DWARF PLANETS

DWARF PLANETS

From : http://lasp.colorado.edu/education/outerplanets/kbos_dwarfplanets.php
From : http://www.librarising.com/space/ceres.html

Difference Planet and Dwarf Planet


Planet define as celestial body that:

• Is in orbit around a star, but is not itself a satellite*
• Has sufficient mass so it is nearly spherical in shape*
• Has cleared the neighborhood around its orbit*

Dwarf Planet define as celetial body that:

• Is in orbit around a star, but is not itself a satellite*
• Has sufficient mass so it is nearly spherical in shape*
• Has not cleared the neighborhood around its orbit*

Dwarf Planets





Orbit Dwarf Planets



 
Dwarf Planet


Pluto

For 76 years (until 2006), Pluto was known as the ninth planet in our solar system. Since then, Pluto has been relegated to dwarf planet status. Discovered in 1930, Pluto is a member of the outer region of our solar system known as the Kuiper belt. It has a highly inclined and eccentric 248-year orbit around the Sun. As the second-largest known dwarf planet, Pluto is approximately 2,390 km in diameter and is composed primarily of ice and rock. It is very difficult to precisely determine the diameter of Pluto since it is so far away. Pluto is, on average, 40 times farther from the Sun than Earth.



Pluto's Moons

In 1978, the discovery of Pluto's largest moon, Charon, gave scientists an opportunity to learn more about Pluto. The two icy objects eclipsed each other from Earth's point of view from 1985-1990 allowing scientists to more precisely determine their diameters and masses. At approximately 1,186 km, Charon's diameter is just less than half of Pluto's. Pluto is also eight times more massive than Charon.



Two more moons were discovered orbiting Pluto in 2005. Nix and Hydra are considerably smaller than Pluto and Charon, at only 40 km and 160 km in diameter, respectively. Nix orbits Pluto at 48,700 km from the center of mass of the system, more than twice the orbital distance of Charon. Hydra is the outermost of Pluto's satellites, orbiting at 64,800 km from the center of mass of the Plutonian system.

Charon, Nix and Hydra Orbit



Ceres

Italian astronomer Giuseppe Piazzi discovered Ceres in 1801. First classified as a planet, Ceres was later catalogued as an asteroid. With the discovery of Eris in 2005, after 150 years as the head of the asteroid belt, Ceres became the solar system's smallest dwarf planet. Ceres is still the largest, and by far the most massive member of the asteroid belt. The diameter of Ceres is about 950 km and it alone makes up one third of the asteroid belt's total mass.



Ceres Orbit



Ceres Size Compared To Our Moon



Eris

Discovered in 2005, Eris is now the largest known dwarf planet in our solar system. Its diameter is estimated at 3000 km, and it weighs roughly 1.66 x 1022 kg, which is about 27% more massive than Pluto. Like Pluto, it is very difficult to make precise measurements of Eris' diameter and mass, but these are the most updated estimates.


Hubble Image

Eris orbits the Sun at the far reaches of our solar system in an area known as the scattered disk. Scattered disk objects (SDOs) tend to have highly inclined and eccentric orbits. Eris' orbit is tilted at an angle of 44 degrees with respect to the ecliptic. You can see from the picture how much more inclined this is compared to Pluto's orbit, which is tilted only 17 degrees to the ecliptic. Eris' orbital period is just over 556 years. Currently, at a distance of about 97 AU, Eris is at aphelion. It won't be closest to the Sun, at perihelion, until March 2257.




























Sedna
From : http://www.cosmosportal.org/topics/view/11910/
From : http://www.daviddarling.info/encyclopedia/S/Sedna.html



The most distant large object yet found orbiting the Sun and a candidate, but not an official, dwarf planet. It is currently 88 AU from the Sun, about three times farther than Neptune. Its classification remains uncertain – some researchers claim it is a detached Kuiper Belt object, while others suspect it might belong to the Oort Cloud. Sedna, named after the Inuit goddess of the ocean, is currently three times further away than Pluto, the average distance of which from the Sun is 5.9 billion km (3.6 billion miles). At its most distant, Sedna is almost 150 billion km (93 billion miles) from the Sun, or 990 times Earth's solar distance. It has an obital period, or year, of some 10,500 years. Its surface temperature is believed to be about -240°C (-400°F).

Sedna, originally designated 2003 VB12, was first seen on Nov. 14, 2003 with the 48-inch Samuel Oschin Telescope at California's Mount Palomar Observatory. Astronomers from the California Institute of Technology, Yale University, and the Gemini Observatory were involved in the discovery. Observations show it measures less than 1,700 km (about 1,000 miles) in diameter, which is smaller than Pluto. Sedna has a high albedo and very red – the reddest large object in the Solar System after Mars. Its size suggests it should not be classified as a true planet, although there is disagreement among astronomers on this point and there are no hard and fast rules about what counts as a planet, planetoid, or minor planet. Sedna rotates more slowly on its axis than expected, suggesting it may have a satellite orbiting it.


Sedna Orbit