Category Archives: The Liminal Zone

Ultima Thule

Today’s blog is focused on the next target of the New Horizons probe, which back in July 2015 sent back such remarkable pictures of Pluto and Charon. But before that, here’s a quick reminder of this week’s Kindle Countdown deals for Far from the Spaceports and Timing – £0.99 / $0.99 for the next couple of days. Follow these links…

New Horizons route, including Pluto and Ultima Thule (Wiki)
New Horizons route, including Pluto and Ultima Thule (Wiki)

Right. New Horizons. After the Pluto flyby, the natural question was, what next? There was enough fuel and energy reserves to consider a small course change… but to what end? Pluto is at the inside edge of the Kuiper Belt, a tenuous and very sparsely populated volume of space. Over the last few years, we have been steadily gaining information about some of the contents, many of which have hugely elongated orbits. The big prize out there is the possibility of a really sizeable planet, acting as a gravitational shepherd to coax the smaller bodies into resonant patterns.

Planet 9 has not yet been found, but several smaller bodies have. And one of them, catalogue number KBO 2014 MU69 , happened to be well placed for New Horizons. So, an appropriate course change was made as Pluto dwindled into the distance, and KBO 2014 MU69 – now provisionally renamed Ultima Thule – became the next goal.

Current New Horizons view of Ultima Thule (NASA/JHUAPL/SwRI)
Current New Horizons view of Ultima Thule (small dot on right-hand frame) (NASA/JHUAPL/SwRI)

But distances out in the Kuiper Belt are large, so there has been a considerable wait. Ultima Thule is about 12% further away from Earth as Pluto is. The actual flyby will occur on January 1st next year, and at this stage we still don’t really know what to expect. The Hubble telescope orbiting Earth shows Ultima Thule as just a slowly moving point of light. New Horizons is about 33 million miles away from it – about 1/3 the Earth-Sun distance – and still can’t resolve it to more than just a point source. We cannot make out any surface detail. We don’t know if it’s roughly spherical, or irregular, or even a little cluster of fragments all moving together. Just about all we know is that it’s less than 40 km across, and although very dark by the standards we are used to in the inner system, is slightly more reflective than expected.

Artist's impression, New Horizons and Ultima Thule (Steve Gribben/NASA/JHUAPL/SwRI)
Artist’s impression, New Horizons and Ultima Thule (Steve Gribben/NASA/JHUAPL/SwRI)

After sending the Pluto and Charon data home, New Horizons went to sleep for a couple of years, with a wake-up call in June for some of the instruments and a course correction. It is now being prepared as best we can for the encounter. It’s a fascinating problem – light or radio signals take around 6 hours to cross the gulf between us and the probe, so there is no possibility of direct control.  Any reply takes another 6 hours to get back. The systems have to be set up in advance, according to our best guess of what will be there. The final course changes will occur in mid December, when the ground crew wil decide just how close to steer towards Ultima Thule. In one sense, the nearer the better… but the higher the risk that the probe will make brief, catastrophic contact with some fragment of rock and ice. On the day, the probe will whistle by at over 30000 km/h, so there’s no opportunity for second chances. Whatever sequence has been set up in advance, will be played out without modifications. After that, New Horizons will spend the better part of two years streaming the data back to Earth. So although the rendezvous will be a New Year treat, we shall have to wait a long time until we get any high-resolution images or other data.

As yet I haven’t written about what life might be like in a suitably protected environment out in the Kuiper Belt… maybe this encounter will be the seed of another book, in the way that the flyby past Pluto and Charon has contributed to The Liminal Zone. And here, just for a bit of fun, are someone’s first impressions of the settlement on Charon, extracted from the early sections of The Liminal Zone

Nina walked steadily along the winding curves of Lethe towards Asphodel. The house AI had finally told her where Lance’s quarters were situated in Acheron, and had transferred directions onto a hand-held to direct her there. From space, the overall shape of the Charon settlement had been clear – five sinuous linear habitats, following curves in the underlying terrain and joined radially to Asphodel. When you were actually down here, it wasn’t nearly so neatly divided. There were extra little corridors and alcoves which broke up the superficial symmetry, and little tunnels that dived underground and then resurfaced at unexpected places. She was glad that the little hand-held router buzzed faintly at junctions to tell her which way to turn.

Weather – away from Earth

Last week I talked about weather on Earth, both in fact and fiction. This week, suitably enough, it’s time to think about the other planets in our solar system. And there’s plenty to talk about.

Dust storm front, northern latitudes of Mars (ESA Mars Express)
Dust storm front, northern latitudes of Mars (ESA Mars Express)

The obvious first place to start is Mars – the atmosphere is thin there (ground level on Mars is about the same as 30 km altitude here, high above the Himalayan peaks), but it’s well able to have weather patterns. There are seasonal changes, with the polar ice caps (frozen CO2, or dry ice, rather than water ice) growing and shrinking as the planet tilts one pole or the other towards the sun. Then there are erratic changes, such as dust storms which can build up over a substantial area. The Martian opened with one such storm, and the book version had a second which threatened Mark Watney’s journey towards rescue (the film skipped over this one). In the real world, back in the summer, one such storm of vast proportions cut off communication between NASA’s Opportunity rover and mission control. The problem here is not actually caused by fierce winds buffering the craft, but that the dust has blocked its ability to capture sunlight and so generate electricity (the exact problem Watney faced late on in The Martian).

Storm on Saturn seen by Cassini probe, 2010 (NASA)
Storm on Saturn seen by Cassini probe, 2010 (NASA)

Venus has ferociously fierce winds, and if ever we try to build a permanent settlement on the surface there (which personally I doubt, since orbital or high atmospheric bases would probably suffice) then they will need immensely strong anchors, and extraordinary resistance to high levels of heat and acidity. There are outline plans at present for building a lander able to survive for a few months, rather than the few hours which is all that has been achieved to date. Jupiter and Saturn have no discernible surface – probably one exists, but the pressure would be intolerable well before you reached it. They also have huge storms spreading thousands of miles across.

Artist's impression, dust storm on Titan (PGP/Labex UnivEarthS/University Paris Diderot – C. Epitalon & S. Rodriguez)
Artist’s impression, dust storm on Titan (PGP/Labex UnivEarthS/University Paris Diderot – C. Epitalon & S. Rodriguez)

But several of the moons of the giant planets are more promising. Recently, dust storms were spotted on Saturn’s moon Titan… not sand as might be on Earth or Mars, but great clouds of organic hydrocarbon molecules are stirred up into its atmosphere. So there’s definitely weather on Titan, and pretty much everywhere else we look.

Moons like Titan have been known to have atmospheres for some time, but as well as this, our solar system contains a lot of small bodies which used to be thought of as entirely airless. Closer investigation has shown that many of these actually have very thin layers of air around them. In some cases these are probably generated by underground deposits of liquid and gas which slowly ooze to the surface and evaporate. In others, we don’t yet know how they came into being. But these discoveries are reshaping how we think of our sibling worlds, and by extension the worlds we are spotting around other stars.

New Horizons image of clouds on Pluto (NASA/JPL)
New Horizons image of clouds on Pluto (NASA/JPL)

Back in 1950, EE (Doc) Smith, in First Lensman, could describe Pluto as being rocky and entirely barren. We couldn’t say that any more, not after the New Horizons probe sent back this fantastic image of air and clouds above Pluto. In Liminal Zone, my protagonists on Pluto’s moon Charon witness such changes both outside the dome where they live, and also when they look up at Pluto. Weather, it seems, is pretty universal, and will go on forming a topic of conversation for a lot of years to come.

And in a final stop-press, the existence of a new dwarf planet has just been announced. The finders were actually looking for the enigmatic Planet Nine, whose existence is suspected from a variety of gravitational anomalies in the orbits of other far-out objects. That has still not been detected, but instead they found 2015 TG387, dubbed The Goblin for simplicity. This newly recognised member of our solar system has a fantastically elongated orbit. At closest approach it is still well outside the orbit of Pluto, and at aphelion it strays 35 times as far away. It takes around 40,000 years to complete an orbit: last time it was in its present position we were sharing much of the planet with Neanderthals.

Orbit of 2015 TG387 (Roberto Molar Candanosa and Scott Sheppard, courtesy of Carnegie Institution for Science)
Orbit of 2015 TG387 (Roberto Molar Candanosa and Scott Sheppard, courtesy of Carnegie Institution for Science)

Red dwarf stars, and life away from Earth

After a few weeks in which I have been thinking about ancient Cumbria, this week I’m back in space again. In particular, this post looks at some possible locations for alien life which, until recently, were considered most unlikely. Over the last few years, thousands of planets have been identified by equipment both on Earth’s surface and in orbit. We now know that planets are exceedingly common in the galaxy, and that on average, each star has more than one planet. There are more planets near us than stars. Many of these are large in size, gas giants like our own Jupiter and Saturn – larger planets are obviously easier to detect than smaller ones – but a great many are small and rocky, more like Earth.

Artist's impression - the seven planets of TRAPPIST-1 (ESO)
Artist’s impression – the seven planets of TRAPPIST-1 (ESO)

The most extreme case we know of is designated TRAPPIST-1 (the acronym originating from the Chilean telescope which first detected them). This has seven planets, so the system is broadly like our own. And a very recent analysis suggests that each of them has liquid water at its surface, and in some cases considerably more water than we enjoy here. If we were to travel the forty light years to get there, we might well find a world which is entirely ocean.

But as well as the striking nature of the planetary system, the sun itself is interesting. Up until fairly recently, the search for life elsewhere was focused on stars which were as similar to our sun as possible. It was assumed that this was necessary in order for the associated planets would be like Earth. But TRAPPIST-1 is not at all like our sun – it is a comparatively cool red dwarf star. Red dwarfs are extremely common in space, but they are small and dim, and until modern orbital telescopes revealed the true situation, were thought to be rare.

Comparison of solar system sizes (ESO)
Comparison of solar system sizes (ESO)

Now, red dwarf stars are much cooler than our sun, between 1/3 and 2/3 of the effective temperature, so for a planet to be in the Goldilocks Zone – neither too hot nor too cold – it must be much closer to its sun. But that’s OK – in the TRAPPIST-1 system, all seven planets orbit well within the distance that super-hot Mercury circles our sun. Indeed, that system is not much larger than that of the moons of Jupiter. Red dwarfs are miserly with their energy, so you have to huddle in close to the fire to get any warmth. But along with that, they burn at their low rate for a hugely longer time than our sun will last. The hotter and brighter the star, the less time it shines for. Too short a stellar lifetime, and their might not be time for life to develop on whatever planets are around. Red dwarfs give their planets massive amounts of time to develop.

Right now we have absolutely no idea whether any of the TRAPPIST-1 planets supports life – or indeed any of the myriad other red dwarfs and their planets in our quadrant of the galaxy. But if you were a betting person, you’d be more likely to bet on life arising around a red dwarf than a super-hot star like Sirius.

Artist's impression, Ross-128b (ESO)
Artist’s impression, Ross-128b (ESO)

Now, 40 light years is inconveniently far away from Earth for exploration in reality or fiction. Our current generation of telescopes can find out a decent amount of information about the 7 planets of circling TRAPPIST-1, but not nearly as much as one would like. And if you consider near-future science fiction, without warp drives, wormholes, or other exotic ways to travel around space -as I do – then 40 light years is well beyond a realistic journey time. Happily, there are other red dwarfs much closer to us. One of these, which has been studied with great excitement for a few years now, is called Ross 128 (the rather boring name coming from a catalogue number). It has at least one planet (Ross 128-b) which appears to be a little larger and more massive than our Earth, and some calculations suggest that its surface temperature may well be around 21C. Ross 128 is only about 11 light years from Earth, so is getting towards the we-might-send-something-there territory.

I thought about using Ross 128 as the focus of interest in my in-progress novel The Liminal Zone, but in the end pitched for the even-closer Gliese 411 – another catalogue name, which for fictional purposes has been rebranded something more interesting. Gliese 411 is under 9 light years away, and is the 4th-closest star system to us. The planet Gliese 411b is, so far as we can tell, larger than Earth, and almost certainly rather hotter, but (probably) not so hot as to preclude interesting things there. And its proximity to us makes it a credible target for the Breakthrough Starshot project, in which tiny “spacecraft” with roughly the capability of a mobile phone are boosted towards their target by a laser beam shining against a light-catching sail. The miniature spaceships are called Sprites, and last year were tested for their ability to communicate from space after being launched from Earth. Each is just a few centimetres square, weighs just 4 grams, and costs a few tens of dollars. The entire actual cost of the mission is in the devices needed to boost these Sprites to their final speed.

Starshot’s current plans are for Proxima Centauri as target – the nearest star to us, a little over 4 light years away – and a boost to 1/5 light speed. Proxima Centauri is in fact another red dwarf star, and a very recent theoretical study suggests its planet may have a large ocean and survivable temperatures… though so far we lack real observations which might confirm or refute this, and other studies have suggested that the radiation levels are uncomfortably high for life to thrive.

My fictional version is a little more ambitious – Gliese 411 and 1/2 light speed. A journey time of about 17 years, plus the time taken for the homeward bound signal on arrival, means about a 25 year lag from lift-off to analysis of results. It’s still a long time, but less so than some space projects – it is now over 41 years since the two Voyager spacecraft left Earth, and we are still following them. A very recent theoretical study

As to what happens in The Liminal Zone once these little ships get there – well, it’s still work in progress, but hopefully you’ll get a chance to see for yourself early next year!

The Liminal Zone (temporary cover)
The Liminal Zone (temporary cover)


With The Liminal Zone foremost in my writing mind just now, I’m always eager to read space news about Pluto. And just recently another paper has been published analysing the surface features as revealed by the New Horizons flyby back in July 2015.

Audiobook cover
Audiobook cover

But before that, a quick reminder of the giveaway competition currently running for the audio version of Half Sick of Shadows. There were 5 copies each on Audible UK and US available free. Just follow this link, listen to the sample snippet, and get back to me with the answer. Some copies have already gone but others remain to be won! It’s absolutely free – if you don’t currently have Audible membership then you can sign up for a trial month at no cost, then cancel if you don’t like it.

Back to Pluto. The specific surface feature that the report found was dunes. Not, of course, sand dunes, but ones made of ice granules, moved about very slowly by the extremely light winds which stir the extremely thin atmosphere there. It’s a remarkable tribute to the way physical phenomena tend to mirror each other. The conditions on Earth and Pluto are radically different in ever so many ways, yet they share the ability for dunes to form on their surfaces. Like everything on Pluto, it all takes place on an immensely slow timescale – I doubt that these dunes move appreciably over a human lifetime. But nevertheless, there they are, adding to the richness and complexity of the surface features of a world which, not so long ago, was assumed to be utterly boring.

Cover - Dune (Goodreads)
Cover – Dune (Goodreads)

A science fiction reader’s first reflex, on hearing of dunes, is naturally to jump to Frank Herbert’s Dune. That world was bakingly hot, dry, and life was absolutely dominated by the survival need for water. The dunes there – sand dunes – covered the vast majority of the desert world’s surface, and concealed both exotic wildlife and a radical human culture. It seems unlikely that much life frequents Pluto, with a surface temperature around -230° Centigrade. But these days, it would be a brave person who would say it’s impossible. And The Liminal Zone is – among other things – about the human settlement on the margins of our solar system.

Finally – and since my main enthusiasm is not so much for Pluto as for its largest moon Charon, here is a video put together by NASA from the New Horizons flyby. It’s partly for fun, and partly because next week – June 22nd – is the 40th anniversary of the discovery of Charon! It’s only short, but quite cool.

After enjoying that, don’t forget the giveaway for Half Sick of Shadows!

Planet 9?

Another space blog post today, complete with some thoughts about life out there, and an extract from my work-in-progress The Liminal Zone.

First, though, the elusive Planet 9. For some time now, astronomers and space scientists have been speculating that an additional planet, of considerable size, lies out beyond Pluto. The evidence is indirect, in that such a planet has not been observed via telescope. Hence the matter is currently unresolved. But a recent paper argues that its presence would solve several unexplained issues, while its absence would create several more.

Orbital resonance in the moons of Jupiter (Wiki)
Orbital resonance in the moons of Jupiter (Wiki)

So what are the problems? Essentially, they come down to the logic of orbital dynamics, which says that you can’t just put a bunch of planets in random orbits around a star and expect them to be stable. Even though the gravitational attraction between two planets is small, it nevertheless exerts a steady regularising influence on the two paths around the sun. So the orbits of our sister planets show all kinds of patterns of ratios which at first sight seem remarkable (they’re still remarkable when you take gravity into account, but in a different way). And the more patterns that you see, the more you can infer about things you can’t see.

This, for example, is how the outer planets beyond Saturn were deduced before they were observed. The planets from Saturn inwards have been known since prehistory. But when careful observations with a telescope could be made, small but noticeable perturbations in their tracks were found. These pointed to the existence of unknown planets further out. The same principle explains why the orbits of Neptune and Pluto are synchronised – two of Pluto’s orbits match 3 of Neptunes. So, although Pluto dips inside Neptune’s orbit for a couple of decades every 248 years (one Pluto year), they are never at risk of colliding. These synchronisations happen all over the place – for example within the moon systems of Jupiter and Saturn, within the asteroid belt, or forming the delicate internal patterns of Saturn’s rings.

Now, Pluto is the first major body in the Kuiper Belt, a disc of space outside Neptune which we now know contains a decent number of small asteroids and similar objects. So it starts around 30AU from the Sun (AU = Astronomical Units, the distance between Earth and Sun). But it then Belt stops, quite abruptly, around 50AU. Why should this be? Why not feather off gradually?

Trans-Neptunian Object orbits (LIve Science / ESO)
Trans-Neptunian Object orbits (LIve Science / ESO)

Additionally, as we have built up a catalogue of these asteroids, a picture is emerging in which a surprising number have orbits around the sun which are aligned with each other. The simplest way to explain this is to suppose that some sizeable, but as yet unknown, object is synchronising them.

So, why has it not yet been found? Well, first of all, as Douglas Adams said, space is “vastly, hugely, mind-bogglingly big” (Hitchhiker’s Guide to the Galaxy, chapter 8). So although the potential planet is several times larger than the Earth, it is on average 20 times further from the sun than Neptune is – 600AU – with an orbit that is quite noticeably elliptical rather than circular. That means that there is a lot of space to search in, and also that it is dark and cold out there. There is not a lot for optical or infrared telescopes to detect. But each new discovery helps narrow the search window down, and some lucky group of astronomers may well announce a discovery soon.

Or, of course, not. It may be that the apparent alignment we see will be eroded by more observations. Which would be a bit of a shame, in that it is always nice to have unknown things to discover. It would also leave several other problems unresolved. Other things being equal, I’d like Planet 9 to be found!

Artist's impression, Planet 9 (Live Science / JPL-CalTech)
Artist’s impression, Planet 9 (Live Science / JPL-CalTech)

So, what might it be like to live there? For one thing, cold and dark. Our sun is still the nearest and brightest star by a huge margin. But at 20 times further away than Pluto, it gets just 1/400 of the solar radiation of any kind. Or if you like, 0.0003% of what we enjoy on Earth. You’d want to know you had reliable sources of heat and light, if you went there. And it will take a long time to get there. It is not a place for a quick jaunt. For reference, Voyager 1 is a little over 100AU from Earth and has spent about 40 years getting there.

Could there be indigenous life out there? Well, life as we know it depends on liquid water, and the surface of Planet 9 is way too cold for that. But possibly, there could be subsurface heat turning ice into water at some depth? Or perhaps, there might be a moon which would be subject to gravitational flexing, just as happens to the inner moons of Jupiter and Saturn. This could – maybe – provide enough heat to give us water. We’ll have to wait and see.

I haven’t yet written anything going that far out from the sun. In the universe of Far from the Spaceports, an Earth-Mars trip takes a couple of weeks. An Earth-Pluto trip takes a few months. An Earth-Planet 9 trip would take anywhere from seven or eight months up to just over a year, depending on whereabouts in its orbit it happens to be. Not a journey you’d make lightly.

The Liminal Zone (temporary cover)
The Liminal Zone (temporary cover)

The Liminal Zone takes place on Charon, the main moon of Pluto. The New Horizons probe returned some fascinatingly detailed pictures to us of these two, transforming them from hazy blobs to detailed worlds. New Horizons is currently en route to an object further out in the Kuiper Belt, 2014 MU69, popularly known as Ultima Thule, and is due to arrive early next year. Finding a second destination more-or-less on the flight path after Pluto was a remarkable thing in itself, as objects are so exceedingly thinly spread out there. Anyway, The Liminal Zone is not a financial fraud book like Far from the Spaceports or Timing – it’s more of a voyage of discovery, both personally for the main character, Nina, and more generally for the society she is part of. So here is a short extract – Nina is talking to Percy, one of the Charon residents, about events surrounding an emergency several years ago…

Something about his expression made Nina stop.
“But you didn’t actually see anything?”
He drew back a little.
“Seeing’s not everything. Haven’t you ever just known something for sure?”
His eyes held hers, suddenly very intense, and she felt a little internal quaver run through her body. She had hoped it wouldn’t show, but then she saw the trace of a smile cross his eyes.
“I’ve got Welsh blood, you know. It helps me comprehend things which maybe can’t be seen with the naked eye. And what about you, Nina? Where do you come from?”
She went blank.
“I grew up in Lacus Gaudii. On the Moon.”
He shook his head.
“Not that recent. Go back a few generations. Where did your family live? Before they came up to settle in that lunar lake of yours.”
The noise of the kettle was maddening. She withdrew inside herself, trying to escape the pressure.
“I… I don’t know. I suppose I could find out. It’s never mattered.”
He looked away, letting the moment pass.
“Ah, but it just might make a difference here.”
She took a long breath and tried again.
“But did you actually see anything?”

I’ll be posting more on progress into The Liminal Zone as it comes along…

How close are personable AI assistants?

A couple of days ago, a friend sent me an article talking about the present state of the art of chatbots – artificially intelligent assistants, if you like. The article focused on those few bots which are particularly convincing in terms of relationship.

Amazon Dot - Active
Amazon Dot – Active

Now, as regular readers will know, I quite often talk about the Alexa skills I develop. In fact I have also experimented with chatbots, using both Microsoft’s and Amazon’s frameworks. Both the coding style, and the flow of information and logic, are very similar between these two types of coding, so there’s a natural crossover. Alexa, of course, is predominantly a voice platform, whereas chatbots are more diverse. You can speak to, and listen to, bots, but they are more often encountered as part of a web page or mobile app.

Now, beyond the day job and my coding hobby, I also write fiction about artificially intelligent entities – the personas of Far from the Spaceports and related stories (Timing and the in-progress The Liminal Zone). Although I present these as occurring in the “near-future”, by which I mean vaguely some time in the next century or two, they are substantially more capable than what we have now. There’s a lot of marketing hype about AI, but also a lot of genuine excitement and undoubted advancement.

Far from the Spaceports cover
Far from the Spaceports cover

So, what are the main areas where tomorrow’s personas vastly exceed today’s chatbots?

First and foremost, a wide-ranging awareness of the context of a conversation and a relationship. Alexa skills and chatbots retain a modest amount of information during use, called session attributes, or context, depending on the platform you are using. So if the skill or bot doesn’t track through a series of questions, and remember your previous answers, that’s disappointing. The developer’s decision is not whether it is possible to remember, but rather how much to remember, and how to make appropriate use of it later on.

Equally, some things can be remembered from one session to the next. Previous interactions and choices can be carried over into the next time. Again, the questions are not how, but what should be preserved like this.

But… the volume of data you can carry over is limited – it’s fine for everyday purposes, but not when you get to wanting an intelligent and sympathetic individual to converse with. If this other entity is going to persuade, it needs to retain knowledge of a lot more than just some past decisions.

A suitable cartoon (from
A suitable cartoon (from

Secondly, a real conversational partner does other things with their time outside of the chat specifically between the two of you. They might tell you about places, people, or things they had seen, or ideas that had occurred to them in the meantime. But currently, almost all skills and chatbots stay entirely dormant until you invoke them. In between times they do essentially nothing. I’m not counting cases where the same skill is activated by different people – “your” instance, meaning the one that holds any record of your personal interactions, simply waits for you to get involved again. The lack of any sense of independent life is a real drawback. Sure, Alexa can give you a “fact of the day” when you say hello, but we all know that this is just fished out of an internet list somewhere, and does not represent actual independent existence and experience.

Finally (for today – there are lots of other things that might be said) today’s skills and bots have a narrow focus. They can typically assist with just one task, or a cluster of closely related tasks. Indeed, at the current state of the art this is almost essential. The algorithms that seek to understand speech can only cope with a limited and quite structured set of options. If you write some code that tries to offer too wide a spectrum of choice, the chances are that the number of misunderstandings gets unacceptably high. To give the impression of talking with a real individual, the success rate needs to be pretty high, and the entity needs to have some way of clarifying and homing in on what it was that you really wanted.

Now, I’m quite optimistic about all this. The capabilities of AI systems have grown dramatically over the last few years, especially in the areas of voice comprehension and production. My own feeling is that some of the above problems are simply software ones, which will get solved with a bit more experience and effort. But others will probably need a creative rethink. I don’t imagine that I will be talking to a persona at Slate’s level in my lifetime, but I do think that I will be having much more interesting conversations with one before too long!

A research snippet

I thought today I’d share some research I have been doing for my WIP science fiction book, The Liminal Zone.

Full moon (NASA/JPL)
Full moon (NASA/JPL)

For various plot reasons I needed to know the answer to the following problem. Suppose you were standing on the surface of Pluto’s moon Charon, looking up at Pluto, fully lit by the sun… how bright would that be compared to looking up at the full moon from Earth?

This depends on a few factors:

  1. How bright is Pluto compared to our Moon?
  2. How big are Pluto and Charon compared to Earth and the Moon?
  3. What is the separation between Pluto and Charon compared to that between Earth and Moon?
  4. How much light from the sun falls on Pluto or Charon compared to Earth and Moon?

The relationship between these various factors boil down to a fairly simple equation – comparing everything to the full moon brightness, which is fairly familiar to us, you have to:

  1. Scale up by the ratio of intrinsic reflectivity of the two bodies (called the albedo)
  2. Scale up by the ratio of the apparent area of sky covered by the two bodies
  3. Scale down by the square of the relative distance from the sun.

The apparent area can be calculated relatively easily knowing the radius of the body in question and the distance apart.

At this point you start looking up the raw figures from any of several science sites (a handy list follows below).

Earthrise from lunar orbit (NASA/JPL)
Earthrise from lunar orbit (NASA/JPL)

Let’s first think about the simpler problem of how bright a “Full Earth” is as seen from the Moon. The Earth is, on average, 2.5 times as reflective as the Moon (that’s averaging over cloudy and clear skies, land and water, etc), and the area of sky it covers is about 14 times that of the Moon. So a Full Earth as seen from the Moon is about 35 times as bright as the Full Moon as seen from Earth. Quite a sight.

Charon from New Horizons spacecraft (NASA/JPL)
Charon from New Horizons spacecraft (NASA/JPL)

Let’s move out to Pluto, and imagine we are standing looking up at a “Full Charon”. Charon is brighter than the Earth, is much smaller, much closer to Pluto than our Moon is to us, and much much further away from the sun (forty times further on average).

When you put all those figures together you find that the apparent diameter of Charon in Pluto’s sky is nearly eight times that of our Moon, so nearly sixty times the apparent area. Scale up for the extra brightness and down for the distance from the sun, and you find that Charon has about 1/6 of the brightness of our full moon. Probably still just enough to cast shadows.

Pluto from New Horizons spacecraft (NASA/JPL)
Pluto from New Horizons spacecraft (NASA/JPL)

And finally, looking up at a “Full Pluto” from Charon. Pluto is about twice the size of Charon so about four times the area. By way of comparison, that means Pluto would nicely fit inside either the top or bottom half of the constellation Orion – between belt and shoulders, or belt and feet. Pluto is also brighter than Charon. Put that all together and you find that Pluto’s full light is about two thirds that of a full moon here.

I found this quite a remarkable fact when I crunched the numbers. Go all the way out from our Earth to the furthest of the standard nine planets, and the experience of standing on Charon looking up at Pluto is almost the same – in terms of brightness – as standing here looking up at the Moon. A useful comparison for my character, who is doing just that.

Facts and figures for the curious…
Albedo values (average)
  • Moon 0.12
  • Earth 0.3
  • Charon 0.45
  • Pluto 0.6
Radius values
  • Moon 1737 km
  • Earth 6371 km
  • Charon 606 km
  • Pluto 1187 km
Distances from planet to moon
  • Earth-Moon distance 384,400 km
  • Pluto-Charon distance 18,384 km
Apparent angular size
  • Moon from Earth 0.5 degrees
  • Earth from Moon 1.9 deg
  • Charon from Pluto 3.8 deg
  • Pluto from Charon 7.4 deg