Dwarf Planets
In 2006, the International Astronomical Union (IAU) made a
decision that changed the way we organize our solar system. The
IAU announced the removal of Pluto from the list of planets.
They reclassified Pluto as a dwarf planet. Instead of nine, we
now have only eight planets in our solar system.
Q How is a dwarf planet different from
other planets?
A According to the IAU’s new definition,
a planet is a space object that orbits the Sun
and has a nearly round shape. Its gravity must
be strong enough to clear all other space
objects (except satellites) out of its orbit.
Dwarf planets also orbit the Sun and have a
nearly round shape. But other space objects
nearby are not cleared by the gravity of the
dwarf planets. They are not big enough for
their gravitational fields to do this. Dwarf
planets are different from satellites, which
orbit a planet and not the Sun.
Promoted
Since 2006, Ceres is
classified as a dwarf
planet. Before that, it was
simply the largest of the
many asteroids that lie
between the orbits of
Mars and Jupiter.
Pluto’s moon
Pluto (left) and its moon Charon actually go around
each other, rather than Charon going around Pluto.
Scientists may soon reclassify Charon as dwarf planet.
Distant Sun
An artist’s impression of
how the Sun would look
from the surface of Eris,
the furthest of the dwarf
planets in the solar
system. The Sun gives
almost no heat at that
distance and looks like
a bright star.
Q How many dwarf
planets are there in
the solar system?
A Apart from
Pluto, Ceres and
Eris (UB313) have also been classified
as dwarf planets. Until recently, Ceres was
called the largest asteroid. It has a diameter
of about 950 kilometres (600 miles) and is
in the asteroid belt between Mars and
Jupiter. Eris is the largest of all the dwarf
planets. It has a diameter of about
3,000 kilometres (1,850 miles).
Q Are there any other dwarf planets?
A Scientists are considering including
Pluto’s moon Charon among the dwarf
planets. Charon does not actually go around
Pluto – they revolve around each other. The
planetoid Sedna and the asteroids Vesta,
Pallas and Hygiea are also being considered.
Dwarf Planets
19
5
6
8
3
1
2
4
7
9
10
Try these too…
The Sun (10–11), The
Planets (12–13), The
Red Planet (16), The
King of Planets (17),
The Last Planets (18),
The Moon (20–21),
Comets and Asteroids
(22–23), Scientific
Revolution (150–151),
The New Millennium –
21st Century (163)
1 Sun
2 Mercury
3 Venus
4 Earth
5 Mars
6 Jupiter
7 Saturn
8 Uranus
9 Neptune
10 Pluto
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