Earth is not the wettest planet, Mercury is not the hottest, nor Saturn the only one with rings.
Every so often, a magazine or TV programme will draw up a list of the Seven Wonders of the Solar System. The first item on the list is always Saturn’s rings. There’s nothing quite like them anywhere in the observed universe. These majestic discs are made almost entirely of water ice, with small amounts of rock thrown in. You’d probably break your teeth if you tried to eat them.
Saturn is often given the romantic name of the ringed planet*. It is unique in its spectacle, but not in its status. We now know that half the planets in our Solar System have rings, for Jupiter, Uranus and Neptune are also engirdled by matter. None, though, are anything like as impressive as the discs of Saturn. Indeed, no one had seen these other hoops until the Voyager space probes visited in the 1970s and 1980s. Jupiter has four rings, Uranus has 13, while Neptune hosts five.
Where do these rings come from? In Saturn’s case, it’s still something of a mystery. The particles in the rings range from tiny specks up to chunks 10m (33ft) across. One theory paints the rocky components as the remains of a lost moon, which was torn apart by the gravitational effects of Saturn. Others think the rings formed early. Rather than being the remnants of an obliterated moon, they are the inchoate ingredients of a world that never was. At least some of the material comes from elsewhere in the Saturn system. One of the rings contains ice spewed out in geysers from the surface of the moon Enceladus.
The Jovian ring system (that’s the fancy way of saying ‘rings of Jupiter’) has been intimately probed by the Galileo spacecraft, which orbited the gas giant between 1995 and 2003. Here, the rings coincide neatly with the orbits of four of Jupiter’s moons. The rings seem to have been formed from dust kicked up from these moons during impacts.
The ring systems of Uranus and Neptune are less well studied. The planets are too distant to observe in detail from Earth, and only one space probe, Voyager 2, has whizzed by. The rings of Uranus, first spotted in 1977, are the most extensive after those at Saturn. They contain little dust and are mostly composed of small rocks, thought to be leftovers from the collision of moons. Neptune’s rings are the most recent to be discovered around a planet in our solar system, first glimpsed in 1984. In contrast to those of Uranus, Neptune’s five rings are dark and dusty, but they are also believed to originate from moon collisions.
All four gas-giant planets have rings, but that doesn’t mean the phenomenon can’t happen round other types of world. In 2013, astronomers discovered two rings around the minor planet 10199 Chariklo, an otherwise unremarkable lump of rock between Saturn and Uranus. Their existence confirms that you don’t need to be huge or gaseous to harbour rings.
Very few objects with ring systems have been spotted beyond our solar system. This might be because they are rare, but more likely it is because they’re hard to discern at such distance. The best candidate observed so far was detected around a star known as J1407, 420 light years from Earth. This planet – or perhaps brown dwarf – is thought to have a colossal ring system that stretches out about 640 times further from the parent planet than do Saturn’s rings. It has been dubbed ‘Saturn on steroids’.
* FOOTNOTE I prefer ‘the floaty planet’. Saturn is the only world whose density is lower than that of liquid water. If you could find a sufficiently capacious ocean, and could somehow stop the dunked planet from coming apart, then it would bob up and down in the water.
Have you ever wondered why scientists talk about launching crewed missions to Mars, the Moon or the asteroids, but never to Mercury? It’s not because it is far away. The distance between Earth and Mercury varies considerably, and is sometimes less than that between Earth and Mars. There are, in fact, several good reasons why Mercury is less alluring than the Red Planet. Radiation dose, tricky orbital mechanics and the lack of any atmosphere all lessen the appeal, but it’s also too darned hot.
As the closest planet to the Sun, Mercury comes in for a bit of a roasting. If you were to stand upon its surface, the Sun would appear about three times larger in the sky than it does from Earth. As a result, the daytime side of Mercury can reach around 430ºC (806ºF). That’s much hotter than the highest setting on a domestic oven. You can see why Mercury does not make it onto the bucket list of many astronauts.
But that’s not the full picture. Mercury spins very slowly. Its day – the time taken to complete one full revolution – is equivalent to 60 Earth days. Large swathes of the planet do not receive any sunlight for many weeks, and the toasted rock gets a chance to cool down. Parts of the dark side of Mercury can drop to as low as -180ºC (-292ºF). Taking this into consideration, the average (mean) temperature on Mercury is an almost-manageable 167ºC (333ºF), though most regions would be much hotter or much cooler.
Even though it is the closest planet to the Sun, Mercury is not the hottest planet. That accolade falls to the next planet out, Venus. You don’t see too many advocates calling for a crewed mission to this planet either. That’s because Venus is enshrouded in a thick, corrosive atmosphere with clouds of sulfuric acid. The surface experiences a pressure almost 100 times greater than you’d find on the Earth. This most spirited of planets also claims more than its fair share of volcanoes, lava flows and lightning storms. It is a terrifying place.
The temperature at the surface of Venus is typically around 462ºC (864ºF). That’s the average temperature, and it is hotter than Mercury at its very hottest. How so? It’s all down to that thick carbon-dioxide atmosphere, which acts as a thermal blanket, trapping heat close to the surface. The phenomenon is often described as a ‘runaway greenhouse effect’, an extreme version of the global warming seen on Earth in recent decades.
Despite the perils, Venus has been visited by a handful of spacecraft. The first to arrive was the Soviet Venera 9 probe in 1975. Its lander sent back the first photographs from the surface – indeed, the first photographs from any extraterrestrial planet’s surface. Venera 9 lasted just 53 minutes. To this day, the longest any probe has survived on the surface is about two hours. Humans are unlikely to pay a visit without a radical leap in materials science. However, our interest in Venus doesn't end there.
Although the surface of Venus is unwelcoming in its current state, there may be possibilities higher up. The atmosphere of Venus quickly cools with altitude. A blimp floating through the skies at 50km (31 miles) would experience surprisingly Earth-like conditions. Here, the outside pressure is 1 Atmosphere (equivalent to sea level on Earth), temperatures are as low as 50ºC (122ºF), and even gravity would be similar to that on our own planet. However, you would not want to crash land.
Water covers about 71 per cent of the Earth’s surface. It isn’t called ‘the blue planet’ for nothing. But our home world is not the only one to contain liquid water. Nor is it the only body to hold oceans.
This is important, for life as we know it needs water. From the smallest microbe to the largest blue whale, every creature on the Earth relies upon the wet stuff. Why? Because biology can’t happen without the movement and mingling of small molecules. Carbohydrates, proteins, lipids, nucleotides and inorganic compounds all need a liquid solvent to interact. They aren’t going to shift much in solids like ice or rock. They could move around very pleasantly in a gas state, but gases have a habit of diffusing away before anything interesting can happen. Plasma, the fourth state of matter found in stars and TV screens, is too hot and electrically charged for the job. No, only a liquid will do. Water has the ideal properties, being both abundant and stable at the right temperatures to support a wide range of chemical and therefore biochemical reactions. Hence, the mantra of exobiologists – those who study the possibility of life on other worlds – is ‘follow the water’.
Water is surprisingly common throughout the Solar System. Many comets are made of ice, and for this we should be thankful. The oceans of Earth probably arrived piecemeal, from the countless impacts of water-bearing comets. Water has been detected on most of the planets, and many of their moons. Space probes have even found signs of ice water on the seemingly barren surfaces of Mercury and the Moon. Here, ice is sheltered from the Sun’s rays within the airless fathoms of impact craters.
Whole oceans are known on other worlds. In 2005, the Huygens probe touched down on the Saturnian moon of Titan. It discovered shorelines, rivers and lakes. Rain falls from clouds, just like on the Earth. There’s one big difference here, though. Titan is a much colder world than Earth and so liquid water cannot exist. The lakes, rivers and rain are all formed from liquid methane and ethane. For various reasons, life as we know it is unlikely to exist in the gloopy oceans of Titan. Water is a much better medium for the complex reactions necessary for life. It was long thought that only the Earth has such environments; now we know better.
The first hints of an extraterrestrial ocean were found on Europa, a moon of Jupiter, in 1979. The Voyager 2 space probe showed an ice-encrusted surface, whose cracks and fissures spoke of activity beneath. Subsequent studies have found that a liquid ocean of water almost certainly lies below the crust. What’s more, the volume of water in this ocean is thought to be greater than we have here on Earth. Incredible, isn’t it? Our planet is not unique in bearing oceans, and it’s not even the wettest world in our neighbourhood. Whether this extraterrestrial ocean contains life remains to be seen, but we may know soon. NASA and other space agencies are developing plans for a lander capable of drilling down into these subeuropan waters.
Europa was thought to be unique. Nowhere else in the Solar System had quite the same conditions that might favour water oceans. Again, we now know better. Other moons of Jupiter, such as Callisto and Ganymede, are thought to have sizeable subsurface oceans. Saturn’s moon of Enceladus not only harbours a hidden ocean, but it also ejects great plumes of water into space, as pictured by the Cassini probe. Titan, besides its methane-rich environment, also contains bountiful reserves of water ice. Even the dwarf planets of Ceres and Pluto have now joined this soggy club. Water is almost everywhere we look. According to an estimate in the 1 January 2016 edition of Scientific American the Solar System could contain up to 50 times as much water as is found in Earth’s oceans.
Such discoveries have put paid to the notion that life is only possible in the so-called ‘Goldilocks Zone’. This is the region of space that is close enough to the Sun for liquid water to exist on the surface (given enough atmospheric pressure). Too near the Sun and the water will boil off; too far and it will freeze. We now know that liquid water can exist regardless of the distance from the Sun, so long as there is some other energy source, such as heat from a moon’s core or radioactive decay. Scientists have also discovered life on Earth that can thrive in extreme environments and is essentially independent from the Sun. Whole ecosystems congregate around hot vents in the deep ocean, where the spark of life is geothermal rather than solar in origin. If such life can exist on Earth, then why not within one of the subsurface oceans elsewhere in the Solar System? We should know, one way or the other, within the next few decades. It is a remarkable time to be alive … on any moon or planet.
Tails always point backwards here on Earth. The waggy bit of a dog might droop or curl, but it invariably emerges from the hindquarters in the opposite direction to the head. The contrail of an aeroplane or the flames of a rocket will always point in the direction opposite to travel. So you might think that a comet’s tail does the same. It does not.
As a matter of fact, comets don’t sport any tail under normal circumstances. Comets spend most of their existence out on the fringes of the Solar System as cold, icy bodies. It is only when they dip inwards and approach the Sun that a tail forms. As the comet approaches, the Sun’s rays eject dust and gas, which form into a tenuous atmosphere around the comet called a coma. A combination of solar wind (charged particles from the Sun) and solar radiation pushes on the coma, forcing out gas and dust into what we call a tail. Actually, if we look carefully, we should see two tails: one of gas and one of dust.
The tails point in very similar directions. But they are not like aeroplane contrails; they do not necessarily extend out ‘behind’ the comet, in the opposite direction to travel. Instead, they stretch out away from the Sun – coaxed that way by the solar wind and radiation. The gas tail points directly away from the Sun while the dust tail tends to curve. When a comet has swung around the Sun and begins its journey back to the outer Solar System, the tails also swing round. During this phase, they point ever closer towards the direction of travel, as the comet recedes from the Sun. The comet’s coma and tails shrink and eventually vanish as the Sun’s rays become weaker.
The city of York in England is famous for its medieval walls and cosy inns, but it also has a flair for the astronomical. Just to the south, near a supermarket car park, you’ll find a model of the Sun the size of a shed. Walk 100m (328ft) down a path and you’ll reach the innermost planet of Mercury. It’s tiny – less than 1cm (⅜ in) across, to put it in scale with the nearby Sun. Carry on down the path and you’ll find all the remaining planets. Earth is about 250m (820ft) from the facsimile Sun, and the size of a baked bean. Jupiter is 1.35km (7/8 mile) out. As the largest planet, it is represented by a sphere with the girth of a basketball. Pluto, which still qualified as a planet when the model was opened in 1999, is 10km (6¼ miles) from the Sun and just millimetres across. There the Solar System ends.
Such models are found throughout the world. They give us a sense of the vast distances between the planets, and their relative sizes. On the York model, to walk from the Sun to Mercury will take most people less than a minute. To travel all the way to Pluto, by contrast, would take at least an hour at brisk pace*. These models are brilliant, and worth seeking out. Yet almost all short change the Solar System, for it extends well beyond the orbit of Pluto.
Pluto, no longer deemed a planet, is one of an untold number of objects in the Kuiper Belt. This region of space can be thought of as a great doughnut of ice and rubble beyond the orbit of Neptune. It goes out a long way. Neptune, where the belt nominally begins, is at a distance of 30 Astronomical Units from the Sun (1 AU is the mean distance from the Earth to the Sun). The far end of the Kuiper Belt is thought to lie at around 50 AU. If we add the Kuiper Belt to our model, then two-fifths of the Solar System lies beyond the realm of the planets. Pluto has an eccentric orbit that straddles the inner and outer bounds of the belt. This enigmatic world even dips within the orbit of Neptune for part of its cycle, an oddity that meant it wasn’t always the farthest planet from the Sun (when it still was a planet).
The Kuiper Belt contains ‘spare’ material from the dawn of our solar system – pieces of ice and rock that never coalesced into full-on planets. Earlier, I compared it to a doughnut, but a better baking analogy would liken it to the offcuts of pastry leftover from a pie crust. The Kuiper belt is a relatively recent discovery. Until 1992, Pluto and its moon Charon were the only known objects confined to this region of space. Astronomers have since catalogued over 1,000 Kuiper-Belt objects. Some are more than half the diameter of Pluto. Hundreds of thousands more are thought to exist and it will be many decades before the belt is adequately charted.
The Kuiper Belt does not yet mark the end of the Solar System. An associated group of objects known as the Scattered Disc can travel out as far as 150 AU – remember, the Kuiper Belt stops around 50 AU, so this effectively trebles the size of our solar system. It is in the Scattered Disc that we find Eris, the troublemaker.
The discovery of Eris in 2005 raised some interesting questions that provoked controversial solutions. This mysterious world is about the same size as Pluto, but 25 per cent more massive. If Pluto deserves planethood, then so too does Eris. And if something the size of Eris could have eluded astronomers for so long, who knew how many other similarly sized worlds were out there? We might end up with a solar system of hundreds of planets.
The decision was made to create a new designation – dwarf planet – for anything massive enough to form a sphere, but not large enough to have cleared its orbit of other debris. The new world was dubbed a dwarf planet along with Pluto and the asteroid Ceres. Eris is now considered the ninth most massive object in the Solar System (not including the Sun), and the largest never to have been visited by a space probe. It is currently about three times as far from us as Pluto, so it’s unlikely to get a visitor for some time.
Not all definitions of the Solar System are beholden to rocks and ice balls. One measure is the border where the solar wind – streams of particles from the Sun – balances with similar forces from outside the Solar System. This boundary is approached at a place called the ‘Termination Shock’, where the solar wind slows abruptly. The Termination Shock is followed by the heliopause, where the solar wind no longer has enough energy to push out from the Sun. The Voyager 1 spacecraft, launched in 1977, has travelled so far that scientists believe it has passed beyond this boundary and is now in interstellar space. That happened at around 121 AU. In one sense, this is the edge of the Solar System.
We’ve passed through the Kuiper Belt and Scattered Disc and marked the boundary where the Sun’s rays are turned in their tracks. Can we push things yet further? Why, yes we can, and flamboyantly so. The objects we’ve seen up to here reach only about 150 times the Earth–Sun distance. But it’s time to meet the Oort Cloud, which resides more than 1,000 times further out. This is way beyond the range of the solar wind, but still within the gravitational influence of the Sun.
Nobody has ever detected an object in the Oort Cloud. It is so distant that reflected sunlight is too feeble for current telescopes. Nevertheless, there are sound theoretical reasons for believing that a reservoir of icy planetesimals is out there, some 50,000 to 200,000 AU away. Observations of certain comets strongly suggest that they must have their origins somewhere in this zone. If that upper distance is to be believed, the Oort Cloud extends most of the way to the nearest star, Alpha Centauri*. Objects in the cloud are only weakly attracted to the Sun and are therefore easily knocked out of orbit – whence came many of the comets that delve into the inner Solar System.
So there we go. If you thought you might reach the end of the Solar System by travelling to Neptune or Pluto, be advised that you’re not even one-thousandth of the way to your goal. It would be like jogging half the length of a football pitch and calling it a marathon. Perhaps it is time to update some of those Solar System models.
We should note in finishing that not all walkable models end at Neptune or Pluto. In particular, we might celebrate the model of the Solar System in Sweden, which spans almost the entire length of that country. The Sun is symbolized by the Ericsson Globe in Stockholm. As the largest hemispherical building on the planet, it’s a pretty good stand-in. The inner planets are all within 12km (7½ miles) of the dome, but you have to head 300km (186 miles) north to find Pluto and its largest moon Charon. Most models would end here, but the Swedish Solar System is more adventurous. Head still further north and you’ll encounter trans-Neptunian objects such as Sedna and Eris. Stray 900km (559 miles) from the Stockholm Sun and you’ll reach the Termination Shock. It’s inside the Arctic Circle, which feels somehow appropriate.
* FOOTNOTE On the same scale, a journey to the nearest star (other than the Sun) would be equivalent to almost two laps of the Earth.
* FOOTNOTE Actually, that’s another fact that’s not quite right. Alpha Centauri is often given as the closest star to Earth (other than the Sun). But what looks like a single star to the unaided eye is actually three stars: a binary pair called Alpha Centauri A and B, and a dim companion star called Proxima Centauri. The latter is currently a little closer to Earth than the binary pair.
It’s commonly said that planets orbit around stars, and that moons orbit around planets. This means that the Sun is at the centre of our solar system, and holds the rest in thrall (although it in turn follows its own orbital tracks around the centre of the galaxy). For most purposes, this is a perfectly good approximation. I’ve probably said as much elsewhere in the book. But if we want to plumb the deepest depths of nitpickery – and, of course, we do – then there’s a flaw in these statements. It’s a small flaw, but one with the power to reveal alien worlds around other stars. Let me explain.
It’s all about centres of mass. If you balance this book on the end of your finger, you’ll find that there’s one place, right in the centre, where it will perch. This is the book’s centre of gravity. If you’re reading an ebook, the balance point might be a little away from the centre, as the mass of the batteries, casing and other components is not evenly distributed. If, for some unfathomable reason, you’re reading these words on the surface of a garden shovel, the balance point would be shifted still further from the centre and close to the heavy business end of the tool. It’s the old ‘law of the lever’ that everyone learns at school. Centres of gravity are found closer to the highest concentration of mass.
Now let’s apply this idea to the heavens. Planets, stars and moons have centres of gravity too. If they are spherical and internally symmetrical, this point is right at the centre. Now put a planet in orbit around a star. This simple system itself has a centre of mass – the point where a god might balance a see-saw of the two objects on the end of a finger. As with the shovel, the centre of gravity is closest to the object with the most mass – in this case the star. But it’s not right at the centre of the star. The mass of the planet pulls the balance point further out. It is this balance point – called a barycentre – which the planet truly orbits.
Most stars are much, much more massive than nearby planets. The Sun, for example, is about 333,000 times bulkier than the Earth. Their barycentre – the point on the giant see-saw where their masses balance – is deep within the Sun. It therefore appears to us that the Earth goes round the Sun rather than the hidden barycentre that it truly orbits. Jupiter, though, is much more massive, and a long way out. The barycentre with the Jupiter–Sun system lies outside the star’s surface. If we could view just these two bodies alone, we would notice the Sun making a tiny orbit around the empty barycentre, with Jupiter doing its usual thing much further out.
Our entire solar system also has its own barycentre. This is the spot where the masses of every object, from the Sun to the tiniest asteroid, would all balance out if you could construct some multidimensional see-saw. The barycentre is always moving, because all the objects in the Solar System are themselves moving. Sometimes it is buried deep within the Sun, other times, it is outside the surface of the Sun. Put the other way, the centre of the Sun is rarely, if ever, right at the very centre of the Solar System.
Imagine what this might look like to somebody observing from far away. The Sun would appear to wobble as it tracked the shifting barycentre. We can detect such wobbles in other stars. It is one of the methods astronomers use to find planets beyond our solar system. A significant wobble means that there must be other centres of mass around the distant star. The patterns in that wobble can help determine how many planets are in the system, and their masses.
So planets do not truly orbit stars – they each orbit a mutual barycentre. The Sun is not at the centre of our solar system – it dances around the shifting barycentre that is the true centre of mass of our local neighbourhood. It’s a small effect, but one that can be detected in other stars. There is no better example of how nitpicking a well-known ‘fact’ – like ‘the Earth orbits the Sun’ – can, quite literally, open our eyes to new worlds.
The Royal Observatory in Greenwich, London, is one of the best places on the planet to learn about the cosmos. Known as the home of time and space, this is the facility through which the zero meridian was defined. The observatory’s staff are a friendly bunch, and always willing and enthusiastic to explain the wonders of the Universe. I asked them to share the commonest misconceptions they hear from the public. First on the list was this: that the Sun is a big ball of fire. They hear it every day.
You can understand where the mistake comes from. The Sun is bright and hot like fire, and its yellow to orange hues* only reinforce that. We suffer ‘sunburn’ and speak of the Sun ‘blazing’ in the sky. To turn the screw of misconception still further, the idea of a fiery sun is branded into our cultural history. Here’s what Hamlet had to say about it:
Doubt thou the stars are fire;
Doubt that the sun doth move;
Doubt truth to be a liar;
But never doubt I love.
Putting aside whether the ‘sun doth move’ (that’s for another chapter – see here), we really should doubt that the stars are fire. Fire, to put it in chemical terms, is the rapid reaction of a substance with oxygen to throw out plenty of heat and light. The second part of that sentence is true of the Sun, but not the first. What’s happening on the Sun is not even close to combustion. If it is a fireball, then where is all the smoke?
Rather, the Sun is powered by nuclear fusion. Hydrogen ions (protons) fuse together near the core to form helium. Put in these tiny, atomic terms that doesn’t sound all that powerful. But the quantities are staggering. Every second the Sun converts 700 million tonnes of hydrogen to helium. If you want an horrific comparison, that’s like consuming the mass of every living human, every second. The process kicks out plenty of energy in the form of photons. These eventually (see here) make their way to Earth where they warm our atmosphere, drive the biochemistry of plants and prevent you from reading your computer screen out of doors.
The Sun, then, is a seething ball of plasma – a hot, electrically charged gas. Sometimes dubbed ‘the fourth state of matter’, plasmas are far less exotic than you might think. Indeed, plasma is by far the commonest form of ordinary matter throughout the Universe. We should call it the ‘first state of matter’. All stars are made of plasma, as is much of the material between galaxies. We don’t encounter it so much on the human scale, but it should still be familiar. Plasma is the streak of white we perceive during a lightning strike. It provides the glow in a plasma TV or a fluorescent light. This is the stuff of the stars. To imagine the Sun is made of fire is like assuming the adverts of Times Square are powered by candles – only on a much, much larger scale.
* FOOTNOTE Those beautiful orange sunsets are an illusion. Any colour we perceive in the Sun is down to the atmosphere scattering light. Observed from space, the Sun is an unromantic white ball.
The speed of light is devilishly fast. It is quicker than any analogy can convey. But it is not instantaneous. A powerful torch – or, hey, let’s spend a bit of our budget and call it a laser – fired from the Moon’s surface would take about a quarter of a second to reach the Earth. The Sun is much further away. From here, light takes about eight minutes and 20 seconds to travel the 150 million km (93 million miles) to our planet. The Sun could have been extinguished seven minutes ago and you would have no idea – it would look exactly the same as ever – until about a minute from now when the shockwave reaches you.
When I say ‘it takes eight minutes’ this is how long it takes light to travel from the surface of the Sun to the surface of the Earth. Much of the light that hits us originates from much deeper in the star. The light we see today set off on its journey long before our species even existed.
Most of the Sun’s light is generated deep in the core. Here, hydrogen atoms undergo nuclear fusion to form helium. The process generates unimaginable numbers of photons (which we eventually perceive as visible light) as a by-product. Once emitted, you might expect that they’d zip off at the speed of light and clear the Sun in a little over two seconds. But they don’t. They can’t. The photons are trapped in the heart of the Sun surrounded by superdense material.
It’s like being in the middle of a football crowd. It can take ages to squeeze through the narrow gaps and reach the edge of the throng. But once out, you can hop into your car and zoom off at much greater speed. In the same way, our frustrated photons must negotiate a squeezed broth of plasma to reach the outer Sun. It can take a million years. Once there, they can zip away with impunity.
To sum up, it takes perhaps a million years for the photons to travel the Sun’s radius of 700,000km (435,000 miles); but then just over eight minutes to shift over 200 times that distance to the Earth.
Our solar system only contains a single sun but, in a whimsical sense, there are plenty of stars out there. Many of the asteroids and other minor planets are named after the stars of popular culture.
The most famous objects in our neighbourhood tend to be named after mythological beings or – in the case of the moons of Uranus – characters from Shakespeare. But there are so many minor planets to label that the naming authorities have had to widen the net. The official list of objects in our solar system now contains hundreds of modern names, and includes scientists, royalty, politicians, teachers and entertainers.
Here you’ll find 78453 Bullock, inspired by actress Sandra Bullock, while 12818 Tomhanks and 8353 Megryan are sleepless in the asteroid belt. The six members of the Monty Python team all have their own minor planets, as do the four Beatles and Yoko Ono. One wonders if there’s a purple haze around 4738 Jimihendrix, or if 14024 Procol Harum is a whiter shade of pale. Certainly, 91287 Simon-Garfunkel orbits to the sound of silence. Does 17473 Freddiemercury want to break free (of orbit)? And is 342843 Davidbowie the ultimate space oddity?
Contrary to some reports you’ll find online, you can’t just buy the rights to one of these objects. In most cases, the person or team who discover a minor planet are entitled to give it a name. The rules are strict. You can’t call your object Donaldtrumpsucks or Pepsicolaworld, though 274301 Wikipedia made the grade. Suggestions should be 16 characters or fewer in length, non-offensive, non-commercial, unique and pronounceable. In addition, you can’t plump for the name of a military or political figure unless that person has been dead a century. To prevent any mischief, the suggestion must then be ratified by the wonderfully named Committee for Small Body Nomenclature, formed of professional astronomers.
Further appellations to persuade the panel include 230975 Rogerfederer, 9341 Gracekelly, and 33179 Arsènewenger, named after the long-running manager of Arsenal Football Club. The system, which has few qualms about honouring living people, isn’t without its risks. Some minor planets now carry the names of the infamous as well as famous. Asteroid 12373 Lancearmstrong was announced in 2001. A decade later, its namesake cyclist fell into disgrace because of long-term doping offences. He was stripped of his seven Tour de France wins, but retains his asteroid. Meanwhile, 18132 Spector is named after producer and songwriter Phil Spector, the man who wrote such hits as ‘You’ve Lost That Lovin’ Feelin’ and ‘Da Doo Ron Ron’. Spector was convicted of murder in 2009, but his name is retained in the heavens.