KELT-9 b

Planet· orbits the Sun

KELT-9 b — the HOTTEST known planet: an ultra-hot Jupiter (1.9 Jupiter radii, ~2.9 Jupiter masses) whose dayside reaches ~4,300°C, hotter than many stars. The heat tears molecules apart into atoms; iron and titanium vapour have been seen streaming from it as its atmosphere evaporates. Because it transits with a measured mass, its density is real. Never imaged.

Open in 3D viewSee KELT-9 b in the live, interactive 3D map

Key facts

Mass

5.47 × 10²⁷ kg

2.88 M♃ (915 M⊕)

Radius

135,065 km

21.2× wider than Earth

Surface gravity

20 m/s²

2.04× Earth's

Year

1.48 Earth days

Distance from KELT-9

5,179,078 km

Science

Physical

Mass: 5.47 × 10²⁷ kg · 2.88 M♃ (915 M⊕)
Radius: 135,065 km · 21.2× wider than Earth
Density: 530 kg/m³ · 0.53× water
Surface gravity: 20 m/s² · 2.04× Earth's
Escape velocity: 73.5 km/s · 6.57× Earth's

Orbital

Semi-major axis: 5,179,078 km
Eccentricity: 0
Inclination: 0.00 °
Orbital period: 35.55 hours
Perihelion: 5,179,078 km
Aphelion: 5,179,078 km
Mean orbital velocity: 254 km/s

Atmosphere

Composition: Vaporised metals — iron and titanium have been detected escaping; the atmosphere is thought to be dissociated into atoms and boiling away.

Composition

Bulk composition: An ultra-hot Jupiter (1.9 Jupiter radii, ~2.9 Jupiter masses, real density from transit + mass). Its dayside (~4,300°C) is so hot that molecules are torn into atoms; iron and titanium vapour have been detected streaming away as its atmosphere evaporates under the blue star's radiation. The hottest planet known. 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: 44,863 S⊕ · 44,863× the sunlight Earth receives
Equilibrium temperature: 4,050 K (3777 °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 2017 orbiting a hot blue star; follow-up spectroscopy detected vaporised metals escaping — a planet being slowly boiled away.

Images

Artist's impression of the hottest known planet, KELT-9 b, its atmosphere streaming away in the blue star's glare — an artist's concept, not a photograph. — NASA / JPL-Caltech (public domain) · Wikimedia Commons

Images from open archives · credit shown per image