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p l a n e t
Two American astronomers, or re
searchers who study the stars and
planets, have recorded an unusual
sight. Using a very powerful tel
escope, they have observed a new
planet taking shape, or being born.
This has never been seen before.
The newly forming planet is going
around, or orbiting, a young star.
Artist’s impression o f a young star, new planets and
material left over from the star-formation process (NASA)
Scientists have often wondered
how the planets in our Solar Sys
tem first formed. This happened
over four billion years ago. Then,
an enormous cloud of dust and gas
surrounded a protostar. (New or
‘very young’ suns are known as pro
tostars.) The material in this cloud
was left over from the formation of
the Sun. As the cloud span around
the Sun, it gradually flattened into a
disc-like shape.
Small pieces o f material in the
cloud then began to stick together.
As these larger clumps orbited the
Sun, they got bigger and bigger.
Gradually, the growing clumps
cleared all the dust and gases in
their paths. Then, they became big
enough to attract other nearby ma
terial with their own gravity. Larger
clumps attracted smaller clumps and
formed very small planets. Eventu
ally, they grew in size to become the
planets that we know today.
It is not known how long this
planet formation took. Some scien
tists think it was between one and
10,000 years. Others believe it was
far longer. Collecting extra material
like this is known as accretion. The
idea that the Solar System’s planets
formed in this way is described as
the ‘accretion disk m odel’.
In our Solar System the four inner
planets, Mercury, Venus, the Earth,
and Mars, are all rocky. The outer,
or more distant planets, Jupiter, Sat
urn, Uranus, and Neptune, are made
mainly of gases. This probably hap
pened because of the makeup of the
disc-like cloud that was around the
younger Sun. Rocky dust debris in
the cloud was closer to the Sun and
the gases farther away.
The first exoplanet was discov
ered in 1995. These are planets that
orbit stars (or suns) beyond our So
lar System. As telescopes became
more powerful, more and more exo
planets have been observed. So far,
about 1,900 exoplanets have been
recorded. They all orbit older stars.
Therefore all of these exoplanets
have already formed.
The star observed by the two
astronomers is called LkCa 15. It
is only two million years old. The
very young star is 450 light years
from the Earth. A light year is the
distance light travels in one year.
(The speed of light is roughly
300,000 kilometres (186,400 miles)
per second.)
The astronomers spotted a planet
orbiting LkCa 15 (there might be
one or two others as well). Because
o f the star’s young age, this must
be a newly formed planet. W hat’s
more, there is a large ring, or cloud,
of cosmic dust and gas, beyond the
planet. It looks as if this part of the
sun’s disc-like cloud is yet to form
any planets. The whole system
looks like a doughnut. The cloud
is the doughnut and the sun and its
new planet (or planets) are within
the hole in the middle.
By studying this new star system,
scientists hope to find out if the ac
cretion disk model is correct. □
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