LTT 9779 b
Planet· orbits LTT 9779
LTT 9779 b — an ultra-hot Neptune (4.7 Earth radii, ~29 Earth masses) skimming its star every 19 hours at ~2,000 K. It is the MOST REFLECTIVE planet known: inferred to reflect ~80% of the light that strikes it, because clouds of metal and silicate condense on its glaring dayside and glint like a mirror. Because it transits with a measured mass, its density is real. Its cloud tops have never been imaged.
Open in 3D viewSee LTT 9779 b in the live, interactive 3D map
Key facts
Mass
1.75 × 10²⁶ kg
29.3 M⊕
Radius
30,071 km
4.72× wider than Earth
Surface gravity
12.9 m/s²
1.32× Earth's gravity
Year
19.0 hours
0.79 Earth days
Distance from LTT 9779
2,511,748 km
Science
Physical
- Mass
- 1.75 × 10²⁶ kg · 29.3 M⊕
- Radius
- 30,071 km · 4.72× wider than Earth
- Density
- 1,537 kg/m³ · 1.5× water
- Computed from mass and radius
- Surface gravity
- 12.9 m/s² · 1.32× Earth's gravity
- Computed from mass and radius
- Escape velocity
- 27.9 km/s · 2.49× Earth's escape velocity
- Computed from mass and radius
Orbital
- Semi-major axis
- 2,511,748 km
- From the NASA Exoplanet Archive (transit + orbit fit)
- Eccentricity
- 0
- From the NASA Exoplanet Archive (transit + orbit fit)
- Inclination
- 0.00 °
- From the NASA Exoplanet Archive (transit + orbit fit)
- Orbital period
- 19.01 hours
- From the NASA Exoplanet Archive (transit + orbit fit)
- Perihelion
- 2,511,748 km
- Computed from the orbital elements
- Aphelion
- 2,511,748 km
- Computed from the orbital elements
- Mean orbital velocity
- 231 km/s
- Computed from the orbital elements
Composition
- Bulk composition
- An ultra-hot Neptune (4.7 Earth radii, ~29 Earth masses, real density from transit + mass). It is the MOST REFLECTIVE planet known: Cheops and JWST (2023) found it reflects ~80% of its starlight, inferred to be clouds of metal and silicate condensing on its glaring ~2,000 K dayside — glinting like a mirror. It survives inside the 'hot-Neptune desert' where such worlds were thought to evaporate. 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 Visual mode; Realism shows a plain spectral colour.
Radiation & temperature
- Insolation
- 2,526 S⊕ · 2,526× the sunlight Earth receives
- Computed from LTT 9779's luminosity and the orbital distance (inverse-square; Earth's sunlight = 1).
- Equilibrium temperature
- 1,978 K (1,705 °C)
- Computed model value for its 19-hour orbit — not measured.
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.
Found transiting by TESS in 2020 inside the 'hot-Neptune desert'; its record albedo was measured by Cheops and JWST in 2023.
Images
Images from open archives · credit shown per image