The Sagan Space Telescope is a proposed next-generation space observatory concept named in honour of the astronomer and science communicator Carl Sagan.
YOUTUBE BIgQpXObjFI JWST's successor: The Carl Sagan Observatory - a 12 METRE optical telescope searching for exo-Earth
The project has been informally discussed in astrophysical white papers and online forums as a potential successor to the James Webb Space Telescope (JWST) - pdf 
It remains a visionary concept rather than a funded or scheduled mission, but it represents the next logical step in humanity’s quest to directly image and characterise habitable exoplanets.
# Origins and Concept The idea of a space telescope named after Carl Sagan emerged during the late 2010s, following discussions within the American Astronomical Society and NASA’s decadal survey process. One early outline — *The Carl Sagan Observatory: A Visionary Space Telescope* (H. Hammel, 2019) — proposed a 12-metre segmented mirror observatory optimised for visible and near-infrared observation. Its primary aim would be to identify Earth-like exoplanets orbiting nearby Sun-like stars and to search for atmospheric biosignatures such as oxygen, methane and ozone.
This would place the Sagan Telescope within the same conceptual family as NASA’s HabEx and LUVOIR proposals — large, high-contrast telescopes designed to detect faint reflected light from distant worlds.
# Design and Technical Vision The baseline concept envisions a **12-metre primary mirror**, more than twice the diameter of JWST’s 6.5 metre mirror, providing roughly four times the collecting area. This would allow the detection of planets hundreds of times fainter than their parent stars. The design would employ advanced **coronagraphs** and **starshades** to suppress starlight and isolate planetary signals.
The telescope would likely orbit around the Sun–Earth L₂ point (like JWST) for thermal and operational stability. Its wavelength range would cover the optical and near-infrared bands (roughly 0.3–2.5 μm), complementing JWST’s mid-infrared specialisation. It would include high-resolution spectrographs to measure exoplanetary atmospheres and determine the presence of water vapour, carbon dioxide and other potential biomarkers - reddit
# Scientific Goals 1. **Direct Imaging of Earth-like Exoplanets** Detect and image terrestrial planets in the habitable zones of nearby Sun-like stars (within 30–50 light years). 1. **Atmospheric Characterisation** Use spectroscopy to identify biosignatures and chemical disequilibria indicative of life processes. 1. **Planetary System Formation** Study protoplanetary disks, debris belts and young star systems to understand how habitable worlds form. 1. **Comparative Planetology** Observe a statistically significant sample of rocky and gaseous planets to understand the diversity of planetary systems.
# Technical Challenges Building a 12-metre class telescope deployable in space would require major advances in lightweight mirror technology, folding and deployment mechanisms, and autonomous alignment systems.
The costs would likely exceed those of JWST, demanding multinational collaboration and a longer development timeline. Maintaining stability for high-contrast imaging (where the telescope must block light a billion times brighter than the target planet) is one of the most difficult technical hurdles.
# Relationship to Other Missions The Sagan Space Telescope is often discussed as a potential unification or successor concept to the **LUVOIR** and **HabEx** designs. LUVOIR proposed two mirror sizes — an 8-metre (LUVOIR-B) and a 15-metre (LUVOIR-A) configuration — while HabEx proposed a 4-metre optical telescope with an external starshade. The Sagan design lies between them in scale and ambition, optimising for both scientific depth and technical feasibility. If constructed, it would work alongside JWST and future infrared observatories such as the Origins Space Telescope, providing the optical counterpart to a multi-wavelength picture of exoplanetary environments.
# Relevance to Exoplanet Habitability Studies
With its extreme sensitivity, the Sagan Telescope could detect Earth-like planets as faint as 10⁻¹⁰ the brightness of their stars. This capability would enable direct detection of reflected starlight and allow spectroscopy of atmospheres only tens of parsecs away. It could test whether Earth is unique or one of many inhabited worlds — fulfilling Carl Sagan’s long-standing vision of understanding life’s place in the cosmos.
- LUVOIR - wikipedia
- HabEx - wikipedia
# Current Status As of 2025 the Sagan Space Telescope remains a **concept**, discussed in decadal survey forums and popular science channels but not yet an active mission. NASA’s focus is currently on completing and operating JWST and developing the Nancy Grace Roman Space Telescope.
However, many astronomers see the Sagan concept as the natural continuation of JWST’s legacy — a flagship observatory capable of answering Sagan’s own enduring question: *Are we alone?*
# See
- The Carl Sagan Observatory - pdf
- Exoplanet Travel
# Assets
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