New Horizons Has Reached Pluto! What Has It Discovered?

Dr. Alan Stern, New Horizon's Principal Investigator, and science team react to first flyby photo.
Dr. Alan Stern, New Horizon's Principal Investigator, and science team react to first flyby photo. | Source

Views of Pluto Through the Years

Above: Pluto observations 1930-2015, starting with original discovery by Clyde Tombaugh, ending with flyby zoom. See "Views of Pluto Through the Years" for info on every frame.

Size Comparison

Pluto and Charon compared to Earth. Side by side, they'd fit inside the United States.
Pluto and Charon compared to Earth. Side by side, they'd fit inside the United States. | Source

TARGET: PLUTO

3.7 billion miles from Sun, 40x farther away than Earth. Half the width of the U.S. It orbits the sun in 248 Earth years. Temperatures? A balmy -396 to -360 F (-238 to -218 C)

New Horizons' #PlutoFlyby

On Tuesday, the New Horizons Spacecraft made its closest approach approach to Pluto. Its daring journey has hurtled it across 3 billion miles in 9 years, reaching speeds over 50,000 miles per hour. It's so far away now that its signal takes 4.5 hours to reach Earth.

The human race has finally reached Pluto.

Performing a beautifully precise dance, New Horizons sailed between Pluto's moons and the planet itself, twisting and turning to bring all its instruments to bear on tiny targets while cruising at 30,800 mph. It worked feverishly all day, pausing only briefly to "Phone Home" and report "I'm alive!" It's continuing to make observations as it speeds away. The public will see beautiful photos, while the scientists can't wait for incredibly detailed information on Pluto's vital signs that will take decades to study.

It's difficult to communicate across 3 billion miles. Signal strength is faint, there's a lot of static, and download speeds are a glacial 1K per second. That's why we're receiving more b&w pictures than color. It will take 16 months to receive all the pictures and data collected during the flyby.

I'll be keeping you up to date with the best Pluto images and discoveries through July 20, as fast as I can gather and summarize them.

But first, a quick review of the epic journey...

The Ride of a Lifetime: This Is Not Science Fiction

Jupiter and Its Moon Io

In infrared, the Great Red Spot is white, and the volcanoes of Io erupt in ghostly blue.
In infrared, the Great Red Spot is white, and the volcanoes of Io erupt in ghostly blue.

The Long Road to Pluto

In 2007, New Horizons used Jupiter for a gravity assist, slingshotting around the giant planet on the way out. It gave engineers a chance to test their instruments and put the spacecraft through its paces.

Among New Horizon's instruments is an infrared camera (RALPH) picking up heat and wavelengths of light that we can't see. The ground team translates them into a "false-color" image we can see. At right, NH snapped an infrared photo of Jupiter and its moon, Io (look for faint blue-white volcanic plume).

For another appetizer, New Horizons took the first-ever video of a volcanic eruption on another world. That's Io, one of the moons of Jupiter.

Skimming the Cloud-Tops of Jupiter

True-color photo of the giant planet Jupiter by New Horizons Spacecraft. [Feb. 28, 2007]
True-color photo of the giant planet Jupiter by New Horizons Spacecraft. [Feb. 28, 2007] | Source

Flawless Flyby Choreography: Every Move Had to Be PERFECT

Where Is Pluto?

Pluto and other Kuiper Belt Objects (small ice worlds) orbit the Sun out beyond Neptune in tilted, elliptical orbits.
Pluto and other Kuiper Belt Objects (small ice worlds) orbit the Sun out beyond Neptune in tilted, elliptical orbits. | Source

Early Glimpses of Pluto

Click thumbnail to view full-size
Clyde Tombaugh discovered Pluto on February 28, 1930.The best view of Pluto before New Horizons arrived.July 11, 2015: 1 million miles to go! Cliffs, impact craters, a polar ice cap, and other details are coming into view.
Clyde Tombaugh discovered Pluto on February 28, 1930.
Clyde Tombaugh discovered Pluto on February 28, 1930.
The best view of Pluto before New Horizons arrived.
The best view of Pluto before New Horizons arrived. | Source
July 11, 2015: 1 million miles to go! Cliffs, impact craters, a polar ice cap, and other details are coming into view.
July 11, 2015: 1 million miles to go! Cliffs, impact craters, a polar ice cap, and other details are coming into view. | Source

What We Knew BEFORE New Horizons Arrived

  • Pluto's approximate size: 1360-1440? miles in diameter
  • Charon's size: ~750 miles
  • Pluto's surface: Nitrogen, methane, carbon monoxide ices. Water ice predicted, but Earth-based instruments couldn't see any. Rocky interior.
  • Charon's surface: Mostly water ice.
  • Pluto's atmosphere: Nitrogen, methane and carbon monoxide that freezes onto its surface as it moves away from the sun.
  • Pluto and Charon are much closer together than any other planet and moon, 12,200 miles apart. They orbit a point between them. They're essentially a binary planet.
  • Uniquely in the solar system, they are "spin locked" so each always shows the same face to the other. Also, Charon is in geosynchronous orbit, so it hangs over the same spot on Pluto's surface.
  • They probably formed in a catastrophic impact between Pluto and another mini-world, similar to the collision that created Earth's Moon.
  • Kuiper Belt objects like Pluto were thought to be cold leftovers from the primordial solar system, which haven't changed for billions of years. Scientist hoped Pluto and Charon might tell us about the formation of the solar system and the collision that created our Moon.

But New Horizons changed everything!

Pluto Sends Us a Valentine

July 13, 2015: 16 hours before closest approach. 475,970 miles (766,000 km) from Pluto.
July 13, 2015: 16 hours before closest approach. 475,970 miles (766,000 km) from Pluto. | Source

New Horizon Photos of Charon, Pluto's Mighty Moon

July 13 photo of Charon shows a younger, more varied landscape than we could've hoped for, with canyons many miles deep! The dark patch at the top is called "MORDOR."
July 13 photo of Charon shows a younger, more varied landscape than we could've hoped for, with canyons many miles deep! The dark patch at the top is called "MORDOR." | Source

New Horizons Spots Pluto's Moons

Orbiting a Binary Planet Isn't Easy

Pluto System Seen By Hubble

Map of Pluto's Moons using Hubble photos, the best images we had before New Horizons.
Map of Pluto's Moons using Hubble photos, the best images we had before New Horizons. | Source

First New Horizon Discoveries

It was only the day before closest approach that Pluto's size was finally pinned down: 1473 miles (2,370 km) in diameter, squeaking past dwarf planet Eris (2336 +/- 12 km).

Other pre-flyby discoveries:

  • Charon's size: 751 miles (1208 km).
  • Pluto's mass is less than Eris, probably due to more ice, less rock.
  • The Hubble Space Telescope assisted by scanning Pluto's neighborhood, looking for hazards. It discovered several moons while the spacecraft was en route. They wobble drunkenly due to the varying gravitational pull of Charon and Pluto (right).
  • By July 10, scientists were seeing signs of geology on Pluto.
  • Pluto has weather! It snows, then the snow sublimates and returns to its atmosphere.
  • Pluto's incredibly thin atmosphere may extend out to 3.7 million miles (6 million km). Scientists expected it to be larger than Earth's (300 miles) because of Pluto's weak gravity, but that's huge!
  • Confirmed: Pluto has a polar cap of nitrogen and methane ice.
  • The "heart" is partly carbon monoxide ice.
  • Pluto's lovely color is caused by tholins, reddish organic molecules created by UV rays altering methane ice. Here's pictures of tholins made in a lab.

Closest Approach Flyby Portrait of Pluto and Charon, July 14, 2015

Here it is! New Horizons traveled a long way to bring us this image. (It's actually a composite photo, but the relative sizes and positioning of Pluto and Charon are accurate.)
Here it is! New Horizons traveled a long way to bring us this image. (It's actually a composite photo, but the relative sizes and positioning of Pluto and Charon are accurate.) | Source

Welcome to Pluto: A Geologically Active World

Norgay Mountains, the zoom above. Named after Sherpa who helped Hillary climb Everest. (The "heart" has been formally named Tombaugh Regio, after Pluto's discoverer.)
Norgay Mountains, the zoom above. Named after Sherpa who helped Hillary climb Everest. (The "heart" has been formally named Tombaugh Regio, after Pluto's discoverer.) | Source
Infrared helps show composition of ices; there's patches of methane, nitrogen, carbon monoxide. Regional variation suggests geological processes, or perhaps climate: what's depositing (or snowing) different things in different places?
Infrared helps show composition of ices; there's patches of methane, nitrogen, carbon monoxide. Regional variation suggests geological processes, or perhaps climate: what's depositing (or snowing) different things in different places? | Source
July 13, 2015: False-color images help bring out differences in terrain and composition.
July 13, 2015: False-color images help bring out differences in terrain and composition. | Source
Artist's concept of Pluto's mostly-nitrogen atmosphere escaping and turning into an enormous tail ionized by the solar wind.
Artist's concept of Pluto's mostly-nitrogen atmosphere escaping and turning into an enormous tail ionized by the solar wind. | Source

"First Look" Discoveries

The first flyby photos revealed the incredible news that Pluto and Charon are not dead worlds, sad little ice balls that froze solid billions of years ago with nothing but the relentless peck of meteors excavating new craters in their skins. They are alive.

Meteor strikes hit planets at a steady rate over time, like rain in Seattle, so a lack of craters is a sign of a young, dynamic world with geological processes resurfacing its face like a cosmic Zamboni. In fact, that Ice Mountain photo shows one of the "youngest surfaces... in the solar system."

Pluto's Mountains of Ice

Aha, there's the water! It's locked into mountains 11,000 feet (3500 meters) tall. They have to be water ice, because methane, carbon monoxide, and nitrogen ices are soft; they don't have the strength to pile up like that. Instead, they form "frosting" on top of the mountains and plains.

Atmospheric Loss

Poor Pluto is losing its nitrogen atmosphere at an astounding rate, such that it must have lost between 300m and 3km worth of nitrogen ice since Pluto formed.

The only plausible explanation, according to New Horizons' Alan Stern, is that some geological process is dredging up nitrogen from deep inside; there just isn't enough on the surface. So scientists are hunting for signs of geysers, cryovolcanoes (ice volcanoes), or other kinds of venting.

New Horizons' measurements show that the solar wind is sweeping Pluto's atmosphere away in a huge tail.

Charon's "Mountain in a Moat"

The feature in the upper left of the close-up baffles scientists: did the mountain sink? Inset close-up is 240 miles (390km) tall, including few visible craters. July 14, 2015, about 1.5 hours before closest approach, from 49,000 miles (79,000 km).
The feature in the upper left of the close-up baffles scientists: did the mountain sink? Inset close-up is 240 miles (390km) tall, including few visible craters. July 14, 2015, about 1.5 hours before closest approach, from 49,000 miles (79,000 km). | Source

Pluto's Small Moons

Click thumbnail to view full-size
First glimpse of tiny Hydra, which means "water monster," shows that it's reflective because it's covered in water ice. Not much to see, but then you could run a marathon from one end to the other. Better resolution photos to come!Cucumber-shaped Nix seen end-on: Screengrab from July 17, 2015 press conference.
First glimpse of tiny Hydra, which means "water monster," shows that it's reflective because it's covered in water ice. Not much to see, but then you could run a marathon from one end to the other. Better resolution photos to come!
First glimpse of tiny Hydra, which means "water monster," shows that it's reflective because it's covered in water ice. Not much to see, but then you could run a marathon from one end to the other. Better resolution photos to come! | Source
Cucumber-shaped Nix seen end-on: Screengrab from July 17, 2015 press conference.
Cucumber-shaped Nix seen end-on: Screengrab from July 17, 2015 press conference. | Source

Fascinating Moons

What's even more surprising is that Charon shows signs of geological activity as well. There's 600-mile-long (!) fractures, a huge canyon 4-6 miles deep, and another 3 miles deep. The bigger canyon dethrones Valles Marineris as the deepest in the solar system!

The north pole's dark patch, nicknamed "Mordor," seems to be coated in an eerie dark reddish stain from...something. (A lonely impact crater or two has excavated through to the ice below, showing the veneer is very thin).

Meanwhile, New Horizons measured a tiny moon, Hydra, at 27x20 miles (43x33km), gleaming white with water ice and darkened by what looks like a sizable impact crater. Nix, the drunken moon whose tumbling was reconstructed from Hubble data in that animation above, is looking end-on to the camera.

Animated Flyover of Pluto's Mountains and Plains

Location of "Sputnik Planum"

Closeup of Sputnik Planum

Wind deposits on the backsides of obstacles, or... plume deposits from a geyser? VERY speculative; we don't know yet. (Screengrab from streaming video, and the original image had JPG compression artifacts, so take details with a grain of salt)
Wind deposits on the backsides of obstacles, or... plume deposits from a geyser? VERY speculative; we don't know yet. (Screengrab from streaming video, and the original image had JPG compression artifacts, so take details with a grain of salt) | Source

Sputnik Planum, Plains Near the Bottom of the "Heart"

Above, the New Horizons Team used photos of Pluto's surface from different angles to determine topography, allowing them to stitch together a 3D "flyover" movie using the "Ice Mountains" photo plus two more tiles of a larger photo mosaic — we're still waiting for the rest! "Sputnik Plains" are an area within Pluto's heart just next to the ice mountains.

The surface of Sputnik Planum is weird. If you look closely, you'll see large polygonal areas bordered by troughs. These could be cracks like those seen in drying mud. Or... maybe? the polygons could be the tops of convection cells, columns of heat rising from Pluto's interior like bubbles in a kettle.

Inside the troughs are lumps of black material and low hills which defy explanation. Are they gunk squeezing up from below, or old structures being exposed as the carbon monoxide ice around them sublimates away?

There's also streaks of wind-blown particles (perhaps frozen methane, tanned reddish-brown by UV light), and perhaps— just perhaps— traces of geyser or volcano plume deposits.

"Sputnik Planum" - Puzzling Details

Another tile of the July 14 b&w mosaic, the carbon monoxide plains in Pluto's "heart." Taken from 48,000 miles (77,000km) away. Note: there's JPG compression artifacts; the spacecraft will send back an uncompressed version later.
Another tile of the July 14 b&w mosaic, the carbon monoxide plains in Pluto's "heart." Taken from 48,000 miles (77,000km) away. Note: there's JPG compression artifacts; the spacecraft will send back an uncompressed version later. | Source

Where Do Pluto and Charon Get All That Energy?

Scientists are delighted and utterly stumped. The problem is one of basic physics: a glob of molten rock and water floating in outer space, hundreds of degrees below freezing, should freeze. It takes a long time for something planet-sized to cool, but mini-worlds the size of Pluto and Charon should have frozen solid billions of years ago ago. Without interior heat, geological processes stop.

And yet they haven't. New Horizon team member John Spencer proposed a couple possible explanations: (a) Planets like Earth are heated by radioactive materials deep down; perhaps water-based geology (cryology?) requires less heat to drive it. Or (b) oddly enough, water has to release heat as it freezes. Maybe there's an interior ocean slowly freezing solid, and that's where the energy comes from.

For now, Pluto and Charon are "baffling in a very interesting and wonderful way."

So What?

These are brand-new discoveries made in the past few days, and they're going to revolutionize planetary science. Not just for the planets you learned about in school, but for the mini-worlds of the Kuiper Belt. The best part is that wherever there's water and energy, there's a possibility of life.

The New Horizon Spacecraft's July 11 portrait Pluto and its large moon Charon. They're not actually this close together; this is 2 photos side by side.
The New Horizon Spacecraft's July 11 portrait Pluto and its large moon Charon. They're not actually this close together; this is 2 photos side by side. | Source

Planet or Dwarf Planet: You Decide!

Pluto is...

  • ...a dwarf planet.
  • ...a planet. Period.
See results without voting

Is Pluto a Planet?

...I was hoping you weren't going to ask that question. I have answered that question, but this page is getting too long, so I've moved my answer here.

I think the "dwarf planet" debate is getting in the way of something far more important: talking about Pluto as a world.

I will say this. The discovery of multiple "ice dwarf" planets the size of Pluto or slightly smaller means Pluto is not the last planet to be explored. It's the first of a new kind of planet. So don't listen to some of the old-guard astronomers from the last century boasting that "We've found everything now, and there's nothing important left for you to explore." That's bunk. We've already found Eris, another Pluto-sized world, and many others larger than Charon. (Yes, some have moons.) There must be many more, waiting to be discovered.

There's another name for these little worlds, by the way: Plutoids. While Pluto may not be an only child, it will always be first in our hearts.

The Heart on Pluto

"Here we go, out into the solar system!" — MOM

—A very tired Alice Bowman. Screengrab from July 14 6:30PM press conference announcing that New Horizons called home to say it's on schedule and working fine.
—A very tired Alice Bowman. Screengrab from July 14 6:30PM press conference announcing that New Horizons called home to say it's on schedule and working fine. | Source

This page is dedicated to my grandmother, Frances Friedman, former director of Hudnall Planetarium. She was present at JPL for some of the Voyager flybys of the outer planets. I wish she could witness this one.

© 2014 Ellen

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2 comments

Blackspaniel1 profile image

Blackspaniel1 20 months ago

I read we have to catch Pluto before it is too far away. There is an underlying reason. Pluto has an atmosphere when it is closer to the sun which collapses in the outer parts of its orbit, and one hope is to study this atmosphere while it is there, or wait over 200 years.


Denmarkguy profile image

Denmarkguy 14 months ago from Port Townsend

Excellent stuff! I'm a total space geek... it's cool to see the whole timeline assembled like this!

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