Category Archives: Space

Currents In Space

I read an article the other day – Magnetic Rivers Feed Star Birth – which I found interesting in its own right, but also provided a connection with a novel written in 1952 by Isaac Asimov, called The Currents of Space.

SOFIA in flight (NASA/ C. Thomas/ Max Planck Institute)

More about the novel in a while… first, the recent science research. This came about when a team of astronomers combined visual images from the (now retired) Spitzer Space Telescope with infra-red images from the SOFIA, the airborne Stratospheric Observatory for Infrared Astronomy. Both devices were pointed at the Serpens South star cluster, a region about 1400 light years from Earth, where stars are being formed.

The combination of these two generated the following image:

Composite image of the Serpens South star cluster, showing magnetic flowlines of star-forming material (NASA/ SOFIA/ T. Pillai/ JPL-Caltech/ L. Allen/ USRA)

The infra-red image showed where magnetic lines of force were aligning along “rivers” of material and funneling this into regions where stars are being actively formed. In the lower left region the magnetic flow is along these “rivers”, whereas in the top part of the image, they are perpendicular to the flow of matter. Sometimes magnetism and gravity reinforce each other: other times they are opposed. Where they are aligned, spatial currents enhance star formation.

Onto fiction, and Asimov’s book. Here, a particular planet – Sark – relies for its enormous wealth on a particular luxury fibre which grows only in one place – a subjugated vassal planet to Sark called Florina. A great deal of political manoeuvring has gone on to try and reproduce this fibre elsewhere, without success. In part, the book is exploring attitudes of colonialism and exploitation, but the science bit of the book has to do with the flow of minuscule quantities of elements through space. The central character has had his memory erased by the Sark government, since he had discovered that this elemental flow – the currents of space – was the root cause of the special fibre, opening the possibility of duplication elsewhere. Moreover, the same currents were driving Florina’s sun towards going nova.

So the real-world effect of matter flows through space – at least in the one case studied – is to help create stars, whereas in Asimov’s fictional universe, they were driving a star to destruction. That aside, both are exploring the same phenomenon, how the almost-vacuum of space nevertheless contains enough atoms to affect the development of stars nearby.

Fascinatingly, this tiny quantity of atoms, once distributed into space by stars which flare up or explode, forms the chemical basis for life. Long long ago, the tangible part of our universe consisted almost entirely of hydrogen, driven about by intense radiation, and pulled here and there by dark matter. All the heavier elements – including every single particle in our bodies – have been produced in the interior of stars, and then scattered nearby as these stars age and die. Some supernova explosions have brought to Earth the chemical constituents of life, and (according to recent research) others may have brought about some of the mass extinctions of life in Earth’s history. Matter currents in space can – in fact as well as fiction – bring both life and death.

The Crab Nebula, thought to be a supernova remnant from long ago (NASA, ESA, Alison Loll & Jeff Hester (University of Arizona))

The Liminal Zone

The Liminal Zone cover

Well, it’s almost time for The Liminal Zone to see the light of day. The publication date of the Kindle version is this Sunday, May 17th, and it can already be preordered on the Amazon site at The paperback version will not be too far behind it, depending on the final stages of proofing and such like. I am, naturally, very pleased and excited about this, as it is quite a while since I first planned out the beginnings of the characters, setting and plot. Since that beginning, some parts of my original ideas have changed, but the core has remained pretty much true to that original conception all the way through.

But I thought for today I’d talk a little bit about my particular spin on the future development of the solar system. My time-horizon at the moment is around 50-100 years ahead, not the larger spans which many authors are happy to explore. So readers can expect to recognise the broad outlines of society and technology – it will not have changed so far away from our own as to be incomprehensible. I tend towards the optimistic side of future-looking – I read dystopian novels, but have never yet been tempted to write one myself. I also tend to focus on an individual perspective, rather than dealing with political or large-scale social issues. The future is seen through the lenses of a number of individuals – they usually have interesting or important jobs, but they are never leaders of worlds or armies. They are, typically, experts in their chosen field, and as such encounter all kinds of interesting and unusual situations that warlords and archons might never encounter. The main character of Far from the Spaceports and Timing (and a final novel to come in that trilogy) is Mitnash Thakur, who with his AI partner Slate tackles financial crime. In The Liminal Zone, the central character is Nina Buraca, who works for an organisation broadly like present-day SETI, and so investigates possible signs of extrasolar life.

Amazon Dot - Active
Amazon Dot – Active

Far from the Spaceports, and the subsequent novels in the series, are built around a couple of assumptions. One is that artificial intelligence will have advanced to the point where thinking machines – my name for them is personas – can be credible partners and friends to people. They understand and display meaningful and real emotions as well as being able to solve problems. Now, I have worked with AI as a coder in one capacity or another for the last twenty-five years or so, and am very aware that right now we are nowhere near that position. The present-day household systems – Alexa, Siri, Cortana, Bixby, Google Home and so on – are very powerful in their own way, and great fun to work with as a coder… but by no stretch of the imagination are they anything like friends or coworkers. But in fifty, sixty, seventy years? I reckon that’s where we’ll be.

Xenon ion discharge from the NSTAR ion thruster of Deep Space 1 (NASA)

The second major pillar concerns solar system exploration. Within that same timespan, I suggest that there will be habitable outposts scattered widely throughout the system. I tend to call these domes, or habitats, with a great lack of originality. Some are on planets – in particular Mars – while others are on convenient moons or asteroids. Many started as mining enterprises, but have since diversified into more general places to live. For travel between these places to be feasible, I assume that today’s ion drive, used so far in a handful of spacecraft, will become the standard means of propulsion. As NASA says in a rather dry report, “Ion propulsion is even considered to be mission enabling for some cases where sufficient chemical propellant cannot be carried on the spacecraft to accomplish the desired mission.” Indeed. A fairly readable introduction to ion propulsion can be found at this NASA link.

I am sure that well before that century or so look-ahead time, there will have been all kinds of other advances – in medical or biological sciences, for example – but the above two are the cornerstones of my science fiction books to date.

That’s it for today, so I can get back to sorting out the paperback version of The Liminal Zone. To repeat, publication date is Sunday May 17th for the Kindle version, and preorders can be made at As a kind of fun bonus, I am putting all my other science fiction and historical fiction books on offer at £0.99 / $0.99 for a week starting on 17th.

The Liminal Zone cover
The Liminal Zone cover

Exoplanets – Some Oddities

Tatooine’s two suns (Twentieth Century Fox/LucasFilm via

In the last couple of blogs, I have talked about exoplanets, what kind of stars they circle around, and what the prospects are for life and story-telling. Today I want to pick out some oddities, to show that alien solar systems are very varied. Old-school planetology made out that the only kinds of solar system that made sense were ones that looked remarkably like our own – now, with the benefit of real data, we can see that that was an extremely parochial view. Let’s start with a classic Star Wars view… the two suns of Tatooine, where Luke Skywalker grew up. This is in fact not just a theoretical or film problem – the majority of stars you can see with the naked eye as you look out at night are in fact binaries (or members of higher multiples), so that single-star solar systems like are own are in fact in the minority.

This view requires that the planet find a stable orbit in a binary star system – no mean feat, as there are a lot of orbits which are unstable and end up with the planet being roasted or frozen at some point in its orbit. Indeed, the “three-body problem” – three sizeable objects moving under each other’s mutual gravity – is one which has proved to have no general solution, despite many years’ work. But it does have some approximate solutions, which can be worked on by computer simulation.

For example, you can imagine a planet in a very wide orbit, with the two suns circling each other at the centre. This could work, though perhaps the planet would end up outside the Goldilocks Zone, and so be inhospitably cold for life to develop comfortably. But in such a case, the suns would always look comparatively close to each other, and you could never have a situation where one sun would be setting as the other was rising.

Another extreme case is where the two suns are much further apart, and the planet orbits just one of them. If the distance between the two suns is large enough compared to the sun-planet distance, then this can also be stable. The view from such a planet’s surface would be quite different to the first case. The two suns could be at any angle relative to each other, and your view from the surface would vary between the two appearing close together, right through to being diametrically opposite, with periods of no night-time.

Of course, there’s nothing to stop a solar system built around binary stars being more complex again, with a mixture of some planets circling one or other of the suns, and others circling both of them as a central object much wider out. The more objects in the system, the more likely it is that orbits will not be stable in the long term, but it would make an interesting place to settle for a while. After all, orbital instability is usually a problem only over millennia or longer timescales.

It’s natural to assume – as I did for the diagrams above – that the orbital plane of the planet(s) is the same as that of the suns. But in fact, recent observations from an observatory in Chile suggest that this probably is not always the case. That observatory is not yet capable of spotting individual planets, but it can detect the discs of matter circling stars, from which planets may well coalesce in time to come. And the disc certainly does give information about the orbital plane of subsequent planets. The following two pictures give a good idea of their contrasting results – stars which are close together and hence orbit quickly, tend to have a planetary disc aligned with the suns’ plane – this is the right-hand case below. Conversely, stars which are far apart and orbit slowly, tend to have the planetary disc misaligned. The views from planets in such systems would be constantly changing as the planets rose above and dipped below the solar plane.

Misaligned (left) and aligned (right) orbital planes (ALMA (ESO/NAOJ/NRAO), I. Czekala and G. Kennedy; NRAO/AUI/NSF, S. Dagnello via

Another curious situation has been seen with the star HD 158259, which is 88 light-years from us , and a little larger than our sun. Six planets have been observed in this system – one like an oversized Earth, and the others like undersized Neptunes. But the remarkable thing about this system is that it shows very neat gravitational resonance. I’ve written about this before – over a period of time mutual gravitational attraction tends to make orbits end up showing regular patterns. In the case of HD 158259 all the planets’ orbits are in the simple geometric ratio 3:2 to each other – each planet carries out 2 orbits while the next one towards the sun carries out three. This happens to be the same as Neptune and Pluto in our solar system, but our other planets don’t show this to anything like the same extent. How, I wonder, would astronomers on such a world, building their first telescopes and looking out at their family of planets, start to understand and rationalise this remarkable degree of ordeliness?

Finally, I should mention a discovery made from data acquired by the Kepler telescope and recently analysed (a couple of people have reminded me about this, and it’s well-worth including here. The exoplanet Kepler-1649c orbits its small red dwarf star within the system’s Goldilocks Zone. It’s almost precisely the same size as Earth and receives about 3/4 of the light that our Earth receives from the Sun. Now, it’s about 300 light-years from us, so we won’t be visiting it anytime soon, but it is, so far, the most similar exoplanet to Earth that we have observed. One of the researchers said “The more data we get, the more signs we see pointing to the notion that potentially habitable and Earth-size exoplanets are common around [red dwarf] stars”.

Artist’s impression, exoplanet circling red dwarf (NASA/Ames Research Center/Daniel Rutter)

Which is all great for story-telling, since there are a great many red dwarfs much closer to us than 300 light-years.

For my own fictional take on all this, The Liminal Zone will be available very soon…

What Kind of Stars have Planets?

This week I am carrying on thinking about exoplanets – planets which we have detected circling other stars. In modern science fiction, this helps us decide the parameters we are putting on life which originated elsewhere.

Light intensity variation as an exoplanet passes in front of its star (Space Telescope Science Institute, via WIki)

It’s worth saying, in passing, that there are several ways we detect such planets, bearing in mind that they are so small as to be normally drowned out in the light of the primary star they orbit. Two are particularly common. The first of these is to accurately measure the path of that primary star through space, and map out small wiggles to that path as the planet(s) in its solar system orbit around it. The second is to accurately measure the light shining from the star, and detect periodic decreases in intensity as the planet(s) pass in front of it. Both ways work best if the orbital plane of the planet is aligned with the direct line between Earth and the star. That means that, at present, our best techniques are unable to give confident results about a great many possible candidates – a star which does not periodically dim might not have a planet, or it might have one whose orbital plane is at a different angle.

Hertzsprung-Russell diagram – our sun is the yellow dot (U Oregon web site)

Now, in the early days of this search, the main focus was on stars which are broadly the same as our sun – stars which are roughly in the middle of the typical path of stellar evolution known as the Hertzsprung-Russell diagram. In this diagram, dimmer stars are towards the bottom and brighter ones towards the top. Hotter stars are to the left and cooler ones to the right. So early researchers picked out stars that were broadly like ours, on the grounds that the conditions on planets there would most likely be ones which we would recognise – a kind of Goldilocks test.

Now, as time has gone on, we have found planets circling all kinds of stars, and our thinking about which ones might be most congenial for life has changed a bit. The most common type of star in the galaxy – so far as we can tell by sampling our neighbourhood as best we can – is a red dwarf. Red dwarfs sit near the bottom right hand corner of the HR diagram – they are low intensity, and also quite cool. Of course, “cool” is a relative thing – their surface temperature is still typically anything from 2000 to 3500 degrees. To give an idea of their ubiquity,  the nearest star to the Sun is a red dwarf, as are fifty of the sixty nearest stars. Red dwarfs may make up three-quarters of the stars in our galaxy. We don’t tend to notice them because they are so very dim – not one of those fifty stars is visible to the naked eye, though if you know exactly where to look, a good pair of binoculars or a small telescope can pick some of them out.

Artist’s impression – planet with moons circling a red dwarf (NASA)

But if you are on the search for extra-solar life, red dwarfs are a good place to start. For one thing, a great many of them have planets circling them. The several different exoplanet mapping telescopes, both on Earth and in orbit, regularly find such solar systems. The star is cool, so the Goldilocks Zone in which surface water can exist is much closer to the star than the one in our own system – but it does exist, and a reasonable proportion of red dwarfs have at least one planet in the zone. Red dwarfs are also extremely long-lived – rather longer than our sun – which would give life an opportunity to develop. On the flip side, some red dwarfs appear to have regular flares, which would tend to be inimical to life.

How, one wonders, would a life form develop on a planet around a red dwarf star? Sunshine would be more orange than yellow, but since we are in the Goldilocks Zone, the daytime temperatures would be much the same. In terms of size, a red dwarf is vastly smaller than our sun – some are around the size of Jupiter. However, because the potentially habitable planets are so much closer, it would appear substantially larger in the sky – perhaps five times the diameter.

The Moon as seen from the Earth – tidal locking means that we never see the other side (Wiki)

It is thought that many planets orbiting red dwarfs may be tidally locked – presenting the same face towards their primary. We are familiar with this regarding the view of our Moon from the Earth – we only see one side, and the other is forever hidden from us. At the moment the earth is not tidally locked to the Moon – we see it move around us through night and day – but in the very remote future this will probably happen. When a planet is tidally locked to its sun, then only one side of the planet receives light and warmth. Air and water circulation will tend to distribute the heat around the globe, but nevertheless there will tend to be extremes. Could life spring up and develop towards complexity and society in these conditions? My guess is yes, though it’s a question that has yet to be answered.

Finally, I am very happy to say that The Liminal Zone is now finished, and I am going through the process of preparing both kindle and paperback versions of it. Will a red dwarf feature in it? You’ll have to wait and see…

Exploring Mars

I thought I’d take this opportunity to share out a recent picture returned by NASA’s Curiosity Rover of its environment. Indeed, although it shows as a single picture, it was in fact assembled from over a thousand separate images, carefully aligned each with the next in order to give a composite panorama.

Panorama taken by Curiosity Rover (NASA/JPL)

There’s also a YouTube video exploring this in more detail and highlighting particular features – the link is below.

Now, as well as the intrinsic interest of this picture, it has also been fun for me to locate it in relation to some of the Martian locations used in my novel Timing, part of which is set on Mars.

Martian sites – base map from NASA/JPL with annotations

Olympus Mons is the largest mountain on Mars – the second highest that we know of in the entire solar system. In Timing, the main characters Mitnash Thakur and his AI persona assistant Slate first investigate a finance training school close to Olympus Mons, and subsequently visit a gambling house in a settlement on Elysium Planitia. Curiosity, and the panorama picture, is right at the edge of Elysium Planitia. So the terrain in that part of Timing would be not unlike the Curiosity picture.

The following extract from Timing is when Mitnash and Slate arrive on Mars, having taken a shuttle down from the moon Phobos. But before that, here’s the link to the video I mentioned (

Extract from Timing

The shuttle had peaked in its hop, and was now descending again. The pilot had flicked the forward view up on one of the screens, so we could all enjoy the sight of the second tallest mountain in the solar system. All twenty-two kilometres of it. We were already below the level of the summit. Gordii Fossae, where the training college was located, was behind the right flank from this angle, and I didn’t expect to see it.

Before long we were grounding at the dock. I stood up, and was treated to some curious looks from the remaining passengers. I was the only one alighting here. At a guess, it was not a popular stop – those hardy souls who wanted to bag the summit of Olympus would normally take a different route altogether, first to Lycus Sulci basecamp, then up and over the scarp before trekking to the peak.

I went through into the reception hall with the minimum of bureaucratic fuss, targeted on all sides by glossy ads inviting me to sample the pleasures of Martian laissez faire. Then after the last gate, the narrow entrance tunnel opened into a wider dome, and there was a heavy-set man with dark hair waiting, looking slightly bored. Seeing me, he stepped forward and held out a hand.

“Mitnash Thakur? I’m Teemu Kalas. Welcome to Gordii Fossae.”

Teemu insisted on taking my bag, though it was hardly a burden, and we chatted idly as he ushered me through several linked domes to a long hall. He had a heavy, northern European accent. I couldn’t decide if he made everything sound very serious, or a complete joke. Slate whispered to me that he was one of the two vice-principals of the training centre. He opened a locker, pulled out two suits and passed one to me, gesturing to the airlock nearby.

“Here you are, Mitnash. We got your size from your persona. Slate, she’s called, isn’t she? Now, be warned that it’s not a perfect fit. Should be close enough though. And it’s the nearest we had, anyway. I’ll signal the truck to attach to the lock by concertina, but we always wear suits on the journey. Protocol, you know.”

“How far is the school from here?”

“About ten kilometres to the main teaching block. A little bit further to the dormitory entrance where I’ll be taking you. A lot can happen on a journey like that.”

He glanced to see how I was fastening the suit and seemed satisfied. We left the lids open, but ready to snap down if need be. Then we cycled through the lock and into a vehicle. At a guess, it was about the size of a small bus. The engine was already filling the cabin with an electric hum, and after a couple of checks he tapped a toggle and leaned back.

The windows looked out on a set of very large tyres on either side, but beyond that, the Martian landscape stretched away to the horizon, drab and dusty, with jagged blackish bands of rock emerging from the sand at intervals. On our right, the slopes of Olympus Mons stretched hugely up into the pale sky. At this point, the scarp which was so prominent around most of the northern rim dipped down, to merge smoothly into the surrounding terrain as you continued on south. It still looked fearsome just here.

“There. The onboard system will get us the rest of the way. It’s twenty minutes from here. I’ve got the centre Sarsen twins supervising it just in case, but it’s hardly a new journey. Now, you’ll have a lot of questions, but Mikko – that’s Mikko Pulkkinen, the principal – said to wait for all that until he meets you tomorrow. The rest of today is yours, to get acclimatised. You’ll get more tired than you expect. Been on Phobos long?”

More maps – and this time of Charon

I’ve been a sucker for maps for as long as I can remember, and as a child took great pleasure in following some story – usually fictional, but sometimes real-world – across a map representation. And where, as in the Narnia series, there was a series of maps that didn’t easily line up with each other, there was even more fun to be had in trying to trace them, then rescale and reposition the separate pieces to try to get to the whole thing.

1998 Hubble pictures of Pluto – the thumbnails at top are typical actual images, with image analysis applied to get the lower ones (NASA/JPL)

Now until fairly recently, the idea of having a map of Pluto or its primary moon Charon was completely out of the question – if you wanted to write a story set out there, you could pretty much draw your own map. It would be almost impossible for anybody to refute your suppositions. In fact, very few people set stories there, except as some incidental waypoint en route to somewhere else, or as a location to meet some alien creature. It was broadly regarded as not only inhospitable, but also likely to be profoundly boring.

Pluto from New Horizons, July 15th 2015 ( NASA/JHUAPL/SwRI )

All that changed when the New Horizons probe flew past Pluto and Charon in July 2015. Blurry pixellated images turned into extraordinary high-resolution ones. Surface features became visible, showing a huge and unexpected diversity of terrain. Pluto was no longer a dull and boring place, but one of the most exciting and rich places to investigate. The New Horizons cameras did not just pick up surface features, but clouds and atmospheric haze. Pluto is still – of course – a very cold place to live, but this fly-by convinced the scientific community that it is an interesting one.

Now, my own interest is more focused on Charon than Pluto – for a variety of reasons my current work-in-progress, The Liminal Zone, is set on Charon. This means that the occupants of the habitat there can look out and up at Pluto whenever they choose – the apparent diameter is rather larger than that of the Earth as seen from our Moon. Charon has deep troughs that plunge 14 km below the mean surface level (deeper that Earth’s Marianas Trench), and mountains that extend some 8 km above it. Here is the raw map of Charon’s surface…

Global map of Charon ( Lunar and Planetary Institute/Paul Schenk/NASA/New Horizons )

And here is a less detailed, but annotated version…

Informal names from New Horizons team, awaiting official ratification (NASA/JPL)

In The Liminal Zone, the habitat area is on the border between Vulcan Planum and Serenity Chasma. The former is reasonably flat, the latter is very rugged. To find out more, you’ll have to wait just a little longer…

A Solar System Map

Just a short blog today as I got caught up in a whole lot of other activities through the day. A solar system map – it combines the love I have had for maps for many decades, since first discovering them in childhood, together with an enthusiasm for space which, in all honesty, goes back almost as far.

What’s special about a map of the solar system? Many of us could have drawn one long ago, with the planets in their correct order, starting with Mercury nearest the sun, and ending with Pluto furthest away. But staying with the traditional nine (eight planets plus one dwarf planet, ever since Pluto was reassigned to this category back in 2006) scarcely does justice to the richness and complexity of our local region of space.

Let’s review that. We’ve known about the main asteroid belt, in the orbital gap between Mars and Jupiter, for a long time now. But over the years we have discovered other asteroids, occupying quite particular niches. There is a whole group of near-earth ones, for example. Nearly 3,000 cross the orbit of Venus at some point, and just one of these (so far) has a stable orbit between Venus and Mercury. There are two large clumps in the Lagrange points ahead of and behind Jupiter in its orbit, known as the Greeks (ahead) and Trojans (behind).

Then there is a large group of objects in the Kuiper Belt, outside the orbits of Neptune and Pluto – indeed, Pluto is often now regarded as the first of the Kuiper Belt objects , rather than the last of the planets. When you add all these individually small items up, you get something like 18,000 objects of 10 km diameter or more. All of a sudden you have a rather complicated map. Which appears just below, with full credit to Eleanor Lutz for creating such a thing:

Solar System map, by Eleanor Lutz ( )

A few words about this. The radial scale is logarithmic rather than linear, as otherwise you’d either get no detail on the inner system, or such vast map you’d never find anything in the outer system. A logarithmic radial scale means that the large increments in distance as you go through the outer planets – Jupiter, Saturn and so on out to the Kuiper Belt – look roughly the same as the small increments between the inner planets – Mercury out to Mars.

You can’t (easily) use a log radial scale for navigation, but that’s not what this is about – it’s a very cool way of visualising the busy and quiet parts of the space environment around us.So even at first glance you can see the crowded nature of the asteroid belt, and the dense groups of Greek and Trojan asteroids. And the Kuiper Belt looks quite populated as well, and since astronomers are constantly spotting new objects out there, this can only increase.

But that apparent density is only apparent, not real, and if you were to travel to either the asteroid or Kuiper belts, you could safely whiz around for a very long time without risk of hitting anything by accident. The entire mass of objects that we know about so far in the Kuiper Belt is rather less than that of Earth’s moon.

But what these areas of comparative population and emptiness tell us is how the gravity of the major planets, especially Jupiter, have shaped our whole environment. A few blogs ago I talked about orbital resonance, in which a larger planet places its stamp on the region around it. It’s no accident that the majority of the asteroids are shepherded into a belt just inside the orbit of Jupiter, or cluster at fixed angles ahead and behind it. Likewise, it is no accident that the Kuiper Belt’s inside edge is defined quite sharply by the orbits of Neptune and Pluto – this is gravity at work, creating regular patterns out of what st first sight appears to be random distribution.

And the other way in which this is a map – it is a map for the imagination, to daydream on what it might be like for there to be regular traffic between a decent number of those 18,000 objects…

Pathways or Navigation?

Across the Sands
Across the Sands (to Lindisfarne)

Some of my favourite walks are along ancient trackways – routes that have been followed for centuries or millennia by a huge range of diverse people. There is something very appealing about these paths, and the sense of lineage which attaches to them. Every country has such pathways – they might be for the purposes of trade, or pilgrimage, or festival, or war, or simply the best and most effective way to cross difficult terrain and link up with other communities. When you walk such paths today, you are quite literally following in the footsteps of many other people.

On Eskdale Moor

Often these paths follow routes which made perfect sense at the time, but nowadays seem odd – for example many of Great Britain’s ancient ways follow ridges, whereas modern transport networks tend to stay in the valleys. From the Ridgeway, or the North and South Downs ways, or the Pennine Way, or High Street running north to south above the eastern shore of Ullswater, you look down from tracks which are almost devoid of buildings, into plains and valleys full of settlements and the roads between them. Some of this shift is the result of the way Britain’s sea level has changed over the last ten thousand years or so, and the rest reflects shifts in vegetation patterns. We used to avoid the valleys because they were hazardous and, often, impassable… now we avoid the hills because it costs more to construct roads and railways there.

Artist's Impression of Dawn in orbit (NASA/JPL)
Artist’s Impression of Dawn in orbit (NASA/JPL)

So far so good… but does this notion of ancient trackways migrate into science fiction? And the answer to that question depends on how the author has conceived of how travel works between inhabited settlements. In my Far from the Spaceports series, set in various habitats within our own solar system, there are no trackways. If you want to get from, say, the asteroid Ceres down to Mars’ moon Phobos, then you would normally reckon to get your ship’s computer to plan out a geodesic – a minimal-energy curve joining start to finish. If you’re in a hurry, you burn a bit more fuel, run the engines a bit hotter, and replan your curve. If you do the same trip a few days or weeks later, you’d go through similar calculations, but the inevitable changes in orbital positions of the two celestial bodies in relation to each other mean that the second path won’t follow anything like the same track through space.

The same applies to the (excellent) Amazon series The Expanse, also set in the fairly near future within our solar system. When the Roccinante sets off from Ceres to Io, the crew do not look back at previous journeys between those places – they calculate afresh the necessary orbital path. Similarly, but on a bigger scale between star systems, Star Trek and Star Wars pick out a flight path according to the star patterns at the time.

There are, however, a few science fiction books and films which presuppose fixed navigation routes between places. Joe Haldeman’s Forever War presumes that journeys had to take place between specific collapsars, meaning that only certain trips are feasible, and the most effective way to travel from start to end may well not be anything like the straight line route. The Mote in God’s Eye, by Larry Niven and Jerry Pournelle, hypothesises the existence of “Alderson Points”, which are the only entry- and exit-points around particular suns. Again, some journeys are possible and others not, and trips between the same start and finish points must necessarily use the same Alderson Points. Stargate has something of a hybrid – the original travel means was by means of wormholes rigidly linked to particular planets – once again, some journeys are possible and others not. However, this was quite quickly relaxed with the introduction of spaceships travelling at superluminal speeds, and the consequent ability to go wherever you liked.

So different authors have had to choose between pathways and navigation when considering space flight, and by far the majority have chosen navigation. All of which, considering my personal delight in following ancient trackways, makes me consider how I could work out such a plot into my own writing.

An old bridge, on the site of an even older river crossing, a little north of the village of Troutbeck

Gravity Patterns

Stephen Hawking in a reduced-gravity aircraft flight, 2007 (Wiki)

Gravity is a curious thing. On an everyday level, almost all of us experience it in such a steady, unchanging way that it vanishes from our conscious attention. From time to time we notice change – the sudden acceleration of a lift in a tall building, or a ride in a theme park. A few people fly aircraft in such a way as to handle serious g-forces, and an even smaller handful have been in the microgravity of Earth’s orbit (or a very specific aircraft trajectory intended to mimic conditions in space). But for most of us, most of the time, it is just there as a constant part of our environment.

In terms of physics, gravity is the odd one out of the standard four forces of nature (the others being electromagnetism, plus the weak and strong nuclear forces). It is odd for a couple of reasons – first, it is immensely weaker than the others, but secondly, it is always an attractive force rather than sometimes attracting and sometimes repelling… so far as we known in 2019. There has been a recent report of a Hungarian team discovering a fifth force, but this has not been confirmed by other teams yet, and in any case will not change the gist of this blog post. The forces other than gravity tend to cancel out over any great distance, and only really affect things on very short distances. But gravity, despite its comparative weakness, really does shape the way the universe looks and behaves.

Poster, Gravity (IMDB)

Gravity in films usually gets treated in very cavalier ways. The most striking example of this is the 2013 film Gravity, which was built on an interesting premise but often failed at the science. In one especially memorable moment, George Cluny’s character tells Sandra Bullock’s, that in order to get over to the Chinese orbital station, she just has to keep it in the centre of the viewport and keep firing the engines. In terms of orbital mechanics, it would be hard to arrive at a less likely option for reaching her target. It would work for fairground dodgem cars, or for boats on a stretch of open water: it would even work pretty well for two aircraft in flight. But two bodies in space, in orbit around a central body behave in ways that can be counter-intuitive, and the whole aim-and-accelerate idea is pretty much doomed to failure.

Voyager 2 slingshot manoeuvres through the solar system (Wiki)

It’s an odd thing that gravity, even in Newton’s classical world where relativity and quantum mechanics play no part, is such a hard system to solve. If the entire universe consisted of just two objects, then their future motion could be exactly predicted for as far ahead as you please. But with more than two objects – starting with the so-called three-body problem – there is no general exact solution. A few special cases can be solved to a good-enough accuracy, and there are some very hypnotic numerical simulations of the resulting tracks, but the general case remains unsolved. Even a partial answer is better than none at all, however, and one of the most strikingly useful examples of three-body interactions is the so-called gravity assist manoeuvre (also called a slingshot) in which a space probe is given a substantial acceleration by means of a close approach to a convenient planet.

Schematic showing the Lagrange points for the Earth-Sun system (Wiki)

From a story-telling perspective, three-body problem solutions are very handy! Gravity assists are a great way to make a journey achievable, which otherwise would take too long to complete. And some other very convenient solutions are the so-called Lagrange points – “fixed” places holding a particular relationship with a planet in its orbit. A small body – a spaceship, or a small asteroid – which is placed into one of those points will remain there in a stable configuration, whereas at other nearby locations, the relative orbits will diverge rather than converge. Most planets in the solar system have accumulated a little cluster of small natural bodies at the points L4 and L5 – these are generically called Trojan satellites, following a convention established for the moons of Jupiter. Even Earth has at least one Trojan satellite, whereas Jupiter has over 7000 of them. The Lagrange points provide a very convenient “resting-place”, where an author can locate an artificial satellite without needing to exert any station-keeping energy.

These represent gravitational solutions which are useful, in a sort-of utilitarian manner. However, the long-distance and always-attractive qualities of gravity also give rise to exciting and rather surprising patterns of motion. These represent resonant patterns which can often stabilise a system, making it longer-lasting than might be expected. For example, the orbit of Pluto occasionally crosses over that of Neptune. One’s first thought is that at some point they would collide, or at least get close enough to seriously interfere with each other’s orbit. In fact their orbits are in a 2:3 resonant pattern with each other – for every three orbits of Neptune, Pluto makes two. This, together with some other resonances in their orbits, means that the two planets never in fact approach one another very closely at all. They remain stable. Similar stable patterns can be seen in the orbits of bodies outside Pluto, in the Kuiper Belt. Resonance can destabilise systems as well – there are gaps in the asteroid belt caused by resonances with Jupiter, and gaps in Saturn’s rings caused by one or other of the moons. But I want to finish this section with a stabilising resonance which turns out to be particularly appealing – Naiad and Thalassa, two of the moons of Neptune, are constantly engaged in an orbital dance to avoid each other. The ratio is particularly complicated in this case: for every 69 orbits of Thalassa, Naiad orbits 73 times.

Orbital resonance of Naiad and Thalassa around Neptune. (NASA/JPL-Caltech)

So gravity is a complicated thing, and at least when you’re in orbit, can’t be solved by simply aiming-and-shooting. But it does give rise to some exciting possibilities for stories, and some fascinating choreography amongst planets, moons, and asteroids. Of which, more another time.

Another trip to Pluto?

Pluto, as seen by New Horizons on July 13, 2015 ( NASA/JHUAPL/SWRI )

In July 2015 the NASA New Horizons space probe passed Pluto at a distance of under 8000 miles, in the process providing us with the first close-up data of this miniature world and its companion moons. The whole package of scientific and image data took over a year to download to Earth, and a complete analysis will take a considerable time yet. It was also roughly a year after that flyby that I started writing The Liminal Zone, set out on Pluto’s moon Charon.

New Horizons went on to have a close encounter with the unromantically named 2014 MU69 (often called Ultima Thule) in January of this year. Data from that meeting will not be fully downloaded until September next year. And mission planners are considering options for possible future encounters: if no suitable Kuiper Belt object is identified, then the on-board instruments will simply continue to return data about the remote environment in which the spaceship finds itself. The power source is finite, and will run out sometime in the late 2030s, the exact time depending on what tasks the craft is called upon to perform.

The face of Pluto looking towards Charon, on July 11, 2015 ( NASA/JHUAPL/SWRI )

But today’s blog remains focused on Pluto and its moons. Not so very long ago, Pluto was regarded as utterly inhospitable and uninteresting. If you were going to locate a science fiction plot within the solar system, you wouldn’t choose Pluto. Pretty much any other planet or moon seemed preferable, and it was hard to conceive of Pluto as anything but bitterly cold and rather featureless. New Horizons has changed that perspective. It now seems that this small body – downgraded in 2006 from being classed as “planet” to “dwarf planet”, in a decision which continues to be fiercely debated and may well be reversed at some point – is one of the most complex and interesting objects anywhere within the solar system. Not only is there a wide range of dramatic geological phenomena, but all the evidence points to ongoing activity out there. Pluto is not a frozen dead world, but one which continues to change and adapt.

Pluto and Charon from one of the other moons – artist’s impression (NASA, ESA and G. Bacon)

So interesting is it, that NASA is currently considering another mission to Pluto, this time with a view to remaining in orbit for an extended period rather than just zooming by at great speed. This would require a different kind of orbital trajectory – New Horizons’ course was deliberately set up to gain as much speed as possible from gravity assists (“slingshots”) in order to minimise the time to get there. If you plan to remain in orbit, you have to approach at a considerably lower speed to allow the modest gravitational pull to draw you in. The outline plan calls for a two-year period in orbit, followed by another onward journey – probably using Charon to slingshot away – to a suitable destination elsewhere in the Kuiper Belt. My guess is that the spaceship would need to use an ion drive, just as the asteroid probe Dawn did – this has vastly lower acceleration than a conventional chemical motor, but remains on for very long periods of time, adding speed minute by minute, hour by hour. It’s an exciting prospect if you like Pluto – two years of extended study rather than an action-packed 24 hours. If given the go-ahead. take-off would be over a decade away, and I will be in my 90s before data starts coming back. I guess it will be something to entertain me in old age!

View of Pluto as New Horizons left the system, catching the Sun’s rays passing through Pluto’s atmosphere (NASA/JHUAPL/SwRI)

Meanwhile, I shall continue writing about Pluto and Charon using the information we already know, and a generous dollop of speculation. Why choose Pluto? Well, The Liminal Zone opens on a research base out on Charon, using a collection of instruments called The Array to study what lies further out. It’s analogous to siting a terrestrial telescope on a high mountain – you avoid most of the light and electromagnetic noise generated by other people, and can concentrate on tiny signals which are easily drowned out. Into this situation comes Nina, curious about strange local tales which have no easy explanation.

For fun, here’s a short extract from when Nina arrives

Finally the landing was complete, with the smallest of jolts as the ship docked. And since she was the only passenger – and had been since the orbit of Ceres – there were no additional delays. All her belongings were already at her side, and she just walked out through the concertina into the entryway for the Charon habitat. It was all quite anticlimactic.

Her accommodation was about two thirds of the way out along the Lethe habitat. She stepped carefully along the corridor to acclimatise herself – the gravity was about a fifth of what she was used to on the Moon, so it needed care, but was manageable. The porter had given her a little hand-held which was directing her to the suite of rooms. That very word, suite, sounded too grand for her taste. She was used to more modest facilities. Indeed, the whole building seemed needlessly large to her, particularly after the weeks of confinement on the freighter. She decided that she could always close some of the doors and just live in one room, if the space in her quarters was overwhelming.

But when she got there, it wasn’t that easy. The ceiling vaulted high above her in the main chamber, and several secondary rooms clustered around it like soap bubbles. A privacy screen shimmered over a gap diametrically opposite the main door – sleeping quarters or comfort facilities, she supposed – but the rest was all open-plan. To her left was an emergency evacuation airlock, displaying all the standard alert signs. There were cupboards in doors on several walls; opening one at random she found some eating utensils. She put her carryall and daypack on one of the chairs, and wandered aimlessly about. With this apparently reckless attitude to the vacuum outside, the room didn’t feel like anywhere else she had visited. The space was daunting.

Finally she perched uncomfortably on a stool, one of half a dozen arranged haphazardly around a long table. The suite of rooms was almost silent, except for a quiet mechanical buzz which she only noticed with deliberate effort. She cleared her throat nervously.

“Is there a domestic system online?”

“Hello. Are you the new occupant?”