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Dwarf planets are miniature planets, similar to the largest

moons of the major planets, but in orbit around the Sun

in the asteroid belt or beyond Neptune. So far, astronomers

have listed five of them. One is the largest asteroid, Ceres.

The others are icy worlds in orbits past Neptune.

WHY IS PLUTO NOW A DWARF PLANET?

When Pluto was discovered in 1930 it was classed

as a major planet but later it was found to be very

small and unlike any other planet. After astronomers

discovered Eris in 2005 and found it was larger than

Pluto, they decided on a new category of Solar

System worlds, called dwarf planets.

WHAT IS THE KUIPER BELT?

The ring of icy bodies found in the outer Solar System

beyond Neptune is called the Kuiper Belt. Dozens of

Kuiper Belt Objects (KBOs) have been detected using

the world’s most powerful telescopes. Many KBOs end

up circling closer to the Sun and become comets.

FIND OUT MORE. Comets 22 • Solar System 14

ICY EXTREMITIES 3

A computer simulation shows icy lumps at the edge of the Solar

System. The large circle is the Oort Cloud, nearly a light year out from

the Sun, and the horizontal band in the middle is the Kuiper Belt.

DWARF PLANETS

Charon, the largest of

Pluto’s three moons

PLUTO

Pluto

FIND OUT MORE. Earth 16 • Elements 160 • Solar System 14 • Storms 54

Diameter (width) at Equator 49,532 km (30,779 miles)

Average distance from Sun 4,498 million km (2,795 million miles)

Time to orbit Sun 164.8 years

Time to spin around own axis 16.11 hours

Mass 17.2 x Earth’s mass

Gravity 1.13 x Earth’s gravity

Cloud-top temperature -200°C (-328°F)

Number of moons 13

NEPTUNE DATA

Neptune is 30 times farther from the Sun than Earth,

and has the most powerful hurricanes of any planet

in the Solar System. It is a gas giant with faint rings.

. TRITON is the largest of its 13 known moons.

WHAT IS NEPTUNE MADE OF?

Neptune’s atmosphere is made of hydrogen, helium,

and methane, flecked with wisps of white clouds.

The methane gas makes the planet appear deep blue.

Underneath, there is a vast liquid mantle and

a small core of silicate rock at the centre.

WHAT IS TRITON’S SURFACE LIKE?

Triton’s beautiful frozen surface is covered with icy

craters and pinkish snow. In some regions, jets of

nitrogen gas erupt like geysers and carry fine dust

in the wind. This dust then falls and settles on the

ground in dark streaks.

Similar to the dwarf Pluto, Triton is

Neptune’s largest moon. It has the coldest

surface in the Solar System, -235°C (-391°F).

TRITON 3

Triton is the only

large moon in the

Solar System that orbits its planet

in the opposite direction to the

way the planet spins. Some

astronomers believe it was once a

separate body that was captured

by Neptune’s gravity.

NEPTUNE

Neptune

TRITON

Fierce winds blow at speeds

up to 1,200 km/h (750 mph)

Dark spots, circled by white

methane clouds, sometimes form

where there is a great storm

Name Diameter in miles/km

Ceres 605/974

Pluto 1433/2306

Haumea 715/1150

Makemake 930/1500

Eris 1490/2400

LIST OF DWARF PLANETS

s.

um,

Neptune

dwarf planets