Australian Science Illustrated – Issue 51 2017

becoming larger, but scientists are still not sure
why some objects accumulated all the material
in their orbits to become planets, whereas
others ended up as dwarf planets.
Astronomers already know quite a lot
about the planets, but by studying dwarf
planets, they can obtain new knowledge about
how the Solar System planets ended up in their
present locations. Pluto’s orbit is synchronized
with Neptune’s, making scientists suspect that
both the dwarf planet and the outermost
planet of the Solar System were formed much
closer to the Sun. Not until later, they were
nudged to their present locations, when the
gas giants of Jupiter, Saturn, and Uranus
moved inwards.

CERES: A PLANETARY EMBRYO
The dwarf planet about which scientists
know the most is Ceres, which was
discovered back in 1801. Ceres is orbiting in
the Asteroid Belt between Mars and Jupite -
much closer to the Sun than Pluto and the
other dwarf planets of the Kuiper Belt.

Diameter: 945 km

Ceres, which was observed for

the first time in 1801, is the

most intensely studied dwarf

planet. Whereas the other

dwarfs are orbiting in the Kuiper

Belt on the outskirts of the Solar

System, Ceres is located in the

Asteroid Belt between Mars and

Jupiter, where it is the largest

object. Pluto is 14 times further

away from Earth than Ceres.

In 2015, the Dawn mission

paid a visit to Ceres, providing

scientists with more detailed

knowledge about the dwarf

planet's make-up. We now know

that up to 25 % ofCeres could be

water in the shape of ice, and so,

the small world might include

more fresh water than Earth.

Ceres has a thin atmosphere,

which includes something as

rare as water vapour. According

to astronomers, the vapour

comes from ice volcanoes, which

carry ice up from the planet's

mantle, convert it into vapour,

and spew it out. Normally, only

comets emit vapour. The large

quantities of water make Ceres

one of the worlds of the Solar

System, on which microscopic

life could exist.

A DISTANT ICE VOLCANOES SPEW VAPOUR
EGG-SHAPED WORLD
Diameter: 1,436 km
Astronomers have calculated
that Haumea is the only dwarf
planet which is ellipsoid, but
its appearance has never been
directly observed. Haumea
was discovered in 2004. NASA
has loose plans of launching
an unmanned mission to
Haumea in 2025.

TEMPERATURES

CLOSE TO ZERO

Diameter: 1,420 km

Makemake, which was

discovered in 2005, has no

atmosphere, and its temperature

is extremely low: minus 243 °C –

only 30 degrees warmer than

absolute zero. So, gases such as

methane and ethane, which

normally ooze away, could exist

in solid versions.

Astronomer Michael Brown
has identified six dwarf
planet candidates, which
ought to have official dwarf
planet status.

In 2015, the Dawn probe

entered into orbit around

Ceres, photographing an

ice volcano emitting

water vapour.

HAUMEA MAKEMAKE CERES

DUSTY, OUT-ER CRUST

ICE LAYER

CORE

NASA

CALTECH

The Moon is 1.5 times as big

as the largest dwarf planet.