2020-04-02_Science_Illustrated

Some jellyfish are only a centimetre
in size, but in two jellyfish species
the bell, in rare cases, grows to a
diameter of two metres. One of the
two species, Nomura's jellyfish
(Nemopilema nomurai), probably
holds the weight record, as it can
weigh up to 200kg. The red lion's
mane jellyfish (Cyanea capillata)
has the longest tentacles. An
individual found on a beach in
Massachusetts Bay in 1870 was
found to have 34-metre tentacles.

Stinging jellyfish

WHERE: The lion's mane jellyfish
exists in the North Atlantic, while
Australia’s most venomous jellyfish
is the sea wasp or Chironex fleckeri.
Despite its fearsome reputation,
only 60-80 deaths have been
recorded off Queensland and the
NT since the first report in 1883.

‘Trojans’ share their orbits

with larger objects such

as planets like Jupiter.

TROJANS

TROJANS

JUPITER

ASTRONOMY In the

Asteroid Belt between Mars

and Jupiter, and in the Kuiper

Belt on the outskirts of the

Solar System, many objects

share the same orbits. But

only a few of them have a

diameter greater than a

kilometre, so they are not the

biggest of heavenly bodies.

Planets do not share their

orbits with other objects.

Part of the definition of a

Solar System planet is that it

has used its gravity to clear

its orbit around the Sun.

When a large heavenly body

such as a planet orbits the

Sun, it will either collide with

other smaller celestial bodies

in that orbit, or interrupt

them, changing their orbits.

The two exceptions to

the rule are a planet’s

moons and ‘trojans’, which

orbit in the same path as a

planet while remaining at a

distance that corresponds to

an angle of 60 degrees in the

elliptical orbit.

EARTH’S ONLY TROJAN ASTEROID

‘2010 TK7’ is our only known ‘trojan’,

a roughly 300-metre asteroid orbiting

the Sun in the same path as Earth but

80 million km ahead. The asteroid

orbits both the sun and Earth’s own

orbit, causing the major fluctuations

marked out in green in the figure.

Jupiter has thousands of trojan

asteroids in two major clusters.

Saturn has two pairs of trojan

moons.

WORLD RECORDS

How big can

jellyfish grow?

Can several worlds

share the same orbit?

3 Can asteroids, planets and moons share an orbit around the Sun?

4

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2010 TK7’s fluctuations

2010 TK7

Earth

GREENLAND

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