Jupiter’s moon Io: some facts

His Name In Lights is set on Jupiter’s moon Io, which has captured my interest for some time. I have at least one other Io story in the making. Expect an announcement about A Perfect Day Off The Farm fairly soon. In that story, I explain the concept of stick farms, which is something that would actually work.

If you came here from the novella His Name In Light’s product page on my author site, click this link to go back after you’ve read this

Io is a body slightly bigger than Earth’s Moon which orbits Jupiter at roughly the same distance as the Moon orbits Earth. It is the closest of the larger moons of that planet. Jupiter, of course, is much, much bigger than Earth, and this has all sorts of consequences for its neighbourhood.

Io was discovered in 1610 by Galileo when he was looking at Jupiter and noticed three little dots close to it. Moreover, the dots were placed in a straight line (that’s a dead giveaway for a planetary or any kind of system that involves things orbiting each other), and on top of that, the next day, the dots were in different positions. The discovery of the four Galilean moons (Io, Europa, Ganymede and Callisto – the god Jupiter’s lovers in ancient mythology), proved Galileo’s hypothesis that other planet-moon systems existed and that, by extrapolation, the Earth was not the centre of the universe, nor the centre of the solar system.

You can see Jupiter and its dancing dots with a decent set of binoculars in the night sky. Because Jupiter is so large and has so much gravity, the moons race around the planet like bats out of hell, and their positions are visibly different every day.

Being the closest moon, Io orbits Jupiter every 42 hours. Since the circle it describes is the same size as the Moon’s orbit around Earth, it means it’s moving at a speed of over 17 kilometres per second. By comparison, the Moon moves at a speed of one kilometre a second. This thing is racing!

The same applies for the other three moons, Europa (3.5 days), Ganymede (7.15 days) and Callisto (16 days). All move at comparatively high speed, which is why they’re so much fun to observe. You can see them move.

The moons’ gravities also interact with each other, since all of them are roughly the size of our Moon and quite close together, astronomically speaking. They have developed a pattern of orbital resonance, where Io will orbit exactly twice within one orbit of Europa, and Europa will orbit twice with each orbit described by Ganymede. Which also means that Io will orbit exactly four times for one orbit of Ganymede. Callisto is the odd one out and isn’t playing this game.

This orbital resonance means that the three moons will frequently line up in a straight path and will be at cross-angles to each other at other times. This means that there are huge tidal forces exerted on each of those moons, but especially on poor little Io.

When telescopes became good enough to observe very fuzzy details of the surface, scientists thought at first that there were two moons. Sections of the surface are highly reflective, and later pictures of the moon show a kaleidoscope of colours in yellows, greens and reds, leading to the nickname ‘pizzaface’.

We now know that Io is made primarily of sulphur and silicates (aka ‘rock’). The atmosphere is very thin and patchy and when present consists of sulphur dioxide. There is no water at all, in contrast to the other three Galilean moons, which have significant percentages of water on their surface. It is thought that radiation from Jupiter has evaporated any water present on the surface.

Because of the huge tidal forces, Io is the most volcanic body in our solar system. On Earth, we think of tides as something that affects water, but that is just because water can easily move, so we notice the effect. Rock can’t move, so it gets hot in response to tidal forces. This is why the interior of Io consists of molten rock.

Geologists on Earth define an active volcano as one that has been known to exhibit activity within the last 400 years. Under that definition, every single feature on the 400-long list of mountains, depressions and rifts on Io is an active volcano.

In fact, the moon is so volcanic that there are no impact craters, like we can see on the Moon or Mars. That’s not because nothing’s ever hit Io, but because the evidence gets covered up pretty quickly. Essentially, Io is continuously being turned inside-out by its own fart-holes.

The spread of volcanic ash across the surface of Io amounts to an average of 1cm per year. At a geological scale, that’s massive.

It also means that any robotic craft or permanent fixture you were to put on the surface would need some sort of mechanism to keep itself un-buried from this material. To make matters worse, it’s most sulphur as well as Sodium and other elements that are Not Conducive to effective mechanical operation of equipment.

Mountains on Io are up to 8 kilometres in height. Some are volcanoes, but many are not, at least not at the top. The volcanic outlets are more likely to be at the bottom of the mountain.

Why? Well, imagine a layer of ice floating on water. Now pile ice chips on, and more ice chips and more ice chips… and eventually the layer of ice will start to protest, to buckle and twist and break, sink in one place and tilt upwards at another. Ah! Now we have mountains. The logic then also dictates that the breaks (= places where magma can rise to the surface) are next to the mountains.

What else would be special about Io?

The day on Io is 42 hours, the same as its orbital period. Because the moon is tidally locked with Jupiter, like our Moon, it always shows the same side to the planet. Which in turn means that a day on the moon is the same length as one orbit around the planet. On Io, however, this has an interesting complication.

As it races around Jupiter, Io experiences an eclipse every day when it goes into the shadow of Jupiter. The eclipse lasts 2.5 hours and in that dark time it gets so cold that the pathetic cover of sulphur dioxide that passes for atmosphere condensates on the surface as snow, only to sublimate again when the sun returns.

In fact, it is highly likely that the time of the eclipse is the darkest time of day on Io. At night, the Jupiter-facing (subjovian) side would have Jupiter in the night sky. To be honest, Jupiter will take up a very significant portion of the night sky. Think of the light it would reflect back to Io.

This only applies for the side that always faces Jupiter, though. On the other side, you would never see the planet, but you probably get some interesting views of the other moons.

No discussion about Io is complete without mentioning radiation. Every celestial body that has a magnetic field has Van Allen radiation belts. A magnetic field traps particles, either from the solar wind or cosmic radiation, in a donut-shaped torus around the planet. Crossing those belts at between 1000 and 60,000km from the Earth was one of the main concerns for the Moon astronauts. At about 370km, the International Space Station stays well clear of them.

Io orbits–you guessed it–smack bang in the middle of Jupiter’s Van Allen belt. Jupiter is the second-most magnetic object in the solar system (after the Sun). Io helps the particle soup along a bit by constantly spewing volcanic stuff into space.

All this amounts to a massive radiation load. So much that if you were to step onto the surface unprotected, you’d be dead in minutes. Radiation would also affect the operation of any robotic equipment you’d send there.

So, as you can see, there are serious challenges to doing anything on Io, and a lot of places in the solar system that are easier to visit. But Io is also one of the most interesting places in the solar system.

Reference: Io After Galileo, A New View of Jupiter’s Volcanic Moon. Rosaly M.C. Lopes and John R. Spencer (2006). Springer. 366pp. ISBN 978-3540346814.

Be warned, this book is pretty darn expensive. For those with a more casual interest, Io’s Wikipedia page has an extensive list of scientific references, some of which can be read or downloaded for free online. If you are interested in buying this book, you can get a copy here: Io After Galileo: A New View of Jupiter’s Volcanic Moon (Springer Praxis Books / Geophysical Sciences)

Find out where to buy His Name in Lights



Alpha Centauri DOES have planets!

Ever since I wrote the two posts about the potential for planets at Alpha Centauri, those posts have been the most popular on this blog. With all the exoplanet action, this discovery was only a matter of time, because it seems that more than 90% of stars–maybe substantially more than that–have planets. I’ve written here about why it can be very hard to detect planets, even in stars that are “close”.

So it seems that Alpha Centauri B has a planet, which is now boringly named Alpha Centauri Bb. I think it needs a more interesting name.

The planet in question is about 13% more massive than Earth, which suggests that it is rocky, but orbits the Sun-like star far too closely to harbour life. The distance between it and the star is a mere 6 million kms (vs 150 million for Earth) and the surface temperature a mere 1200-odd degrees which makes it, as scientists wryly remark “unsuitable for life”. Or at least life as we know it. Science Fiction writers can go crazy here.

It is my prediction that if this planet exists this close to the star, others will be found. Already, some scientists say that the signal is too complex to suggest the planet’s existence with certaintly. A complex signal could well mean more planets. Trouble is, finding a Mars or Earth-sized planet possibly orbiting in a plane at an angle to the line of observation, as part of a triple-star system, and orbiting at a fair distance–as in 1 AU or more–is going to be like the proverbial needle in the proverbial haystack.

Meanwhile, get your space ships ready.

How many people are needed for a space colony?






Or is it?
















But, you can automate tasks.




Once more on the search for exoplanets, and Alpha Centauri

Excuse me for the absence of regular science posts, but my brain has turned to mush from writing fantasy. Isn’t it easy when you’re allowed to make everything up and as long as it makes sense, no one cares about accuracy? But, yes, I will return to where I left my characters in the Jupiter system, or in a space station orbiting the fictional gas giant Sarasvati, in the not-too-distant future.

This morning I came across this very interesting article on the Centauri Dreams website. By the way, Centauri Dreams, the website of the Tau Zero Foundation, is a very rich source for writers of realistic SF, especially in relation to planetary exploration and interstellar travel.

The article summarises results and speculation arising from new planets discovered by the European Southern Observatory’s HARPS spectrograph, which provides the most accurate Radial Velocity measurements we currently have (see an earlier post on how planets are discovered). Because of its increased sensitivity, HARPS can detect smaller planets. The smallest planet found at this point in time is a mere 1.5 times Earth’s mass. One of the, perhaps expected, outcomes of the spectrograph’s bevy of newly found low-mass planets (super-Earths or near Earth-mass) is that there are many of these smaller planets, a lot more than there are very large planets, and that the previous bias was merely a product of larger planets being easier to detect. The galaxy is swarming with smallish rocky planets. It is quite likely that some will be found inside the habitable zone.

We may already have found some of these planets. Much was made last year of the ‘discovery’ of Gliese 581g, supposedly in the habitable zone of an M class star. However, further analysis has so far failed to confirm the existence of this planet. But the star has two other planets which orbit at the edge of the habitable zone, and out of these, Gliese581d looks the most promising. The width of the habitable zone is not absolute, but varies with the planet’s albedo (basically, how much light it reflects) and composition and (if any) atmosphere composition (see another post on that here). So a newly discovered planet, HD85512b, at 3.6 Earth masses, may also fit the bill. It is a little close to its K class parent star, but could harbour liquid water on its surface if certain conditions of composition and atmosphere are met (see original paper by Kaltenegger et al. here).

Using the HARPS spectrograph, another group of researchers report on the search for planets orbiting sun-like stars within 40 light years from our solar system. (original paper by Pepe et al here). This work has resulted in a the discovery of a number of planets, again, most in the smaller size category. One of the main targets for the hunt is Alpha Centauri B, but there are some problems, one of the main ones being that it is part of a triple star system, and that any model the describes the wobble of the star that is caused by an orbiting planet must take into account that there are two other stars in the system, and as you could understand that is tricky business.

Image depicting an exoplanet system snarfed from NASA JPL

Farming on Mars

Let’s presume the collective world has gotten out of its space-exploration budget-funk, and has decided it’s worth sending people to Mars. The first have gone and have returned, and now it’s time to set up a colony.

Of course that colony will have to be self-sufficient. Thankfully, there are a number of very useful things on Mars, so the colonists won’t need to bring everything, but the more they can find locally, the better. Ideally they should not need anything from elsewhere to survive after an initial supply of resources.

Most importantly, the colonists will have to grow their own food.

At its distance from the Sun, sunlight on Mars is about 40% up to half that on Earth, but still sufficient as power source.

Unless the colonists choose to grow plants in hydroponic systems, they will have to use Martian soil. Preliminary analysis shows that the basic composition of Martian soil is fairly similar to certain soil types on Earth. To be sure, no one has ever taken a sample from Mars and returned it to Earth, but we have two methods for determining composition of Martian soil and/or rocks. In the first place, there are meteorites that have reached Earth from Mars, of which 34 are known. Without going into a lot more detail, they are all igneous rock, in other words, hardened lava. These rocks tell us about the composition of the Martian crust, but very little about sediments, water and free elements in the soil. Secondly, in 2008, the Phoenix lander carried equipment that allowed it to perform an in-situ analysis of the soil near Mars’ north pole. The soil turned out to be alkaline, and contain elements necessary for plant growth, such as sodium, magnesium, potassium and chloride.

However, things are unlikely to be as simple as that. For one, it’s not correct to refer to the substrate as ‘soil’ (but failing a different, similarly evocative word, I will use it anyway), since the definition of soil includes the presence of organic material. The Martian regolith (which is a word I should use instead) contains none. Plants need soil for two basic purposes: for anchoring, and for their nutrition. Plants can anchor themselves in virtually anything (which is why you get plants growing in concrete and on roofs), as long as they have enough water and food. Water is available on Mars in the form of ice. The colonists will be deposited somewhere close to a source of this ice.

But what do you think would happen if you wet a soil that has been dry for billions of years? A soil that has been subject to direct radiation and dust storms. For one, there will be a lot of fine material. On Earth, growing crops in heavy, gluggy soils with lots of fine particles (clays) is hard. Plants need adequate aeration to grow properly. If the soil becomes too compacted (either because it is too fine or because people walk over it) plants don’t grow properly. This is why there is frequently no grass in a soccer goal. So you’ll have to get rid of excess dust before you wet the Martian soil else the stuff will turn into something akin to cement and be of no use for cropping. Also, there will be something like four billions years’ worth of accumulated salts that are freed if you wet this soil. When the Phoenix lander wetted the Martian soil, it released perchlorates, which are poisonous to plants. The soil pH was alkaline (8.3), which indicates accumulated salts of one type or another.

There are plants, notably those that are native to deserts, that tolerate a high salt concentration in the soil, but in order to grow highly-strung and finicky crop species, it’s necessary to get rid of excess salt. This probably requires a lot of (recycled) water, but at the very least, it will require lots of detailed testing, and time.

Next: the air. Mars has lots of carbon dioxide. Plants grow better with a higher concentration of carbon dioxide than present on Earth. It makes sense to run the glasshouses with a high carbon dioxide level. But at high carbon dioxide concentrations, the plants are likely to take up an increased percentage of poisonous elements from the soil, such as arsenic, cadmium and lead. Some areas of Mars are known to have fairly high concentrations of arsenic.

The big trouble is going to be nitrogen, because there is very, very little of that on Mars. Nitrogen is an element that does not easily form bonds with other elements. Whereas oxygen facilitates chemical reactions by reacting with other elements (for example by burning or rusting), atomic nitrogen just does… nothing. Since we have seen in an earlier post that Mars is too small to hold onto its atmospheric nitrogen, there may not be all that much of nitrogen to be found on Mars in any of its forms. So unless early explorers locate a deposit of nitrogen-rich substrates, the colonists will have to import nitrogen from elsewhere. And nitrogen is the most essential of the essential elements for plant growth.

All of which is not suggesting that using Martian soil for cropping is impossible, but that it likely isn’t easy or straightforward, and that early colonists are probably better off starting with hydroponic installations while all this other testing takes place.

Is there other life in the universe?

Let’s start with the solar system. People very much want there to be life in the solar system. We’d like to think that the presence of life on Earth is not unique, and that life in some form also exists, or has existed, in other places. But where would this life have come from?

There are two main theories about the emergence of life from the soup of hydrogen, oxygen, carbon and nitrogen in primordial soup. One, the geocentric model, is that life emerged on Earth and is therefore unique to Earth. The other theory takes a more holistic view in that Earth is not central to the universe. We are uncommon, but not special or precious.

Panspermia has life originate in microbial form elsewhere in the universe and being spread through comets. While we have no definitive proof for either theory, there are some pointers. Firstly, the elements for life exist everywhere in the universe. In limited, but still reasonably numerous, places, temperatures are right for liquid water. Life on Earth evolved in liquid water. Secondly, certain bacteria are known to survive exposure to space for extended periods. Certain bacteria can lie dormant for many, many years. It is feasible to assume that these bacteria would not have developed these abilities unless there was a need for them.

How could we find out?

Sample return missions to places of interest are expensive. They will eventually be necessary, but there are other things we can do to pinpoint things to look for when eventually we send such missions.

We can look at comets. If comets carried the first microbes to Earth, they would also have carried them to other bodies. There is no reason to believe that if comets carried microbes millions of years ago, they have suddenly stopped doing so.

We can look at how and where organisms have survived in environments on Earth that are too hostile for most other life. This explains the interest in extremophiles, organisms that thrive in such places. It is with this in mind that scientists look for life in hydrothermal vents in the dark depths of the oceans, where the water welling up is extremely hot, where it is extremely dark and there is little oxygen to be had. It is for this reason that scientists look for adapted life in Antarctica, or in environments that are too poisonous for ‘normal’ life to exist.

We can look at bits of other celestial bodies that have found their way to Earth

That said, in recent months, we’ve seen a number of disappointing reports. First, there was the big kerfuffle over the discovery of bacteria that can substitute arsenic for phosphorus. While the research was officially announced, a big hoo-hah soon broke out over the validity of the results.

Then, last month, there was a report that fossil bacteria had been found in meteorites that are of Martian origin. Again, a big bunfight broke out, this time including claims against the reputation of the magazine in which the paper had been published.

This is starting to sound very much like the boy who cried ‘wolf’ too often, or maybe too soon, when the wolf was in fact the neighbour’s dog. It’s sad because as described above, a discovery would probably fall along those lines. This hyped-up (pseudo) news desensitises people to the real possibilities.

Meanwhile, a good number of well-informed scientists express the quiet opinion that we will ‘probably’ find evidence of microbial life elsewhere in the solar system. Candidates for such finds would be fossil life on Mars, extant life in the seas of Europa and possibly methane-based life on Titan. They also think that any such life is likely to be primitive, possibly no more evolved than bacteria. No one thinks we’ll be meeting little green men any time soon.

Humans in space

A while ago, I asked on Twitter what people would like me to blog about. One person (you know who you are) said: the effect of space travel on human beings. I promised that I would write about it, but that I wanted to read one more book before I did so. That book is Packing for Mars by Mary Roach. I have now read it (highly recommended), so here we go: the effect of space travel on human beings, with an eye on the future and the science fiction writer.

As one might expect, there are two types of effects long-term space travel has on human beings: physiological and psychological effects. Each of these effects mentioned below is probably worthy of a separate blog post, but let’s start with the overall first.

The physiological effects themselves can be split into two sections: lack of gravity and what I shall call external threats.

External threats are simple: accidents and radiation. Both are managed at the space ship design level and crew training stages. Good design will limit radiation exposure. The risk is solar flares, but it is a known and theoretically manageable risk. Manned missions to—say—Mars will contain shielding (best material: water, since the ship will have to carry plenty of that anyway). There will be advanced warning for the crew to take shelter in a fortified part of the craft. Accidents are obviously less predictable, and can be expected to be serious and fatal. Space travel is not without risk. Nor is getting into a car.

By far the most serious and insidious effect of space travel on human beings is the bevy of problems caused by the lack of gravity. We have evolved to live with gravity. On the short term, its absence causes disorientation and nausea. Individuals vary in their responses to weightlessness and astronaut training famously involves weeding out those most seriously affected. People with abnormalities to the inner ear may be completely unaffected, but having a deaf crew member could pose challenges of its own. It’s interesting to note that all mammals can be made to suffer from motion sickness, except rabbits and guinea-pigs (thanks to Mary Roach for that tidbit of information).

Other short-term effects of the absence of gravity are the loss of taste and appetite, the disruption of the digestive system, the pooling of blood in the upper body and the inability to sleep. Most of these effects will disappear, or at least become less prominent, after a few days as the body adjusts.

Far more serious is the loss of bone and muscle mass. Exercise helps, but doesn’t completely prevent the decrease of bone density in long-term space-travellers. And that loss can be significant, comparable with that suffered by a sufferer of extreme osteoporosis.

That said, there is a fairly simple solution: artificial gravity through rotation. At the moment, it is beyond the engineering limits of current missions, but once people overcome problems associated with sending manned missions to Mars or further, giving the inhabited section of a ship or station a constant rotation should not be too hard.

The psychological effects of space travel are associated with the fact that you’re isolated in a tin can, a long way from anywhere, with people who, like partners in a stifling marriage, start to irritate you more and more.

This makes psychological screening important. The first chapter of Packing for Mars describes seemingly inane tests done by the Japanese Space Agency (JAXA) in order to select possible astronauts, and unravels some reasons for these tests. Most importantly: how do you react to boredom? How do you react when something unexpected happens? There are huge differences between people, and in an isolated group of people, these differences may make or break a mission.

An obvious partial remedy is to send larger missions in larger ships. The lack of privacy and the inability to get away from each other conspire to make any inter-personal problems worse. The human being is a curious type of herd animal. We want to be close, but not too close to each other. It seems that a larger mission will be the answer in the long term.

How the size of a planet determines its atmosphere










So you want to be a space farmer?

You are writing space-based Science Fiction, and have decided your world is going to have a self-sufficient space station, base or space ship. A lot of Science Fiction books have this assumption in common. Any human colony, whether on a moving vessel, space station or on the surface of a planet, will need to produce its own food, since vast distances and transportation costs will make import unpractical. Being self-sufficient means growing stuff to eat. Here are a few points to consider to make your food production system more realistic.

There is a fair bit written about the design of the habitat. It ideally needs to be in the habitable zone of a star or closer to make optimal use of light. Artificial light is expensive and mineable energy is scarce in the depths of space. If you do position a habitat far from a star, make allowances for vast amounts of energy needed to grow plants. Without cheap and easy solar energy, the energy source would probably have to be nuclear and would have to be shipped in.

Other requirements run parallel with those for human habitation. The habitat needs to have radiation shielding. It needs to have adequate air circulation, temperature control and day-night cycles.

(ETA: this interesting article was published a week or so after I wrote this post. It deals with the effect of radiation on crops and how it seems plants can evolve to deal with it)

As an agricultural scientist, I often get annoyed when SF books suggest that ‘magic happens’ inside a food-producing habitat. You just chuck in the necessary elements, wave your fingers and POOF, there is food on the table.

In reality, things are lot more tricky than that. Once you add a biological element to your controlled environment, the system becomes complex and liable to unexpected and sudden failure.

The nutritional needs for plant growth are simple enough, but since you’re in space, you’ll have to cart everything in. Plants need the following to grow: Main elements: C, H, O. Main nutritional elements: N, P, K. Also essential: S, Ca, Fe, Mg, Mo, Mn, B, Cl, Zn and Cu. A lot can be recycled, but you’ll need to replenish occasionally.

One of the lessons learned from the Biosphere 2 experiment is that maintaining a viable ecosystem in a closed environment is damn hard. Biosphere 2 was a mixed ecosystem, containing many species. An agricultural centre aboard a facility in space is more likely to contain a much smaller range of species, making it much more vulnerable. For example, the grass family (maize, wheat, rice), the nightshade family (potato, tomato, capsicum, egg plant), the cabbage family and the cucumber family (pumpkin, cucumbers) provide a huge chunk of our daily vegetable needs. A virus only need take out one of those families and you have a severe problem.

Closed ecosystems are extremely vulnerable to pests & diseases resulting from less-than-optimal air circulation and light conditions. When something goes bad, it does so in spectacular fashion, quickly and without easy remedy. I’ve seen this happen several times… in glasshouses… on Earth.

For that reason, you’ll want backups. Don’t rely on one system, or one crop, or one station.

There will have to be some artificial tofu-like foodstuff produced for easy protein and nutritional value. Most plants are extremely wasteful in their useful crop/waste ratio. Compost works very well on a farm in the open air, but in a space station, it just…. stinks.

A process of rigorous, dare I say neurotic, quarantine will be necessary. You cannot risk anyone bringing in the tiniest mite or aphid from outside.

Some crops and livestock are much more suited to high production per unit area than others. Use tropical crops with a fast cropping cycle (C4 crops such as rice and corn) over temperate crops. Breed varieties of crops which can efficiently utilise a higher-than-usual CO2 percentage. Plants grow bigger in low-gravity conditions, and use more water.

There are some crops you won’t be able to grow no matter what. They’re either too expensive to grow or for some mysterious reason defy all attempts at growing them in any sort of health or quantity in a controlled environment. You can’t always explain why this happens. Biology is funny like that. Of course, those crops will be the most valued.

Where are you going to get your initial seed-stock and how are you going to conduct breeding and renewal? I could see a situation where each growing condition requires a different type of plant. The more variety, the less risk of wipe-out due to disease.

To sum up, a food production scheme needs to be reliable and robust. Diversity is the key to risk-spreading. My guess is you’ll probably end up having to resort to some quick & dirty chemical shortcuts, such as mining O2 from comets to make sure you have the capacity to quickly act in case of impending ecosystem collapse due to disease.

Communication in space




This time lag becomes larger the further you go.


Mars 19 minutes
Jupiter, 47 minutes
Saturn 74 minutes
Uranus 174 minutes
Neptune 258 minutes
Pluto 271 minutes



Think of the consequences:






