground-based infrared observations suffer from many problems such as limited observation bands and difficulty in improving signal-to-noise ratio [1]. For this reason, using satellites to conduct infrared observations outside the atmosphere has become the current mainstream practice.
Compared to point observations, sky surveys can observe and analyze a large sample of the entire sky, understanding overall trends and identifying rare samples. Therefore, infrared sky surveys have become a very important component of modern astronomical observation.
This article first introduces the development history and current important achievements of infrared space survey observation. Then, it introduces two important space survey projects operating in the near-mid-infrared band − WISE and SPHEREx − and their main research areas. Finally, it summarizes the current achievements and existing problems of space infrared surveys and discusses the future development direction of this field.
1 . History and background of infrared space observation
1.1 Evolution from ground to space
Ground-based infrared observations face two major physical limitations: First, atmospheric components such as water vapor and carbon dioxide strongly absorb most of the infrared radiation from celestial bodies, limiting observations to only a few narrow "atmospheric windows" (Figure1 shows the absorption of infrared light by the Earth's atmosphere) ; second, the thermal radiation from the atmosphere and the telescope itself generates strong thermal radiation background noise, severely restricting detection sensitivity.
Early explorations using balloons, sounding rockets, and airborne platforms (such as the Kuiper Airborne Observatory (KAO) [3]) validated the potential of space exploration (avoiding atmospheric interference) , but were still limited by short observation time and residual atmospheric interference. The real revolutionary breakthrough was achieved by the IRAS satellite launched in 1983, whose liquid helium-cooled telescope effectively avoided atmospheric absorption and its own thermal noise. During its 10-month mission, IRAS completed the first infrared all-sky survey across four independent broad-band wavelengths of 12 μm, 25 μm, 60 μm, and 100 μm, covering96% of the sky. IRAS not only discovered more than 350, 000 infrared sources, but also pioneered the study of new physical phenomena such as stellar dust disks and Luminous Infrared Galaxies (LIRGs) . This marks the arrival of a new era in infrared space astronomy and lays a solid foundation for the development of subsequent missions [5-7].
1.2 Key milestone tasks
IRAS pioneered the infrared all-sky survey, and subsequent survey missions have continued to advance in the direction of improving sensitivity, resolution and spectral coverage. The ground-based Two Micron All-Sky Survey (2MASS) mission (1997−2001) provided key position and brightness references for many infrared sources discovered by IRAS in the near-infrared band, and the stellar reference frame it established is still the cornerstone of astronomical research [8]. In the space field, the AKARI satellite launched by Japan in 2006, as the direct successor to IRAS, further improved the sensitivity and spatial resolution of the survey [9]. The WISE telescope launched by the National Aeronautics and Space Administration (NASA) in 2009 achieved an order-of-magnitude leap in sensitivity, enabling it to detect extremely cold and dark celestial bodies in the universe, greatly expanding our understanding of cold and dark celestial bodies in the nearby universe [10].
The massive amounts of data generated by the sky survey missions have also created a need for detailed studies of some of the key scientific targets. To this end, a series of observatory-level missions have formed a crucial supplement through high-precision pointing observations. The Infrared Space Observatory (ISO) , launched by the European Space Agency (ESA) in 1995, was the first to apply grating spectrometers to infrared space exploration, opening up detailed studies of astrophysical and chemical processes [11]. The Spitzer Space Telescope (SST) , launched by NASA in 2003, has provided in-depth analysis of protoplanetary disks and distant galaxies discovered by the sky survey with its excellent sensitivity [12-14]. The Herschel Space Observatory (HSO) , launched by ESA in 2009, has provided detailed characterization of the dense structures in star-forming regions with its high angular resolution [15-16]. This research model that combines "sky survey" with "precise characterization" has become a key paradigm for achieving fruitful results in infrared astronomy.
1.3 Overview of Current Achievements
The massive datasets generated by previous infrared sky surveys have systematically answered several fundamental questions in astrophysics and opened up entirely new research fields.
In the field of low-mass astrophysics, the2MASS survey discovered hundreds of L-type and T-type brown dwarfs, and WISE subsequently discovered Y-type brown dwarfs with temperatures as low as room temperature. These discoveries provided a large-scale statistical sample of brown dwarfs and established spectral classifications, ultimately establishing an observational mass sequence from the lowest-mass stars to giant planets [17-19]. Furthermore, these surveys also completed observations of our solar system's nearest neighbors (approximately 20 million stars) . A survey of low-mass objects within the pc discovered systems such as Luhman 16AB (2013) [21].
In the field of galaxy evolution, IRAS first discovered LIRGs and ultra-luminous infrared galaxies (ULIRGs) [22]; decades later, WISE discovered even more extreme hot dust-obscured galaxies (Hot DOGs) and identified millions of active galactic nucleus (AGN) candidates [23-24]. These discoveries revealed the "invisible universe" obscured by dust and finally confirmed that about half of the starlight energy in the universe is absorbed by dust and re-radiated in the form of infrared light, fundamentally correcting our understanding of the energy of the universe [25].
In the field of planetary science, IRAS detected infrared supersonic signals around Vega in 1984, which was later identified as the first “fragment disk”, providing the first direct observational evidence for the theory that “planetary birth occurs in dust disks” [26]. In addition, it also discovered the ecliptic dust belt in our solar system, which was generated by asteroid collisions. Subsequent infrared surveys (such as WISE) identified tens of thousands of candidates for stellar disks, making it possible to conduct statistical studies on the evolution and lifespan of planetary disks, thus transforming the field from a theoretical hypothesis into a precise science with a solid observational foundation [27-28].
2 WISE–a fruitful infrared space survey mission
2.1 Task overview
As an all-sky near/mid-infrared space survey mission covering the entire sky, WISE was launched into orbit in 2009 and operated in a sun-synchronous polar orbit, completing its final data acquisition on July 31, 2024. The telescope is equipped with four scientific bands, W1 to W4, achieving unprecedented all-sky sensitivity in the mid-infrared at the time. WISE surveyed the entire sky across four infrared bands (3.4 μm, 4.6 μm, 12 μm, and 22 μm) until September 2010, when the cryogenic helium cooling the telescope was depleted. During its operation, it achieved numerous significant scientific breakthroughs and mapped the cosmos in all directions around Earth. After a hibernation period from 2011 to December 2013, it was reassigned to a new mission called Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) and continued to collect data in the two shortest wavelength bands after restarting. With its long-term observation capability and infrared sensitivity, WISE not only provides highly uniform single-epoch full-skycoverage, but also forms a time-domain baseline in some sky regions, laying the data foundation for multi-theme studies from the solar system to the outer Milky Way [29]. The typical angular resolution is on the order of arcseconds in the W1 and W2 bands, while it is coarser in the W3 and W4 bands. The point source sensitivity and position accuracy vary with the band (see Table1) .
2.2 Main research areas and achievements
2.2.1 Brown Dwarfs and Neighboring Stars
WISE conducted multiple infrared observations of the sky between January 2010 and February 2011. Each observation typically involved more than a dozen infrared exposures at a designated location, with each exposure spaced two days apart. During the WISE mission, many important celestial objects were discovered, including the closest and coolest brown dwarf to Earth [21]. The cool brown dwarf exhibits significant methane absorption and continuous spectral morphology changes in the3–5 μm band, making it abnormally reddish in the W1–W2 color, while it is relatively weak in longer bands. Based on the all-sky mid-infrared survey using WISE/NEOWISE, multiple rounds of repeated observations were conducted across the sky at 3.4 μm and 4.6 μm wavelengths. Multi-year data were combined to create the CatWISE preview catalog, providing position and proper motion measurements for approximately one billion sources. This catalog achieves greater depth, longer time baselines, and higher proper motion accuracy than AllWISE. Based on this, infrared color source selection combined with high proper motion screening and machine learning methods greatly improves the detection capability of brown dwarfs; a number of extremely cold brown dwarfs (including several Y-type dwarf candidates) have been discovered and confirmed. At the same time, a large number of high proper motion, low luminosity neighboring stars and sub-stars have been discovered, significantly enriching the sample of high proper motion stars and sub-stars in the solar neighborhood [30].
2.2.2 Infrared Galaxy and Nearby Galaxy
WISE can effectively distinguish AGNs from star-forming galaxies. By using the color judgment criterion of W1–W2>0.8, AGN candidates can be systematically screened across the entire sky. This significantly makes up for the omission of obscured active galactic nuclei by optical selection methods. Related studies (such as the LASr project) have used WISE color combined with multi-band data to construct the most complete sample of AGNs in the nearby universe to date [31].
The W3 and W4 bands of WISE is strongly correlated with the total infrared luminosity, which can effectively calibrate the star formation rate of galaxies. Studies have shown that the W3 band is particularly closely related to the total infrared luminosity (LTIR) of galaxies, with a1σ scattering of only 0.15 dex, making it a reliable tracer of star formation rate (SFR) in nearby galaxies and large-scale surveys, and it is not sensitive to changes in metallicity [32].
Based on this, WISE data has led to the creation of a large-scale AGN catalog (including the R90 and C75 catalogs, which contain millions of candidates) , which has optimized the reliability and completeness of the data and supported diverse scientific research, such as identifying highly variable sources, discovering quasar groups, and exploring the interaction between AGN and hostgalaxies [33].
2.2.3 Asteroids and celestial bodies in the solar system
The WISE mission has made great breakthroughs in the study of asteroids and other small bodies in the solar system by conducting a full-sky mid-infrared survey. For the first time, the mission has achieved a large-scale, systematic survey of near-Earth objects and main-belt asteroids in the thermal infrared band, enabling researchers to directly estimate the diameter of small bodies and deduce the geometric albedo without relying on the assumption of visible light albedo, which greatly reduces the systematic uncertainty when calculating the size solely from luminosity [34].
NEOWISE was restarted, it continued to monitor for many years, which extended the physical parameter database of small bodies over time. During the mission, more than 157, 000 asteroids were detected. Based on this data, researchers constructed the largest diameter-albedo sample of main-belt asteroids, near-Earth asteroids, Trojans and resonants to date, providing a statistical basis for the study of the size distribution, compositional differentiation and dynamic evolution of asteroid groups [35]. At the same time, it has basically completed the general survey of near-Earth objects in the kilometer range, playing an important role in the rapid assessment of the size and thermal properties of potentially threatening asteroids, and becoming an indispensable data source for planetary defense and the overall study of small bodies in the solar system [36].
2.2.4 Planetary debris disk and interstellar dust
Dust around stars is an important indicator of the existence and evolution of planetary systems. For pre-main sequence and main sequence stars, this dust records the continuous processes of planet formation and small body collisions [37]; while dust observed in the white dwarf stage reveals the destruction and redistribution processes that the remnant planetary system underwent in the post-main sequence evolution [38]. The diagnosis of infrared overshoot caused by dust around stars essentially depends on the systematic deviation of its spectral energy distribution in the mid-infrared band from the pure photosphere model.
The W3 and W4 bands of WISE are located in the peak region of thermal radiation of typical warm dust (such as temperatures of about 100 to 1000 K) , so they have high detection sensitivity for detecting debris disks around main sequence stars, dust structures generated during the formation of protoplanetary systems, and dense dust rings formed by tidal fragmentation of planetary material around white dwarfs.
2.3 Limitations and supplementary role in subsequent tasks
WISE survey data stems from its spatial resolution and sensitivity. Its angular resolution of about 6″ is prone to severe source confusion in crowded regions (such as the Milky Way disk or compact galactic fields) , that is, multiple objects cannot be distinguished within the beam, resulting in inaccurate photometry or false infrared supersound. In addition, its longest band W4 has relatively limited sensitivity, making it difficult to detect cold dust radiation in low-luminosity or high-redshift universes. For extended sources, WISE's point source processing model will decompose them into multiple point sources, affecting the accurate measurement of total luminosity [39].
Subsequent space and ground-based observation facilities have provided crucial complements to these limitations in multiple dimensions. The SST telescope [12] has played an important role in identifying weak WISE sources, eliminating source aliasing, and accurately measuring flux in dense or crowded environments, thanks to its higher angular resolution and stronger infrared imaging capabilities.
The James Webb Space Telescope (JWST) [40] further extends infrared observation capabilities to the parameter space that WISE cannot cover. Its outstanding sensitivity and spectral resolution can not only perform fine imaging and spectral diagnosis of extreme or anomalous sources discovered by WISE, but also reveal new types of celestial objects beyond the detection limits of WISE.
Meanwhile, large-scale ground-based surveys such as the Sloan Digital Sky Survey (SDSS) and the Legacy Survey of Space and Time (LSST) , as well as the high-precision astrometry measurements by the Gaia telescope, have provided WISE sources with a unified optical counterpart, distance scale, and multi-band photometry, thereby significantly improving the reliability of source classification, physical quantity inversion, and statistical studies, and building a more robust foundation for multi-band joint analysis.
3 SPHEREx–a new generation of infrared sky survey missions
3.1 Task introduction
SPHEREx is a space telescope project led by NASA, launched on March 18, 2025. It is the first spectroscopic survey project to be carried out in the infrared band. Table2 shows the wavelengths and corresponding resolutions of SPHEREx in each band. This resolution enables SPHEREx to resolve key spectral lines such as water and methane, and can better detect the existence and abundance of interstellar ice [41].
Meanwhile, SPHEREx also boasts high detection sensitivity. Pre-launch simulations indicate that under 5conditions, it can achieve limiting magnitudes of 18.5 to 19 (AB magnitude) for all-sky point sources across the 0.75–3.8 μm wavelength range, comparable to the sensitivity of the Euclid space telescope. Sensitivity in the3.8–5.0 μm band is slightly lower, with limiting magnitudes ranging from 16.6 to 18. For deep fields near the north and south ecliptic poles, sensitivity can be10–20 times higher than that of a single observation [43].
In terms of optical structure, SPHEREx is equipped with two focal plane arrays (FPAs) . Each assembly consists of three linearly graded filters (LVFs) and a subsequent HgCdTe infrared detector array, enabling the detection of optical flux at different wavelengths. During observation, a dichroic mirror splits the incident light into long-wavelength and short-wavelength components, allowing it to simultaneously enter both focal plane arrays. The telescope adjusts its pointing to ensure the incident light passes sequentially through the infrared detector array, thus measuring the infrared spectrum. Figure2 shows the optical path design of the SPHEREx telescope.
SPHEREx's main objectives include exploring the expansion of the universe, large-scale structures, galaxy evolution, and searching for water and biomolecular ice in the universe. During its two-year mission, SPHEREx will complete four full-sky surveys, providing important data support for research in cosmology, galaxy evolution, interstellar dust, stellar science, and asteroids [42].
3.2 Main research areas and expected results
3.2.1 Cosmological and dark matter research
In cosmology, SPHEREx focuses on the study of the large-scale structure and reionization process of the universe. SPHEREx can use template fitting methods to combine galaxy continuum spectrum and emission line information to perform high-precision redshift measurements on approximately 19 million galaxies. Its accuracy can reach <0.003 (1+ z) [44]. In addition, existing studies have shown that SPHEREx can measure the large-scale distribution of galaxies with redshifts between 1 and 4 by mapping the intensity of emission lines without obtaining the spectrum of a single galaxy [45].
By observing the large-scale structure of the universe, combined with power spectrum and bispectral analysis, SPHEREx's multi-band data can jointly constrain multiple primordial non-Gaussianity (PNG) related parameters and reduce the uncertainty of local parameters by an order of magnitude, obtaining the most accurate measurement of primordial non-Gaussianity to date [46-47], thereby constraining the physical processes during the period of cosmic inflation.
The study of cosmic reionization is also an important area of SPHEREx. SPHEREx can observe lines with redshift z=7 and in the cosmic reionization period and calculate their intensity mapping data [48]. Combined with 21 cm neutral hydrogen, it can form a power spectrum [49] as infrared background, and jointly constrains the evolution of the neutral fraction of its reionization.
Axion-like particles (ALPs) are a strong candidate for dark matter. SPHEREx's wide field-of-view and near-infrared observation range enable it to detect photons produced by the decay of ALPs with masses ranging from 0.5 eV to 3 eV, and the properties of such particles are constrained [50-51].
3.2.2 Ice and interstellar dust detection
Ice in star-and planet-forming regions is an important source of water and organic molecules in planets. Currently, about 200 relatively bright ice absorption sources in the Milky Way have been observed by missions such as AKARI [52]. SPHEREx, with its infrared survey capabilities, is expected to obtain more than 700, 000 ice absorption spectra, covering all stages of star and planetary evolution, and answering a series of questions about the ice evolution process in stellar systems [53].
SPHEREx also has unique advantages in detecting dust in galaxies. It can measure the emission intensity of polycyclic aromatic hydrocarbons (PAHs) in hundreds of thousands of nearby galaxies[54], indicating the distribution and radiation characteristics of nanoscale dust particles in these galaxies. For fainter galaxies, SPHEREx can also use characteristic intensity distribution maps to model the overall PAH emission of the entire galaxy group [55], thereby helping us to study the star formation process and the evolution of dust in galaxies on a large scale.
3.2.3 Stars and Brown Dwarfs
SPHEREx is expected to obtain more than 100 million stellar spectra during the mission. This makes it an important complement to missions such as Gaia, helping to determine important parameters such as stellar mass [56] and to build a picture of the distribution of stellar mass in the Milky Way. The observation band of 0.75 μm to 5.0 μm also gives SPHEREx a unique advantage in studying low-temperature stars and brown dwarfs. The hundreds of brown dwarf spectra expected to be obtained will significantly expand the current sample and advance the study of brown dwarf atmospheres and the history of the Milky Way [57-58].
Although most planetary debris disks are relatively cool, current theoretical analysis suggests that SPHEREx is sufficient to detect extremely bright debris disks around stars and violent planetary impact events [57], which will provide valuable samples for studying the evolution of exoplanetary systems.
Simultaneously, the infrared spectra produced by SPHEREx enable it to rapidly screen samples of these early stars by exploiting the absence of molecular absorption features at 2.3 μm and 4.6 μm characteristic of metal-poor stars [59], thereby excluding the influence of circumstellar disks or thermal dust. This approach imposes constraints on the history and chemical composition of the Milky Way [57].
3.2.4 Asteroids and comets
The study of asteroids and comets is also one of the important scientific goals of SPHEREx. It is expected to obtain high-quality spectra of about 10, 000 asteroids, thereby expanding the existing sample by an order of magnitude [60]. At the same time, SPHEREx's spectroscopic observations will also cover a range of diagnostic features, including water ice, organic matter, hydrated minerals, etc [61]. These features will support the study of asteroid classification, surface composition and comet activity, and help calculate the orbits of these objects, providing assistance for asteroid defense [62].
Currently, SPHEREx has observed the interstellar comet 3I/ATLAS and found that it has strong water ice absorption and carbon dioxide enrichment characteristics [63]. This is considered to be the result of cosmic ray processing on a scale of billions of years [64]. These simulation and actual observation results demonstrate SPHEREx's powerful capabilities in asteroid and comet observation, and therefore it has broad prospects.
3.3 Complementarity of SPHEREx with other tasks
In addition to its excellent performance, SPHEREx's unique infrared spectrum and fast data release make it very effective for collaborative observation with other missions [42], further improving the accuracy of the results.
In terms of observation mode, SPHEREx can be well coordinated with high-precision point observations such as JWST. After SPHEREx finds high-value targets through sky surveys, JWST can quickly conduct high-precision, high-resolution follow-up observations to quickly determine more accurate physical properties [42].
In its operating band, SPHEREx can conduct joint observations with telescopes in different bands to jointly constrain various parameters in the process of celestial bodies and the evolution of the universe, such as constraining stellar mass with the Gaia telescope [56] and constraining theevolution of neutral hydrogen fraction with the Square Kilometre Array (SKA) telescope [49].
Combining different research methods can also lead to better physical constraints. For example, cross-correlation between SPHEREx line intensity mapping and CSST and LSST weak gravitational lensing surveys can provide more accurate estimates of the mass of axion-like particles and their coupling constant with photons [51, 65]. SPHEREx infrared super data and light variation data of various stars (including white dwarfs) from the Earth 2.0 (ET) survey can also be combined to study companion stars, debris disks, and dust accretion around stars [66-70].
4 . Conclusion
The WISE satellite completed a mid-infrared all-sky survey with unprecedented sensitivity, providing high-quality images ranging from 3.4 μm to 22 μm, and achieving significant results in the fields of stars, small bodies, and extragalactic objects. The mission explored hundreds of thousands of asteroids (more than 3, 000 of which were officially numbered) and discovered several comets and nearby brown dwarfs. Its infrared observations revealed young stellar disks, white dwarf disks, and several nebulae, while efficiently identifying AGNs and LIRGs; long-term temporal data also revealed various types of infrared transients, establishing its important position in infrared astronomy.
As a significant follow-up mission to WISE/NEOWISE, SPHEREx will conduct the first true all-sky spectral survey in the 0.75–5 μm wavelength range. Over its two-year mission, SPHEREx will acquire low-resolution spectra in the 0.75–5 μm range for every 6.2″×6.2″pixel across the entire sky. The spectral resolution is approximately R≈41 between 0.75–2.42 μm, R≈35 between 2.42–3.82 μm, R≈110 between 3.82–4.42 μm, and R≈130 between 4.42–5.00 μm. Its sensitivity is approximately AB≈19–19.5, enabling high signal-to-noise ratio measurements of all sources in 2MASS while achieving spectral detection for most WISE sources.
In terms of scientific objectives, SPHEREx will utilize its unique all-sky near-infrared spectral data to achieve three core scientific tasks: (1) to explore the inflationary physics of the early universe through precise measurements of large-scale structures; (2) to construct a comprehensive survey of star formation, molecular clouds and ice in the Milky Way; (3) to conduct unified spectral diagnostics of galaxies, stars and solar system objects, providing an unprecedented basic database for infrared astronomy.
Despite their important roles in all-sky surveys, WISE and SPHEREx still have significant limitations in their observational capabilities. WISE provides imaging data only across four bandwidths from 3.4 to 22 µm, lacking spectral information, and its limited spatial resolution (6″–12″) and sensitivity make it difficult to finely characterize complex or dense environments or provide in-depth diagnostics of key physical processes. While SPHEREx will achieve the first all-sky spectroscopic survey of 0.75–5 µm, its low spectral resolution (R≈35–130) , coarse spatial sampling (6.2″) , and limited sensitivity (AB≈19–19.5) make it unsuitable for high-redshift galaxies, fine spectral line analysis, or deep-field studies. Therefore, both are considered "broad but shallow" survey missions.
Compared to WISE and SPHEREx, the currently operating large-scale space astronomy projects JWST and Euclid have significant advantages in spatial resolution, sensitivity, and spectroscopic diagnostic capabilities. JWST, with its high spatial resolution and deep spectroscopic coverage from near-infrared to mid-infrared, can finely resolve compact sky regions, weak light sources, and dust-dominated interstellar environments, providing physical constraints for planetary systems, galaxy formation, and the early universe far exceeding those of shallow surveys. Euclid, through its wide-field visible and near-infrared imaging and spectroscopic capabilities, has achieved high-precision measurements of the large-scale structure of the universe, weak lensing distortion, and statistical properties of galaxies, significantly improving its ability to characterize redshift, galaxy morphology, and environmental effects.
However, while JWST and Euclid can compensate for the shortcomings of WISE and SPHEREx in terms of depth observation and high-resolution imaging, they cannot completely replace the latter's ability to conduct large-area, uniform, all-sky surveys. JWST, limited by its narrow field of view and observation schedule, is unsuitable for constructing large-sample statistical analyses or conducting systematic surveys from the local universe to high redshifts; Euclid, while covering a wide area, has a limited spectral range and lacks mid-infrared capabilities, and cannot provide continuous spectral information like SPHEREx. Therefore, these two types of missions complement each other; neither single mission can independently cover all needs from large-sample statistical analysis to high-resolution physical diagnostics.
The Nancy Grace Roman Space Telescope (NGRST) and the future Habitable Worlds Observatory (HWO) will also play crucial roles in space infrared astronomy. NGRST, with its wide field of view, high-resolution near-infrared imaging, and high-contrast coronagraph, will provide more precise statistical surveys and direct imaging capabilities for exoplanet candidates and planetary systems across the entire sky. It will complement the wide-field spectroscopic data from SPHEREx, providing higher spatial resolution global constraints for the distribution, age, metallicity, and disk structure of planetary systems. Furthermore, NGRST's deep wide-field imaging and weak lensing capabilities will play a significant role in extragalactic astronomy research, enabling the construction of large-scale galactic surveys, constraint of galactic dark matter halo properties, and advancements in the precision of cosmological parameter measurements.
As a future flagship observatory, the core objective of the High Earth Observatory (HWO) is to achieve direct imaging and atmospheric spectroscopic characterization of Earth-like habitable planets. This will bring revolutionary breakthroughs to planetary habitability research across the entire sky. In the extragalactic realm, HWO's high-sensitivity continuous spectral capabilities are expected to capture the detailed structure of nearby galaxies, the state of the interstellar medium, and star formation activity, thereby greatly advancing our understanding of the physics of galaxy evolution.