Unit 4: A Brief History of Pluto

Pluto has captured people’s imagination for nearly a century.

Register to explore the whole course here: https://school.bighistoryproject.com/bhplive?WT.mc_id=Slideshare12202017

1. BY NOLA TAYLOR REDD
Pluto has captured people’s imagination for nearly a
century.
4
A BRIEF HISTORY
OF PLUTO
From Its Discovery to New Horizons Flyby

2. BIG HISTORY PROJECT A BRIEF HISTORY OF PLUTO 2
The frigid world at the solar system’s outer reaches that was discovered in 1930 re-
mains mysterious to this day: because Pluto is relatively small and so far away, tele-
scopes on and near Earth haven’t been able to take its measure.
But that is changing, and rapidly. NASA’s New Horizons spacecraft is already getting
good looks at Pluto, and will return history’s first up-close photos of the dwarf planet
during a July 14 flyby.
With Pluto’s unveiling on the horizon, here’s a quick look at past and present efforts to
study the elusive world.
THE HUNT FOR THE NINTH PLANET
Irregularities in the orbits of Uranus and Neptune led a handful of astronomers to con-
clude that a ninth planet existed beyond these two “ice giants.”
Chief among these searchers were American astronomers Percival Lowell and William
Pickering. Lowell, who had been enthusiastically investigating the “canals” of Mars,
which he attributed to an alien culture, had constructed an observatory in Arizona to
better study the planets. In addition to observing Mars and Venus, he spent the last
decade of his life searching for the mysterious ninth planet, which he dubbed “Planet
X.”
In March and April 1915, Lowell Observatory managed to photograph Pluto, although
the object remained unrecognized because it was fainter than anticipated. At the time
of Lowell’s death, on Nov. 12, 1916, Pluto still had not been found.
Lowell was not alone in hunting for the ninth planet. Pickering also sought to find the
last planet in the solar system. His calculations for the object’s supposed orbit con-
stantly shifted, however. Though at one point his prediction came close to Pluto’s ac-
tual position, another revision led him to look elsewhere, and Pluto continued to elude
him.
Lowell’s death left the observatory with significant funds to continue the search. Legal
issues regarding his will ended up consuming much of the money, however, temporar-
ily halting the search for the unseen Planet X.
In 1929, Clyde Tombaugh arrived at Lowell Observatory from his Kansas home. An am-
ateur astronomer, Tombaugh had no formal education or training, but he had im-
pressed the head of the observatory. Tombaugh soon began a painstaking search for
the predicted ninth planet.
For 10 months, Tombaugh photo-
graphed the night sky. Using a tool
known as a blink comparator, he
studied images two at a time,
searching for movement between
the plates that would point to Low-
ell’s missing planet. On Feb. 18,
1930, Tombaugh spotted a small,
faint object beyond the orbit of Nep-
tune. The discovery of the elusive
Planet X was officially announced
on March 13, 1930 — Percival Low-
ell’s birthday.
Suggestions poured into the obser-
vatory about what to name the solar
system’s newest known member.
Ultimately, the proposal of an
11-year-old English girl named Vene-
tia Burney made the cut, and the
ninth planet took its name from the
Roman god of the underworld.
Studies eventually showed that Pluto doesn’t have the mass necessary to interfere
with the orbits of Uranus and Neptune. The errors in calculation that helped lead to its
discovery were later attributed to an incorrect mass estimate for Neptune, a value that
was refined by NASA’s Voyager 2 mission.
THE MOONS OF PLUTO
For decades, Pluto seemed like the sole occupant of the outer solar system.
Then, on June 22, 1978, American astronomer James Christy noticed that what ap-
peared to be a sizable bump on Pluto changed positions. A series of photos from 1970
showed that the bump — which Christy realized must be a satellite — traveled around
Pluto once every six days. Named Charon, after the ferryboat pilot who takes the dead
into Pluto’s domain in Greek mythology, the big moon provided the break scientists
needed to finally understand Pluto itself.
With the help of Charon, astronomers were finally able to pin down a mass and radius
Percival Lowell observing Venus at the Lowell
Observatory, Flagstaff, Arizona.

3. BIG HISTORY PROJECT A BRIEF HISTORY OF PLUTO 3
for Pluto. They also managed to calculate a mass and radius for Charon, determining
that it is about half the diameter and one-seventh the mass of Pluto. This makes Pluto-
Charon the largest planet-moon system in the solar system.
The center of mass for the pair actually lies outside of Pluto, at a point between the
two bodies. As a result, many astronomers regard Pluto-Charon as a double dwarf
planet system.
Pluto and Charon lie so far away from Earth, at the outer edges of the solar system,
that astronomers were unable to resolve them as two bodies until NASA’s Hubble
Space Telescope studied them in 1990.
Charon remained the only known satellite of Pluto for nearly 30 years. Then, scientists
turned their attention back to the dwarf planet in search of moons that could cause
problems for New Horizons, which launched in January 2006. As a result, Hubble
spotted the two small moons Nix and Hydra in 2005. Researchers using Hubble also
discovered two additional tiny satellites, eventually named Kerberos and Styx, in 2011
and 2012, respectively.
Anticipation mounted as New Horizons began closing in on Pluto earlier this year, and
many wondered if more small, hidden moons might be found around the dwarf planet.
But on July 2, the mission team sounded the all-clear, announcing that no new moons
had been found around Pluto. The lack of new satellites means that the spacecraft will
stay on its original course through the dwarf planet system and serves as an impres-
sive reminder of Hubble’s capabilities.
THE KUIPER BELT
After Pluto’s discovery in 1930, many scientists speculated about the existence of oth-
er small, icy bodies in the outer solar system. Compared to its neighbor Neptune and
the other gas giants, Pluto seemed to stand out.
Despite these speculations, it wasn’t until 1992 that astronomers David Jewitt and
Jane Luu discovered a second small, icy body in the neighborhood of Pluto. Six
months later, they had found a third. Within a handful of years, the once-empty region
of space beyond the ninth planet quickly filled with a population of small, icy rocks.
Tombaugh’s discovery ultimately became the first of an entirely new part of the solar
system dubbed the Kuiper Belt, after astronomer Gerard Kuiper. Ironically, though Kui-
per speculated that such a distant disc of objects might have formed in the early solar
system, he did not think it remained.
The Kuiper belt was the beginning of Pluto’s downfall as a planet. Today, there are
thought to be hundreds of thousands of icy bodies larger than 62 miles (100 kilome-
ters) wide in the Kuiper Belt, and more than a trillion comets.
In 2005, astronomers discovered a large, Pluto-size object eventually named Eris or-
biting in the belt. At first, Eris was hailed as the 10th planet. However, in a controver-
sial 2006 ruling, the International Astronomical Union revised the definition of a plan-
et, reclassifying Pluto and giving it the status of “dwarf planet.” Both Eris and
asteroid-belt occupant Ceres received the same title.
In addition to Eris, two other dwarf planets were later discovered. In 2008, both Make-
make and Haumea were classified as dwarf planets in the Kuiper Belt region.
The reclassification of Pluto raised a great deal of ire when it happened, and feelings
continue to run high today. Some people speculate that the upcoming visit by New Ho-
rizons could help Pluto regain its status as a full-fledged planet.
NEW HORIZONS
On July 14, 2015, the New Horizons probe will make the first-ever close approach of
Pluto. The spacecraft should provide an unprecedented view of the double dwarf plan-
et system.
The orbits of Pluto and its moons Charon, Styx, Nix, Kerberos and Hydra are illustrated around
their common center of mass.

4. BIG HISTORY PROJECT A BRIEF HISTORY OF PLUTO 4
When New Horizons launched from Florida on Jan. 19, 2006, Pluto still reigned as a
full-fledged planet. It took nine and a half years for the spacecraft to make the journey
to the outer edges of the solar system. Along the way, New Horizons performed flyby
observations of Jupiter and its moons in 2007, when the massive planet gave the
spacecraft a gravity boost.
At the end of May 2015, New Horizons reached the range where its photos were as
sharp as images taken by the Hubble telescope. Throughout June, images that sur-
passed those captured by the space telescope were released to the public almost daily,
introducing people to the dwarf planet that had once been merely a blur of pixels.
Chief among the surprises was the strong difference in coloration between Pluto and
its largest moon, Charon. While Pluto is reddish brown, Charon has shown itself to be
quite gray. The craft has gathered images showing the changing faces of the two, in-
cluding unusual poles and puzzling spots.
On July 4, the spacecraft suffered a heart-skipping anomaly that caused the craft to
enter safe mode only 10 days before its closest approach. The problem turned out to
be a timing flaw in the command sequence of the craft — one that should not be re-
peated. While some science studies were lost, the team announced that the primary
objectives of the mission were not affected. New Horizons returned to normal science
operations on July 7.
The close approach images that New Horizons returns to Earth will be inspiring, but
they will not represent the end of the mission. The spacecraft will continue beaming
data home from the flyby for months, and planetary scientists will work to understand
the significance of the data for years to come.
And New Horizons will continue to cruise the outer edges of the solar system. The
mission team has proposed a mission extension that would — if approved and funded
by NASA — send the probe to fly by a second Kuiper Belt object in 2019.
The path of New Horizons from Earth towards Pluto and beyond into the Kuiper Belt. Dwarf
planets Eris, Makemake, Haumea also shown.
This composite of enhanced color images of Pluto (lower right) and Charon (upper left), was
taken by NASA’s New Horizons spacecraft as it passed through the Pluto system on July 14,
2015. Shown with approximately correct relative sizes, but their true separation is not to scale.

5. BIG HISTORY PROJECT A BRIEF HISTORY OF PLUTO 5
About the Author
Nola Taylor Redd is a contributing writ-
er for Space.com. She loves all things
space and astronomy-related, and en-
joys the opportunity to learn more. She
has a Bachelor’s degree in English and
Astrophysics from Agnes Scott college
and served as an intern at Sky & Tele-
scope magazine. In her free time, she
homeschools her four children.
Source
Space.com http://www.space.
com/29911-pluto-exploration-history-
new-horizons.html
Cover image: Artist’s concept of the
New Horizons spacecraft as it ap-
proaches Pluto and its largest moon,
Charon, in July 2015. The craft’s minia-
ture cameras, radio science experiment,
ultraviolet and infrared spectrometers
and space plasma experiments will
characterize the global geology and
geomorphology of Pluto and Charon,
map their surface compositions and
temperatures, and examine Pluto’s at-
mosphere in detail. Credit: Johns Hop-
kins University Applied Physics Labora-
tory/Southwest Research Institute
(JHUAPL/SwRI). Public Domain. http://
pluto.jhuapl.edu/Multimedia/Images/
Artist-Renderings.php
Image of Percival Lowell observing Ve-
nus in the daytime from the observer’s
chair of the 24-inch (61 cm) Alvan Clark
& Sons refracting telescope, installed in
the summer of 1896 at the Lowell Ob-
servatory, which he established in Flag-
staff, Arizona (USA). Public domain.
https://en.wikipedia.org/wiki/
File:Percival_Lowell_observing_Ve-
nus_from_the_Lowell_Observatory_
in_1914.jpg
Image of the orbits of Pluto and its
moons Charon, Styx, Nix, Kerberos and
Hydra are illustrated around their com-
mon center of mass. Credit: SwRI/S.
Porter. Public Domain. https://blogs.
nasa.gov/pluto/2015/10/05/plutos-
small-moons-nix-and-hydra/
The path of New Horizons with dwarf
planets Pluto, Eris, Makemake, and
Haumea. Credit: NASA/HUAPL/SwRI/
Alex Parker. http://pluto.jhuapl.edu/
Participate/learn/What-We-Know.
php?link=The-Kuiper-Belt
Image of Pluto and Charon taken by NA-
SA’s New Horizons spacecraft as it
passed through the Pluto system on
July 14, 2015. Credit: NASA/JHUAPL/
SwRI. http://www.nasa.gov/feature/
pluto-s-big-moon-charon-reveals-a-
colorful-and-violent-history