Buzz
On January 19, 2006, New Horizons launched from Earth at an incredible speed of over 58,000 kilometers per hour (36,000 mph), embarking on a long journey through space. By February 2007, it harnessed a bit of Jupiter’s orbital energy, increasing its speed to 84,000 kilometers per hour (52,000 mph). After traveling nearly 5 billion kilometers (3 billion miles) over 9.5 years, the spacecraft reached Pluto on July 14, 2015. It is currently more than 35 AU (astronomical units) away from Earth, heading toward the Kuiper Belt.
10. Pluto’s Tail
The New Horizons probe, about the size of a piano, is equipped with seven instruments, one of which studies Pluto’s interaction with the solar wind, traveling at a staggering 1.6 million kilometers per hour (1 million mph).
The SWAP (Solar Wind Around Pluto) instrument discovered that, like much of Pluto, its solar influence is unlike anything else in the solar system. Smaller, comet-like bodies gently disturb the solar wind, while larger planets crash into it with the force of a wrecking ball. Pluto does a bit of both, acting as a quirky cross between a planet and a comet. It creates a distinct bow shock but also an abrupt shift in solar wind, known as the Plutopause.
SWAP also uncovered that Pluto has an ionic tail extending from 77,000 to 110,000 kilometers (48,000 to 68,000 miles) behind it. This dense region of cold gas consists of Pluto’s methane- and nitrogen-rich atmosphere escaping its weak gravity. These particles become ionized when they interact with ultraviolet radiation from the Sun and are carried downstream by the solar wind.
9. Surprising Smoothness
As New Horizons passed Pluto, the images it sent back revealed expected signs of damage, such as craters from past impacts. However, the probe also discovered an unexpected surprise—smooth surfaces.
Located 6 billion kilometers (4 billion miles) from the Sun, Pluto could have appeared lifeless, like Mercury or the Moon, with its surface covered in craters. But instead, its icy heart, Sputnik Planum, appears polished, and astronomers believe it is constantly being remodeled, with a surface that replenishes itself and smooths over any imperfections.
The source of Pluto’s energy remains unclear. However, it’s possible that the ancient collision that led to its formation happened more recently than previously thought, and that chemical-rich ices are being melted by residual inner heat. Alternatively, Pluto’s small radioactive reserves could be supplying energy as they decay.
8. Pluto’s Spider
A portion of the dwarf planet appears to be covered by a shape resembling a spider, with six massive legs extending across the surface in a unique network of cracks not seen anywhere else in the outer solar system.
The smaller cracks stretch an impressive 100 kilometers (60 miles), but the largest, Sleipnir Fossa (named after the eight-legged horse from Norse mythology), spans over 580 kilometers (360 miles).
These cracks are different from the parallel lines found elsewhere on Pluto, which are likely the result of the planet's crust slowly cracking. The spider-like cracks, however, intersect at a central point, indicating localized subterranean stress that is cracking Pluto like a walnut. Strangely, the cracks also reveal a reddish subsurface.
Astronomers have observed similar cracked surfaces on Mercury and Venus, and they believe these fractures are caused by subsurface materials pushing their way to the surface.
7. Some Of Pluto’s Atmosphere Is Moving Toward Charon
Pluto and Charon share a unique relationship. Pluto, with a diameter of just 2,370 kilometers (1,470 miles), is less than twice the size of its close companion, Charon, which measures 1,208 kilometers (750 miles) in diameter. The two are also remarkably close, with an average distance of less than 20,000 kilometers (12,400 miles) between them.
Pluto and Charon are close enough to share an atmosphere, much like an interplanetary Snuggie. This phenomenon was predicted by researchers in the 1980s, who observed that binary star systems and planets orbiting close to their stars also have shared atmospheres.
Nearly four decades later, astronomers have confirmed that some of Pluto’s nitrogen is captured by Charon. While most gases directed toward the gravitationally weak moon escape into space, some remain trapped. The polar temperatures range from 60 Kelvin (-351 °F) to 15 Kelvin (-433 °F), and at these frigid conditions, the gases cling to the surface.
The Sun’s ultraviolet radiation transforms these gases into tholins. With higher sublimation points, tholins remain frozen even during Charon’s summer, creating a reddish blotch at its north pole.
6. Pluto’s Enigmatic Nitrogen Source
In Pluto’s atmospheric ‘hot pot’, the Sun heats methane and nitrogen, transforming them into more intricate hydrocarbons that group together in tiny clusters. These particles scatter sunlight, giving Pluto its distinctive blue haze.
However, the dwarf planet is too small to maintain its atmosphere, which is leaking into space at an alarming rate of hundreds of tons every hour. While it’s unclear why Pluto hasn’t depleted its atmosphere, it’s possible that this process was slower in the past and has recently accelerated due to factors only Pluto can explain.
More likely, Pluto has a hidden nitrogen reservoir deep within its icy interior. This nitrogen likely wells up from beneath, replenishing what escapes into space and adjusting to seasonal variations.
Comets may have delivered substantial amounts of nitrogen in the past and even dug up more by crashing through Pluto’s surface, but probably not enough to explain the current supply. Instead, Pluto is likely generating its own nitrogen and releasing it in dramatic ways, possibly through geysers and volcanoes.
5. Pluto’s Heart
As New Horizons neared Pluto, the dwarf planet turned toward us, greeting us with a heart-shaped feature, informally named “Tombaugh Regio” in honor of Pluto’s discoverer, Clyde Tombaugh.
This area boasts an unusually smooth plain, devoid of craters. Astronomers speculate that this “very young” region, Sputnik Planum, was geologically active within the last 100 million years—a mere heartbeat in cosmic terms.
Sputnik Planum’s frozen plains are a collection of planetary oddities. Some parts resemble cracked mudflats on Earth, while others feature uncharacteristically hilly terrain. The region is lined with troughs, and dark substances seep from beneath to fill the cracks. Dark streaks across the plains suggest the influence of Pluto’s winds.
So why is Pluto’s surface so diverse? It could be due to convection, or the lava lamp effect. Just like wax globules rising in a lava lamp, Pluto’s frozen carbon monoxide, nitrogen, and methane may be pushed toward the surface by internal heat.
Alternatively, these features may be the result of a contracting crust. Similar to cracking paint, Pluto’s surface may chip and fracture under the stress of shifting materials beneath.
4. Pluto’s Pits
Pluto is so frigid that it nearly reaches absolute zero. At these temperatures, frozen materials seem to bypass one stage of matter. Instead of melting, methane-rich ices sublimate, changing directly from solid to gas when exposed to the weak sunlight.
Sublimation can carve out large sections of the dwarf planet. The western hemisphere’s Piri Rupes escarpment, often compared to tooth marks, is a barren, jagged landscape. The plateau is lined with steep cliffs and overlooks a flatter, lower area called Piri Planitia.
The highlands are rich in methane ice, while the lowlands are filled with water ice, likely acting as the planet’s bedrock. This chemical difference implies that the plains are surfaces exposed after methane-ice cliffs have sublimated.
Tombaugh Regio also has its own pits, which remain mostly crater-free and are likely the result of recent geological activity, possibly caused by ice fracturing and evaporation. While the pits may appear small, their size is deceptive due to the vast distance.
3. Pluto’s Wandering Hills
Pluto’s hills are truly captivating. Rather than remaining fixed, they continuously shift across Sputnik Planum. These hills are likely broken cliffs from the surrounding highlands, reinforced with rock-solid water ice. Similar to icebergs, they glide across Pluto’s frozen nitrogen glaciers.
Because nitrogen ices are lighter than water, they provide an ideal surface for the hills to move on. Driven by internal convective forces, the hills are deposited at the boundaries of “convective cells,” forming landforms as large as 20 kilometers (12 miles) wide. The largest of these is named Challenger Colles in honor of the Challenger crew.
However, the hills are only miniature versions of Pluto’s gigantic water-ice mountains. Coated with frozen nitrogen, methane, and carbon dioxide, they soar 3,500 meters (11,500 feet) into the thin atmosphere. At less than one hundred million years old, these mountains are some of the youngest features in the solar system and may even be growing!
2. Pluto’s Blades
In the eastern section of Tombaugh Regio, Tartarus Dorsa is recognized for its snakeskin-like surface. Its “scales” are separated by several miles and rise hundreds of feet, yet their exact origin remains a mystery. They could either be methane ice deposits or marks left by substances evaporating from the crust.
These formations seem solid and are likely reinforced by methane clathrates, which form in extremely cold temperatures. Clathrates are microscopic structures, or cages, made of water, and on Pluto, they encase methane in a rigid shell.
On Earth, clathrates formed in the deep ocean are fragile and break easily. However, on Pluto’s icy surface, the cages might be durable enough to support the overlying snakeskin pattern.
Excitingly, clathrates have been observed in the Kuiper Belt and may be older than the solar system itself, potentially acting as time capsules from the protosolar nebula that gave birth to our Sun and planets.
1. Methane Snow
Pluto features a mountain range dusted with snow, rising from a vast dark area known as Cthulhu Regio. This region stretches almost 3,000 kilometers (1,850 mi) across and wraps around the dwarf planet, reaching nearly halfway around its small equator.
From above, Cthulhu Regio appears as a mix of pits, craters, ravines, and dark red regions. It seemed lifeless until New Horizons surprised us with photos of snow-capped peaks made of methane.
The glittering methane snow stands out starkly against the much darker lowlands in the image, captured from just 34,000 kilometers (21,000 mi) away. Scientists believe the snow forms in an unusual version of the same process seen on Earth.
