29th October 2015
N e w s a d e m ic .co m ™
- British English edition
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a s s in i
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n c e l a d u s
flyb y
On 28th October the Cassini un
manned
spacecraft, or space probe,
completed an unusual flyby. It
flew about 50 kilometres (31
miles) above the surface o f Encela
dus. This is one o f Saturn’s many
moons. As it flew over the m oon’s
surface, Cassini deliberately passed
through one o f Enceladus’ icy jets.
These jets, or plumes, erupt from
the m oon’s surface.
Saturn is the sixth planet from the
Sun. It is named after the Roman god
o f farming, or agriculture. The plan
et is the Solar System’s second larg
est. The biggest is Jupiter. Saturn is
famous for its rings. (It is sometimes
called the ringed planet.) Saturn’s
rings are no more than 20 metres
(66 feet) thick. Yet they are about
113,000 kilometres (70,200 miles)
wide. The rings are made up o f bil
lions o f small pieces o f ice and dust.
E nceladus and its p lum es o f ic y sp ra y (NASA)
It takes Saturn about 30 ‘Earth
years’ to orbit the Sun.
The planet
has at least 150 moons, or natural sat
ellites. M ost are very small. About
50 o f the larger moons have been
named. The largest is Titan. Encela-
dus is roughly 500 kilometres (310
miles) across. It is Saturn’s sixth-
biggest moon. Enceladus is named
after a giant from Greek Mythology.
Cassini was launched in 1997. It
is a joint project between the USA’s
space agency (NASA) and the Euro
pean Space Agency (ESA). Cassini
finally reached Saturn in 2004. It
has been circling the ringed planet
for over ten years.
During this time,
Cassini has recorded large amounts
o f information about Saturn and its
rings. It has also flown past several
o f Saturn’s moons. In 2005 Cassini
discovered that Enceladus had gey
ser-like jets o f water vapour erupt
ing from part o f its surface.
A rtis t’s im pression o f C assini and S a tu rn ’s rings
The jets were a surprise. Ence-
ladus was thought to be a large
ball o f ice that was ‘geologically
dead’. Planets and moons are of
ten described as being geologi
cally active or dead. The Earth is
geologically active,
but the Moon
is geologically dead. The Earth’s
outer layer, or crust, is made up of
huge pieces called tectonic plates.
These ‘plates’ move very slowly.
It is these plate movements that
cause earthquakes and volcanoes.
The Moon does not have any mov
ing plates. The water vapour jets
on Enceladus show that the moon
is geologically active.
Later, it was discovered that the
m oon’s icy plumes were erupting
from four long fractures. NASA
scientists nicknamed them ‘tiger
stripes’.
The fractures are near En-
celadus’ south pole. The jets are
now thought to run the length o f the
tiger stripes. If so, they are hundreds
o f kilometres long. If you were
standing on Enceladus, they would
look like a long wall o f water va
pour many kilometres high. These
types o f long plumes are known as
curtain eruptions.
NASA scientists believe that the
water
vapour comes from a salty
ocean under Enceladus’ icy surface.
The m oon’s hot core is probably
heating this ocean. Cassini will test
the water vapour it detected during
its latest flyby. If it finds hydrogen
molecules, there could be hot vents
on Enceladus’ ocean floor. These
would probably be similar to the
ocean vents deep below the Earth’s
oceans. These are also called ‘black
smokers’.
On Earth, bacteria live
around these hot vents. If Enceladus
has black smokers, they could be
home to tiny microbes.
Many scientists think that Ence-
ladus might be the only other planet
or moon in the Solar System that has
any life. □
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