Download Trans Neptunian Objects (TNOs)

2.1a
describe the location and nature of the main constituents of our Solar
System, including planets, dwarf planets, asteroids, comets, centaurs and
Trans Neptunian Objects (TNOs)
ASTEROID BELT
TRANS NEPTUNIAN
OBJECTS
CENTAUR REGION
CERES
ROCKY DWARF PLANETS
PLUTO
COMET PATH
ERIS
MERCURY
VENUS
EARTH
MARS
JUPITER
ROCKY INNER
PLANETS
SATURN
URANUS
NEPTUNE
GAS OUTER PLANETS
OUR SOLAR SYSTEM
NOT TO SCALE
Picture credit : (Sun) SOHO-ESA&NASA
The 8 planets of the Solar System are clearly divided between the 4 inner, smaller,
rocky planets and the 4 outer, much larger, gas planets. The inner planets orbit the
Sun at faster speeds and within a two year period. Temperatures are warmer, being
closer to the Sun and there are few moons (only three). All the outer planets have
ring systems, are very cold and have large numbers of moons in orbit around them.
There is a gap where a planet had been thought to orbit the Sun between the orbits
of Mars and Jupiter. This planet is now known not to have ever existed. In the early
Solar System, small pieces of rock would have collided and merged together
(ACCRETION). These rocks, coming close to the gravity of Jupiter, speeded up so
when they collided with others, they were broken apart to create smaller pieces.
These lumps of rock make up the asteroid belt, formed in an orbit between Mars and
Jupiter. Collisions with other celestial objects caused some to fly off in new
directions and cross Earth’s orbit.
Satellite views of asteroids
Picture credit : Galileo Project, JPL and NASA
The asteroid Ida shown with a small asteroid Dactyl which acts as its moon
Picture credit : NASA/JPL
Views of the asteroid Kleopatra (217 km long)
If all the material so far discovered in the asteroid belt was packed together, a planet
with a diameter no bigger than 1,500 km would be formed.
When Pluto was found to be smaller than some of the objects being discovered in
the Kuiper Belt, the classification of a dwarf planet was given to objects of
substantial size, but not big enough to be labelled a planet (on 24th August 2006).
Pluto is substantially smaller than Mercury and objects of the order of size of Pluto
were therefore named as dwarf planets. This left the largest asteroid Ceres as a
dwarf planet as it was big enough (974 km long and 909 km wide) to fit the new
classification.
The Kuiper Belt object that led to the downgrading of Pluto was originally named
Xena, but is now officially called Eris. Eris has a diameter exactly half that of
Mercury and is the biggest dwarf planet so far discovered. The dwarf planet is found
well beyond the orbit of Pluto. One of the 3 co-discoverers of Eris, Mike Brown, has
produced an excellent piece of information about his work, with moving images
showing the way that Eris was first discovered. This can be viewed from the
following link:The Discovery of Eris
http://www.gps.caltech.edu/~mbrown/planetlila/
Web credit : Mike Brown and Caltech
There are many icy/rock objects (planetesimals) in the Kuiper Belt and an area called
the Scattered Disc. If one of these has an orbit that crosses inside the orbit of
Neptune, the object becomes classified as a Trans Neptunian Object (TNO). Pluto is
the biggest TNO. Some of the Kuiper Belt Objects (KBOs) have been dislodged from
their orbits and have ended up wandering in variable orbits where the objects (called
Centaurs) can cross the orbits of Saturn and Uranus – not quite reaching inwards to
Jupiter, or outwards to Neptune. The first Centaur, discovered in 1977, was Chiron.
This was thought to be an asteroid, but has since developed the coma of a comet.
Half asteroid/half comet gave the link to the new group of objects in the Solar
System (the Centaur, in Greek mythology, was half man/half horse). Chiron and
other Centaurs may become short period comets.
The shortest period for all comets is comet Encke, with a period of 3.3 years. The
orbit of the comet around the Sun is so short that it only reaches out into the
Asteroid Belt. Most short period comets (returning within 200 years) fly out to the
Kuiper Belt before returning. This type of comet usually flies close to the plane of
the Solar System. Long period comets appear from any direction as they started life
amongst the Oort Cloud, about 2 l.y. away. These, as with the short period comets,
are made of ice and dust.