New Scientist Essential Guide 13

2022·21.9 MB·

H O W T H E S U N W O R K S
E A R T H A N D T H E M O O N
T H E P L A N E T S
ESSENTIAL
T H E U N K N O W N S O L A R S Y S T E M
E X O P L A N E T S
AND MORE
GUIDE№13
THE SOLAR
SYSTEM
A J O U R N E Y T H R O U G H O U R C O S M I C
N E I G H B O U R H O O D – A N D B E Y O N D
E D I T E D B Y
STEPHEN BATTERSBY

N E W
S C I E N T I S T
E S S E N T I A L
G U I D E
O
T H E S O L A R
UR solar system isn’t much in cosmic terms:
a single star, just one of hundreds of billions
in our galaxy – itself one of many billions in a
practically unending universe – and its retinue
S Y S T E M
of eight planets and assorted other hangers-on.
And yet what a wonderful place it is, harbour of
many surprises and not a few mysteries. In this 13th
New Scientist Essential Guide, we will take a peek
behind the bright curtains of the sun’s photosphere
to investigate the mysteries of our star, ask what Earth
and moon tell us about the formation of the solar
system and consider what it would take to send people
to Mars, as well as tour the gas and ice giants of the
outer solar system and frigid moons and beyond. We
will round off by visiting the other planetary systems
we now know exist around other stars, guided by a
central existential question – does life exist elsewhere?
And all this without leaving the ground. All titles in
the Essential Guide series can be bought by visiting
shop.newscientist.com; feedback is welcome at
[email protected].
Stephen Battersby
NEW SCIENTIST ESSENTIAL GUIDES SERIES EDITOR Richard Webb ABOUT THE EDITOR
NORTHCLIFFE HOUSE, 2 DERRY STREET, EDITOR Stephen Battersby Stephen Battersby is a freelance writer and New Scientist consultant
LONDON, W8 5TT
DESIGN Craig Mackie specialising in space, based in London
[phone]
© 2022 NEW SCIENTIST LTD, ENGLAND SUBEDITOR Bethan Ackerley
NEW SCIENTIST ESSENTIAL GUIDES
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ARE PUBLISHED BY NEW SCIENTIST LTD
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1 | New Scientist Essential Guide | The solar system
C H A P T E R 1 C H A P T E R 2 C H A P T E R 3
T H E S U N E A R T H A N D T H E I N N E R
T H E M O O N P L A N E T S
The sun dominates the solar system – Nowhere else in the solar system Mercury, Venus and Mars, the three
in its centre, its source of warmth and does such a huge moon orbit such closest planets to Earth, are all small,
the location of 99.99 per cent of its a small planet. That could be solid worlds. All of them have iron
mass. Yet for all its dominance, our connected to another phenomenon, cores, bound with rock. Yet they are
home star still holds many mysteries. unique to Earth as far as we know: all spectacularly, intriguingly
the presence of life. But our planet different from one another.
p. 6 What powers the sun? could hold clues to how the whole
p. 11 The mystery of the solar corona solar system formed. p. 36 Mercury: The iron planet
p. 13 Touching the sun p. 39 Venus: The veiled one
p. 14 Long-lost solar siblings p. 18 The pale blue dot p. 41 Mars: Home from home?
p. 21 Goldilocks planet p. 42 A walk on Mars
p. 23 Why the moon matters p. 44 INTERVIEW: Tanja Bosak
Life on the Red Planet
p. 26 Going back to the moon
p. 46 How to get to Mars
p. 28 When planets migrate
p. 49 Ceres: Queen of the asteroids
p. 30 The meaning of meteorites
p. 50 INTERVIEW: Lindy Elkins-Tanton
p. 31 Defending Earth
Mission to a metal world
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C H A P T E R 4 C H A P T E R 5 C H A P T E R 6
T H E G I A N T J O U R N E Y B E Y O N D
P L A N E T S T O T H E E D G E T H E S O L A R
S Y S T E M
Beyond the asteroid belt, four Beyond Neptune lies the Kuiper belt, The discovery of exoplanets beyond
heavyweight planets reign: Jupiter, the dark domain of Pluto and its kin, our solar system is one of the most
Saturn, Uranus and Neptune. Their plus even more distant ice balls, stunning of recent decades. The
powerful gravity has remodelled the interlopers from other star systems remarkable range of alien worlds
solar system, but their remarkably and hints of a distant presence – and systems we have already found
diverse moons are perhaps the most perhaps the fabled planet X, perhaps is making us rethink the history of
fascinating – not least because they something stranger still. our own solar system and expand
might harbour life. our quest for alien life.
p. 76 Pluto: Head of the Kuiper clan
p. 54 Jupiter: The ruler p. 79 How to be a planet p. 88 Worlds beyond
p. 58 The Galilean moons p. 80 Comets: A top six p. 90 Five offbeat exoplanets
p. 60 Saturn: The ringmaster p. 81 Planet X? p. 91 How green is our galaxy?
p. 62 Hidden oceans p. 83 The Oort cloud p. 93 Mission to Proxima Centauri
p. 64 I NTERVIEW: Kevin Hand p. 84 ‘Ouamuamua: p. 95 Is our solar system unique?
Life on ice worlds An interstellar interloper
p. 66 Titan: Methane world
p. 69 U ranus and Neptune:
The ice giants
p. 71 Triton: The cantaloupe moon
p. 72 Probing the outer solar system
New Scientist Essential Guide | The solar system | 3
C H A P T E R 1
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The sun dominates the solar system. It is our centre, our source of
warmth, the origin of the word “solar” in “solar system”, of course;
and, in terms of sheer mass, it is overwhelming.
Essential Guide
If the contents of this were in proportion to the mass
of their subject matter, this chapter would run for well over 30,000
words, leaving a total of four words to be shared between the other
four chapters on our solar system. Yet for all its dominance, our
home star still holds many mysteries.
Chapter 1 | The sun | 5
WHAT POWERS
THE SUN?
Although we understand the basics of N EVERY way, the sun is the odd one out.
Unlike the solid or gaseous planets and other
how the sun shines, there appears to be
bodies around it, the sun is made of plasma –
something missing in there. It could be gas that has been ionised, with electrons
stripped from its positively charged nuclei.
elements behaving in a way we didn’t
The solar core, at ultra-high pressure and
expect under crushing pressure. It could temperatures of around 15 million kelvin, is
where nuclear fusion happens, the source of
be an unexpected ingredient, perhaps
the sun’s power. Above that is the radiative
dark matter. Or maybe we are just zone, where the heat generated in the core
slowly percolates very slowly outwards and upwards.
looking at the sun in the wrong way.
Then comes the convective zone, where churning
plasma somehow generates the sun’s skittish,
pulsating magnetic field. Sunlight comes to us from
a thin skin called the photosphere, where sunspots
blossom. Finally, the chromosphere and corona form
the sun’s atmosphere, which streams out into space,
sometimes in cataclysmic eruptions known as
coronal mass ejections.
Understanding the sun is important not just
because it supplies the heat and light that sustain
us. It is also our key to the wider universe, the
reference against which we measure stars: their
brightness, their age, how likely their solar systems
NASA/GODDARD SPACE FLIGHT CENTER are to support life. Mess with the sun, and the >
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Chapter 1 | The sun | 7
consequences stretch as far as our telescopes can see. in scientific papers about solar fusion – it isn’t simple to
Generally speaking, stars shine because gravity calculate how much energy is released in each reaction,
has pulled enough hydrogen plasma into such close and how frequently they occur, combining nuclear
quarters that its nuclei (protons) start to fuse together theory with nuclear experiments on Earth, but mostly
to make helium. Every star starts this way. When the this is a matter of filling in the details.
hydrogen runs out, the helium starts fusing together, However, one recently discovered anomaly
and so on, producing heavier and heavier elements. might be pointing to something quite peculiar
This is the source of much of the matter that makes happening deep in our parent star. There seems to
up our planet and us. be something missing.
It sounds like a simple matter of gluing protons There are two main ways to investigate what is
together, but it isn’t. The conditions have to be right. inside the sun. Helioseismologists look at sound
The plasma has to be hot and dense enough to get vibrations on the sun’s surface, which give outward
protons to fuse. Fusion happens in several stages evidence of the vast quantities of energy being
and via several different reactions. The theories that unleashed within. That energy depends on the sun’s
describe how all this happens aren’t the classical internal structure and ingredients. Then there are
Newtonian physics that describes, for example, two spectroscopists, who look at the light from the sun,
football players colliding when they both want to splitting it into a range of wavelengths that reveal the
control the ball. Instead, we need quantum mechanics barcodes of constituent elements.
and nuclear physics. For years, these two methods painted the same
Whatever the complexities of the process, the end picture of the sun: a vast and dense ball of matter, made
products are helium and heat. The energy in gamma- mostly of hydrogen and helium, that clumped together
ray photons and the kinetic energy in other particles some 4.6 billion years ago and formed our solar system.
is passed on and outwards through the layers of the Included in the mixture was a sprinkling of other
sun. Eventually, after tens of thousands of years, it elements carried by the explosions of larger, dying
reaches the outermost visible layer, the photosphere, stars. Astronomers refer to all these heavier elements –
which, at about 6000 kelvin, radiates life-giving which include carbon, oxygen, nitrogen, magnesium,
sunlight (and some life-threatening ultraviolet light). iron and sulphur – as metals. Metals make up less than
Almost all of the neutrinos, meanwhile, fly right out 2 per cent of the sun’s total mass, but play a crucial role,
of the sun. A vanishingly small number are then snared shuttling energy from the core out to the surface.
in underground particle detectors on Earth, reassuring In the late 1990s, Martin Asplund was a young
us that these once-theorised reactions are really researcher in Copenhagen, Denmark, when he first
happening in there. There are still some inconsistencies realised this picture wasn’t quite right. He was studying
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