Pluto
What is Pluto?
Dwarf planets· Diameter 2,377 km. King of the Kuiper belt. Reclassified a dwarf planet in 2006, then beloved again when New Horizons revealed its heart-shaped nitrogen plain in 2015.
The orbit of Pluto at this moment: https://nowsky.org/solar/orbit?fw=pluto&sp=110 — replayed live, no login.
Orbit and size
| Diameter | 2,377 km |
|---|---|
| Distance | 29.7~49.3 AU |
| Year | 248 yr |
| Heart | Sputnik Planitia |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Moons of Pluto
Related events
Frequently asked
- How big is Pluto?
- 2,377 km.
- How far is Pluto from Earth?
- 29.7~49.3 AU.
- What are the main moons of Pluto?
- Charon.
The season when the atmosphere freezes
Pluto's nitrogen atmosphere freezes onto the surface as the planet recedes from the Sun and sublimates again as it approaches. Since perihelion in 1989 Pluto has been moving outward, yet stellar occultations showed the atmosphere unexpectedly growing until 2015 and only beginning to decline after 2019 — a lag from heat stored in the surface ice. Calculations put the freeze-out of most of the atmosphere within the 2030s.
This is why New Horizons was in a hurry. Once the atmosphere freezes the blue haze layers vanish too, and the next thaw is more than two centuries away. Pluto's sky is in its last visible phase for a hundred years, and an occultation in the sky view, with Pluto passing in front of a star, is exactly the method ground-based telescopes use to measure that atmosphere.
The dwarf planet in depth
Pluto is famous for its 2006 demotion to dwarf planet — but when New Horizons arrived in 2015, the surprise ran the other way. The presumed dead ice ball had flowing nitrogen glaciers, a convecting heart-shaped plain (Sputnik Planitia), and layered blue hazes. Pluto is geologically alive.
Its moon Charon is half Pluto's diameter; the pair essentially waltz around a barycenter that lies outside Pluto itself. Zoom in within the orbit view and you can see Pluto tracing its own small circle.
The 248-year orbit is eccentric enough that from 1979 to 1999 Pluto was closer to the Sun than Neptune. That won't happen again until the 23rd century.
Pluto's demotion was triggered by Eris — once a second Pluto-sized body turned up, 'planet' finally needed a definition. In 2006 the IAU added 'has cleared its orbital neighborhood' to the criteria, and Pluto fell short. The irony: New Horizons then revealed a world so geologically alive that its reputation rose even as its rank fell.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.