Download What is a planet? - The Science Queen

What is a planet?
Technically, there was never a
scientific definition of the term Planet
before 2006. When the Greeks
observed the sky thousands of years
ago, they discovered objects that
acted differently than stars. These
points of light seemed to wander
around the sky throughout the year.
We get the term "planet" from the
Greek word "Planetes" - meaning
wanderer.
What is a planet?
In the 1600's scientists began to use telescopes
to view our solar system.
As technology got better, scientists discovered
more planets orbiting our Sun such as Uranus in
1781, Neptune in 1846 and Pluto in 1930.
Then, in 1991, advances in telescope technology
enabled scientists to discover many more objects
in a disk-shaped cloud beyond Pluto called the
Kuiper Belt. These objects were classified as
Kuiper Belt Objects (KBO) partly because they
are smaller than Pluto. This classification of KBO
seemed to work fine as long as objects weren't
bigger than Pluto.
Eris, the Goddess of Discord
It was the recent discovery of an object larger than Pluto
within the Kuiper Belt that changed everything.
Is this object, now named Eris, our 10th planet since it is
larger than Pluto?
This discovery and the naming of this new object prompted
the IAU to discuss a scientific definition for the term planet.
What if Eris is given planet status? Then our solar system
could grow to dozens of planets as more and more Kuiper
Belt Objects are discovered. Try remembering all those planet
names. But if Eris is not a planet, then is Pluto still a planet?
What is a planet?
Astronomers of the International Astronomical Union
(IAU) voted on and passed the first scientific
definition of a planet in August 2006. According to
this new definition, an object must meet three
criteria in order to be classified as a planet.
What is a planet?
1. It must orbit the Sun.
2. It must be big enough for gravity to squash it into a
round ball.
3. It must have cleared other objects out of the way in
its orbital neighborhood.
•
To clear an orbit, a planet must be big enough to pull
neighboring objects into the planet itself or sling-shot
them around the planet and shoot them off into outer
space.
The problem for Pluto
The problem for Pluto is the fact that its orbit is in
the Kuiper Belt along with 43 other known Kuiper
Belt Objects (KBOs).
Dwarf Planet Definition
1. It is in orbit around the Sun
2. It has sufficient mass for its self-gravity to
overcome rigid body forces so that it assumes a
hydrostatic equilibrium (nearly round) shape
3. It has not cleared the neighborhood around its
orbit.
4. It is not a satellite (a moon)
Pluto
Pluto is the second closest
dwarf planet to the Sun
Discovered in 1930 by Clyde
W. Tombaugh in Flagstaff.
It was considered the 9th
planet until 2006.
It is the second largest dwarf
planet.
Pluto Day = 6.4 days
Pluto Year = 248 years
Pluto
Pluto has 5 moons: Charon, Styx, Nix, Kerberos and
Hydra
Charon is the largest of the moons.
Charon is also so large that Pluto-Charon are
sometimes considered a double object, a double
dwarf planet or a binary system.
Pluto
In Roman mythology, Pluto (Greek: Hades)
is the god of the underworld.
In Greek mythology, Charon is the ferryman of
Hades who carries souls of the newly deceased
across the rivers Styx and Acheron that
divided the world of the living from the world
of the dead.
Styx -river that formed the boundary between
Earth and the Underworld.
Nix - Greek goddess of the night
Kerberos – Greek name for Cerberus – three
headed hellhound.
Hydra - gigantic, nine-headed water-serpent
killed by Hercules
New Horizons Mission
•New Horizons launched on Jan. 19, 2006
•Pluto closest approach on July 14, 2015.
•It takes one-way radio transmission from
Pluto to Earth in July 2015: 4 hours, 25
minutes.
Eris
Eris is the largest dwarf planet in the
Solar System, exceeding Pluto’s mass
by 28%.
Eris is the object the precipitated the
definition of the category "dwarf
planets" and the demotion of Pluto.
Eris (Latin Discordia) is the Greek
goddess of strife and discord.
Revolution (Year) : 561.4 Earth Years
Rotation (Day) : 25.90 hours
Ceres
Ceres is by far the largest of the
asteroids, comprising more than a
third of the total mass of the main
asteroid belt.
Ceres is also the smallest of the
dwarf planets.
Discovered in 1801 by Guiseppe
Piazzi.
Visited in 2015 by the NASA Dawn
Mission.
Rotation (Day) – 9.1 hours
Revolution (Year) – 4.6 Earth Years
MakeMake
Discovered in 2005 by a team of
astronomers at the Palomar Observatory in
San Diego.
One of the largest known objects in the
outer solar system, just slightly smaller and
dimmer than Pluto. Scientists think it is
about two-thirds the size of the more wellknown dwarf planet.
It orbits beyond the range of Pluto, but
closer to the sun than Eris.
Makemake is named for the god of fertility
in Rapanui mythology. The Rapanui live on
Easter Island in the southeastern Pacific
Ocean.
Rotation (Day) – 22.5 hours
Revolution (Year) – 310 Earth Years
Haumea
Discovered in 2003 by a team of astronomers
at the Palomar Observatory in San Diego.
Haumea is the third closest dwarf planet from
the Sun and is unique in its elongated shape
making it the least spherical of the dwarf
planets.
Named for the Hawaiian goddess of childbirth
and fertility. Its two moons were named for
daughters of the goddess, Hi'iaka and
Namaka.
Rotation (Day) – 3.9 hours
Revolution (Year) – 281 Earth Years
References
http://missionscience.nasa.gov/nasascience/what_i
s_a_planet.html
http://nineplanets.org/pluto.html
http://theplanets.org/pluto/
http://pluto.jhuapl.edu/NewsCenter/Resources/PressKits/NHPlutoFlybyPressKitJuly2015.pdf
http://www.space.com/23122-makemake.html