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.

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”.

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…

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.

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.

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.

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.

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…

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.

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.

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…

And here is a less detailed, but annotated version…

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…

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.

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.

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!

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?”