Since the discovery of 51 Pegasi b in 1995, more than 6,000 confirmed exoplanets and approximately 7,700 candidates (NASA Exoplanet Archive) have been recorded, primarily through transit and radial velocity methods. Some of these are located in the habitable zone (HZ)—a region where liquid water can exist. Worlds like Proxima Centauri b (4.24 light-years away), Kepler-442b, or the planets of the TRAPPIST-1 system illustrate the diversity of rocky candidates and super-Earths. The identification of these objects, combined with atmospheric modeling, guides astrobiology toward the search for biosignatures, although confirmation remains a major observational challenge.
Astronoo's article provides a quantitative and qualitative overview of candidate and confirmed exoplanets, focusing on those in the habitable zone of their star. According to NASA data, there are currently about 7,700 candidates and over 6,000 confirmed exoplanets, a gap reflecting the validation work needed to eliminate false positives (eclipsing binaries, stellar activity). The Kepler and TESS missions are behind this harvest. Among the most emblematic candidates are Kepler-22b (first detected by Kepler in the HZ), Kepler-186f (first Earth-sized planet in the HZ), Proxima Centauri b (4.24 light-years away), and the TRAPPIST-1 system with three planets in the HZ (d, e, f). The article emphasizes that the habitable zone depends on stellar luminosity, orbital distance, and atmospheric properties. Planets like Kepler-442b or LHS 1140 b are considered particularly promising for habitability. Research is now focusing on atmospheric characterization (via JWST) to detect potential biosignatures, although definitive confirmation of habitability remains a challenge for the coming decades.
Since the discovery of 51 Pegasi b (1995) by Michel Mayor (1942-) and Didier Queloz (1952-), astronomy has recorded a growing number of exoplanets. There are currently two main categories: confirmed exoplanets and candidates awaiting confirmation. Observation techniques include transit, the Doppler method, and direct imaging.
The current catalog includes over 6,000 candidate exoplanets and approximately 5,500 confirmed exoplanets. Space missions like TESS and Kepler have significantly increased this number.
Confirmed exoplanets exhibit varied characteristics: gas giants close to their star (hot Jupiters), super-Earths, or Earth-like planets. Candidates require additional observations to rule out false positives and validate their nature.
| Category | Number | Main Method | Comment |
|---|---|---|---|
| Confirmed Exoplanets | ≈ 6,298 | Transit, Radial Velocity | Validated by repeated observations |
| Candidate Exoplanets | ≈ 7,931 | Mainly transit | Often from Kepler and TESS missions, awaiting confirmation |
Source: NASA Exoplanet Archive (updated exoplanet numbers) and NASA Exoplanet Exploration Program.
Scientists are also working to identify exoplanets located in the habitable zone of their star, i.e., where liquid water can exist. These studies contribute to astrobiology and the search for extraterrestrial life.
Note:
The habitable zone of a planetary system corresponds to the region around a star where conditions allow for the presence of liquid water on the surface of a planet. It depends on the star's luminosity and temperature, as well as the planetary atmosphere's properties. Exoplanets in this zone are considered the most promising for the search for extraterrestrial life.
| Exoplanet | Host Star | Distance (light-years) | Mass (M⊕) | Radius (R⊕) | Type | Comment |
|---|---|---|---|---|---|---|
| Kepler-22b | Kepler-22 | 620 | ≈ 36 | ≈ 2.4 | Super-Earth | First planet detected by Kepler in the habitable zone |
| Kepler-442b | Kepler-442 | 1,206 | ≈ 2.3 | ≈ 1.3 | Rocky | High habitability potential according to models |
| Kepler-186f | Kepler-186 | 492 | ≈ 1.4 | ≈ 1.1 | Earth-like | First Earth-sized exoplanet in the habitable zone |
| Kepler-452b | Kepler-452 | 1,402 | ≈ 5 | ≈ 1.6 | Super-Earth | Nicknamed "Earth's cousin" for its orbital similarity |
| Proxima Centauri b | Proxima Centauri | 4.24 | ≈ 1.27 | ≈ 1.1 | Earth-like | Closest exoplanet to Earth in the habitable zone |
| TRAPPIST-1d | TRAPPIST-1 | 39.5 | ≈ 0.41 | ≈ 0.77 | Earth-like | Part of a compact system of 7 planets |
| TRAPPIST-1e | TRAPPIST-1 | 39.5 | ≈ 0.62 | ≈ 0.91 | Earth-like | Considered the most habitable in the TRAPPIST-1 system |
| TRAPPIST-1f | TRAPPIST-1 | 39.5 | ≈ 0.68 | ≈ 1.05 | Earth-like | In the outer habitable zone of the system |
| Kepler-62f | Kepler-62 | 1,200 | ≈ 2.8 | ≈ 1.4 | Super-Earth | Receives about 41% of the energy Earth receives |
| Kepler-69c | Kepler-69 | 2,430 | ≈ 1.7 | ≈ 1.2 | Super-Earth | Located in the habitable zone of its star |
| LHS 1140 b | LHS 1140 | 40 | ≈ 6.6 | ≈ 1.7 | Super-Earth | Rocky exoplanet in the habitable zone of a red dwarf |
| Kepler-283c | Kepler-283 | 1,080 | ≈ 1.8 | ≈ 1.2 | Super-Earth | Candidate planet for a potentially habitable atmosphere |
| Gliese 667 Cc | Gliese 667 C | 23.6 | ≈ 4.5 | ≈ 1.5 | Super-Earth | Rocky exoplanet in the habitable zone of a red dwarf |
| Kepler-1544b | Kepler-1544 | 1,100 | ≈ 2.3 | ≈ 1.3 | Super-Earth | Located in the inner part of the habitable zone |
| Kepler-1229b | Kepler-1229 | 870 | ≈ 2.7 | ≈ 1.4 | Super-Earth | Habitable zone favorable for liquid water |
Source: NASA Exoplanet Archive, NASA Exoplanet Exploration Program.
An exoplanet candidate is a detected signal (usually by transit or radial velocity) that exhibits the characteristics of a planet but whose nature has not yet been validated by additional observations. False positives—such as eclipsing binary stars or starspots—are common. Confirmation often requires Doppler surveys or cross-transit measurements (such as with TESS or Cheops). Thus, out of ~7,700 candidates, about 6,000 are now confirmed, but the catalog evolves every month.
Several candidates (some now confirmed) have marked history: Kepler-22b (620 light-years away, super-Earth, first discovery by Kepler in the HZ), Kepler-186f (492 light-years away, Earth-sized), Proxima Centauri b (4.24 light-years away, the closest), and the three planets of the TRAPPIST-1 system (d, e, f) located in the habitable zone of their red dwarf. Others like Kepler-442b (1,206 light-years away) or LHS 1140 b (40 light-years away) are considered to have high habitability potential according to climate models. The article's table lists about fifteen with their characteristics (mass, radius, type).
The habitable zone (HZ) is the region around a star where a rocky planet can maintain liquid water on its surface, an essential condition for life as we know it. It depends on the star's luminosity and temperature, as well as the planet's atmosphere (greenhouse effect). Red dwarfs (like Proxima or TRAPPIST-1) have a closer HZ and are often subjected to stellar flares, which complicates habitability. The article notes that the HZ is a first filter, but parameters like atmospheric composition and rotation are equally decisive.
The two major missions are Kepler (launched in 2009) and TESS (2018). Kepler observed a fixed region of the sky and discovered thousands of candidates, while TESS scans the entire sky in sectors, focusing on nearby and bright stars. The Gaia mission (astrometry) and ground-based observations (HARPS, ESPRESSO) contribute to confirmation via radial velocity. The JWST (James Webb) now plays a key role in atmospheric characterization of certain candidates, paving the way for studying their composition.
The main challenge is the robust confirmation of candidates and the characterization of their atmospheres to detect biosignatures (oxygen, methane, water vapor). Future missions (PLATO, Ariel, or the HabEx observatory) will aim to improve measurement precision and study rocky planets in the HZ around solar-type stars. Climate modeling and consideration of stellar effects (radiation, activity) are also major research axes, as mentioned in the article.
Exoplanet Overview: Candidates and Confirmed 
Gliese 581 g: A Serious Candidate for Habitability 
Discovery of solid buckyballs 
Kepler-22b: First Habitable Exoplanet Discovered in the Temperate Zone 
Exoplanets: Techniques and Discoveries 
Cheops, characteristics of exoplanets 
Mini-Neptunes: A Fascinating Class of Extrasolar Planets 
Turn Off the Stars to Detect Life! 
The New Promised Lands: Top Candidates for Habitability 
JWST, the end of the dark ages 
The Milky Way: A Galaxy Teeming with Habitable Worlds 
HD 100546 b: A Giant Exoplanet Forming in an Extended Habitable Zone 
Super-Earths: Habitable Planets in Sight? 
The habitable zone of the Kepler-186 system 
Rogue Exoplanets: Lost Worlds in the Cosmic Darkness 
55 Cancri e, the diamond planet 
Number of candidate and confirmed exoplanets 
Trappist or the harmony of the cosmos