Sky Tonight — May 31, 2026
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Current Viewing Status
Pluto is not visible without a large telescope (magnitude +14.4 in Sagittarius). Requires an 8"+ aperture and precise star charts to locate. Currently in the pre-dawn sky. Despite its faintness, Pluto is the most talked-about world in the Solar System right now — NASA is preparing papers to challenge its 2006 demotion.
Pluto was discovered on February 18, 1930 by 24-year-old astronomer Clyde Tombaugh at Lowell Observatory in Flagstaff, Arizona. For 76 years it was the ninth planet. In 2006, the International Astronomical Union voted to reclassify it as a "dwarf planet" — triggering a controversy that rages more intensely than ever.
In April 2026, NASA Administrator Jared Isaacman told the U.S. Senate: "I am very much in the camp of Make Pluto a Planet Again." NASA is now preparing scientific papers to formally challenge the IAU's 2006 definition, which requires a planet to "clear its orbital neighborhood" — a criterion critics note would also disqualify Earth and Jupiter, which share orbits with asteroids.
NASA's New Horizons made the first (and so far only) close flyby of Pluto on July 14, 2015, returning breathtaking images of an unexpectedly complex world: a heart-shaped nitrogen ice plain, towering water ice mountains, a surprisingly complex atmosphere with 12 haze layers, and flowing nitrogen glaciers. Pluto is far more geologically active than anyone expected.
Classification
Dwarf planet (IAU 2006) / 9th Planet (disputed)
Discovery
Feb 18, 1930 — Clyde Tombaugh
Distance from Sun
5.9 billion km · 39.5 AU
Diameter
2,377 km (18.5% Earth)
Day length
6.39 Earth days
Year length
247.9 Earth years
Surface temp
−233°C to −223°C
Moons
5 (Charon is huge — near half Pluto's size)
Atmosphere
Thin N₂, CH₄, CO — expands/collapses seasonally
Surface
Nitrogen, methane, water ice
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Tombaugh Regio (The Heart)
The most iconic feature on Pluto — a brilliant heart-shaped plain of nitrogen ice ~1,590 km wide named for Pluto's discoverer. The left lobe (Sputnik Planitia) is a vast convecting nitrogen ice plain 3 km below the surrounding terrain, with slowly churning convection cells.
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Water Ice Mountains
Mountain ranges 3,500 m tall rivaling the Rocky Mountains — made of water ice, which is rigid enough at Pluto's temperature to support mountains. Pluto has active, complex geology despite being billions of miles from the Sun.
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Charon — Giant Moon
Charon is so large (1,212 km diameter) relative to Pluto that neither truly orbits the other — they both orbit a common center of mass in space between them. Charon has a deep red polar cap made of complex organic compounds that escaped from Pluto's atmosphere.
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Atmospheric Hazes
Pluto has 12 distinct atmospheric haze layers reaching 200 km altitude — discovered by New Horizons. Sunlight reacts with methane and nitrogen to create complex organic "tholins" that give Pluto its reddish-brown color. The atmosphere partially collapses as Pluto moves farther from the Sun.
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NASA
New Horizons (Pluto flyby July 14, 2015)
After a 9.5-year, 3-billion-mile journey, New Horizons flew 12,550 km from Pluto at 14 km/s. Revealed the heart-shaped plains, water ice mountains, complex atmosphere. Now studying the Kuiper Belt. Still transmitting data.
● ActiveNASA
New Horizons — Arrokoth Flyby (2019)
On January 1, 2019, New Horizons flew past Arrokoth — a contact-binary Kuiper Belt Object. The most primitive Solar System object ever studied. Revealed it formed by gentle merger of two lobes rather than violent collision.
✓ Historical
