The extended
family of Solar
System objects
Astronomers classify all
objects of the Solar System
according to size, make-up,
and position as compared to
other objects.PLANETS
The Solar System has 8 planets
which orbit the Sun. They are large
enough to be round and have cleared
their paths of other planets.DWARF PLANETS
The difference between dwarf
planets and real planets is that the
dwarf planets are too small to have
cleared their paths of other objects.
Our Solar System has 5 so far.ASTEROIDS
Asteroids are even smaller than
dwarf planets. They are so small that
their gravities have not made them
round, and they cannot maintain
their own atmosphere.MOONS
The natural satellites are not
orbiting the Sun, but rather a planet
or dwarf planet and are very
different in size. The
Solar System
includes at least
149 moons.COMETS
Are about the same size as asteroids,
but with extremely elliptical orbits.
Made up of ice and dust, they leave a
cloud of water vapour behind, which
interacts with solar wind to produce
the characteristic plasma tail.2005 Improved images from Hubble
come so close to the dwarf planet that
three of its moons – Nix, Hydra and
Charon – become visible.
2015 The New Horizons probe flies by
Pluto, taking the first close-ups which reveal
details such as hills and valleys on the dwarf
planet's surface.NIXPLUTOHYDRA
CHARONafter 2000 along with dozens of others which
have not yet been officially recognized. The
group of dwarf planets could also soon include
the recently discovered DeeDee and several
other worlds. However, this would require that
the discoveries be recognized by the
International Astronomical Union (IAU), which
determines the status of heavenly bodies.
No matter if the IAU chooses to expand
the group of official dwarf planets, one thing
is for sure: We will find much more small
worlds in the outer Solar System in the years
to come. According to astronomer Michael
Brown, who has discovered several of them
himself, the Solar System probably includes
hundreds of dwarf planets.
Previously, astronomers systematically
searched the sky with a telescope to find
new objects. Today, discoveries are typically
made based on existing images or other data,
which is analysed in new ways. Huge
quantities of data already exist from former
observations, and at the same time,
computers have become more powerful.
This was how DeeDee was discovered by
astronomer David Gerdes and students from
the University of Michigan. Gerdes used aseries of very detailed images taken by the
Dark Energy Camera, which is used to
determine the universe’s contents of dark
energy. Although the instrument takes
images of galaxies and supernovas, Gerdes’
students found a way to computerize the
recordings, so they could be used to study
much closer objects in our own Solar System.
By comparing recordings from different dates,
the scientists found an unknown moving
luminous point – DeeDee had been discovered.
Scientists still only know the new dwarf
planet’s size and distance from the Sun, but
analyses of the light reflected by the remote
object can reveal the make-up of its surface.
However, no telescope observations can
compete with the close-ups taken by a probe,
and scientists are very interested in missions
to dwarf planets. Apart from Ceres, which
was paid a visit by the Dawn probe in 2015,
Pluto has been photographed by the New
Horizons probe. After its fly-by of Pluto, the
probe was redirected to another small world
in the Kuiper Belt: 2014 MU69, which New
Horizons is to zoom in on in 2019, according to
plan. The search for the secrets of dwarf
planets continues.scienceillustrated.com.au | 29