Far out! New Horizons space probe gets first close-ups of
mysterious Pluto
By Scientific American, adapted by Newsela staff
08.06.15
At 8:52 in the evening, the New Horizons control center in Maryland received radio
confirmation from the most distant reaches of our solar system. The space probe, now world
famous, let the team back on earth know it had survived its closest approach to Pluto. The New
Horizons spacecraft successfully passed 12,500 kilometers above Pluto's sunlit hemisphere.
This was just one of the achievements that New Horizons can boast. Its mission to Pluto
sent the spacecraft to the most distant object ever visited, the first trip to the Kuiper Belt of icy
worlds that ring the outer solar system. It was also the fastest spacecraft launched.
Pluto: "The People's Planet"
What really makes the New Horizons mission a triumph, however, is that it ever
happened at all. Funding to pay for the mission had been drying up and the mission had been all
but shelved. But public support was strong and this is what ultimately got it over the line. Pluto
could be called the “People’s Planet.”
Even before scientists knew anything substantial about Pluto, they were convinced it was
a fascinating place. Observations in the 1950s had shown that its surface varies widely in
brightness. In the mid-1990s the Hubble Space Telescope created a very coarse map, with a
resolution of 500 kilometers, revealing little other than some light and dark regions. At the very
least, this indicated some degree of geologic activity like ice or craters. The New Horizons
mission has added so much more information to Pluto's story.
Scientists at the control center at the Applied Physics Laboratory of Johns Hopkins
University in Maryland have examined the last image the spacecraft sent before going into radio
silence. With a resolution of four kilometers, it merges a gray-scale image with a lowerresolution color one taken earlier in the day. It shows the hemisphere of Pluto that faces away
from its main moon, Charon. On the surface of Pluto there appears to be a heart-shaped area. The
scientists believe it may be an icy region. The two sides of the heart have two distinct colors
which indicates different chemical compositions.
More Pictures To Come
New Horizons is not finished beaming back images. It is scheduled to send more in even
higher resolutions, including images of three of Pluto's five moons.
The New Horizons mission has led to a revision of earlier estimates of the planet's size.
Now scientists believe Pluto’s diameter is about 3 percent wider than previously thought, making
the "dwarf" planet larger than the next object beyond Neptune when traveling away from the sun.
This information sheds new light on the planet's atmosphere too. The lowest layer of Pluto's
atmosphere (the troposphere) is much thinner than thought — a kilometer or two, at most.
The spacecraft was equipped with a number of different measuring devices, including a
particle detector, which picked up evidence of nitrogen molecules. The molecules must have
escaped from Pluto’s atmosphere but were much farther from the planet than had been predicted.
It is unclear how they could have strayed so far from the atmosphere but one theory connects it
with variations in the solar wind washing over the outer atmosphere.
Pluto's Fab Five Moons
Images have showed no new moons beyond the five already known about. These are
called Charon, Hydra, Nix, Styx and Kerberos. Nix and Hydra are 30 to 50 kilometers in
diameter, the first size measurements of these bodies.
Images from the spacecraft also confirm the difference between the varied and active
surface of Pluto and the darker, grayer, cratered terrain of its largest moon Charon. “Now we see
how dramatically different they really are," said New Horizons principal investigator Alan Stern
of the Southwest Research Institute in Colorado. "These images show a much younger surface on
Pluto and an older, more battered surface on Charon." Pluto appears to have craters that have
been filled in and are now smooth areas.
It is also now clear that Pluto is quite different from Neptune’s moon Triton. For a long
time researchers considered the two to be similar. “It’s unbelievable how alien this place is,”
Stern said. For example, it is much redder than Triton, so much so that its surface evokes that of
Mars. Charon’s polar cap is also oddly reddish. These surfaces presumably take their color from
hydrocarbons that have been baked by solar radiation, creating dark tars known as “tholins.”
Powered By Plutonium, Of Course
The most recent flyby is only the beginning of New Horizon’s overall mission. The probe
will also study Pluto’s moonlit night side and search for planetary rings backlit by the sun. In
September the spacecraft will begin downloading all the information it has gathered to radio
telescopes on Earth at a rate of about two kilobits per second. This is equal to a 1980s-era dial-up
internet modem so will take 10 weeks, even in a compressed low-fidelity format.
Thanks to its plutonium power source, an element which was of course named after the
planet, New Horizons still has enough juice to operate though the 2030s. By then it will be about
twice as far from the sun as it is now. Eventually it will leave our solar system entirely and join
NASA’s four other spacecraft that are also headed to or already in interstellar space: Pioneers 10
and 11, and Voyagers 1 and 2.
Instructions:
In your journal, using Cornell note style (2-column notes)
Define the bold faced words
Answer the following questions:
1. Why could Pluto be called “The People’s Planet”?
2. What are three new pieces of information New Horizon’s has shown?
3. What element is named after Pluto?
4. Where will New Horizon’s end up eventually?