| |
Jump
to: Page 1: Intro,
The Surface, Page 2: Composition,
Brief
History, Something Cool, Note
INTRO:
Pluto, being one of the two planets that cannot be seen without a telescope,
is the only planet discovered in the 20th century. It is also the most distant and smallest planet in the solar system. Just how small is Pluto? Seven moons in the solar system are bigger than Pluto- our own Moon, Io, Europa, Ganymede, Callisto, Titan, and Triton. Pluto is so far away from the sun that the sun is barely less than a minute of an arc on Pluto, looking more like a bright star or distant street light than the Sun. The brightness of the sunlight on Pluto is about .15 the brightness on Earth. Not much is known about Pluto because of its distance away from Earth, but scientists believe that it has a diameter of approximately 1,430 miles, or 2,300 kilometers and combined with its moon, Charon, have a mass of approximately 1.27 x 10e22 kilograms,
about one fifth of Earth's size. Pluto's mass, excluding Charon, is hard to confirm. Temperatures on the surface of the planet range from -387° Fahrenheit
to -369° Fahrenheit, about -233° Celsius to
-223° Celsius. Because those are some of the coldest
temperatures in the solar system, scientists believe that Pluto
consists of mainly of ice or frozen methane, with is concentrated at
the poles.
  |
Picture of Pluto (left)
and Charon (right) taken by the Hubble Space Telescope.
top... |
THE SURFACE:
The
surface of Pluto is mostly icy. With a density between 1.8 and 2.1
g/cc, Pluto is believed to be 50% to 75% rock; the rest composed of
ice. Nitrogen (98%), solid methane and carbon monoxide make up the
surface. Because of the solid methane, scientists believe that the
surface temperature of Pluto never reaches above 70 Kelvin.
Pluto's
temperature depends greatly on its orbit. Pluto comes as close as 30
A.U. to the Sun and as far as 50 A.U. away from the Sun. As Pluto's
orbit takes it away from the Sun, its atmosphere actually freezes
and falls to the ground. Only when Pluto is in perihelion is the
atmosphere in gas form. The bright areas of Pluto's surface
are believed to be ices of nitrogen and smaller amounts of methane,
ethane, and carbon monoxide. The dark areas may be due to primordial
organic material or photochemical
reactions. Obviously, mankind has
never reached Pluto. However, in 2001, NASA plans to launch the
Pluto-Kuiper Express to study Pluto.
The first image-based surface map of Pluto, taken by the Hubble Space Telescope.
Pluto's surface is not uniformly dark or bright,
comprising of many different materials with different chemical compositions and
reflectivity. In fact, Pluto's brightness can vary depending on
its rotation.
The bright areas on
Pluto's surface are believed to be a smorgasbord of solid
nitrogen and other molecules like methane and carbon monoxide.
Nitrogen tends to form crystals in laboratories on Earth. Because of
this, scientists believe that the nitrogen on Pluto's surface
must "anneal and sinter" into large semi-transparent
chunks (in more scientific terms- expanses). Because nitrogen has a
transition temperature (meaning it changes phases at this
temperature) of 35.6 K, the nitrogen ice may sometimes change into
liquid state when Pluto reaches its perihelion epoch. The
temperature when this usually occurs is around 40 K. This change in
phase causes physical and optic disruptions in Pluto's
nitrogen ice surface. Underneath all these chunks of nitrogen, it is
believed that there is some methane, and possibly carbon monoxide,
trapped. Because of Pluto's diurnal and seasonal cycles, the
distribution of this smorgasbord varies.
The darker region of Pluto, with a lower
albedo and red color, has a higher temperature. These darker areas
tend to be near the equator of Pluto. The composition of these dark
areas are not known, but are believed to be made up of refractory
organic solids produced by photochemistry of the ice molecules and
atmosphere and material from outside sources and bombardment of
cosmic rays. The polar caps appear to be made up of nitrogen ice.
Scientists also believe patches of pure methane may exist on
Pluto's surface where the temperature is higher.
Pluto has the second largest surface
contrast (The first is Iapetus). Pluto's brightness varies
about .35 mag. When Charon started shading Pluto during the mutual
event season in the 1980s, scientists were able to finally map the
locations of the albedo markings on Pluto's surface (at least
on one side of Pluto's surface because the same faces of Pluto
and Charon face each other all the time.) The Hubble Space Telescope
allowed for a more accurate map to be created. Although the
telescope did not offer as high a resolution as the mutual event, it
did allow scientists to view the other side of Pluto, providing
global coverage. The telescope was the first to show polar caps and
large spots around the equator. Pluto's surface reflectivity
varies from the 40 to 60 percent.
Unfortunately, the Hubble Space Telescope
was not able to get clear pictures of Charon. Using mutual event
data to map one hemisphere and rotational lightcurve (don't
ask) information to guess the other hemisphere, scientists believe
Charon has less than 0.1 mag variation on its surface.
Charon's surface is, therefore, more uniform. Charon
reflectivity is around 40 percent.
|
|
