From Titan's Doom Mons to Mercury's Pourquoi-Pas: how did the landscape of space get its names?

A detail from Ordnance Survey's new map of Mars. Image: OS.

The Ordnance Survey recently made a very nice map of Mars’ Arabia Terra region. This map shows an alien crater-pocketed landscape, peppered with mysterious names like “Aram Chaos”, “Meridiani Planum” and “Marth”.

When the OS makes a map of Britain, it is making a map of a place with history – reflected in place names that come from the many different languages that people have spoken here. But where are the names on the Mars map coming from?

The romance of naming

Space used to be like the Wild West, with different names used by different people. So, in 1911, the International Astronomical Union started to become the official clearing house for space names.

It legitimised features from previous maps (like Schiaparelli’s map of Mars) and made rules for how new names would be picked. It now publishes its database online, and I used this and various NASA maps of other planets to build We Name The Stars – a way of exploring these rules and places.

The IAU conventions seem to understand that there is something magical and important about naming things. We don’t end up with Crater 62 on asteroid BXM-2: each kind of feature (mountains, ridges, craters, lakes) on each different world has a different naming convention, so that similar places are thematically linked. Often revolving around a particular ancient myth, this lends a sense of grandness and history to what is otherwise just some slightly different coloured pixels.

A screenshot from the "We Name the Stars" page on Mars. Click to expand.

Not all names are mythical. Craters on Mercury are named after historically significant artists, while escarpments are named after ships of discovery. This is how you end up with a slope on Mercury named “Pourquoi-Pas”.

Craters on the asteroid Eros are named after “mythological and legendary names of an erotic nature” (which gives us Casanova and Abelard), while Saturn’s moon Titan has places named after mountains in Middle Earth. The largest mountain on Titan is called Doom Mons.

Places We’ll Never Go

Part of the appeal of the OS map is that it reinforces the idea of Mars as a place. It’s a technical challenge, but ultimately we understand how we’d get there, walk around, and get back.

Similarly you can vaguely imagine the 22nd century equivalent of the Arctic Explorer taking the journey my virtual rover is making across the Moon, visiting every crater. But there are plenty of other places to which we’ve given names that will probably never be walked on by people.

Take Mercury – it’s right next to the sun and spins very slowly. Every place on the planet spends every other month staring into the furnace. In several of his books Kim Stanley Robinson solves this problem with Terminator – a city that travels on rails around the planet. The sun heats the rails, which expand and push the city onward – permanently keeping it just beyond dawn.

But this is a fragile solution. Valleys on Mercury are named after ancient abandoned cities – a poor omen for the success of future settlement. Maybe maps of Mercury are for visitors, driving slowly to stay ahead of the sun.


A screenshot from the "We Name the Stars" page on the Moon. Click to expand.

Venus we can’t even visit. In the day the surface can get hot enough to melt lead, and the atmospheric pressure is the equivalent of being a kilometre under the ocean on Earth. On the other hand, it turns out that, if you build floating cities 50km up, the pressure and temperature are pretty much the same as on Earth. To our cloud-dwelling descendants it’ll probably seem odd that we put so many of our goddesses on features as unimportant to them as the floor of the ocean is to us.

There is something strange and wonderful about a system that produces such evocative names for places that in all likelihood no one will ever visit. These names don’t have to be pretty or coherent – but the effort is made anyway.

The European Sky

The IAU was founded at a time when “international cooperation” mostly meant “European cooperation”. The conventions emerging on using old myths and Latinised names were good, because that seemed like common ground.  Astronomers looked into space and then looked back on their shared classical heritage, pillaging the myths of the Romans and Greeks for important sounding but politically neutral names.

Except, of course, it’s not really neutral because not everyone comes from that heritage. Some 60 per cent of feature names are European in origin, and so European myth and history punches a little above its weight in the space naming race.

As the composition of the IAU has changed over time, this shift has been reflected in patterns for future names. Many conventions are now ecumenical: Io is littered with thunder and sun gods from different cultures, and Ceres has features named after the “agricultural festivals of the world”. Rhea uses names from “people and places from creation myths (with Asian emphasis)”; names on Triton are explicitly “aquatic names, excluding Roman and Greek”.

Fragile Monuments

But these are all faraway places, what about European domination of the places we’re actually likely to go – like the Moon and Mars? If the future of space turns out to be non-western, this issue ends up solving itself.

After the Chinese Yutu rover landed on the moon, the landing site was named Guang Han Gong (Moon Palace) and three local craters were given names from Chinese astrology by the IAU. When the asteroid 1998 SF 36 was selected as the target for the Japanese Hayabusa spacecraft, it was designated Itokawa after a Japanese rocket scientist. Where robotic feet go, naming rights follow.

On the Moon there are areas where naming is reserved to honour dead astronauts and cosmonauts, with the ominous note that “this convention may be extended if other space-faring countries suffer fatalities in spaceflight”. And why not? There’s plenty of Moon left, thousands of craters have been identified that have yet to receive an official name.

And even if a feature has a name with a history, will people honour it? Will a Martian Chinese colony in the Rutherford Crater still call it Rutherford? Will Indian settlers in Inuvik keep the name of a small town in Canada – or rename it something closer to home?

There’s a long history of name changes in space. British astronomers carried on with George’s Star (chosen by the discoverer of the planet to honour George III) for many years after everyone else switched to “Uranus”. The Galilean moons were once the ‘Medician stars’ – after the family whose patronage Galileo sought. When Cassini discovered the moons of Saturn he called them ‘the stars of Louis’ after King Louis XIV, hoping to create “a Monument much more lasting than those of Brass and Marble”. That we don’t use any of these names reflects the fragility of monuments that only exist on paper.

European myths may end up the Lingua Franca of empty places – only kept for areas to which no one has any interest in going. If in the future there are settlers in Arabia Terra, that OS map might be an interesting historical artefact for them – a perfectly correct map with all the wrong names. 

You can learn more about space names over at We Name The Stars


What are Europe’s longest train journeys?

The Orient Express was a pretty long train. Image: Getty.

For reasons that aren’t clear even to me, a question popped into my head and refused to leave: what’s longer? Britain’s longest train joruney, or Germany’s?

On the one hand, Germany is quite a bit larger – its area is 70 per cent more than Great Britain’s. On the other hand, Great Britain is long, skinny island and Germany is much rounder – the distance from John O’ Groats to Lands End is over 1,400 km, but you never have walk over 1,000 km to cross Germany in any direction.

And it turns out these factors balance almost each other out. Britain’s longest train, the CrossCountry from Aberdeen in Scotland to Penzance in Cornwall, runs 785 miles or 1,263 km. Germany’s longest train, the IC 2216 from Offenburg in the Black Forest to Greifswald on the Baltic coast, is exactly 1,300 km. Germany wins by a tiny distance.

Except then I was hooked. What about the longest train in France? Spain? Italy?

So I did what anyone would do. I made a map.

The map above was all drawn with the Deutsche Bahn (Germany Railways) travel planning tool, which rather incredibly has nearly every railway in Europe. The data quality is better for some countries than others (the lines in France aren’t quite that straight in real life), and the measurements may be a bit off – it’s not always easy to find the length of a train service, especially when routes can vary over the year – but it gives us a good idea of what the routes look like.

Let’s start with the UK. The Aberdeen to Penzance route isn’t really for people who want to go all the way across the country. Instead, it’s a way to link together several railway lines and connect some medium-to-large cities that otherwise don’t have many direct services. “Cross-country” trains like these have existed for a century, but because they crossed multiple different company’s lines – and later, multiple British Rail regions – they tended to get ignored.


That’s why, when it privatised the railways, the government created a specific CrossCountry franchise so there was a company dedicated to these underused routes. If you want to get from Edinburgh to Leeds or Derby to Bristol, you’ll probably want a CrossCountry train.

The usual route is Edinburgh to Plymouth, but once a day they run an extra long one. Just one way though – there’s no Penzance to Aberdeen train. 

The longest train in Germany is weird – at 1,400 km, it’s substantially longer than the country itself. On the map, the reason is obvious – it takes a huge C shaped route. (It also doubles back on itself at one point in order to reach Stuttgart).

This route takes it down the Rhine, the biggest river in west Germany, and through the most densely populated patch of the country around Cologne and Dusseldorf known as the Ruhr. Germany’s second and third longest trains also have quite similar routes – they start and end in remote corners of the country, but all three have the Rhine-Ruhr metropolitan area in the middle.

You’re not meant to take the IC 2216 all the way from north east to south west – there are much more direct options available. Instead, it’s for people who want to travel to these major cities. They could run two separate trains – say, Offenburg-Dusseldorf and Griefswald-Cologne – but making it a single route means passengers benefit from a bit more flexibility and helps DB use its rolling stock more effectively.

France’s longest train exists for a very good reason. Most of France’s high-speed lines radiate out from Paris, and it’s very hard to get around the country without going to the capital. Usually to get from Marseille on the Mediterranean to Nantes near the Atlantic, you’d need to take a TGV to Paris Gare de Lyon station, then get the Métro across the city to Gare Montparnasse.

Once a day though, this TGV avoids this faff by stopping in the suburb of Juvisy and turning around without going into the centre. This lets passengers travel direct between the coasts and reduces the traffic through Paris’s terminals in the rush hour. The exact length of this route isn’t clear, but Wikipedia says it’s about 1,130 km.

Spain’s longest train is very different. This is the Trenhotel sleeper service from Barcelona to Vigo, and it’s pretty fancy. This is a train for tourists and business travellers, with some quite luxurious sleeping cabins. But it is a regularly scheduled train run by the state operator Renfe, not a luxury charter, and it does appear in the timetables.

Being dry, hot and quite mountainous in its middle, most of Spain’s cities are on its coast (Madrid is the one major exception) and as a result the train passes through relatively few urban areas. (Zaragoza, Spain’s 5th largest city, is on the route, but after that the next biggest city is Burgos, its 35th largest,) This is partly why overnight trains work so well on the route – without many stops in the middle, most passengers can just sleep right through the journey, although there are occasional day time trains on that route too if you want to savour the view on that 1,314 km journey.

Finally, there’s Italy. This is another sleeper train, from Milan in the north to Syracuse on the island of Sicily. It goes via Rome and travels along the west coast of... wait, it’s a train to the island of Sicily? How, when there’s no bridge?

Well, this train takes a boat. I don’t really have anything else to add here. It’s just a train that they literally drive onto a ferry, sail across the water, and then drive off again at the other side. That’s pretty cool.

(As I was writing this, someone on Twitter got in touch to tell me the route will get even longer in September when the line to Palermo reopens. That should be exciting.)

So those are the longest trains in each country. But they aren’t the longest in Europe.

For one thing, there are some countries we haven’t looked at yet with very long trains. Sweden has some spectacular routes from its southern tip up into the Arctic north, and although the Donbass War appears to have cut Ukraine’s Uzhorod to Luhansk service short, even Uzhorod to Kharkiv is over 1,400 km. And then there are the international routes.

To encourage the Russian rich to take the train for their holiday, Russian Railways now run a luxury sleeper from Moscow to Nice, passing through France, Monaco, Italy, Austria, Czechia, Poland, Belarus and Russia. This monster line is 3,315 km long and stretches across most of the continent. That’s got to be the longest in Europe, right?

Nope. Incredibly, the longest train in Europe doesn’t actually cross a single border. Unsurprisingly, it’s in Russia, but it’s not the Trans-Siberian – the vast majority of that’s route is in Asia, not Europe. No, if you really want a long European train journey, head to Adler, just south of the Olympic host city Sochi. From there, you can catch a train up to Vorkuta on the edge of the Arctic Circle. The route zigzags a bit over its 89 hour, 4,200 km journey, but it always stays on the European side of the Ural mountains.

Bring a good book.

Stephen Jorgenson-Murray often tweets about this kind of nonsense at @stejormur.

All maps courtesy of Deutsche Bahn.