Newsademic British English edition 260

n e w
 
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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