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    Lonely Planet The Universe
    Lonely Planet The Universe
    Lonely Planet The Universe
    Ebook1,423 pages11 hours

    Lonely Planet The Universe

    By Lonely Planet

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    About this ebook

    Let Lonely Planet take you further than ever before with the world's first and only travel guide to the Universe. Developed with the latest data from NASA, we take you from our home on Earth and out into the far reaches of the solar system, then into our neighbouring stars and planetary systems, and finally into the rest of our galaxy and the Universe.

    This fascinating journey will help you explore space as you would the world with a Lonely Planet guide. Unique to these pages are wonderful comparisons of Earth with the other worlds of our solar system and even those exoplanets orbiting other stars.

    You'll discover as much as we know about our celestial neighbourhood, and our place in it. In addition to planets and moons, get to know our Sun, explore the asteroid belt and the Kuiper Belt, and learn what lays beyond, in interstellar space. Outside our solar system, travel to some of the notable neighbouring stars, stellar systems and exoplanets we've discovered. You'll understand how we search for planets where life might exist and the stars they orbit.

    Finally, discover the edge of the observable Universe. Get to know the structure of the Milky Way as well as an orientation to neighbouring galaxies like the Andromeda Galaxy which is visible from Earth. Then explore other galactic formations and learn about galactic clusters and superclusters. By the end of the book, you'll have a sense for the structure of the entire Universe as well as some of the big questions we still have as we ponder our place in it.

    About Lonely Planet: Lonely Planet is a leading travel media company and the world's number one travel guidebook brand, providing both inspiring and trustworthy information for every kind of traveller since 1973. Over the past four decades, we've printed over 145 million guidebooks and grown a dedicated, passionate global community of travellers. You'll also find our content online, on mobile, video and in 14 languages, 12 international magazines, armchair and lifestyle books, ebooks, and more.

    LanguageEnglish
    PublisherLonely Planet
    Release dateOct 1, 2019
    ISBN9781788687058
    Lonely Planet The Universe
    Author

    Lonely Planet

    Lonely Planet has gone on to become the world’s most successful travel publisher, printing over 100 million books. The guides are printed in nine different languages; English, French, German, Spanish, Italian, Brazilian Portuguese, Russian, Chinese and Korean. Lonely Planet enables curious travellers to experience the world and get to the heart of a place via guidebooks and eBooks to almost every destination on the planet, an award-winning website and magazine, a range of mobile and digital travel products and a dedicated traveller community.

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      Book preview

      Lonely Planet The Universe - Lonely Planet

      The Universe Contents

      Foreword

      Introduction to the Universe

      Scale of the Universe

      Modern Observing Methods

      Today’s Telescopes

      How to Use This Book

      Naming Conventions

      Highlights

      The Solar System

      Transits & Eclipses

      Introduction to the Planets

      Manned Space Flight

      The Quest for Orbit

      Race to the Moon

      Shuttle Programme

      The Present Day

      The International Space Station

      The Sun

      Orientation

      Atmosphere

      Heliosphere

      Solar Flares

      History

      In Popular Culture

      Mercury

      Orientation

      Magnetosphere

      History

      BepiColombo Mission

      In Popular Culture

      Caloris Planitia

      Pantheon Fossae

      Raditladi Basin

      Rachmaninoff Crater

      Caloris Montes

      Venus

      Orientation

      Atmosphere

      History

      In Popular Culture

      Mariner 2

      Magellan Mission

      Signs of Life

      Baltis Vallis

      Maat Mons

      Alpha Regio

      Maxwell Montes

      Aphrodite Terra

      Earth

      Orientation

      Atmosphere

      Magnetosphere

      History

      NASA Earth Science

      Mt Everest

      Challenger Deep

      Atacama Desert

      Mauna Kea

      Chicxulub Crater

      Silfra

      Death Valley

      Antarctica

      Great Barrier Reef

      Amazon Rainforest

      Ngorongoro Conservation Area

      Great Wall of China

      The Moon

      Orientation

      History

      In Popular Culture

      Apollo 11

      Orbital Gateway

      Lunar Eclipses

      Sea of Tranquility

      South Pole-Aitken Crater

      Copernicus Crater

      Montes Apenninus

      Oceanus Procellarum

      Mars

      Orientation

      Mapping Mars

      Martian Moons

      Atmosphere & Magnetosphere

      History

      In Popular Culture

      Investigating Mars

      Curiosity Rover

      InSight Lander

      Travelling to Mars

      Polar Caps

      Tharsis Montes

      Olympus Mons

      Valles Marineris

      Hellas Planitia

      Bagnold Dune Field

      Gale Crater

      Elysium Planitia

      Syrtis Major Planum

      Utopia Planitia

      Vastitas Borealis

      Jupiter

      Orientation

      Atmosphere

      History

      Great Red Spot

      Ring System

      Surface

      Clouds

      Oceans

      Magnetosphere

      Juno Mission

      Io

      Europa

      Ganymede

      Callisto

      Saturn

      Orientation

      History

      Cassini Mission

      Saturn’s Rings

      Magnetosphere

      Surface

      Titan

      Enceladus

      Rhea, Dione & Tethys

      Iapetus

      Mimas

      Phoebe

      Uranus

      Orientation

      History

      Surface/Atmosphere

      Aurorae

      Magnetosphere

      Ring Systems

      Miranda

      Ariel

      Umbriel

      Oberon

      Titania

      Shepherd Moons

      Neptune

      Orientation

      Magnetosphere

      History

      In Popular Culture

      Surface/Atmosphere

      Rings

      Proteus

      Triton

      Nereid

      Other Moons

      Non-Planetary Solar System Objects

      Asteroid Belt/Asteroids

      Bennu

      Ceres

      Chariklo

      EH1

      Eros

      Ida

      Itokawa

      Phaethon

      Psyche

      Vesta

      Kuiper Belt

      Dwarf Planets

      Eris

      Farout

      The Goblin

      Haumea

      Makemake

      Pluto

      Comets

      Borrelly

      C/1861 G1 Thatcher

      Churyamov-Gerasimenko

      Hale-Bopp

      Halley

      Hartley 2

      ISON

      ’Oumuamua

      Shoemaker-Levy 9

      Swift-Tuttle

      Tempel 1

      Tempel-Tuttle

      Wild 2

      Oort Cloud

      Exoplanets

      2MASS J2126-814b

      51 Pegasi b

      55 Cancri

      Barnard’s Star b

      CoRoT-7b

      CVSO 30b and c

      Epsilon Eridani

      Fomalhaut b

      Gliese 163 b, c & d

      Gliese 176 b

      Gliese 436 b

      Gliese 504 b

      Gliese 581 b, c & e

      Gliese 625b

      Gliese 667 cb & cc

      Gliese 832 b & c

      Gliese 876 b, c, d & e

      Gliese 3470 b

      GQ Lupi b

      HAT-P-7b

      HAT-P-11b

      HD 40307 g

      HD 69830 b, c & d

      HD 149026 b

      HD 189733 b

      HD 209458 b

      HIP 68468 b & c

      Kapteyn b & c

      KELT-9b

      Kepler-10b & c

      Kepler-11b to g

      Kepler-16 (AB)-b

      Kepler-22b

      Kepler-62b to f

      Kepler-70b & c

      Kepler-78b

      Kepler-90b

      Kepler-186b to f

      Kepler-444b to f

      Kepler-1625b

      Kepler-1647 (AB)-b

      Lich System (PSR B1257+12)

      Methuselah’s Planet

      Pi Mensae b & c

      Pollux b

      Proxima b

      PSO J318.5-22

      Ross 128 b

      TRAPPIST-1

      TrES-2b

      WASP-12b

      WASP-121 b

      Wolf 1061 b, c & d

      YZ Ceti b, c & d

      Stellar Objects

      Nebula & Protostars

      Main Sequence Stars

      Giant Stars

      Binaries & Clusters

      End of Life

      Life Cycle of Stars

      Spectra Classification

      1E 2259+586

      3C 273

      Achernar

      Aldebaran

      Algol

      Alpha Centauri A

      Alpha Centauri B

      Altair

      Antares

      Arcturus

      Barnard’s Star

      Betelgeuse

      California Nebula

      Canopus

      Capella

      Cat’s Eye Nebula

      Crab Nebula

      Cygnus X-1

      Deneb

      Dumbbell Nebula

      Epsilon Aurigae

      Eta Carinae

      Ghost of Jupiter

      GRS 1915+105

      HE 1256-2738

      HE 2359-2844

      Helix Nebula

      Herschel’s Garnet Star

      HLX-1

      Horsehead Nebula

      HV 2112

      IGR J17091-3624

      Iris Nebula

      Kepler’s Supernova

      Kes 75

      Little Dumbbell Nebula

      Mira

      MY Camelopardalis

      North America Nebula

      Omega Centauri

      Orion Nebula

      Owl Nebula

      Pleiades

      Polaris

      Procyon

      RCW 86

      Regulus

      Rigel

      Ring Nebula

      Rosette Nebula

      Sagittarius A*

      SAO 206462

      SDSSJ0927+2943

      SGR 1806-20

      Sirius

      Spica

      Tabby’s Star

      T Tauri

      ULAS J1120+0641

      UY Scuti

      Vega

      Veil Nebula

      VY Canis Majoris

      W40

      Galaxies

      Andromeda Galaxy

      Black Eye Galaxy

      Bode’s Galaxy

      Canis Major Dwarf

      Cartwheel Galaxy

      Centaurus A

      Cigar Galaxy

      Circinus Galaxy

      Condor Galaxy

      Grand Spiral Galaxy

      Hoag’s Object

      Large and Small Magellanic Clouds

      Malin 1 Galaxy

      Markarian 231

      M77

      M87

      NGC 1512

      NGC 3370

      Pinwheel Galaxy

      Sagittarius Dwarf Elliptical Galaxy

      Sculptor Galaxy

      Sombrero Galaxy

      Sunflower Galaxy

      Tadpole Galaxy

      Triangulum Galaxy

      W2246-0526

      Whirlpool Galaxy

      Colliding Galaxies

      Antennae Galaxies

      Arp 273

      Mayall’s Object

      NGC 2207 & IC 2163

      NGC 2623

      NGC 3256

      Galaxy Clusters

      Abell 1689

      Bullet Cluster

      El Gordo

      Fornax Cluster

      Local Group

      Musket Ball Cluster

      Norma Cluster

      Pandora’s Cluster

      Perseus Cluster

      Phoenix Cluster

      Virgo Cluster

      Glossary

      Acknowledgements

      Author Biographies

      A star being distorted by its close passage to a supermassive black hole at the centre of a galaxy.

      © SCIENCE PHOTO LIBRARY / ALAMY STOCK PHOTO

      Welcome to the Universe

      Bill Nye

      Lonely Planet’s The Universe gives us more perspective, often breathtaking, more insight, often deep – and more unusual facts, often ones you can’t find anywhere else, regarding the profound happenstance of our existence. Simply put, the remarkable sequence of cosmic accidents required to enable us to be here on this planet and publish books like this one is astonishing. Unique to these pages are wonderful comparisons of Earth with the other worlds of our solar system and even those exoplanets orbiting other stars. They drive home the jaw-dropping idea that you and I, and everything we can observe around us, are made of the dust and gas blasted spaceward by exploding ancient Suns. And from the stardust and drifting gas, the extraordinary diversity of living things, including animals like you and me, emerged. You and I are at least one way that the cosmos knows itself. An utterly amazing idea that fills me with reverence every time I think on it.

      While you are going about your business every day, thinking about what’s happening on Earth right now, this book will help you think about a much grander timeline as well. From the comfortable surface of Earth, our deep-thinking ancestors observed our planet and its relationship, their relationship, to the night sky and the Sun. They learned where to live and how to survive. From the icy blackness of space, our spacecraft, built by our best scientists and engineers, make further observations that relentlessly show us Earth is like no other place in the solar system, and remains the only place we can live and thrive. By understanding the changes here over recent millennia, we can see that, if we’re going to continue to thrive, we must preserve our environment. Otherwise, we’ll go extinct, like 90% of the species that gave it a go on Earth before we showed up.

      This cosmic perspective induces all of us to compare Earth to our neighbouring worlds out there. It’s one thing to consider Earth as a pretty big place, especially if you tried to walk around it. It’s another thing to think that 1300 Earths would fit inside a sphere the size of Jupiter, and over a million Earths would fit inside the volume of the Sun. While we’re appreciating the visible differences of the traditional planets, what you might call their qualitative differences, this book helps us take it all in by the numbers, the planets’ (and exoplanets’) quantitative differences, and beyond that, the differences between our own Sun and the uncountable stars above, visible and invisible. In here, these essential distinctions are spelled out – or counted up.

      The rocky and metallic compositions of Mars, Venus, and Mercury are very much like Earth’s, but the environments of these other worlds are completely different. The text and pictures here will help you understand why. The unique chemical composition of the rocks, craters, and sands of the other worlds in the solar system has caused these extraterrestrial environments to have chemistries that are literally other worldly. These processes have conspired to produce radically different surface temperatures on Mars and Venus. Our discoveries in planetary science offer us a planet-sized lesson in the importance of the greenhouse effect, how our planet became habitable, and how the biochemistry of life changed the chemistry of the atmosphere and sea.

      The story carries out away from the Sun, where we find the gas-giant planets: Jupiter and Saturn. They don’t seem to even have surfaces as such. There’s nowhere to stand, but they’re so massive that, if you got too close, their gravity would crush you quick. On out further from the Sun we find Uranus and Neptune. They’re very large and very cold, with enormous icy storm systems and winds moving at fantastic speeds. All of these other worlds in our solar system, the ones that are not Earth are very different, very interesting – and utterly hostile.

      As you turn these pages, learning the facts of everything from our solar system to the far reaches of intergalactic space, consider that there’s no other planet that we know of anywhere, upon which you could even catch a breath to be taken away, or seek a deciliter of water to be sipped – let alone be afforded an opportunity to live long and prosper. The Earth is unique, amazing, and our home.

      From a cosmic perspective, we are a pretty big deal. We’ve changed the climate of a whole planet. Run the numbers for yourself. Climate change is our doing. If we’re going to make it much farther on this world, we’re going to have to engage in some un-doing. Right now, it’s our chance to change things. We are but a speck in the cosmic scheme. But it’s our speck, and the more we know and appreciate it, the better chance we have keeping it hospitable for species like us.

      Barred spiral galaxy NGC 1300.

      © DESIGN PICS INC / ALAMY STOCK PHOTO

      Introduction to the Universe

      With 2 trillion estimated galaxies and uncountable stars, our Universe is filled with wild examples of exoplanets, stars, black holes, nebulae, galaxy clusters and more, which scientists are still probing.

      Our Universe began in a tremendous explosion known as the Big Bang about 13.7 billion years ago. We know this by observing light in our Universe which has travelled a great distance through space and time to reach us today. Observations by NASA’s Wilkinson Anisotropy Microwave Probe (WMAP) revealed microwave light from this very early epoch, about 400,000 years after the Big Bang.

      A period of darkness ensued, until about a few hundred million years later, when the first objects flooded the Universe with light. The first stars were much bigger and brighter than any nearby today, with masses about 1000 times that of our Sun. These stars first grouped together into mini-galaxies; the Hubble Space Telescope has captured stunning pictures of earlier galaxies, as far back in time as ten billion light years away.

      By about a few billion years after the Big Bang, the mini-galaxies had merged to form mature galaxies, including spiral galaxies like our own Milky Way. It had also expanded, racing under the force of the so-called Hubble constant. Now, 13.7 billion years from the Big Bang, our planet orbits a middle-aged Sun in one arm of a mature galaxy with a supermassive black hole in the middle. Our own solar system orbits the Milky Way’s centre, while our galaxy itself speeds through space.

      Under the Milky Way in San Pedro de Atacama, Chile.

      © MAVENVISION / ALAMY STOCK PHOTO

      Scale of the Universe

      Throughout history, humans have used a variety of techniques and methods to help them answer the questions ‘How far?’ and ‘How big?’. Generations of explorers have looked deeper and deeper into the vast expanse of the Universe. And the journey continues today, as new methods are used, and new discoveries are made.

      In the third century BC, Aristarchus of Samos asked the question ‘How far away is the moon?’ He was able to measure the distance by looking at the shadow of the Earth on the moon during a lunar eclipse.

      It was Edmund Halley, famous for predicting the return of the comet that bears his name, who three centuries ago found a way to measure the distance to the Sun and to the planet Venus. He knew that the planet Venus would very rarely, every 121 years, pass directly between the Earth and the Sun. The apparent position of the planet, relative to the disc of the Sun behind it, is shifted depending on where you are on Earth. And how different that shift is depends on the distance from both Venus and the Sun to the Earth. This rare event, the transit of Venus, occurred again most recently on June 8, 2004. It was knowing this fundamental distance from the Earth to the Sun that helped us find the true scale of the entire solar system for the first time.

      A timeline of the Universe since the Big Bang.

      © COURTESY NASA/WMAP SCIENCE TEAM

      When we leave the solar system, we find our star and its planets are just one small part of the Milky Way Galaxy. The Milky Way is a huge city of stars, so big that even at the speed of light, it would take 100,000 years to travel across it. All the stars in the night sky, including our Sun, are just some of the residents of this galaxy, along with millions of other stars too faint to be seen.

      The further away a star is, the fainter it looks. Astronomers use this as a clue to figure out the distance to stars that are very far away. But how do you know if the star really is far away, or just not very bright to begin with? This problem was solved in 1908 when Henrietta Leavitt discovered a way to tell the ‘wattage’ of certain stars that changed their pulse rate linked to their wattage. This allowed their distances to be measured all the way across the Milky Way.

      Beyond our own galaxy lies a vast expanse of galaxies. The deeper we see into space, the more galaxies we discover. There are billions of galaxies, the most distant of which are so far away that the light arriving from them on Earth today set out from the galaxies billions of years ago. So we see them not as they are today, but as they looked long before there was any life on Earth.

      Finding the distance to these very distant galaxies is challenging, but astronomers can do so by watching for incredibly bright exploding stars called supernovae. Some types of exploding stars have a known brightness – wattage – so we can figure out how far they are by measuring how bright they appear to us, and therefore the distance to their home galaxy. These are called ‘standard candles’.

      So how big is the Universe? No one knows if the Universe is infinitely large, or even if ours is the only Universe that exists. And other parts of the Universe, very far away, might be quite different from the Universe closer to home. At the time of publication using our most advanced technology and given the current size of the ever-expanding Universe, scientists estimate it is roughly 46 billion light years, or 440 sextillion km (274 sextillion mi). If it’s hard to wrap your head around that number, welcome to the club. The Universe is almost inconceivably big, and we have only observed a small portion of it (astronomers estimate we have observed roughly 4% of the known Universe).

      This Hubble Space Telescope image captures the effect of gravitational lensing by dark matter in a galaxy cluster.

      © SCIENCE PHOTO LIBRARY / ALAMY STOCK PHOTO

      Modern Observational Methods

      In 1609 an Italian physicist and astronomer named Galileo became the first person to point a telescope skyward. Although that telescope was small and the images fuzzy, Galileo was able to make out mountains and craters on the moon, as well as a ribbon of diffuse light arching across the sky – which would later be identified as our Milky Way Galaxy. After Galileo’s and, later, Sir Isaac Newton’s time, astronomy flourished as a result of larger and more complex telescopes. With advancing technology, astronomers discovered many faint stars and the calculation of stellar distances. In the 19th century, using a new instrument called a spectroscope, astronomers gathered information about the chemical composition and motions of celestial objects.

      Twentieth century astronomers developed bigger and bigger telescopes and, later, specialised instruments that could peer into the distant reaches of space and time. Eventually, enlarging telescopes no longer improved our view, because the atmosphere which helps sustain life on Earth causes substantial distortion and reduction in our ability to view distant celestial objects with clarity.

      Hubble Space Telescope in orbit.

      © JURGEN FALCHLE/ALAMY STOCK PHOTO

      That’s why astronomers around the world dreamed of having an observatory in space – a concept first proposed by astronomer Lyman Spitzer in the 1940s. From a position above Earth’s atmosphere, a telescope would be able to detect light from stars, galaxies, and other objects in space before that light is absorbed or distorted. Therefore, the view would be a lot sharper than that from even the largest telescope on the ground.

      In the 1970s the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) began working together to design and build what would become the Hubble Space Telescope. On 25 April 1990, five astronauts aboard the space shuttle Discovery deployed the eagerly anticipated telescope in an orbit roughly 600 km (380 mi) above the Earth’s surface. That deployment and, later, the unprecedented images that Hubble delivered represented the fulfillment of a 50-year dream and more than two decades of dedicated collaboration between scientists, engineers, contractors, and institutions from all over the world.

      Since Hubble was launched, a number of other space telescopes have been successfully deployed to advance our knowledge of the Universe. These include the Spitzer Space Telescope, named for the man whose idea sparked a new era in telescopes and observation.

      Today’s observatories have significantly larger apertures than the basic telescopes of Galileo’s day, but the principle is the same.

      © ALEXANDER CASPARI/SHUTTERSTOCK

      Today’s Telescopes

      Around the world, astronomers, space scientists and astrophysicists plying the depths of the Universe work in a variety of scientific fields, combining physics, chemistry, biology and other sciences to advance human knowledge of space. Much of their work relies on data from telescopes devoted to the observation of celestial objects. These can be either ground-based (located here on our planet) or space-based, rotating in orbit around Earth.

      Ground-based telescopes are typically located in places around the world that meet a certain set of observing conditions. Broadly speaking, this includes locations with good air quality, low light pollution, and often high altitude to reduce the impact of the atmosphere on observations. Generally, you’ll find the world’s top observatories on mountains, in deserts, and/or on islands – sometimes a combination of all three. Well-known locations with multiple ground-based telescopes include Mauna Kea in Hawaii, the Atacama Desert in Chile, and the Canary Islands.

      Space-based telescopes are, as their name suggests, located outside the Earth’s atmosphere in orbit. As such, they often have much greater ability to capture high-resolution images of celestial objects, unaffected by the interference of our atmosphere. The most popular space telescopes include the Hubble and Spitzer Space Telescopes, both operated by NASA’s Jet Propulsion Lab (JPL) in California. Other space telescopes include the Transiting Exoplanet Survey Satellite (TESS) and forthcoming James Webb Space Telescope (which will replace the Hubble).

      For non-professional astronomers, the Zeiss Telescope at Griffith Observatory, CA, offers a glimpse at the heavens.

      © CHECUBUS/SHUTTERSTOCK

      Types of Telescopes

      Astronomers gain knowledge by looking across the spectrum of light frequency. Typically, the tools they use fall within two broad categories: optical telescopes and radio telescopes. The instruments used to gather this data comb across the entire electromagnetic spectrum. Visible light rays (what we see when we view the stars with the naked eye) are actually only a small part of this spectrum; radio waves, infrared, ultraviolet, X-rays and gamma-rays are all also examined for the information they contain about far-off objects.

      Ground-based observatories often focus on radio waves, which can be captured by antennas, and visible and infrared light, which are gathered at large optical telescopes. The technique of spectroscopy can help parse the information encoded in these rays. Other electromagnetic waves such as X-rays are best received in space, and these are monitored by telescopes in orbit where Earth’s atmosphere doesn’t get in the way.

      Lowell Observatory in Arizona.

      © LISSANDRA MELO/SHUTTERSTOCK

      How to Use This Book

      Like its namesake, the book you hold is big – and like our understanding of the Universe, it is also, by necessity, incomplete. Astronomers continue to explore the Universe with ever-improving technology, unlocking previously unknown secrets and mysteries. In these pages, you’ll discover some you likely don’t already know, and undoubtedly have questions and hypotheses about what we’ll discover next.

      As you work through this text, the general organisation of the book will lead you from home on our Earth out into the far reaches of the solar system, then into our neighbouring stars and planetary systems and finally into the rest of our galaxy and the Universe as a whole, via carefully selected examples of known exoplanets, stars, nebulae and galaxies, as well as even more exotic deep-sky objects. You’ll discover as much as we know about our celestial neighbourhood, and our place in it. In addition to planets and moons, get to know our Sun, explore the asteroid belt and the Kuiper Belt, and learn what lays beyond, in interstellar space.

      This artist’s illustration gives an impression of how common planets are around the stars in the Milky Way.

      © COURTESY NASA, ESA, AND M. KORNMESSER (ESO)

      Outside our solar system, the book guides you to some of the notable neighbouring stars, stellar systems, and exoplanets we’ve discovered. You’ll understand how we search for planets where life might exist and the stars they orbit. Some of these are located within the Milky Way; others we’ve observed from our particular perspective in the Universe though they live far beyond the boundaries of what we consider our galaxy.

      Finally, the book steps out to the edge of the observable Universe – at least what we’ve observed with the technology available today. You’ll get to know the structure of the Milky Way as well as an orientation to neighbouring galaxies like the Andromeda Galaxy which is visible from Earth. You’ll explore other galactic formations and zoom even further out to learn about galactic clusters and superclusters. By the end of the book, you’ll have a sense for the structure of the entire Universe as well as some of the big questions we still have as we ponder our place in it. You may not be able to plan your next vacation on the basis of the planetary moons, exoplanets and stunning nebulae featured, but you’ll find lots to amaze and awe.

      An artist’s concept of our Milky Way Galaxy.

      © COURTESY NASA/JPL-CALTECH

      Naming Conventions

      As you work through this book, you’ll discover objects that go by a variety of names. Some you will recognise, but others may seem encoded. Celestial nomenclature has long been a controversial topic. At its inaugural meeting in 1922 in Rome, the International Astronomical Union (IAU) standardised the eighty-eight constellation names and their abbreviations. Over half of these date back to Ptolemy, with the rest being more recent additions. Since standardising the constellations, the IAU has gone on to certify the names of other astronomical objects, though common usage doesn’t always immediately follow suit

      Additionally, there’s the added layer of complication between an object’s name and its official designation. Generally, a celestial object’s name refers to the (usually colloquial) term used in everyday speech, while designation is solely alphanumerical and used almost exclusively in official catalogues and for professional astronomy.

      Pictured is the Helix Nebula, otherwise known as NGC 7293.

      © GIULIO ERCOLANI/ALAMY STOCK PHOTO

      The cataloguing of stars has a long history. Since prehistory, cultures and civilisations around the world have given their own unique names to the brightest and most prominent stars in the sky. As astronomy developed over the centuries, a need arose for a universal cataloguing system, whereby stars were known by the same labels, regardless of the country or culture from which the astronomers came.

      To solve this problem, astronomers during the Renaissance attempted to produce catalogues of stars using a set of rules. The earliest example that is still popular today was introduced by Johann Bayer in his Uranometria Atlas of 1603. Bayer labelled the stars in each constellation with lowercase Greek letters, in the approximate order of their (apparent) brightness (for example, Alpha Tauri).

      1661 ‘map’ of Andromeda constellation.

      © SCIENCE HISTORY IMAGES / ALAMY STOCK PHOTO

      Nearly 200 years after the introduction of Bayer’s Greek letter system another popular scheme arose, known as Flamsteed numbers, named after the first English Astronomer Royal, John Flamsteed. In this scheme, stars are numbered in their order of right ascension within each constellation (for example, 61 Cygni). Other designation schemes for bright stars have been used, but have not seen the same degree of acceptance. One such scheme was introduced by the American astronomer Benjamin Gould in 1879. Only a handful of stars are occasionally referenced with the Gould scheme today (for example, 38G Puppis).

      Stars discovered more recently are fainter than those catalogued under the Bayer or Flamsteed schemes, as they are found by higher-powered telescopes and means of detection. As astronomers discover these new stars, it is standard practice to identify them with an alphanumeric designation. These designations are practical, since star catalogues contain thousands, millions, or even billions of objects. There are also special rules regarding binary and multiple stars, variable stars, novae and supernovae. All of these approaches build on the very first such systems. Messier’s 1771 catalogue is one of the best known compilations of non-stellar deep-sky objects, created to list known ‘nebula’. At the time this meant objects that were neither comets nor stars. The later 1888 New General Catalogue (NGC) compiled by John Louis Emil Dreyer added to the number of classified objects previously found by the Herschel family, from star clusters and nebulae to galaxies. The prefixes ‘M’ and ‘NGC’ indicate objects from these respective catalogues, and many deep-sky objects carry both numbers as well as a more common name.

      Within this book, you will find both the name and the more official catalogue designation; if you see only a designation, that means the object has not been given a formal name. Equipped with this foundation of knowledge, you’re ready to begin your exploration. Whether you stay close to home or jump straight to the distant edges of our knowledge, the Universe is an endlessly interesting space to let your mind journey.

      A portrait of the astronomer Charles Messier.

      © GL ARCHIVE/ALAMY STOCK PHOTO

      Top Highlights

      Get to Know Our Sun

      1In the Universe, our Sun may not be special or unique – but it is very important to us on Earth. Learn about the Sun, what’s happening deep inside the fiery corona, and the research we’re currently doing to better understand our nearest, life-giving star.

      Learn About Mars, Our Next Home?

      2Zoom in to Mars, the neighbouring planet that continues to captivate our hopes for an off-Earth colony. Learn more about why Mars is such a compelling destination for the human race and discover what may have changed this planet from an Earth-like place to the one it is today.

      The Mars Curiosity rover at Namib Dune.

      © COURTESY NASA/JPL-CALTECH/MSSS

      Meet Other Objects in the Solar System

      3Get to know beloved Pluto and other overlooked dwarf planets in greater detail, as well as the asteroids and comets that punctuate the solar system. You’ll discover there are a variety of other objects in our area than just the Sun, eight planets, and 193 known moons.

      Discover Earth-Like Exoplanets

      4Peer deep into other stellar systems like TRAPPIST-1 and Keppler-22, where exoplanets sit within the ‘habitable zone’. Scientists believe some of these exoplanets may have conditions similar to those on Earth – including those which led to life on our planet.

      Journey to the Nearest Star

      5Visit Proxima Centauri, the closest star to our Sun, a mere 4.243 light years away. With neighbouring Alpha Centauri and Beta Centauri as well as a potentially Earth-like exoplanet of its own, Proxima Centauri gives us a good example of the variety of solar systems in the galaxy.

      Wonder at Supernovas and Black Hole Quasars

      6Stars come in more types and stages than the yellow dwarf we are most familiar with. Explosions like Kepler’s Supernova leave fantastical nebulae in their wake. ULAS J1120+0641 is a distant, supermassive black hole-powered quasar emitting jets of intense radiation.

      Orient Yourself in the Milky Way

      7Learn about the arms of our spiral Milky Way Galaxy and where we sit within ours, the Orion Arm. You’ll gain context on which parts of the galaxy we can see – and the mysteries our galaxy still holds for researchers.

      Understand How Galaxies Interact

      8Taking a wider view, gain an understanding of the variety of different galactic formations in the Universe and how, on a larger scale, vast clusters which gather thousands of galaxies bound together by gravity.

      © NASA IMAGES/SHUTTERSTOCK

      A colourised image of barred spiral galaxy NGC 1672; its arms are home to stellar nurseries.

      THE SOLAR SYSTEM

      © COURTESY NASA/JET PROPULSION LABORATORY-CALTECH

      Solar System Highlights

      Living on Planet Earth

      1Our Universe has many wonders, but the greatest wonder of all is the one that’s closest to home. As far as we know for now, it’s the only place amongst all the stars, moons, asteroids and planets where life has developed in all its diverse, strange and dazzling forms. So if you only take one thing from your trip around the Universe, it has to be this: Planet Earth is a very special place indeed.

      Watching ‘Earthrise’ from the Surface of the Moon

      2There are plenty of iconic photographs out there, but few can have had the epoch-changing impact of Earthrise – the image of our own planet appearing above the moon’s horizon, a brilliant blue globe suspended in the infinite blackness of space, revealing for the first time the wonder – and fragility – of the planet we call home.

      Earthrise from the moon.

      © COURTESY NASA/GODDARD/ARIZONA STATE UNIVERSITY

      Following in Neil Armstrong’s Footsteps

      3As every schoolkid knows, the Mare Tranquillitatis, or Sea of Tranquillity, is the landing site of the Apollo 11 mission, where Neil Armstrong and Buzz Aldrin took ‘one small step for man, one giant leap for mankind.’ Thanks to the moon’s lack of atmosphere, the landing site will be preserved for as long as the moon is there – meaning that humanity’s first footsteps outside Earth will be visible long into the future. That’s quite a thought, isn’t it.

      Climbing the Crater of Olympus Mons on Mars

      4Three times as high as Mount Everest, and covering an area roughly the size of Arizona, Olympus Mons is the biggest volcano on Mars and – as far as we currently know – the biggest anywhere in the solar system. But with a slope of around 5%, it would be relatively easy to climb – and one day, perhaps, the volcano might be a highlight on the itinerary of every Mars space tourist.

      Hiking through the Valles Marineris on Mars

      5The Grand Canyon is big, but it’s not nearly as big as this mighty Martian valley – an epic five times the length of the Grand Canyon and four times its depth, running for nearly a fifth of the planet’s equator. It’s the largest canyon in the solar system, and hiking beneath its towering rust-red cliffs would undoubtedly be a memorable experience.

      Storm-chasing the Great Red Spot on Jupiter

      6Even the worst storms on Earth pale in comparison to Jupiter’s gargantuan Great Red Spot – an enormous tempest that’s been raging for centuries and still going. In fact, it’s so big, it could fit the entire Earth inside its diameter with room to spare.

      Sailing through Saturn’s Rings

      7The unmistakeable sight of Saturn’s seven mighty rings is one of the solar system’s great spectacles, swirling out around the planet at a distance of up to 282,000 km (175,000 mi). Formed of ice, rock and dust, they’re visible from Earth with a half-decent pair of binoculars – but just imagine how incredible they’d look up close if you were to sail past in a spacecraft.

      Getting a Tan on Mercury

      8Frazzled and dazzled by its proximity to the Sun, the solar system’s littlest planet probably isn’t a place you’ll want to linger for long. Sunlight here is 11 times brighter than on Earth, and daytime temperatures can hit scorching pizza oven levels – so if you really want to get that all-over, lasting tan, Mercury is most definitely the planet to head for.

      Watching the Backwards Sunrise on Venus

      9Despite its beatific name, Venus is an altogether inhospitable place: a hothouse world ravaged by a rampant greenhouse effect that has created a hellish atmosphere hot enough to melt lead – so not really ideal for sunbathing. But there is at least one reason for taking a trip to Venus: due to its unusual backwards rotation, the Sun here appears to rise in the west and set in the east.

      Being Dazzled by the Aurorae of Uranus

      10 Just like the Northern Lights on Earth, Uranus has its own aurorae – spectacular, shimmering light displays caused by charged particles interacting with gases in the planet’s atmosphere. But many scientists think they could be way more spectacular than any you’d see on Earth, due to Uranus’ unique sideways rotation and lopsided magnetic field.

      Getting Swept Up in Neptune’s Vortices

      11 Like Jupiter, Neptune is a ‘gas giant’, with a swirling atmosphere composed mainly of hydrogen, helium and methane. The tempestuous atmosphere creates powerful storm systems known as ‘vortices’, where winds are believed to reach speeds many times faster than any storms on Earth (up to 2400 km/h, or 1500mph). One of these, dubbed the Great Dark Spot, was seen by Voyager 2 in 1989 – and although it had disappeared by 1994, other similar vortices have since been spotted.

      Diving into Europa’s Hidden Ocean

      12 Of all the moons in our solar system, Europa may be the likeliest place to find life outside Earth. Beneath its icy crust, the moon is thought to conceal a huge, salty ocean where volcanic or hydrothermal vents are believed to exist on the seafloor – creating very similar conditions to the ones in which many scientists believe life on Earth began.

      Marvelling at Gigantic Ice Geysers on Enceladus

      13 Enceladus, the sixth-largest moon of Saturn, is in many ways the most interesting one. Encased in a thick shell of ice, it’s the brightest object in our solar system – and one of the coldest, with surface temperatures of about -201˚C (-330˚F). It also has a unique feature: giant ice geysers that erupt at its South Pole, intensifying its already dazzling albedo effect (that’s a measure of how it reflects solar energy).

      Watching the Lava Flow on Io

      14 Well over 150 volcanoes have been observed on the little moon of Io, although scientists think that’s just a fraction of the total. Squeezed and contorted by the gravitational pull of Jupiter, it’s the most geologically active body in the solar system – making it a must-see moon for avid vulcanologists.

      If You Like…

      Geological Wonders

      Mt Everest At 8848 m (almost 5.5 mi), Everest is the highest mountain on Earth.

      Valles Marineris, Mars Deeper than six Grand Canyons, this mighty 400 km-long (250 mi) valley is a Martian wonder.

      Verona Rupes On the Uranian moon Miranda, this is the tallest cliff in the entire solar system, rising over 10 km (6 mi) straight up.

      Caloris Basin, Mercury 1545 km (960 mi) across, this vast impact basin was caused by a meteorite strike.

      Enceladus This Saturnian moon has spectacular geysers of ice spouting at its South Pole.

      The Methane Lakes of Titan Liquid lakes and rivers of methane are thought to flow on Saturn’s moon Titan.

      This mosaic of Mars shows the entire Valles Marineris canyon.

      © COURTESY NASA/USGS

      Volcanoes

      Kilauea One of Earth’s most active volcanes can be found on Hawaii’s Big Island.

      Olympus Mons, Mars Though dormant, this is the largest volcano (and mountain) in the solar system, 22 km (14 mi) high and 600 km (375 mi) across.

      Anywhere on Io This Jovian moon has hundreds of active volcanoes to choose from: don’t get too close.

      Maat Mons, Venus A massive shield volcano, and the second-highest mountain on Venus.

      Triton Along with Venus, Io and Earth, Neptune’s moon Triton is one of the few places in our solar system known to be volcanically active.

      Titan This Saturnian moon is home to ‘cryovolcanoes’ which spew not fire, but ice.

      Olympus Mons on Mars rises up in this Viking image mosaic.

      © COURTESY NASA/MOLA SCIENCE TEAM

      Ice

      Antarctica Earth’s continent of ice holds approximately 90% of the planet’s fresh water.

      Uranus One of two ‘ice giants’ in the outer solar system, Uranus’ surface is a swirling, dense fluid made of icy materials.

      Neptune The second of our ice giants, more than 80% of Neptune’s mass is a dense fluid of icy water, methane and ammonia.

      Ganymede The largest moon in our solar system, Jupiter’s moon Ganymede has a coat of ice lined by many ridges and grooves (known as ‘sulcus’).

      Europa The surface of this Jovian moon is completely encased in ice – but beneath it, a huge watery ocean exists.

      Triton Ice volcanoes on Triton spout liquid nitrogen, methane and a dust that falls back to the surface as snow.

      An ice floe in Wilhemina Bay.

      © PETE SEAWARD/LONELY PLANET

      Seas & Oceans

      Earth An astonishing 70% of the Earth’s surface is ocean.

      Europa Though covered by ice, Europa’s ocean may be 60 to 150 km (40 to 100 mi) deep.

      Titan Giant seas of methane churn on the surface of Titan – and may contain forms of life.

      Callisto Like its sister moon Europa, Callisto’s icy crust may conceal a liquid salty ocean.

      Earth’s very own Indian Ocean as viewed from space.

      © COURTESY NASA

      Weird Landscapes

      Utopia Planitia, Mars 3300 km (2050 mi) across, this enormous impact crater is the largest anywhere in the solar system.

      The Cracks of Europa The surface of this frosty Jovian moon is covered in huge striations, ridges and cracks, some measuring hundreds of miles long.

      The Yin-yang world of Iapetus This Saturnian moon is deeply peculiar: it’s half-black, half-white.

      The Canyons of Miranda Miranda’s deeply fissured surface is split by giant canyons, including some 12 times deeper than the Grand Canyon.

      The ‘Death Star’ Moon A huge impact crater gives the Saturnian moon of Mimas a disturbing resemblance to Darth Vader’s planet-killing space station.

      The Ice Mountain of Ceres A lone dome of ice exists on the dwarf planet Ceres.

      Europa’s frozen surface presents dramatic cracks.

      © COURTESY NASA/JPL/UNIVERSITY OF ARIZONA

      Rings

      Saturn Seven in number, Saturn’s giant rings are many thousands of kilometres long, but only around 10 m (30 ft) thick.

      Uranus After Saturn, Uranus has the most impressive rings: 13 in all, split into three distinct zones.

      Neptune Neptune’s rings are so faint, they’re practically invisible.

      Saturn’s C-ring, pictured here, is only one of several.

      © COURTESY NASA/JET PROPULSION LABORATORY;

      Storms

      Tornado Alley, Earth Cutting across the southern United States, this belt of land is home to some of the most powerful winds on Earth.

      The Great Red Spot, Jupiter Storms on Jupiter really are on a different scale: some are big enough to swallow up entire planets.

      The Vortices of Neptune Like Jupiter, Neptune is ravaged by truly apocalyptic winds and storms.

      The Great Red Spot would be the trophy of any storm chaser.

      © COURTESY NASA/JPL-CALTECH/SWRI/MSSS/GERALD EICHSTADT/SEAN DORA

      Transits & Eclipses

      Viewed from our position on Earth, the solar system can be a pretty tricky place to get your head around. From where we are, it always seems like we’re standing still, in a fixed position in space – when in fact, we’re rotating at thousands of miles an hour in a complex dance of interplanetary orbits, circling in space around a common central point, the Sun. Because the distances and scales involved are so large, it’s hard to notice the fact that the positions of the stars and planets are in fact changing all the time literally before our eyes, and the night sky we see is subtly different every single time we view it.

      There is one phenomenon that brings the constant motion of our solar system into sharp focus, however: during an eclipse, we actually get to see the effect of another planetary body in motion right before our eyes.

      A solar eclipse at totality.

      © MMOSURE PHOTOS/SHUTTERSTOCK

      These spectacular events come in two flavours, lunar and solar. A lunar eclipse occurs when Earth moves between the Sun and the moon, blocking out the Sun’s light and casting the Earth’s shadow onto the lunar surface. A lunar eclipse can either be partial, when only some of the Earth’s shadow appears on the moon, or total, when the moon and the Sun are on exact opposite sides of Earth and the Earth’s shadow completely covers the moon. During a total lunar eclipse, the Earth’s atmosphere blocks out most of the blue light coming from the Sun, which makes the moon appear to turn a vivid shade of blood-red. Total lunar eclipses are quite rare, but at least two partial lunar eclipses happen every year, each lasting several hours at a time.

      Even more spectacular is a solar eclipse, when the moon moves into a position between the Sun and the Earth. A solar eclipse also comes in two main flavours, partial and total. A partial solar eclipse happens when the Sun, moon and Earth are not exactly lined up. During a partial solar eclipse, the moon’s crescent moves over the Sun’s surface, and only a part of the Sun is covered up by the moon.

      During a total solar eclipse, the moon moves directly in line with the Sun relative to our position on Earth. The moon appears first as a crescent, then continues to move across the Sun’s face until it becomes a solid black disk, leaving only a thin halo of sunlight around its outer edge, known as the corona. The sky becomes very dark and night-like as the moon’s shadow falls onto the Earth. A total solar eclipse is only visible from a small area on Earth: the people who are standing in the centre of the moon’s shadow when it hits Earth (known as the umbra) will witness a total eclipse, while those standing outside this zone (in the shadow zone known as the penumbra) will only see a partial eclipse. Unlike lunar eclipses, solar eclipses only last for a few minutes.

      There is actually a third type of solar eclipse: the annular solar eclipse, which happens when the moon is furthest from Earth. Because the moon is further away from Earth, it seems smaller, and doesn’t completely block the Sun, making the moon appear as a dark disk on top of a larger solar disc. This creates what looks like a ring around the moon.

      Eclipses are not unique to Earth, the moon and the Sun, however. The same phenomena, known as transits, occur between different planets and moons. Like an eclipse, a transit occurs when one object appears to pass in front of another object. But in a transit, the apparent size of the first object is not large enough to cast the second into complete shadow. Instead, a much smaller dark shadow makes its way across the face of the further planet or star. On occasion, these events can be seen from Earth (with the help of telescopes and other instruments) or by satellites.

      Why Does NASA Study Eclipses?

      Hundreds of years ago, when people observed the moon during an eclipse, they discovered that the shape of Earth is round. Even after all these years, scientists are still learning from lunar eclipses. In December 2011, NASA’s Lunar Reconnaissance Orbiter gathered data about how quickly the moon’s day side (the side that always faces Earth) cools during a lunar eclipse. NASA can determine what the moon’s surface is made of from this data. If an area of the moon’s surface is flat, it will cool quickly. Scientists use this data to know which areas of the moon are rough with boulders and which are flat.

      NASA also studies solar eclipses. Scientists use solar eclipses as an opportunity to study the Sun’s corona (the Sun’s top layer). During an annular eclipse, NASA uses ground and space instruments to view the corona when the moon blocks the Sun’s glare.

      The most recent transit was that of Venus across the face of the Sun in 2012. There have been many such events recorded by astronomers throughout history, although they occur very rarely – transits of Venus, for example, come in pairs, eight years apart, separated by a gap of approximately 120 years. From Earth, the only transits we can see directly are those of Venus and Mercury. The next transits of Mercury are scheduled for 11 November 2019, then again on 13 November 2032. The next transits of Venus won’t be until 11 December 2117 and 8 December 8 2125 – so if you missed the one in 2012, unfortunately you may be out of luck.

      Perhaps the most famous example of transit-hunting was Captain Cook’s voyage across the Pacific in 1769. The official purpose of the expedition was to observe the transit of Venus from the newly discovered island of Tahiti; the hope was that it would enable astronomers to measure the size of the solar system, one of the great mysteries of 18th-century science. But after observing the transit, Cook was also charged with another task: searching for the fabled Terra Australis Incognita, the unknown ‘south land’ that was believed to exist on the southern edge of the Pacific Ocean. Unfortunately, after months of searching, Cook didn’t find it, as it didn’t exist! But he did reach Australia and New Zealand instead, and nearly wrecked his ship on the Great Barrier Reef in the process.

      The search today is much easier. Those interested can see the next solar eclipses on 4 December 2021, over Antarctica; 20 April 2023 in Western Australia and West Papua; 8 April 2024, across North America; and 12 August 2026 over parts of Europe. While many of these eclipses will be narrow paths over land, planning to see a total solar eclipse is a venture well worth undertaking. Lunar eclipses, by contrast, are much more widely visible.

      Introduction to the Planets

      Of the 4.5 billion years since the formation of the solar system, humans have been around for a mere sliver of time, and our studies of our solar system neighbours occupy an even shorter period.

      An artist’s illustration of the planets (and Pluto) as they might be imagined to reach into space from Earth.

      © VADIM SADOVSKI/SHUTTERSTOCK

      Ancient civilisations charted the course of the Sun and moon as far back as megaliths from 10,000 to 11,000 years ago, while ancient Sumeria had its own lunar calendar. In the subsequent centuries, astronomers around the world made astonishing discoveries with modest technology. All were equipped with enquiring minds and in some cases, such as the 6th century Indian scholar Aryhabata, a dazzling grasp of mathematics. The advent of the telescope, in the 17th century, allowed the likes of Galileo to observe planetary features with his own eyes. In 1963, Yuri Gagarin was the first human in space; in 1969, Neil Armstrong became the first person on the moon, the first to walk on the surface of another celestial body. But humans have yet to visit another planet. If any should take your fancy, here’s a snapshot, in order of their distance from Sun, of what you need to know.

      Mercury

      Mascot

      The winged messenger.

      Size isn’t everything

      The smallest planet in our solar system is also, at 0.4 astronomical units away, the nearest to the Sun. So close, in fact, that sunlight on Mercury is seven to eleven times brighter than it is on Earth depending on distance from the Sun, yet without an atmosphere that’s still not sufficient to make it the hottest body in the solar system – that’s Venus. Mercury is, however, the fastest planet and speeds around the Sun at a blistering average clip of 170,505 km/h (105,947mph). Following an elliptical orbit, in which its proximity to the Sun can vary by as much as 24 million km (15 million mi), it makes a complete orbit of the Sun in just 88 days. That means each Earth year is more than four Mercurian years.

      When was it discovered?

      As a bright satellite visible to the naked eye, Mercury was known to antiquity as a non-fixed object in the sky. It was one of the Greek planets (though they weren’t defined in exactly the same way) as well as being known to the Babylonians. The first sighting of Mercury in the scientific age came in 1631, thanks to the invention of the telescope. This led to simultaneous observations, by the English astronomer Thomas Harriott and the Italian scientist Galileo Galilei. That same year it was observed transiting before the Sun.

      © DOTTED YETI/SHUTTERSTOCK

      Fascinating fact

      Despite its reputation as a hot, speeding mass, more recent observations have shown Mercury to be a planet of contrasts. For example, the interiors of the deep craters found at Mercury’s north and south poles lie in permanent shadow; while the rest of the planet is exposed to temperatures as high as 427˚C (800˚F), the craters may contain water-ice according to 2012 observations by the MESSENGER mission.

      Any features of particular interest?

      The intriguing spines of Pantheon Fossae on Mercury’s surface catch the eye. The 40 km (24 mi) crater was discovered during MESSENGER’s first flyby of the planet, in 2008, and is situated upon Caloris Planitia, the ‘fire plains’ of northern Mercury. The feature takes its name from the ancient Roman Pantheon, the celebrated roof of which was built by the equally celebrated Apollodorus of Damascus. It consists of a central core, from which sections radiate outwards. In the case of Pantheon Fossae, the main crater sends out long, thin troughs – tectonic fault lines that earned Pantheon Fossae the nickname of the ‘spider crater’.

      Are there moons or rings?

      Small Mercury makes its orbit of the Sun all on its own, without the company of any moons or rings.

      Could it support life?

      Mercury’s environment is not conducive to life as we know it. Battered by the Sun’s heat and lacking an atmosphere to protect it from the solar wind or from meteor impacts, life on sweltering Mercury isn’t considered to be a possibility.

      Mercury in popular culture

      With little hard data to go on, Mercury’s appearances in popular culture relied on a blend of guesswork and artistic license. Isaac Asimov was drawn to Mercury’s, well, mercurial nature, famously harnessing it for ‘I, Robot’, a story whose anti-hero is a robot built to withstand extreme solar radiation. (Not to be confused with ‘Sonny’, the robot with human aspirations, who appears alongside Will Smith in the 2004 movie that borrows Asimov’s title.) Elsewhere, the Zanzibar-born Farrokh Bulsara took the planet’s name as his own, and thus gave the world Freddie Mercury. The show Invader Zim included the planet being turned into a spaceship.

      Has there been a key mission?

      More recent flybys of Mercury by MESSENGER have provided scientists with a wealth of data about the composition of the planet: we now know, for example, that Mercury’s large, metallic core represents about 85% of its total radius. Images from MESSENGER have also shown ‘crater rays’, vast streaks on the planet’s surface formed by ejecta material following meteor strikes. In 2015, MESSENGER was crashed into the surface of Mercury, bringing its mission to an end.

      What are the scientists saying?

      The next mission to Mercury, which scientists hope will yield yet more of the planet’s secrets, is already on its way. Launched by the European Space Agency (ESA) in 2018, the BepiColombo mission will

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