Hello, Pluto!Hello, Pluto!

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September 2015

Science Newsinthe

Written by Rhonda Lucas Donald

Pluto has a heart! New photos of Pluto show a large heart-shaped formation on the surface. A closer look shows a mountain range on one side of the heart.

Our Favorite Non-Planet

Meet the Moons!

Clyde Tombaugh: The Man Who Discovered Pluto

Clyde Tombaugh: The Man Who Discovered Pluto

Meet the Moons!

Our Favorite Non-Planet

What’s Inside:What’s Inside:

P o w e r e d b y , a d i v i s i o n o f L e a r n i n g A - Z

Credits: Front cover (both), page 2 (all): courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

PlutoNew Horizons

Earth

Neptune

Saturn

Uranus

Mars

Jupiter

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After traveling for more than five billion kilometers (three

billion miles) on a trip that took nine years, NASA’s New Horizons space probe finally reached Pluto. On July 14, 2015, the probe sent back the first close-up photographs ever taken of the dwarf planet. The visit only lasted about twenty hours, but the probe collected so much data that it will take more than a year to send all of it back to Earth.

Getting ThereOn January 19, 2006, New Horizons blasted off from Cape Canaveral, Florida. NASA scientists planned a route to Pluto that would send the probe past Jupiter. The gas giant’s strong gravity sped up the probe. This extra speed helped propel New Horizons to the far reaches of our solar system.

The nine-year trip was mostly smooth sailing until a processing glitch almost put an end to the historic mission. On July 4, 2015, New Horizons went silent just days before it was going to fly by Pluto. While processing big chunks of data, the probe got overloaded and went into backup mode. Its main computer shut down. Back on Earth, NASA scientists scrambled to send the probe instructions to reboot itself, or to turn back on. On July 7, New Horizons was back on track. Whew!

New DiscoveriesDuring its flyby of Pluto, New Horizons mapped and studied the dwarf planet and its five moons. Scientists are only beginning to sift through the massive amount of data. But right away they made some exciting discoveries.

Steep mountains on Pluto suggest that there is a bed of solid ice below the surface. Scientists think the ice might be helping support the large mountains. Both Pluto and its largest moon, Charon, have surfaces that are rugged but not covered with craters. This means that geologic forces, such as volcanic activity or erosion, are at work. These forces are likely reforming the surface constantly and covering over impact craters, as they do on Earth.

New Horizons has now left the Pluto system. The probe is traveling even farther from Earth into the Kuiper Belt. There, it will encounter thousands of unexplored rocky, icy objects in the far reaches of our solar system. v

September 2015

New Horizons Reaches Pluto

An artist’s drawing shows New Horizons approaching Pluto.

New Horizons crossed the orbits of five planets on its journey from Earth to Pluto.

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To honor Clyde Tombaugh, the astronomer who discovered Pluto, scientists named the heart-shaped feature on the surface Tombaugh Regio. A regio is a region on a space object that has different coloration from the surrounding area.

Tombaugh Regio

Credits: top: © AP Images; bottom (both): courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

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Growing up on a Kansas farm, Clyde Tombaugh was so fascinated with outer

space that he made his own telescope. He used it to make detailed drawings of Jupiter and Mars. Then he sent his drawings to the Lowell Observatory in Arizona. The scientists there were so impressed that they offered him a job. His keen observational skills were perfect for a very tough task. He was asked to find a planet that astronomers thought existed but had yet to confirm.

Tombaugh looked for what they called Planet X by taking photos of the sky a few days apart and then comparing them. The background stars would stay in place, but any orbiting object would appear to move between the images. On February 18, 1930, Clyde found what he was looking for. He discovered the ninth planet in our solar system! But what should it be called?

In England, eleven-year-old Venetia Burney heard about the new planet. She knew the other planets were named for gods in myths. Pluto was the god of the underworld and seemed like a good name for this new, faraway world. Her grandfather passed the idea on to an astronomer friend, and the rest is history. v

Much about Pluto’s five moons has been a mystery for decades.

New Horizons is getting the first good look at them, and they are full of surprises.

The first image of Charon, Pluto’s largest moon, shows that it has cliffs and deep canyons that are much deeper than Earth’s Grand Canyon. At Charon’s north pole is a very dark splotch. And like Pluto, Charon has few craters.

For the first time, we can see the shape of the moon Hydra. It is oblong, or stretched in shape, and measures about 45 kilometers (28 mi.) long.

As New Horizons passed through the Pluto system, it also got a look at Nix, Styx, and Kerberos. Pluto and its moons are all named for mythical characters or features of the ancient Greek underworld. v

September 2015

Clyde Tombaugh The Man Who Discovered Pluto

Meet the Moons!

This image shows the surface of Charon.

New Horizons gave us our first look at Pluto’s moons Nix and Hydra.

Clyde Tombaugh in 1931 with the telescope he used to discover Pluto

NixHydra

Charon

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Credit: courtesy of NASA

Writ

ing

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Until 2006, Pluto was considered

the ninth planet in our solar system. But astronomers had found other similar-sized objects in the Kuiper Belt that were not considered planets. So a group of them got together to officially decide what makes a planet a planet.

First, a planet must orbit a star. It must have enough mass and gravity to be spherical (ball-shaped). And it must also have strong enough gravity to either suck in or shove away other objects in its orbit. Astronomers refer to this as “clearing” its orbit. Pluto doesn’t meet this last requirement because several objects that are similar in size are nearby.

Now we know that there are numerous rocky objects similar to Pluto orbiting the Sun in the Kuiper Belt. Three such objects are Eris, Makemake, and Haumea.

So if Pluto isn’t a planet, what is it? It’s now considered to be a plutoid, or dwarf planet. v

Do you agree with the decision that downgraded Pluto from a planet to a dwarf planet? Why or why not?

What Do YOU Think?

September 2015

Here are some of the largest known objects in the Kuiper Belt, along with their smaller moons. Earth is shown for size comparison.

Dysnomia

Eris

Sedna

Earth

QuaoarHaumea

Hi‘iaka

Namaka

MakemakeHydraPluto

Charon

Nix

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