Exoplanets · Space Codex
WASP-12 b
One of the darkest planets known and one of the hottest, stretched into an egg shape by its star.
A pitch-black planet spiralling into its star
Artist's concept. No telescope has seen WASP-12 b as more than a point of light, and most exoplanets not even that. What we know comes from how a planet dims or tugs its star. Any picture of its surface, colour or sky, anywhere, is an illustration, not an observation.
At a glance
Key points
Its orbit is shrinking measurably every year.
- Darker than fresh asphalt
- Orbit shrinking 29.8 ms per year
- Measured colour: black
How it was found
SuperWASP caught its transits in 2008, and the discovery paper called it the hottest transiting planet yet found. It also had the largest radius and the shortest orbit then known: about 1.4 Jupiter masses circling a slightly evolved, metal-rich F-type star once every 26 hours.
Watching an orbit shrink
Since 2008 the transits have arrived a little earlier than a fixed schedule predicts. Two other explanations had to be excluded: a slightly oval orbit slowly turning, and the whole system accelerating towards us. In 2020 new transit and eclipse timings favoured decay by a large margin, and fresh radial velocities ruled out acceleration. WASP-12 became the first planetary system confidently known to be spiralling in, and TESS timings since have backed it up.
Being eaten
Tides raised on the star are draining the planet's orbital energy. It is the first planet seen to be spiralling inward, and it nearly fills the region where its own gravity can hold onto its gas.
Black and glowing
Too hot for reflective clouds, it absorbs almost all visible light. Its own heat makes the dayside glow a dull red-orange.
Losing its air
Hubble ultraviolet transits look deeper than visible ones, as if the planet is wrapped in a cloud of escaping metal-rich gas that overfills the zone its gravity controls. Spitzer phase curves later showed infrared light that may come from gas stripped off the planet. How fast it loses mass is still uncertain.
Missions
- 1990–
Hubble Space Telescope
NASA / ESAActiveUltraviolet to near-infrared imaging from low Earth orbit.
- 2018–
TESS
NASAActiveAll-sky transit survey; over 1,000 confirmed planets.
Related entries
- WASP-76 bWhere it may rain iron
- HD 189733 bA cobalt-blue world that smells of rotten eggs
Sources
- Yee et al. 2020, ApJL (arXiv) (opens in a new tab)
- Bell et al. 2017, ApJL 847:L2 (arXiv) (opens in a new tab)
- Fossati et al. 2010, ApJL (arXiv) (opens in a new tab)
- Bell et al. 2019, MNRAS (arXiv) (opens in a new tab)
- NASA Exoplanet Archive: WASP-12 overview (opens in a new tab)
- ESA: Hubble: pitch-black planet (heic1714) (opens in a new tab)
- Wong et al. 2022 (arXiv) (opens in a new tab)
- Hebb et al. 2009, ApJ 693:1920 (arXiv) (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.