Extreme-class world
WASP-121
Glass and iron rain in the atmosphere — extreme thermal asymmetry.
- Planets
- 1
- Distance
- 880.3 ly
- Host
- F-type
About WASP-121
Discovery
WASP-121 b was discovered in 2016 by Delrez and colleagues with the SuperWASP-South survey — an ultra-hot Jupiter on a 1.27-day orbit around an F-type star, nearly filling its Roche lobe.
Why it matters
WASP-121 b's atmosphere is so hot that heavy refractory elements — iron, magnesium, chromium, vanadium — exist as gas on the dayside but condense out on the much cooler nightside, raining as metallic and silicate droplets.
Current research
JWST NIRSpec produced the first full phase curve of WASP-121 b in 2023, mapping a 'three-layer' atmospheric circulation; a 2025 study reported thermal dissociation and SiO signatures.
Comparable to
A puffed-up gas giant where the dayside is a vapor of iron and silicates, and the nightside is cool enough for those metals to fall as rain.
System geometry
At a glance
- Hostname
- WASP-121
- Spectral type
- F6 V
- Distance
- 880.3 ly · 269.90 pc
- Stellar mass
- 1.33 M☉
- Stellar radius
- 1.46 R☉
- Luminosity
- 4.403 L☉
- Effective temp
- 6628 K
- Confirmed planets
- 1
- Habitable zone
- 1.993 – 2.875 AU
Top-down orbital diagram
Orbits to scale within this system. Dashed green = habitable-zone edges.
Planet positions are illustrative (evenly spaced in phase). For live motion see the 3D scene.
The planets
1 confirmed.
Gas giant
WASP-121 b
- Orbit
- 0.026 AU
- Period
- 1.27 days
- Radius
- 19.53 R⊕
- Mass
- 371.86 M⊕
- Eq. temperature
- 2409 K
- Eccentricity
- 0.000
- Discovered
- 2016 · Transit
Compared to our Solar System
Each row shows the closest Solar-System analog by radius (log-space). Earth is pinned at the bottom as the constant frame of reference.
| Planet | Radius (R⊕) | Mass (M⊕) | Orbit (AU) | Period (days) | Eq temp (K) | Solar analog |
|---|---|---|---|---|---|---|
| WASP-121 b | 19.53 | 371.86 | 0.026 | 1.27 | 2409 | Jupiter |
| Earth (reference) | 1.00 | 1.00 | 1.000 | 365.25 | 255 | — |
Research status
◇ JWST observation status
1 planet has confirmed JWST observation time across Cycles 1–3.
- WASP-121 b
JWST programs include transit spectroscopy, thermal phase curves, and direct imaging coronagraph observations depending on planet class.
Discovery timeline
- 2016
WASP-121 b
via Transit
If you liked this
Other systems in the same theme:
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First exoplanet ever found around a sun-like star (1995, Nobel Prize 2019).
HD 209458
1 planets · 157.5 ly · G0 V
First exoplanet seen transiting its star (1999) — atmospheric studies pioneer.
WASP-12
1 planets · 1393.5 ly · G2V
A hot Jupiter being literally devoured by its star — losing 6×10⁹ tonnes/sec.
Experience it
See WASP-121 in interactive 3D
Fly through the system, click any planet, watch orbits play out at 100× speed.
▶ Launch 3D scene