WASP-17 b

Planet· orbits the Sun

WASP-17 b — one of the PUFFIEST planets known: about 2.0 Jupiter radii but only ~0.5 Jupiter masses, giving an extraordinarily low density — it would float on water. It also orbits RETROGRADE, backward relative to its star's spin, betraying a violent dynamical past. Its density is real (transit + measured mass). JWST has detected quartz cloud crystals. Never imaged.

Open in 3D viewSee WASP-17 b in the live, interactive 3D map

Key facts

Mass

9.72 × 10²⁶ kg

0.512 M♃ (163 M⊕)

Radius

142,201 km

22.3× wider than Earth

Surface gravity

3.21 m/s²

33% of Earth's

Year

3.74 Earth days

Distance from WASP-17

7,704,290 km

Science

Physical

Mass: 9.72 × 10²⁶ kg · 0.512 M♃ (163 M⊕)
Radius: 142,201 km · 22.3× wider than Earth
Density: 80.7 kg/m³ · 0.081× water
Surface gravity: 3.21 m/s² · 33% of Earth's
Escape velocity: 30.2 km/s · 2.7× Earth's

Orbital

Semi-major axis: 7,704,290 km
Eccentricity: 0
Inclination: 0.00 °
Orbital period: 3.7 days
Perihelion: 7,704,290 km
Aphelion: 7,704,290 km
Mean orbital velocity: 150 km/s

Atmosphere

Composition: Hydrogen-dominated; JWST detected silica (quartz) nanocrystal clouds — the first clear silicate clouds identified in an exoplanet.

Composition

Bulk composition: One of the PUFFIEST planets known: ~2.0 Jupiter radii but only ~0.5 Jupiter masses, an extraordinarily low density (real from transit + mass) — it would float on water. It also orbits RETROGRADE, backward to its star's spin, evidence it was flung onto a backward path by a past gravitational encounter. JWST has detected quartz (silica) nanocrystal clouds in it. Never imaged.
Cloud appearance: Appearance based on NASA/JPL-Caltech's artist's concept. No spacecraft has imaged this world, so its real appearance is unknown — The banded clouds shown are a representation of its class, shown only in Vision mode; Realism shows a plain spectral colour.

Radiation & temperature

Insolation: 1,388 S⊕ · 1,388× the sunlight Earth receives
Equilibrium temperature: 1,755 K (1482 °C)

Discovery & history

Method: Transit detection
Name: Designated 'b' under the IAU convention that letters a star's planets 'b', 'c'… in the order found (the star is the unwritten 'a'); no IAU proper name is assigned.

Announced in 2009 as a hugely inflated planet on a retrograde orbit; JWST later found silica (quartz) nanocrystal clouds in it.

Images

Artist's impression of the vastly inflated, retrograde-orbiting WASP-17 b, in which JWST found quartz clouds — an artist's concept, not a photograph. — ESA / Hubble & NASA (CC BY 4.0) · Wikimedia Commons

Images from open archives · credit shown per image