However, in 1998 the Mars Global Surveyor did find signs of an ancient ocean on Mars. At some point in the planet's history, huge amounts of water gushed out of the highlands and flowed into the northern lowlands. It was thought that this water just seeped away or evaporated, but it now turns out that the edges of the northern lowlands are ail at much the same height, like shorelines eroded by an ocean. The ocean, if it existed, covered a quarter of Mars's surface. If it contained life, there ought to be Martian fossils for us to find, dating from that period.
The current favourite for life in the solar system is a surprise, at least to people who don't read science fiction: Jupiter's satellite Europa. It's a surprise because Europa is exceedingly cold, and covered in thick layers of ice. However, that's not where the life is suspected to live. Europa is held in Jupiter's massive gravitational grasp, and tidal forces warm its interior. This could mean that the deeper layers of the ice have melted to form a vast underground ocean. Until recently this was pure conjecture, but the evidence for liquid water beneath Europa's surface has now become very strong indeed. It includes the surface geology, gravitational measurements, and the discovery that Europa's interior conducts electricity. This finding, made in 1998 by K.K.Khurana and others, came from observations of the worldlet's magnetic field made by the space probe Galileo, The shape of the magnetic field is unusual, and the only reasonable explanation so far is the existence of an underground ocean whose dissolved salts make it a weak conductor of electricity. Callisto, another of Jupiter's moons, has a similar magnetic field, and is now also thought to have an underground ocean. In the same year, T.B.McCord and others observed huge patches of hydrated salts (salts whose molecules contain water) on Europa's surface. This might perhaps be a salty crust deposited by upwelling water from a salty ocean.
There are tentative plans to send out a probe to Europa, land it, and drill down to see what's there. The technical problems are formidable, the ice layer is at least ten miles (16 km) thick, and the operation would have to be carried out very carefully so as not to disturb or destroy the very thing we're hoping to find: Europan organisms. Less invasively, it would be possible to look for tell-tale molecules of life in Europa's thin atmosphere, and plans are afoot to do this too. Nobody expects to find Europan antelopes, or even fishes, but it would be surprising if Europa's water-based chemistry, apparently an ocean a hundred miles (160 km) deep, has not produced life. Almost certainly there are sub-oceanic 'volcanoes' where very hot sulphurous water is vented through the ocean floor. These provide a marvellous opportunity for complicated chemistry, much like the chemistry that started life on Earth.
The least controversial possibility would be an array of simple bacteria-like chemical systems forming towers around the hot vents, much as Earthly bacteria do in the Baltic sea. More complicated creatures like amoebas and parameciums would be a pleasant surprise; anything beyond that, such as multicellular organisms, would be a bonus. Don't expect plants, there's not enough light that far from the sun, even if it could filter down through the layers of ice. Europan life would have to be powered by chemical energy, as it is around Earth's underwater volcanic vents. Don't expect Europan lifeforms to look like the ones round our vents, though: they will have evolved in a different chemical environment.
THE DAWN OF DAWN
PONDER OPENED HIS EYES and looked up into a face out of time. A mug of tea was thrust towards him. It had a banana stuck in it. 'Ah ... Librarian,' said Ponder weakly, taking the cup. He drank, stabbing himself harmlessly in the left eye. The Librarian thought that practically everything could be improved by the addition of soft fruit, but apart from that he was a kindly soul, always ready with a helping hand and a banana.
The wizards had put Ponder to sleep on a bench in the storeroom. Dusty items of magical gear were stacked from floor to ceiling. Most of it was broken, and all of it was covered in dust.
Ponder sat up and yawned.
'What time is it?'
'Ook.'
'Gosh, that late?'
As the warm clouds of sleep ebbed, it dawned on Ponder that he had left the Project entirely in the hands of the senior faculty. The Librarian was impressed at how long the door kept swinging.
Most of the main laboratory was empty, except for the pool of light around the Project.
The Dean's voice said, 'Mappin Winterley ... that's a nice name?'
'Shutup.'
'Owen Houseworthy?'
'Shutup.'
'William.'
'Shut up, Dean. That's not funny. It never was funny.' This was the voice of the Archchancellor.
'Just as you say, Gertrude.'
Ponder advanced towards the glowing Project.
'Ah, Ponder,' said the Senior Wrangler, stepping in front of it hurriedly. 'Good to see you looking so…'
'You've been ... doing things, haven't you,' said Ponder, trying to see around him.
'I'msure everything can be mended,' said the Lecturer in Recent Runes.
'And it's still nearly circular,' said the Dean, 'Just ask Charlie Grinder here. His name's definitely not Mustrum Ridcully, I know that.'
'I'm warning you, Dean...'
'What have you done?'
Ponder looked at his globe. It was certainly warmer now, and also rather less globular. There were livid red wounds across one side, and the other hemisphere was mainly one big fiery crater. It was spinning gently, wobbling as it did so.
'We've saved most of the bits,' said the Senior Wrangler, watching him hopefully
'What did you do?'
'We were only trying to be helpful,' said the Dean. 'Gertrude here suggested we make a sun, and...'
'Dean?' said Ridcully
'Yes, Archchancellor?'
'I would just like to point out, Dean, that it was not a very funny joke to begin with. It was a pathetic attempt, Dean, at dragging a sad laugh out of a simple figure of speech. Only four-year-olds and people with a serious humour deficiency keep on and on about it. I just wanted to bring this out into the open, Dean, calmly and in a spirit of reconciliation, for your own good, in the hope that you may be made well. We are all here for you, although I can't imagine what you are here for.' Ridcully turned to the horrified Ponder. 'We made a sun...'
‘...some suns...' muttered the Dean.
‘...some suns, yes, but ... well, this "falling in circles" business is very difficult, isn't it? Very hard to get the hang of.'
'You crashed a sun into my world?' said Ponder.
'Some suns,' said Ridcully.
'Mine bounced off,' said the Dean.
'And created this rather embarrassingly large hole here,' said the Archchancellor. 'And incidentally knocked a huge lump out of the place.'
'But at least bits of my sun burned for a long time,' said the Dean.
'Yes, but inside the world. That doesn't count.' Ridcully sighed. 'Yet your machine, Mister Stibbons, says a sun sixty miles across won't work. And that's ridiculous.'
Ponder stared hollow-eyed at his world, wobbling around like a crippled duck.
'There's no narrativium,' he said dully. 'It doesn't know what size a sun should be.'
'Ook,' said the Librarian.