Australian Science Illustrated – Issue 51 2017

26 | SCIENCE ILLUSTRATED

H

undreds of times further away

from the Sun than our own

Earth, the Solar System is

surrounded by a belt of

"pebbles". Among the many

anonymous objects in the Kuiper Belt, you will

find Pluto, which was the only known world

that far away from the Sun for decades. But

since the discovery of the dwarf planet of Eris

in 2005, astronomers are finding new dwarfs

all the time.

As of now, five worlds have official dwarf

planet status, but according to prominent

scientists, other worlds of about the same

sizes ought to be defined as dwarf planets. In

recent years, modern telescopes and

supercomputers have made the list of dwarf

planet candidates grow to about 100, and

there could be up to 200 dwarfs in the Kuiper

Belt, estimates say. Now, astronomers from

the American University of Michigan have

discovered another new dwarf planet

candidate: 2014 UZ224 nicknamed DeeDee.

Located 13.5 billion km from the Sun,

DeeDee is more than twice as far away as

Pluto, and its orbit time is four times longer –

or no less than 1,100 years. Moreover, the

new dwarf has a diameter of 635 km, i.e.

about 25 % of Pluto’s, making DeeDee a tiny

dot in the sky. Apparently, the most remote

regions of the Solar System are swarming

with unknown worlds, and the new light in the

sky is just another piece in the puzzle which

astronomers are putting together to

understand how the Solar System formed.

SMALL WORLDS CLASSIFIED DIFFERENTLY

Dwarf planets are very much like real planets,

and Pluto was even classified as a planet,

until it was downgraded to dwarf planet

status in 2006. In the years after 2000,

scientists discovered more small worlds with

about the same weights as Pluto, making

them introduce the term dwarf planet.

According to the official definition, a

dwarf planet is a world orbiting the Sun, and

just like a planet, it is so large that its own

weight has provided it with a round shape.

But unlike a planet, it is not big enough to

have cleared its own path of other objects

the way Earth has done it.

Astronomers’ intense search for dwarf

planets is due to the fact that they can help us

find out how the Solar System and Earth were

formed 4.6 billion years ago. Scientists do not

know exactly how the planets formed, but

according to the most popular theories, they

formed from a protoplanetary disc - a large

collection of microscopic material. The majority

was used to form the Sun at the centre of the

disc, whereas all planets, dwarf planets, and

other smaller objects formed from the remains.

The distribution of the rest was subject to

a complex "game", by which the objects’ own

gravities became ever more important, the

bigger they grew. But other factors such as

the distance to the Sun, orbit times, and the

size of the microscopic dust grains and

"pebbles" also played a role.

Like Earth and the seven other Solar

System planets, the dwarf planets were

probably formed by smaller objects slowly

The Solar System

has 5 confirmed

dwarf planets ...

The dwarf planet category was introduced in

2006 as a definition of worlds which are too small

to be planets. Five objects have officially been

recognized as dwarf planets, and studies show

that they are just as different as real planets.

PROBE REVEALS

ACTIVE GEOLOGY

Diameter: 2,374 km

The most famous dwarf planet

was discovered in 1930, and

until 2006, it was considered

the ninth Solar System planet.

In 2015, the New Horizons

probe flew by Pluto, revealing

a geologically active surface.

Pluto has 5 moons (Charon is

the biggest).

ICY AND DISTANT

FAR FROM THE SUN

Diameter: 2,326 km

Eris is almost the same size as

Pluto, but it is orbiting three

times as far away from the Sun

in an elliptical orbit, i.e. it is the

most remote of the confirmed

dwarf planets. It was discovered

in 2005, and just like Pluto's , its

surface is covered in ice.

Astronomers have discovered about 100

objects on the outskirts of the Solar System,

which could be dwarf planets. American

astronomer Michael Brown, who discovered

several himself, has identified 6 objects, which

should have dwarf planet status, according to

him, and 5, which are plausible candidates. All

of them were discovered in 2002-2007. Of

Brown’s 6 definite dwarf planets, the 2007

OR10 is clearly the biggest. With a diameter of

1,500 km, it is larger than the official dwarf

planets of Haumea and Makemake. Heavenly

bodies with dwarf planet status are appointed

by the the International Astronomical Union.

... and 100s of

unofficial ones

PLUTO ERIS

NASA & ESA

THE SOLAR SYSTEM DWARF PLANETS