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The First Close-Up Image of Pluto Is Here

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Water ice mountains 11,000 feet tall. No impact craters. The provocative possibility that Pluto's surface is much, much younger than we thought—and that the planet is still geologically active. So too is Charon, one of its four moons.

These are just a few of the conclusions scientists on the New Horizons mission are drawing from the first closeup images of Pluto and two of its moons. After a journey of 9.5 years and 3 billion miles, yesterday NASA’s New Horizons spacecraft got within 7800 miles of the surface, the closest encounter with Pluto the human race has ever had. Its scientific payload went into high gear as the probe flew by at more than 30,000 miles an hour, taking in reams of data via seven high-tech instruments.   

The probe was out of contact with mission headquarters for 13 hours so it could focus on gathering rather than transmitting data. When it reestablished contact last night at 8:52:37 p.m. ET, there was jubilation at the Johns Hopkins University's Applied Physics Laboratory (APL), mission headquarters. All the systems reported back as normal. "We have a healthy spacecraft," said Alice Bowman, mission operations manager.

Now we're seeing the first images from that superfast data grab. The new black-and-white image of Pluto shows a mountain range made of water ice, with peaks jutting as high as the Rocky Mountains, the team says. Here's a close up:

"The most striking thing is that we haven't found a single impact crater, which means this is a very young surface—less than 100 million years old," project scientist John Spencer said in a NASA press briefing. Collisions and the resulting impact craters were common in the volatile early years of our solar system's formation.

"It's clear that Pluto has remarkably varied terrain, and that the different colorations and textures of the large surface features point to diverse geological processes—surprising, perhaps, in a planet with so little external energy coming from the sun," Gettysburg College astronomer and professor emeritus Lawrence Marschall, co-author of Pluto Confidential, tells mental_floss. "The strong tidal interaction of Charon and Pluto may be responsible for the geological diversity you see. The very high mountains are particularly impressive."

We also spoke to the man responsible for Pluto's demotion to a dwarf planet: Mike Brown, the CalTech planetary astronomer whose discovery in 2005 of the planet Eris led to Pluto's reclassification as a dwarf planet. Because Eris was thought to be bigger than Pluto, some floated the idea that Eris be considered the 10th planet in the solar system. Instead, Pluto was "demoted," angering schoolchildren everywhere. (Eris, too, is considered a dwarf planet.)  

Brown calls the ice mountains on Pluto "very strange," but he doubts they are as young as the New Horizons team thinks. "It seems to me that they could be old mountains poking through some young icy terrain," he says. "The footprint of the mountains is so small that you'd have a hard time finding a crater on one even if it were there."

Brown's Twitter handle may be @plutokiller, but he was struck by the image of Charon. Here it is:

"My first thought upon opening up the Charon image was: 'Where are all of the impact craters?'" says Brown. Like Pluto, Charon's surface seems to be relatively baby-faced among objects in the solar system. "Pretty cool: we've known for 15 years that there would be ancient ice floes on the surface, but I would have thought that they were ancient enough that they were still covered in craters. Seems like the ice floes were more recent."

We'll have more details about the discoveries coming soon from contributor David Brown, who spoke to scientists at the NASA press briefing. Stay tuned.

In the meantime, consider that New Horizons is already more than a million miles past Pluto. It now heads into the Kuiper Belt, a gigantic zone of icy bodies and mysterious small objects orbiting beyond Neptune, where it will explore the origins of the outer solar system and how planet-satellite systems evolve. Because it's so energy efficient, New Horizons could, in theory, send us data for the next 30 years.

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8 Useful Facts About Uranus
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Uranus as seen by the human eye (left) and with colored filters (right).

The first planet to be discovered by telescope, Uranus is the nearest of the two "ice giants" in the solar system. Because we've not visited in over 30 years, much of the planet and its inner workings remain unknown. What scientists do know, however, suggests a mind-blowing world of diamond rain and mysterious moons. Here is what you need to know about Uranus.


Uranus is the seventh planet from the Sun, the fourth largest by size, and ranks seventh by density. (Saturn wins as least-dense.) It has 27 known moons, each named for characters from the works of William Shakespeare and Alexander Pope. It is about 1784 million miles from the Sun (we're 93 million miles away from the Sun, or 1 astronomical unit), and is four times wider than Earth. Planning a trip? Bring a jacket, as the effective temperature of its upper atmosphere is -357°F. One Uranian year last 84 Earth years, which seems pretty long, until you consider one Uranian day, which lasts 42 Earth years. Why?


Most planets, as they orbit the Sun, rotate upright, spinning like tops—some faster, some slower, but top-spinning all the same. Not Uranus! As it circles the Sun, its motion is more like a ball rolling along its orbit. This means that for each hemisphere of the planet to go from day to night, you need to complete half an orbit: 42 Earth years. (Note that this is not the length of a complete rotation, which takes about 17.25 hours.) While nobody knows for sure what caused this 98-degree tilt, the prevailing hypothesis involves a major planetary collision early in its history. And unlike Earth (but like Venus!), it rotates east to west.


You might have noticed that every non-Earth planet in the solar system is named for a Roman deity. (Earth didn't make the cut because when it was named, nobody knew it was a planet. It was just … everything.) There is an exception to the Roman-god rule: Uranus. Moving outward from Earth, Mars is (sometimes) the son of Jupiter, and Jupiter is the son of Saturn. So who is Saturn's father? Good question! In Greek mythology, it is Ouranos, who has no precise equivalent in Roman mythology (Caelus is close), though his name was on occasion Latinized by poets as—you guessed it!—Uranus. So to keep things nice and tidy, Uranus it was when finally naming this newly discovered world. Little did astronomers realize how greatly they would disrupt science classrooms evermore.

Incidentally, it is not pronounced "your anus," but rather, "urine us" … which is hardly an improvement.


Uranus and Neptune comprise the solar system's ice giants. (Other classes of planets include the terrestrial planets, the gas giants, and the dwarf planets.) Ice giants are not giant chunks of ice in space. Rather, the name refers to their formation in the interstellar medium. Hydrogen and helium, which only exist as gases in interstellar space, formed planets like Jupiter and Saturn. Silicates and irons, meanwhile, formed places like Earth. In the interstellar medium, molecules like water, methane, and ammonia comprise an in-between state, able to exist as gases or ices depending on the local conditions. When those molecules were found by Voyager to have an extensive presence in Uranus and Neptune, scientists called them "ice giants."


Planets form hot. A small planet can cool off and radiate away heat over the age of the solar system. A large planet cannot. It hasn't cooled enough entirely on the inside after formation, and thus radiates heat. Jupiter, Saturn, and Neptune all give off significantly more heat than they receive from the Sun. Puzzlingly, Uranus is different.

"Uranus is the only giant planet that is not giving off significantly more heat than it is receiving from the Sun, and we don't know why that is," says Mark Hofstadter, a planetary scientist at NASA's Jet Propulsion Laboratory. He tells Mental Floss that Uranus and Neptune are thought to be similar in terms of where and how they formed.

So why is Uranus the only planet not giving off heat? "The big question is whether that heat is trapped on the inside, and so the interior is much hotter than we expect, right now," Hofstadter says. "Or did something happen in its history that let all the internal heat get released much more quickly than expected?"

The planet's extreme tilt might be related. If it were caused by an impact event, it is possible that the collision overturned the innards of the planet and helped it cool more rapidly. "The bottom line," says Hofstadter, "is that we don't know."


Although it's really cold in the Uranian upper atmosphere, it gets really hot, really fast as you reach deeper. Couple that with the tremendous pressure in the Uranian interior, and you get the conditions for literal diamond rain. And not just little rain diamondlets, either, but diamonds that are millions of carats each—bigger than your average grizzly bear. Note also that this heat means the ice giants contain relatively little ice. Surrounding a rocky core is what is thought to be a massive ocean—though one unlike you might find on Earth. Down there, the heat and pressure keep the ocean in an "in between" state that is highly reactive and ionic.


Unlike Saturn's preening hoops, the 13 rings of Uranus are dark and foreboding, likely comprised of ice and radiation-processed organic material. The rings are made more of chunks than of dust, and are probably very young indeed: something on the order of 600 million years old. (For comparison, the oldest known dinosaurs roamed the Earth 240 million years ago.)


The only spacecraft to ever visit Uranus was NASA's Voyager 2 in 1986, which discovered 10 new moons and two new rings during its single pass from 50,000 miles up. Because of the sheer weirdness and wonder of the planet, scientists have been itching to return ever since. Some questions can only be answered with a new spacecraft mission. Key among them: What is the composition of the planet? What are the interactions of the solar wind with the magnetic field? (That's important for understanding various processes such as the heating of the upper atmosphere and the planet's energy deposition.) What are the geological details of its satellites, and the structure of the rings?

The Voyager spacecraft gave scientists a peek at the two ice giants, and now it's time to study them up close and in depth. Hofstadter compares the need for an ice-giants mission to what happened after the Voyagers visited Jupiter and Saturn. NASA launched Galileo to Jupiter in 1989 and Cassini to Saturn in 1997. (Cassini was recently sent on a suicide mission into Saturn.) Those missions arrived at their respective systems and proved transformative to the field of planetary science.

"Just as we had to get a closer look at Europa and Enceladus to realize that there are potentially habitable oceans there, the Uranus and Neptune systems can have similar things," says Hofstadter. "We'd like to go there and see them up close. We need to go into the system." 

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ESO / M. Kornmesser
Astronomers Discover Another Earth-Like Planet Near Our Solar System
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ESO / M. Kornmesser

Astronomers with the European Southern Observatory (ESO) have discovered an exoplanet orbiting a star just 11 light-years from our own Sun. It's roughly the size of Earth and is predicted to have a temperate climate, making it the second-nearest Earth-like planet known to exist.

As reported in the journal Astronomy & Astrophysics [PDF], the planet, dubbed Ross 128 b, circles the inactive red dwarf star Ross 128. Its orbit is 20 times closer to its star than Earth's is to the Sun, but the exoplanet receives only 1.38 times more radiation than we do. Ross 128 is much cooler than our Sun, and calmer than typical red dwarfs. Researchers estimate the planet's equilibrium temperature to be between -76°F and 68°F, making it temperate like our home planet.

The discovery was made by an international team of astronomers working with the ESO's High Accuracy Radial Velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile. Popular Mechanics reports that instead of waiting for the exoplanet's shadow to pass across its star (what's known as the transit method), the scientists monitored the star's radial velocity. The gravitational pull of orbiting planets can cause their stars to wobble slightly, and by measuring these disturbances, researchers can estimate everything from a planet's mass to its location.

At just 11 light-years away, Ross 128 b is close, though not close enough to make it our nearest Earth-like neighbor. That title belongs to Proxima b, a planet similar in size, mass, and temperature to Earth that orbits the star Proxima Centauri. But Ross 128 is creeping closer to Earth, and in just 79,000 years, it could occupy the No. 1 slot. In the meantime, scientists will study Ross 128 b along with other close exoplanets to determine if they can support life.


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