BBC Focus

PHOTOS: SCIENCE PHOTO LIBRARY

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TOP 10

LONGEST LASTING LANDFILL ITEMS

1. Glass bottles
   Time to break down:one million years

2= Disposable nappies

Time to break down:450 years

2 =Plasticbottles

Time to break down:450 years

4. Plastic bags
   Time to break down:200-500 years


5. Aluminium cans
   Time to break down:80-200 years
   7. Ti ncans
   Time to break down:50 years
   6. Rubber-soled shoes
   Time to break down:50-80 years
   8. Clothing
   Time to break down:up to 40 years

9 .Plasticfilm*

Time to break down:20-30 years

*clingfilm, magazine wrappers,

crisp packets, etc

10. Paper coffee cups

Time to break down: 20 years

Jupiter’s large gravitational field makes it prone to

impacts from asteroids, comets and other Solar System

flotsam. This was spectacularly demonstrated in 1994

when the comet Shoemaker-Levy 9 plunged into the

atmosphere of Jupiter, adding at least one trillion

kilograms to the planet’s mass in a single event. It is

estimated that Jupiter’s rate of mass increase from

impacts or accretion is up to 8,000 times that of the

Earth’s. Events like Shoemaker-Lev y 9 are rare but

even adding up the smaller bombardments of

Jupiter that continuously rain down on the planet,

the increase in mass is still a tiny fraction of

Jupiter’s overall total. However, this does not mean

that Jupiter’s mass is increasing. Jupiter’s

atmosphere is warm; so warm that gas molecules

are moving fast enough to escape the gravitational

pull of the planet. Furthermore, the solar wind

actually ionises many of the atoms in the Jovian

atmosphere. Since these atoms become neutrally

charged, they can easily escape Jupiter’s magnetic f ield

and float off into space. This slow but constant loss of

mass from Jupiter’s atmosphere is actually greater

than the gain in mass from collisions so, overall,

Jupiter is shrinking not growing in mass. AG

As Jupiter’s gravity pulls in so much

matter, is the planet growing?

LOUIS GOODWIN, LEWES

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