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What New Horizons Found at Pluto

The 2015 flyby showed a Pluto with glaciers, mountains, dunes and layered haze. This guide sorts the main findings and what is still uncertain.

Dwarf planetsBy the duorolt.com editorial teamPublished Facts checked 7 min read

At 11:49 Universal Time on July 14, 2015, NASA's New Horizons spacecraft reached its closest point to Pluto after nearly a decade in flight. Just 15 minutes later it looked back and photographed Pluto's atmosphere lit from behind by the Sun. The picture, taken from about 18,000 km (11,000 miles) away, shows more than a dozen layers of haze rising above rugged mountains and a smooth frozen plain.

That image was the first close look at a world that no spacecraft had visited before. This article walks through what the flyby revealed: the heart-shaped glacier, the mountains and dunes, the haze, and the surprises that forced scientists to revise their models. It also notes what remains uncertain as of November 2026.

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From launch to Pluto

New Horizons launched on January 19, 2006, on an Atlas V rocket from Cape Canaveral, Florida. That was about seven months before the International Astronomical Union voted that Pluto is a dwarf planet, a decision explained in why Pluto is a dwarf planet. The spacecraft kept flying, and it reached Pluto about nine and a half years after launch.

  • 2006: New Horizons launches on January 19.
  • 2015: closest approach to Pluto on July 14, at 11:49 UT.
  • 2016: NASA reports that Pluto's glacier surface is made of churning ice cells less than a million years old.
  • 2019: New Horizons flies past Arrokoth, a small Kuiper Belt object, on January 1.
  • 2026: a study published July 31 proposes that liquid nitrogen may reach the surface in one part of Pluto's heart.

NASA's mission page says the flyby measured Pluto at about 2,370 km (1,470 miles) across, slightly larger than earlier estimates, and Charon at about 1,208 km (750 miles).

The heart: Tombaugh Regio and Sputnik Planitia

The most famous feature is a bright, heart-shaped region named Tombaugh Regio. Its left (western) lobe is Sputnik Planitia, a basin filled with ice. NASA describes the heart as a vast, million-square-mile nitrogen glacier. The Sputnik part is more than 1,000 km (620 miles) across, and its ice sheet is at least 4 km (2.5 miles) thick. NASA's mission page calls it the largest known glacier in the Solar System.

A glacier is ice that flows slowly under its own weight. Dozens of smaller nitrogen glaciers flow into the basin from the east. The basin itself is thought to have formed when a Kuiper Belt object 50 to 100 km (30 to 60 miles) across hit Pluto about 4 billion years ago.

The glacier surface is not still. NASA reported in June 2016 that the ice is divided into churning, convective cells 16 to 48 km (10 to 30 miles) across, and that they are less than a million years old. Convection means warmer ice rises, cooler ice sinks, and the surface keeps recycling, about once every 500,000 years or so. On a world that formed billions of years ago, that counts as a very young surface.

Mountains, dunes and a young surface

The terrain around the heart is just as striking. West of Sputnik, rugged mountains rise up to 3,500 meters (11,000 feet), according to NASA. The Johns Hopkins Applied Physics Laboratory says water-ice mountains line the northwest edge of the glacier. The contrast is one of the main discoveries: mountains made of water ice standing beside glaciers made of nitrogen ice.

Along the glacier's western edge, hundreds of dunes stretch at least 75 km (45 miles). Scientists think they are grains of methane ice pushed by winds of no more than about 32 km/h (20 mph), and the nearby water-ice mountains may supply some of the grains.

Pluto may also have ice volcanoes. NASA says Wright Mons and Piccard Mons are believed to be cryovolcano vents, which are volcanoes that erupt icy slush instead of molten rock. Red material in the Virgil Fossae region is thought to come from ammonia-rich icy lava that appeared no more than 1 billion years ago.

Haze, wind and a thin atmosphere

Pluto's atmosphere is extremely thin: NASA says it is only 1/100,000th that of Earth's. Even so, it is active. Each day, nitrogen ice at the surface turns directly to gas in sunlight, which is called sublimation, and then freezes again. That daily cycle drives winds of up to about 32 km/h (20 mph) and appears to shape the dunes and the wind streaks.

The haze is the most photogenic part of the atmosphere. In the backlit image taken 15 minutes after closest approach, NASA counts more than a dozen separate layers. NASA's mission page adds that the haze and the rate at which gas escapes from the atmosphere both required scientists to revise their models.

What surprised scientists, and what is still open

NASA's mission page says scientists were surprised by how much activity Pluto shows today. The flyby showed a young glacier, mountains, dunes and haze on a world very far from the Sun's warmth. Pluto and Charon also have few small craters, which scientists read as a sign that the Kuiper Belt holds fewer objects under about 1.6 km (1 mile) across than expected.

Several questions remain open. NASA's summary says a liquid-water ocean likely lies beneath Pluto's crust, isolated in most places by almost 200 miles (320 km) of ice. That is an inference, not a direct detection. Charon shows a belt of tectonic cracks around its equator that suggests it too once had a water-ice ocean, and its large plain Vulcan Planitia is at least the size of California. More on that moon is in Charon and Pluto's four small moons.

The newest result is tentative. In an article dated August 5, 2026, NASA reported a study published on July 31 in the Planetary Science Journal. The authors reprocessed the 2015 images and suggest that dark features in the northern part of Sputnik Planitia may be wetted from time to time by liquid nitrogen rising from beneath the glacier. They rule out rain. The wording is careful ("may be"), so the idea is a proposal waiting for further tests.

As for the spacecraft, NASA's mission page, last updated May 11, 2026, describes it as healthy in the Kuiper Belt and says that, as of 2025, it was gathering heliophysics data, meaning data on the Sun's effects on space. Check that page for current status. Other encounters with small worlds are collected in a timeline of missions to asteroids, comets and dwarf planets.

Common mistakes and myths

  • Myth: New Horizons orbited or landed on Pluto. It was a flyby. NASA describes the event as a flight through the Pluto system, and the spacecraft kept going toward other targets.
  • Myth: the heart is a crater or a frozen lake of water. It is a nitrogen glacier in an impact basin. Water ice does appear nearby, but it forms the mountains.
  • Myth: Pluto is a dead, frozen rock. NASA says scientists were surprised by the amount of present-day activity, from flowing glaciers to winds and haze.
  • Myth: Pluto's air is like Earth's. NASA says Pluto's atmosphere is only 1/100,000th that of Earth's.
  • Myth: Pluto's ocean is confirmed. NASA says a liquid-water ocean likely exists, but it has not been measured directly.
  • Myth: "dwarf planet" means a lesser world. It is a category, not a ranking, and the definition of a dwarf planet says nothing about how interesting a body is.

Frequently asked questions

When did New Horizons reach Pluto?

Closest approach was on July 14, 2015, at 11:49 UT, according to NASA's mission page.

How big did New Horizons find Pluto to be?

About 2,370 km (1,470 miles) across, slightly larger than earlier estimates. Charon measured about 1,208 km (750 miles).

Does Pluto have an ocean?

Possibly. NASA says a liquid-water ocean likely lies under the crust, but the evidence is indirect.

Is New Horizons still working?

NASA's mission page, updated May 11, 2026, describes it as healthy in the Kuiper Belt. Check the page for the latest status.

Sources