Mission to Pluto: Live coverage

New Horizons spacecraft to provide closest look yet at dwarf planet

Pluto's mountains

Mountains of water ice more than 3,000 meters high tower over the landscape in this New Horizons' image of a region south of Pluto’s “heart”.


The New Horizons spacecraft flew by Pluto at 7:49 a.m. EDT on July 14, 2015. Astronomy writer Christopher Crockett wrote several updates from mission control at the Johns Hopkins University Applied Physics Lab in Laurel, Md., from July 12-15, and reviewed some of the mission’s major milestones from the last several months. Check our Mission to Pluto editor’s pick for the latest on New Horizons and the dwarf planet.

Updated 5:39 p.m., July 15, 2015

Dynamic worlds

Where to start?

An elongated Hydra is composed of largely water ice. Charon has canyons up to 10 kilometers deep. And Pluto has mountains of water ice over 3,000 meters high.

Let that sink in: water-ice mountains that could hold their own next to the Rockies. “Who would have supposed ice mountains?” asked New Horizons project scientist Hal Weaver at a July 15 news conference.

“We’re not saying Pluto looks like this world or that world,” said planetary scientist Cathy Olkin of the Southwest Research Institute in Boulder, Colo. “There’s nothing like it.”

One of Pluto’s smaller moons, Hydra (shown), looks like a pixelated potato. Future images will have two times as much detail. JHUAPL, SWRI, NASA
Mission scientists showed off three new pictures (and one spectrum) captured by New Horizons as the spacecraft hurtled toward Pluto July 14. The pictures included the first ones to show the shape of one of the dwarf planet’s smaller moons, Hydra, plus a more detailed look at the largest moon, Charon.

“We thought Charon would be an ancient terrain covered in craters,” said Olkin. But “it just blew our socks off.”

Troughs and cliffs 1,000 kilometers long slash across the moon. The dark pole appears to be a relatively thin film, as evidenced by a crater that has smashed through it and dug up something bright underneath. And swaths of landscape are relatively smooth with few craters, which means the moon has been actively resurfacing itself over the last several billion years.

However, it was a close-up view of a 240-kilometer-wide swath of terrain on Pluto just south of the “heart” — now dubbed Tombaugh Regio in honor of Pluto’s discoverer — that elicited the most gasps from the gathered crowd.

Charon, Pluto’s largest moon, shows off a diversity of terrains that include 10-kilometer-deep canyons. JHUAPL, SWRI, NASA
“I screamed,” said planetary scientist Bill McKinnon of Washington University in St. Louis, when he first saw the pictures early this morning.

Mountains draped across the landscape must be made of water ice, said mission leader Alan Stern. Other ices on Pluto aren’t strong enough to hold up a mountain. Water ice at these temperatures, however, is stiff enough to do it.

“We’re seeing the bedrock — or bed-ice — of Pluto,” said Stern.

There’s not a single impact crater to be seen among the mountains. That means the surface is very young, probably less than a hundred million years old. “It might be active right now,” said Stern.

So how did these mountains get there? Who knows?

Signs of geological activity on both worlds are far and away the most surprising thing to come out these images so far. On icy moons of the giant planets, similar features are usually attributed to the gravitational influence of the nearby planet through a process known as tidal heating.  But that can’t happen on Pluto.

Pluto over time
Our perception of Pluto has change significantly in 85 years, as this animation shows. Courtesy of NASA
“You don’t need tidal activity to power activity on icy worlds,” said Stern.

So where’s the energy coming from? The question elicited mostly shrugs from the gathered panel of researchers.

A couple of ideas include heating from radioactive elements such as uranium buried deep in a rocky core. Another more tantalizing possibility is that there was once — or still is — a liquid layer lurking beneath the surface. As the liquid freezes, it releases heat into the planet’s interior and that heat might be enough to drive geysers and cryovolcanoes.

What’s clear to the team, and to everyone gathered in the auditorium at the Applied Physics Laboratory in Laurel, Md., is that even with just a handful of images on the ground, Pluto and Charon have not let anyone down. These are complex, dynamic worlds with many, many stories yet to tell.

“This is what we came for,” said planetary scientist Will Grundy of Lowell Observatory in Flagstaff, Ariz. Olkin quickly corrected him: “This exceeds what we came for.”

Updated 9:10 p.m., July 14, 2015

Phone home

“We have a healthy spacecraft. We’ve recorded data from the Pluto system. We are outbound from Pluto.” So came the announcement from mission operations manager Alice Bowman at mission control.

The signal took 4 hours and 25 minutes to travel across nearly 5 billion kilometers of interplanetary space. The burst was relatively brief, a cryptic code of 1s and 0s loaded with engineering data about spacecraft status and health. But to most of the world it meant one thing:

“Hi, Earth! It’s New Horizons. I’m OK.”

At 8:53 p.m. EDT, a Deep Space Network radio antenna near Madrid received the first message from New Horizons since it tore past Pluto and its five moons, breaking a nearly 22-hour-long radio silence.

During that time, the spacecraft had its hands full taking hundreds of pictures, spectra, plasma measurements and particle tallies while hurtling past Pluto at nearly 50,000 kilometers per hour.

The spacecraft is continuing on past Pluto now, learning more about this far-flung world. Around 7 a.m. tomorrow, the first close encounter image should reach Earth.

But for now the spacecraft is healthy and happy. And now we wait to see Pluto like we never have before.

Updated 7:00 p.m., July 14, 2015

On color and moons

New color images of Pluto and Charon show off the diversity of what the surfaces are made of and are providing crucial evidence of a link between the two worlds.

The images come courtesy of the Ralph camera, which uses several filters to isolate certain wavelength ranges of light. By exaggerating the contrasts between images taken in different filters and painting the images with different colors, the team is able to make false color maps that highlight the compositional differences on the various terrains.

The already famous “heart” splits into two distinct regions when viewed this way, which indicates that the two “ventricles” are composed of different substances.

Pluto and Charon
False color maps of Pluto (left) and Charon (right) show off the compositional diversity of both worlds. JHUAPL, SWRI, NASA

What’s most interesting though is that Charon’s dark spot is the same color as the dark regions on Pluto, indicating they are made of the same material: hydrocarbons that have been exposed to ultraviolet light from the sun, turning them into a tarry substance known as “tholins.”

This supports an idea floated around that Charon’s dark pole comes courtesy of Pluto dumping this gunk on its moon. As Pluto’s atmosphere escapes, some of it lands on Charon. Most of the surface is too warm for the fleeing particles to stick, but the pole might be cold enough to grab them and hold on.

But, as everyone here keeps saying, we won’t know until we get the rest of the data from the spacecraft.

In other Pluto news, John Spencer, of the Southwest Research Institute in Boulder, Colo., reported that if Pluto has any more moons, they’d have to be less than two kilometers across. Unfortunately, the team missed their last best chance to hunt for more moons. Those images would have been taken while New Horizons was recovering from its July 4 computer crash.

They have, however, narrowed the size of Nix and Hydra down to between 30 and 50 kilometers across. Styx and Kerberos are still too faint to estimate.

Meanwhile, somewhere between Earth and Pluto, a radio signal is currently (hopefully) racing across space at the speed of light with a message from New Horizons.

Stay tuned.

Updated 2:29 p.m., July 14, 2015

Sitting and speculating

Scientists haven’t had much time to fully wrap their brains around the latest image from New Horizons. But that isn’t stopping them from excitedly speculating about what they’re seeing — and what’s still to come.

Besides, they need something to do while waiting for the spacecraft to phone home around 9 p.m. EDT tonight.

First up is the prominent heart-shaped landscape on Pluto. The area is brighter than the darker terrains that surround it, and that’s a good sign. “Bright is good,” said Bonnie Buratti of the Jet Propulsion Laboratory in Pasadena, Calif., during a talk at mission control. “That means the planet is active.” If other icy moons are any indication, the bright spots arise from recently deposited ice, possibly condensing out of Pluto’s tenuous, nearly pure-nitrogen atmosphere.

Pluto and its "heart," July 13, 2015
New Horizons sent back this image of Pluto on July 13 right before going radio silent for 22 hours. The spacecraft was 766,000 kilometers from the dwarf planet. JHUAPL, SWRI, NASA

The heart itself could be remnants of an impact crater. Or it could be a raised platform, like a mesa. The easternmost region of the heart gradually gives way to dark splotches, which could be signs of ice that recently sublimated, exposing a dark layer underneath. If that’s the case, the heart may actually be eroding.

“We’ve been monitoring Pluto for 60 years,” Buratti said. From those Earth-based observations, researchers already knew about the heart — or at least that there was a bright patch. And over those six decades, the bright patch has been dimming. “It looks like the heart is eroding away,” she said. Though, she noted, it isn’t likely to disappear.

Images taken during the probe’s closest pass will map a swath across the heart at 50 times greater resolution than the color picture (above) taken July 13, which should help solve some of the shape’s mysteries.

As for the surrounding dark material, the consensus is that it’s hydrocarbons that have been exposed to ultraviolet light from the sun. At the edge of a dark feature dubbed “the whale,” it looks like a crater punched through the hydrocarbon layer, excavating more ice below. 

“We’re calling that the whale’s blowhole,” said Cathy Olkin of the Southwest Research Institute in Boulder, Colo.

The biggest surprise so far though is not on Pluto, but on its largest moon, Charon.

“The dark pole on Charon was a complete surprise to the science team,” said Bill McKinnon, a planetary scientist at Washington University in St. Louis. Nothing like it exists in the solar system. The scientists will have to wait for composition data already sitting on the spacecraft before they can figure that one out.

New Horizons is racing away from Pluto and Charon, making its way into the Kuiper belt. And, the probe is still out of radio communication — as expected. The odds that the spacecraft ran into anything are quite low. Mission leader Alan Stern puts the probability at no more than two parts in 10,000. But there’s still an element of uncertainty.

“I don’t think we’re going to lose the spacecraft,” Stern said, “but we are flying into the unknown.”

Updated 9:54 a.m., July 14, 2015

Pluto, in living color

This latest picture of Pluto (above) must be what NASA scientist Kimberly Ennico was looking at when she tweeted the tantalizing phrase “wow^wow” (that’s wow raised to the wow power).

Here it is, Pluto, in full color. The picture was taken July 13 when New Horizons was 766,000 kilometers from the dwarf planet and 16 hours from closest approach. And, in true 21st century fashion, NASA first released the image on Instagram.

At four kilometers per pixel, this image is about 1,000 times better than what the Hubble Space Telescope can see from 5 billion kilometers away.

And the really high-resolution pictures are still to come!

The science team has only had a few hours to look at this image, but that isn’t stopping them from speculating about everything that Pluto is trying to tell them.

“We see a history of impacts, a history of surface activity, and some features we might identify as tectonic, indicating internal activity at some time in the past,” said New Horizons principal investigator Alan Stern at a July 14 news conference. “This is clearly a world where both geology and atmospheric climatology play a role.”

There are no signs of plumes or hazes yet, but that doesn’t mean they’re not there, Stern said. And when asked if it snows on Pluto, he said: “Sure looks that way.”

Now we wait until New Horizons phones home around 9 p.m. EDT tonight. Stay tuned…

Updated 7:49 a.m., July 14, 2015

Hello, Pluto

This is it! Right now the New Horizons spacecraft is (hopefully) hurtling at nearly 50,000 kilometers per hour just 12,500 kilometers above the surface of Pluto — its closest approach to the dwarf planet.

The probe is spending this time with its cameras and its ultraviolet spectrometer trained on Pluto’s largest moon, Charon. These data will be used to map the moon and look for a possible tenuous atmosphere.

Next, New Horizons will start photographing Pluto’s nightside in the glow of sunlight reflecting off Charon. The probe will then begin one of its radio experiments, where antennas on Earth will blast a signal through Pluto’s atmosphere at New Horizons. Using the deflection of the radio signal, the probe will measure the temperature and density of the lower atmosphere.

While the team back on Earth is deservedly celebrating, the real sigh of relief comes shortly before 9 p.m. Eastern when New Horizons phones home to let the team — and the world — know how it’s doing.

The ride is far from over!

Updated 11:15 p.m., July 13, 2015

Going quiet

Well, that’s it.  At 11:15 p.m. EDT, New Horizons wrapped up its final transmission before it meets up with Pluto at 7:49 a.m. on July 14. The spacecraft has now entered a nearly 22-hour radio blackout period, during which it will spend every precious minute doing as much science as possible during its brief encounter with the dwarf planet.

PLUTO’S HEART A heart-shaped landscape (left) rotates into view in this image of Pluto taken on July 12 when New Horizons was 2.5 million kilometers from the dwarf planet. JHUAPL, SWRI, NASA
New Horizons can’t talk to Earth and observe Pluto or its moons simultaneously. So mission engineers decided early on that the spacecraft would go quiet for the period during closest approach. That’s nearly a full nail-biting day when no one will hear a peep from the busy probe.

The Earthlings are just going to have to be patient.

Around 8:53 p.m. on Tuesday, the first trickle of post-encounter data should hit a radio dish in Madrid that is part of the Deep Space Network, NASA’s link to spacecraft roaming the solar system. For 15 minutes, New Horizons will send back information on the status of the spacecraft and instruments. And then it will go right back to doing science for about another eight hours.

That whisper from the spacecraft won’t tell us anything about Pluto or its moons. It’s just New Horizons way of saying: “Hello, Earth. I made it!” The first encounter images won’t hit the ground until around 7 a.m. on July 15. By that time, Pluto will already be a fading image in New Horizons’ rearview mirror.  

Updated 6:21 p.m., July 13, 2015

Hearts, chasms and craters

New Horizons continues to tease us with a couple of images taken July 12. The pictures are just a sampling of the torrent of data that are starting to flood the spacecraft’s instruments.

BETTER VIEW Craters and chasms come into focus as New Horizons closes in on Pluto and its largest moon, Charon (shown). JHUAPL, SWRI, NASA

A heart-shaped swath of bright terrain, first seen July 8, is coming into view on the western horizon in a new image taken about 2.5 million kilometers from Pluto. New Horizons will get a far more intimate look at this region when it flies just 12,500 kilometers above the surface of the dwarf planet tomorrow morning.

Charon, meanwhile, is showing clear signs of chasms larger than the Grand Canyon and a large impact crater surrounded by rays of bright material excavated from deep below the moon’s surface.

Tomorrow’s images will show details at roughly 180 times the resolution of these latest images, said New Horizons project scientist Hal Weaver before a packed auditorium on July 13.

One more color picture is already on the ground, and another even more detailed black-and-white image will be downloaded later tonight. That will be the last image we see until after the probe’s close encounter with Pluto.

Updated 12:16 p.m., July 13, 2015

Pluto rules the Kuiper belt

Pluto is officially the largest (known) object in the Kuiper belt, the zone of icy debris that floats beyond the orbit of Neptune. The dwarf planet is 2,370 kilometers across, give or take 20 kilometers.

“This is very new news,” said planetary scientist Cathy Olkin of the Southwest Research Institute in Boulder, Colo., at a July 13 news conference. “It’s too early to say what the implications are.”

Even though far better data will be collected over the next 24 hours, mission scientists are having fun speculating about everything they’re seeing so far.

A dark spot on Charon’s pole could be a dumping ground for material lofted off of Pluto, said Paul Schenk of the Lunar and Planetary Institute in Houston. A polar dark spot is something completely new in the solar system, he says. No other icy moons show anything similar.

BETTER BY THE MINUTE Pluto is coming into sharper focus as New Horizons races towards its July 14 meeting with the dwarf planet. This image was captured on July 11. JHUAPL, SWRI, NASA
“The most surprising thing so far is that Pluto and Charon are unrecognizable,” he said. With its amoeba-like and blobby splotches, Pluto “looks like somebody painted it for a Star Trek episode.”

New color data that come down tomorrow will help the team figure out the composition of various terrains on both Pluto and Charon. But even with the data on the ground, fully coming to grips with what these icy worlds are telling us will take time.

“Science on the fly tends to be wrong,” said  New Horizons principal investigator Alan Stern.  “We need time to understand the data.”

Updated 10:03 a.m., July 13, 2015

Timing is everything

With less than 24 hours to go until New Horizons tears past Pluto, all systems are go for what’s shaping up to be a near-perfect flyby.

“I’m feeling pretty good about the next couple of days,” said engineer Chris Hersman July 12 to a room packed with journalists.

The spacecraft is past the point where engineers can make course corrections if they discover that New Horizons is coming in too fast or too close to Pluto. But they can shift the times at which the probe snaps pictures or gathers spectra.

Each instruction stored in the spacecraft’s memory is stamped with a time at which it’s supposed to happen. Engineers can upload a timing adjustment should they need to. According to the latest data, Hersman says, mission control is planning on just leaving the probe alone.

The strictest timing requirements come courtesy of a radio experiment dubbed REX. As New Horizons passes through Pluto’s (and Charon’s) shadow, radio antennas on Earth will blast a signal at the spacecraft that will skim the dwarf planet’s atmosphere.  By watching how much the radio beam bends, mission scientists will be able to measure the temperature and density of Pluto’s lower atmosphere.  They’ll also learn whether or not the dwarf planet’s largest moon has any atmosphere at all — the instruments are sensitive enough to detect just 1 nanobar of pressure.

But to get it right, New Horizons has only a couple hundred seconds of wiggle room. That’s a couple hundred seconds after the nearly 300 million seconds that have elapsed since launch.

Remarkably, New Horizons is just 70 seconds off schedule, well within the margin of error, Hersman says.

Updated 11:00 p.m., July 12, 2015

Million miles to go

At 11:23 p.m. Eastern, New Horizons passes the one-million-miles-to-Pluto mark, and to help celebrate, the spacecraft has sent back a new round of images that were captured on July 11.

Pluto is starting to reveal what might be a series of cliffs that are about to vanish beyond its eastern horizon. And a circular region that looks suspiciously like an eye staring back at New Horizons shows signs of a long-ago run-in with a space rock. The side of Pluto that will be facing the spacecraft when it buzzes the dwarf planet on July 14 is just starting to rotate into view.

Not to be overshadowed, Pluto’s largest moon, Charon, is getting some camera time as well. Chasms and possible craters scar a dark, barren landscape. And instead of a bright polar cap like on Earth or Mars, Charon’s pole is marked by a dark splotch roughly 400 kilometers across.

Pluto’s largest moon Charon shows off crater, chasms and a dark spot on its pole in this image taken July 11. JHUAPL, SWRI, NASA

As the cameras continue to wow with their stunning photographs, the other instruments aboard are just beginning to snag signals from the Pluto system. The onboard spectrographs and particle detectors need to get right up close to Pluto before they sense details from the atmosphere and surrounding space environment. Starting July 13, New Horizons will be flooded with information from this remote world, nearly 5 billion kilometers from Earth.

Updated 4:42 p.m., July 12, 2015

Last spot shot

Pluto shows off a variety of terrains in this New Horizons image taken July 11 just 4 million kilometers from Pluto. JHUAPL, SWRI, NASA

New Horizons has gotten the best look it will ever get at the chain of Missouri-sized spots that surprised everyone on July 2. The image, taken when New Horizons was 4 million kilometers from the dwarf planet, shows off the side of Pluto that will be facing away from the spacecraft when it buzzes the icy world on July 14.

The spots link up to a dark belt that wraps around Pluto’s equator. A few polygon-shaped regions lie just to the north. No word yet on what it all means. 

Updated 7:00 a.m., July 10, 2015

Fly with New Horizons

Do you wish you could ride alongside the New Horizons spacecraft as it swings past Pluto on July 14? “Eyes on Pluto” has you covered. This program for your computer provides a “live” simulated view from the spacecraft. And with the click of a button, you can watch the entire encounter unfold before it even happens.

Updated 12:10 p.m., July 2, 2015

Pluto has spots!

A chain of enigmatic dark spots mark the surface of Pluto in recent New Horizons images, taken when the spacecraft was about 22 million kilometers from the dwarf planet. Each splotch is about 500 kilometers across and covers roughly the same area as the state of Missouri.

The pictures, taken on June 25 and 27, show two faces of Pluto and its largest moon, Charon, in true color; this is how the duo would appear to a human along for the ride. The original images, taken by the spacecraft’s zoom lens, are in black-and-white; the color comes from recent low-resolution images taken by the probe’s wide-field camera.

Pluto and Charon in orbit
Pluto and Charon show off two of their sides in pictures taken by the New Horizons spacecraft. Each of the dark spots on Pluto (orange, right) is roughly the size of Missouri.


Updated 3:38 p.m., May 13, 2015

Pluto family portrait

Pluto moons
Pluto’s four outermost moons whirl around the dwarf planet in these images from the New Horizons spacecraft. Pluto and its largest moon Charon are hidden in the glare at the center of each image. The colors (right) mark the moons and their orbits.


Pluto’s family portrait (as far as we know) is complete. The New Horizons spacecraft finally spied the dwarf planet’s two tiniest satellites, Kerberos and Styx, in a series of images taken from April 25 to May 1, when the probe was nearly 90 million kilometers from Pluto. The moons were discovered in images from the Hubble Space Telescope in 2011 and 2012.

Updated 6:28 p.m., April 29, 2015

Pluto’s largest moon, Charon, orbits in just over 6 days while the dwarf planet spins on its axis in this series of images from the New Horizons spacecraft as it looks down on Pluto’s north pole. NASA, Johns Hopkins University Applied Physics Laboratory, Southwest Research Institute

Land, ho!

The landscapes of Pluto are starting to take shape. Bright and dark regions rotate in and out of view in new images from the New Horizons spacecraft. A bright spot at Pluto’s north pole might be a never-before-seen polar ice cap, researchers reported at a April 29 news conference. Mission scientists won’t know more, however, until the spacecraft is close enough to measure the chemical composition. The images were taken while New Horizons was just over 100 million kilometers from its target.

Updated 7:08 p.m., February 4, 2015

Smile for the camera

pluto images taken by New Horizons
Pluto and its largest moon, Charon, are seen from over 200 million kilometers away in new pictures taken January 25 and January 27 by the New Horizons spacecraft.

NASA, Johns Hopkins University Applied Physics Laboratory, Southwest Research Institute

Pluto and its largest moon, Charon, were captured in a couple of snapshots, the first taken by the New Horizons probe since the spacecraft awoke from a long slumber in December. The spacecraft was just over 200 million kilometers from the duo when it took the pictures on January 25 and 27.

Updated 3:37 p.m., December 8, 2014

Wakey, wakey!

NASA’s New Horizons spacecraft, scheduled to fly by Pluto on July 14, came out of hibernation for the last time to get ready for the final six months of its cruise to the dwarf planet. Mission controllers received word from the probe on December 6 at 9:53 p.m. Eastern time that it was awake and ready to work.

Excerpt from ‘Rendezvous with Pluto’ (SN: 6/27/15, p. 16)

On July 14, NASA’s New Horizons spacecraft will reach Pluto and try to learn all it can about the dwarf planet and its five known moons. Then the probe will leave Pluto behind, vanishing into the frigid darkness beyond the planets.

In its wake, New Horizons will introduce Earth to the last of the “classical planets.” Probes have flown past, orbited, crashed into or landed on every other world that orbits the sun. Now Pluto is getting its turn.

“This is the last picture show,” says Alan Stern, the mission’s leader. “It’s the capstone moment to the reconnaissance of the planets.”

Read more on the mission in “Rendezvous with Pluto,” and see all of our coverage of the New Horizons mission.

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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