Habitable Exoplanet Observatory (HabEx)

The HabEx Space Observatory along with its starshade
Mission type	Space observatory
Operator	NASA
Website	www.jpl.nasa.gov/habex/
Mission duration	5 to 10 years (proposed)[1]
Spacecraft properties
Launch mass	18,550 kilograms (40,900 lb) (maximum)[1]
Dry mass	≈10,160 kg (22,400 lb)
Payload mass	≈6,080 kg (13,400 lb) (telescope + instruments)
Power	6.9 kW (maximum)[1]
Start of mission
Launch date	2035 (proposed)
Rocket	Observatory:Space Launch System (SLS) Block 1B[1] Starshade:Falcon Heavy
Orbital parameters
Regime	Lagrange point (Sun-Earth L2)
Main
Diameter	4 m (13 ft)
Wavelengths	Visible; possibly UV, NIR, IR (91 – 1000 nm)
Resolution	R ≥ 60,000; SNR ≥ 5 per resolution element on targets of AB ≥ 20 mag (GALEX FUV) in exposure times of ≤12 h[1]
Instruments
VIS camera, UV spectrograph,coronagraph,starshade[1][2]
Large strategic science mission

TheHabitable Exoplanet Observatory (HabEx) is aspace telescope concept that would be optimized to search for and image Earth-sizehabitable exoplanets in thehabitable zones of their stars, whereliquid water can exist. HabEx would aim to understand how commonterrestrial worlds beyond theSolar System may be and determine the range of their characteristics. It would be an optical,UV andinfrared telescope that would also usespectrographs to study planetary atmospheres and eclipsestarlight with either an internalcoronagraph or an externalstarshade.^[3]

The proposal, first made in 2016, is for alarge strategic science missionsNASA mission. It would operate at theLagrange point L2.

In January 2023, a new space telescope concept was proposed called theHabitable Worlds Observatory (HWO), which draws upon HabEx and theLarge Ultraviolet Optical Infrared Surveyor (LUVOIR).^[4]

In 2016, NASA began considering four differentspace telescopes as the next Flagship (Large strategic science missions) following theJames Webb Space Telescope andNancy Grace Roman Space Telescope.^[3] They are the Habitable Exoplanet Observatory (HabEx),Large Ultraviolet Optical Infrared Surveyor (LUVOIR),Origins Space Telescope, andLynx X-ray Surveyor. In 2019, the four teams turned their final reports over to theNational Academy of Sciences, whose independentDecadal Survey committee advises NASA on which mission should take top priority.^[3]

The Habitable Exoplanet Imaging Mission (HabEx) is a concept for a mission to directly image planetary systems around Sun-like stars.^[5][6] HabEx will be sensitive to all types of planets; however its main goal is to directly image Earth-size rocky exoplanets, and characterize theiratmospheric content. By measuring the spectra of these planets, HabEx will search for signatures of habitability such as water, and be sensitive to gases in the atmosphere potentially indicative of biological activity, such as oxygen or ozone.^[6]

In 2021, the National Academy of Sciences released its final recommendations in the Decadal Survey. It recommended that NASA consider a new 6-meter (20-foot) aperture telescope combining design elements of LUVOIR and HabEx. The new telescope would be called theHabitable Worlds Observatory (HWO). A preliminary launch date was set for 2040, and the budget was estimated to be $11 billion.^[7][8][9]

HabEx's prime science goal is the discovery and characterization of Earth-sized planets in the habitable zones of nearby main sequence stars, it will also study the full range of exoplanets within the systems and also enable a wide range of general astrophysics science.

In particular, the mission will be designed to search for signs ofhabitability andbiosignatures in the atmospheres of Earth-sized rocky planets located in thehabitable zone of nearby solar type stars.^[10] Absorption features fromCH
₄,H
₂O,NH
₃, andCO, and emission features fromNa andK, are all within the wavelength range of anticipated HabEx observations.

With a contrast that is 1000 times better than that achievable with theHubble Space Telescope,^[10] HabEx could resolve largedust structures, tracing the gravitational effect of planets. By imaging several faintprotoplanetary disks for the first time, HabEx will enable comparative studies of dust inventory and properties across a broad range ofstellar classifications.^[5] This will put theSolar System in perspective not only in terms of exoplanet populations, but also in terms of dust belt morphologies.^[10]

Generalastrometry andastrophysics observations may be performed if justified by a high science return while still being compatible with top exoplanet science goals and preferred architecture. A wide variety of investigations are currently being considered for HabEx general astrophysics program. They range from studies of galaxy leakiness andinter-galactic mediumreionization through measurements of the escape fraction ofionizing photons, to studies of the life cycle ofbaryons as they flow in and out of galaxies, to resolved stellar population studies, including the impact of massive stars and other local environment conditions on star formation rate and history.^[10] More exotic applications includeastrometric observations of localdwarf galaxies to help constrain the nature ofdark matter, and precision measurement of the local value of theHubble Constant.^[10]

The following table summarizes the possible investigations currently suggested for HabEx general astrophysics:^[10]

Based on the science drivers and purpose, the researchers are considering direct imaging andspectroscopy of reflected starlight in thevisible spectrum, with potential extensions to theUV and thenear infrared parts of thespectrum. The telescope has a primary monolithic mirror that is 4 metres (13 ft) in diameter.

An absolute minimum continuous wavelength range is 0.4 to 1 μm, with possible short wavelength extensions down below 0.3 μm andnear infrared extensions to 1.7 μm or even 2.5 μm, depending on the cost and complexity.^[10]

For characterization ofextraterrestrial atmospheres, going to longerwavelengths would require a 52 m (171 ft) starshade that would launch separately on aFalcon Heavy,^[1] or a larger telescope in order to reduce the amount of background light. An alternative would be to keep thecoronagraph small. Characterizing exoplanets at wavelengths shorter than ~350nm would require a fully UV-sensitive high contrast optical train to preserve throughput, and will make all wavefront requirements more stringent, whether for a starshade or a coronagraph architecture.^[10] Such high spatial resolution, high contrast observations would also open up unique capabilities for studying the formation and evolution of stars and galaxies.

HabEx would search for potentialbiosignature gases in exoplanets' atmospheres, such asO
₂ (0.69 and 0.76 μm) and itsphotolytic productozone (O
₃). On the long wavelength side, extending the observations to 1.7 μm would make it possible to search for strong additional water signatures (at 1.13 and 1.41 μm), and would also allow to search for evidence that the detectedO
₂ andO
₃ gases were created by abiotic processes (e.g., by looking for features fromCO
₂, CO,O
₄). A furtherinfrared capability to ~2.5 μm would allow to search for secondary features such as methane (CH
₄) that may be consistent with biological processes. Pushing even further in the UV may also allow distinction between a biotic, high-O₂ atmosphere from an abiotic,CO
₂-rich atmosphere based on the ozone absorption of 0.3 μm.^[10]

Molecular oxygen (O
₂) can be produced by geophysical processes, as well as a byproduct ofphotosynthesis bylife forms, so although encouraging,O
₂ is not a definite biosignature, unless it is considered in its environmental context. I.e., while O2 production to ~20% of atmospheric content seems to be part of life on Earth, too much oxygen is actually poisonous to life as humans know it and could easily be created by planetary situations like a incredibly deep world spanning ocean.^{[11][12][13][14][15]}

• Final report 2019 at JPL/NASA
• HabEx documents at JPL/NASA

• Space telescopes
• Infrared telescopes
• Exoplanet search projects
• Proposed astrobiology space missions
• Proposed NASA space probes

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