Mercury’s Tidally Locked Orbit

Mercury is weird

Mercury’s tidally locked orbit is a good example of how the universe always throws astronomers a few surprises.

The planet is tidally (or gravitationally) locked to our Sun, but this is not the typical “synchronous” tidal locking with a 1:1 ratio of rotation and orbit, such as the Moon and Earth, with the same face always presented to the larger partner. Mercury is locked into a what’s known as a 3:2 spin-orbit resonance, which is unique in our solar system.

The thing about the universe is that things look different from different places. Although Mercury’s orbital period is around 88 Earth days, from Earth it appears to move around its orbit in around 116 days (because we are moving too).

With Mercury’s 3:2 resonance it rotates exactly three times for every two revolutions the planet makes around the Sun. Yet the Sun is also turning. From the Sun’s frame of reference, Mercury appears to rotate only once every two Mercurian years. So the little yellow men who live in the caves there have to wait two years to see a single day go by, or about 176 Earth days. Birthdays must be complicated!

So how did astronomers get the idea that Mercury was synchronously locked to the Sun? This was because whenever Mercury was best placed for observation it was nearly always in the some point in its freaky 3:2 orbital resonance, so was showing the same face to observers on Earth. Since, by coincidence, Mercury’s rotatation (58.7 Earth days) is almost exactly half of its orbital period as observed from Earth (116 days). It was not until the radar observations of the planet in 1965 that astronomers learned the truth of its orbital antics.

Mercury's Tidally Locked Orbit

Thermal underwear a must on Mercury

Mercury has virtually no atmosphere, and is at the mercy of the Sun. Its surface temperature can rise on its equator to 427C (800F) during the day, and plummet to -173C (-280F) at night, while the poles are little more stable at around -93C (-136F). Although the planet has a small tilt, it has the highest orbital eccentricity of all the solar system planets, its orbital distance from closest (perihelion) to furtherest from the Sun (aphelion) varying by as much as 1.5 times.

Like our own Moon, the surface of Mercury is heavily cratered, indicating that the planet has been geologically inactive for billions of years.

My novel, The Tau Ceti Diversion, is a story about our search for new planets to colonise outside our solar system. Much of the action takes place on planet tidally locked to Tau Ceti that has some rather unique characteristics. The novel is due to be launched on September 1st 2016, and pre-order is now available on Amazon! Read more about what happens in the story here!

Stay tuned for a free chapter download, coming soon!

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Day Side & Night Side – Tidal Locking of Planets

So what is tidal locking? Our Moon is tidally locked to the Earth, always presenting the same face to us. That doesn’t mean that the Moon is stationary, far from it, it just means that it takes just as long to rotate around its own axis as it does to revolve around the Earth. The same thing can happen for planets, which can be tidally locked to their stars, always presenting the same side of the planet to their star, giving those planets a permanent ‘day’ side and ‘night’ side.

We could expect these planets to have some pretty unique characteristics, with a hot, dry side, and a frigid frozen night side. Some scientists have even dubbed them ‘eyeball’ Earth’s due to the likely combination of features that might develop.

one-side-planet eyeball earth


In my SF novel, the Tau Ceti Diversion, the action is set on a planet that is tidally locked to Tau Ceti, always divided into a hot day side and a cooler night side. This set up was crucial to the novel, and to the civilisation that the stranded crew of the starship Starburst find when they land on the planet’s night side. Actually they were aiming for the terminator – the dividing line between the day and night sides – expecting this to be a temperate zone. But I can’t say much more without spoilers:-)

Tau Ceti is a G-class sun, around 12 lightyears from Earth. One of our close stellar neighbours. Could we expect that one of its planets would be tidally locked to its star?

Well, it did not take me too much research to realise that this is one very complex question. It would indeed be surprising to find a tidally locked planet around Tau Ceti. Finding a tidally locked planet might be more likely around a smaller M class star. But there are many, many variables that might allow a planet to become tidally locked to its star within a reasonable fraction of that star’s lifetime. The variables that might increase the likelihood of a planet becoming tidally locked early in the star’s lifetime include the lack of a companion satellite (i.e. more likely if there is no moon), a low initial rate of planetary spin, a low dissipation function (the rate at which mechanical energy is converted into heat), a low rotational inertia . . . even the rigidity of the planet can be variable.

So, all these variables gave me enough wiggle room to allow my planet to be tidally locked. Plus I had a secret weapon – a key bit of backstory that affected the planet’s spin at a key point of its history. But I can’t say anything about that either, not without giving away the story!

Stars are classified based on their spectral characteristics. The M-class spectrum contains lines from oxide molecules, particularly TiO, with absorption lines of hydrogen typically absent. M-class are the most common of stars, representing over 76% of our stellar neighbours.  So we might expect more than a few tidally locked planets out there. Of course these will be the smaller bodies, Earth-sized and smaller, so will not be well represented in our current exoplanet catalogue, which features a lot of big, Jupiter-sized and heavier planets due to the methods used to identify exoplanets (so far). M-class stars are light orange red in colour, from 0.08-045 solar masses and low luminosity (less than 0.08 of our Sun’s). This class features rare and exotic creatures that can rarely be seen by the naked eye, mostly red dwarfs, although some are red giants, or even red supergiants. The class also includes the intruiging brown dwarfs, which are ‘late’ class M stars.

My novel, The Tau Ceti Diversion, a story about our search for new planets to colonise outside our solar system, is due to be launched on September 1st 2016, and pre-order is now available on Amazon! Read more about what happens in the story here!

Stay tuned for a free chapter download, coming soon!

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Postcard from Jupiter – First Snaps from Juno

The Juno spacecraft’s JunoCam camera is now operational, and is sending data back to Earth. The camera was switched on six days after the exploration craft entered orbit around Jupiter. Although the first high-resolution images are weeks away, we have our first assembled image of the planet. The shot below was taken at a distance of 4.3 million kilometers from Jupiter (2.7 million mi) as it was moving into its capture orbit. Our remote pair of eyes, JunoCam, captured an image of Jupiter, complete with Great Red Spot, and shots of three of Jupiter’s four bigger moons.

First Juno Photo NASA

Image credit: NASA/JPL-Caltech/SwRI/MSSS

It’s fantastic to have received this tangible evidence of Juno’s operational status, and its survival of the extreme radiation that surrounds Jupiter. Juno has been specially designed to cope this this intense radiation environment, which can cause degradation of the spacecraft and instruments, noise from particle collision with detectors, and electric charging of the spacecraft itself. And Jupiter has a lot radiation to share. The huge planet’s magnetosphere extends out to 100 Jupiter radii – pretty astounding when you compare it to Earth’s magnetosphere, which extends to 10 Earth radii. This magnetosphere acts to concentrate and reflect solar radiation and cosmic rays from outside the solar system, and holds gases, like those ejected by Io’s volcanic activity, which get ionized and energized and emit their own radiation.

Juno’s detectors and electronics are shielded by a half-inch thick titanium vault. Its external camera also has additional shielding – enough to make it four times heavier than even the biggest star trackers to date. The spacecraft’s orbit has also been specially designed to avoid the most intense radiation zones.

In completing its mission, Juno will orbit Jupiter 37 times, going as low as 4,100 kilometers (2,600 mi) over the planet’s cloud tops. Juno’s scientific instruments will probe beneath the cloud cover and also study its auroras, allowing us to learn more about Jupiter’s origins, structure, atmosphere and magnetosphere.

JunoCam will continue to send back images on each of its many capture orbits.

But for our first high-resolution images, we will have to wait until August 27 when Juno makes its next close pass to Jupiter.

My novel, The Tau Ceti Diversion, a story about our search for new planets to colonise outside our solar system, is due to be launched on September 1st 2016! Read more about what happens in the story here!

Stay tuned for a free chapter download, coming soon!

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Hot Young Planets

One of the real mysteries of identified exoplanets is the how many very large planets – the size of our Jupiter and even larger – are so close to their parent stars. This is a strange thing for us Terrans, because in our solar sytem, all our gas giants are in outer orbits. A situation so familiar anything else just seems plain wrong.

hot jupter

These ‘hot jupiters’ – heated by their proximity to their parent stars – are often in very close orbits to their suns, more equivalent to the orbit of say Mercury in our own solar system.

So how did they get there? Did they form there, or did they somehow migrate there? Were they wandering planets that were captured by their new suns?

At first these hot jupiters were considered anomalies, but as the list of exoplanets grew, astronomers found – to their surprise – that these type of planets were common. So what’s up? Is our solar system really the odd one out? It would be interesting if that was true, since the position of our own gas giants was crucial to the formation of higher life forms on Earth. Jupiter acted like a cosmic vacuum cleaner, stopping the multiple asteroid impacts that would have driven life on Earth back to basics time and time again.

The Spitzer telescope has been observing a hot Jupiter called HD 80606b, 190 lightyears from Earth, that has a highly eccentric orbit, swinging around its star every 111 days.

The theory is that these hot jupiters start out in highly eccentric orbits around their stars (like a very flat or ‘skiny’ ellipse), swinging first closer, then further out from their star. Over a period of hundreds of millions of years, gravitational influences from nearby stars or planets drive them into circular orbits, which are close to their parent stars. Part of this process is thought to be the loss of the planet’s gravitational energy as heat as it passes close to its parent star.

In HD 80606b, astronomers think they are observing one of these gas giant exoplanets in the middle of its migration. We still see the highly eccentric orbit, but it is now swinging very close to its parent star, moving toward its final, closer, circular orbit.

I don’t think we have a hundred million years to find out if this theory is correct, but at the rate our exoplanet discoveries are coming in, we will certainly have more data, and perhaps enough snapshots of multiple hot jupiters to get a good idea of exactly what’s happening in solar system formation.

My novel, The Tau Ceti Diversion, a story about our search for new planets to colonise outside our solar system, is due to be launched on September 1st 2016! Read more about what happens in the story here!

Check out the NASA post on HD 80606b, and the cool graphics, here.


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Thank You Kepler! Thousands of New Exoplanets Now Confirmed

The number of new confirmed exoplanets – planets located outside our own solar system – continues to grow at an impressive rate.

A massive amount of data is collected by space-based telescopes, which has to then be analysed and verified by astronomers. In the largest single announcement yet, NASA scientists have released information on 1,284 new verified planets, pared down from 4,302 potential candidates. When only decades ago there was not a single verified exoplanet, that number becomes staggering.

kepler - thousands of new planets

This announcement more than doubles the number of confirmed planets identified by the Kepler space telescope. And with every new verified planet identified, the odds of identifying a true Earth-analogue increase.

Before Kepler was launched, astronomers had no idea how common planets really were. Now it is thought that there are likely to be more planets than stars. When you realise there are billions of galaxies, each with millions of stars, that’s a lot of planets! Even if the chance of life was extremely low, the likelihood of life, possibly even intelligent life out there somewhere starts to look good.

Missions like Kepler, combined with new technologies for getting actual pictures, spectrographic analysis and thermal maps of exoplanets (check out this post on capturing planetary snapshots), all point to some very exciting discoveries in the not-so-distant future.

Of the newly identified Kepler planets, around 550 could be Earth-like rocky planets. Nine of these orbit in their sun’s habitable zone, now making a total of 21 confirmed exoplanets in the so-called ‘goldilocks’ zone where liquid water can exit on the planet’s surface, allowing the potential for the formation of life as we know it. Two of these habitable zone planets are in the Tau Ceti system (see here). The potential for life on one of these planets is explored in my novel The Tau Ceti Diversion, due to be launched on September 1st 2016! Read more about what happens in the story here!

Kepler truly is the workhorse of planet-finding. Of the 3.200 exoplanets identified to date, more than 2,325 of these were discovered by Kepler. Launched in March 2009, Kepler spent four years monitoring the same patch of sky – some 150,000 stars – watching for the telltale tip in a star’s brightness that indicates a transiting planet.

Let’s hope that Kepler, and other missions like it, continue to increase our knowledge of exoplanets far into the future.


Capturing our First Planetary Snapshots


Kepler has confirmed more than 1000 planets outside our solar system, but so far only a few of Earth-like size and in the habitable zone — rocky planets with just the right temperature for liquid water. And none of those potential Earth-analogues have been observed directly, but through the interpretation of astronomical data, such as the wobble of the star, or the dimming on the star’s light due to planetary transit.


So far, some pictures of other planets have been taken from ground-based telescopes, but those planets are large, bright and orbit far from their suns — not like potential Earth-twins which will be far smaller and orbit closer to their suns.

NASA scientists and engineers are working on two new technologies to help look for new planets, a starshade and a coronagraph, which will both work to block the light of the star, allowing the telescope to examine the reflected light of the planet itself.

This means we can not only take pictures of prospective Earth-like planets, but also use spectrographic analysis to analyse what in their atmospheres as well. This will give us clues to what might exist there. For example, evidence of plant life and animals similar to those on our Earth would show up as a series of simple signature compounds in the planet’s atmosphere: such as oxygen, ozone, water and methane.

A starshade is a type of spacecraft that actually flies in front of the telescope to block the light of the sun under observation. Despite the fact it will be only tens of metres wide, it will fly quite a bit in front of the telescope — in fact around 50,000 km away — more than four Earth diameters. Getting it into space is a challenge. It will be folded up like a super-origami prior to launch to unfurl in space,  somewhat like an unwinding spring, into to a crazy-sized sunflower. The pointed petals are crucial to its design: they control the light the right way to reduce the glare to levels where planets can be seen. The petal-fringed shape creates a softer edge that causes less bending of the light waves.

Both the starshade and the telescope will be independent spaceships, allowing them to move into just the right position for observations. The petals of the starshade need to be positioned with millimetre accuracy.

Blocking out the starlight while preserving the light emitted from the planet is called starlight suppression.

The light of a sun can be billions of times brighter than the reflected light from the planet. Our own sun is 10 billion times bright than Earth.

Coronagraphs were originally introduced in the early 20th century to study our own sun, blocking out the light from the sun’s disk to allow scientists to study its outer atmosphere, or corona; hence coronagraph. They are much smaller than the starshade, located within the telescope itself.

These starlight-blocking coronagraphs will be more sophisticated.

These new generation coronagraphs uses multiple masks as well as smart mirrors that can deform, to suppress starlight in sequential stages. There are many other challenges in delivering the coronagraph technology, including being able to suppress or compensate for the warping and vibrations that all space telescopes experience.

New Calvanni Review

Writer Tracy Joyce recently published a great independent review of The Calvanni. Here’s the whole review from Tracy’s blog:

The Calvanni (Book 1, The Jakirian Cycle) by Chris McMahon – Monday 27th July 2015

Calvanni front cover (Small)

“If you’re after a fast paced, complex adventure with detailed world building, politics and characters, then The Calvanni may be just what you’re looking for.

The Calvanni is set upon the world of Yos – a world where all metal is magical and cannot be forged. The weapons and armour must be made from natural materials and special ceramics – a nice point of difference from other novels I’ve read. The magic system has been well thought out and for those who like a lot magic in their reading, this book has plenty and some excellent battle sequences.

When the story opens the reader is plunged into the scene dealing with the assassination of the Sarlord of Athria. The depth of the political intrigue and old rivalries within the novel are quickly revealed. McMahon has also created a world with complex social and religious classes and many unusual animals.

This detail is one of the greatest strengths of The Calvanni, yet it may also be an initial obstacle to reading enjoyment for some. There is an array of unique terminology for this world within the novel. Fortunately, there is a glossary at the beginning of the book, which many may find useful. I actually enjoyed all the new terms and creatures that McMahon adds to the world of Yos – for me it added to its sense of authenticity. If you find this initially difficult, then persevere because your patience will reward you with a great read. The pace and the construction of the story are such that you just keep reading and pick up the terminology, or what is implied by it quickly.

On first glance the cover of The Calvanni seemed to me to be more akin to the type of illustration one would see on the cover of an romance novel that masquerades as epic fantasy – Don’t let that fool you because this is a high fantasy with some of the most original and intricate world building I have read in long while.

I’m looking forward to reading the rest of the series.

Four Stars!”

Back to Dune

I recently set myself the task of reading all of the Frank Herbert Dune books, and the additional prequels written by Kevin J Anderson and Brian Herbert. Fourteen books in all. What spurred me on to do this was coming across the first set of Dune prequels in a second-hand bookstore and reading them for the first time. These prequels — House Atreides, House Harkonnen and House Corrino — sustained my interest and re-ignited my enthusiasm for the Dune Universe.

So here I go. This is not a formal review — I don’t pretend to be a SF critic — this is just me with a journal, sitting in a coffee shop, writing down my thoughts after reading the book; as insightful, incomplete or tangential as they were . . .

Dune – Frank Herbert

Dune Ciover

Herbert’s world has amazing scope, and its creation is an incredible achievement.

Re-reading this book after so many years was a different experience. I can see now how frustrated I would have been as a younger reader at the lack of action.

As an older reader, I could appreciate Herbert’s writing much more.

I would have to say though, for all the confusing wordage of his pre-chapter ‘wisdom’ excerpts and his in-prose philosophical insertions — which occupy much of the prose and dialogue — I have taken away no powerful insights. For me there was no true transfer of wisdom, no higher knowledge. At worst I felt the Herbert was sewing confusion and word-games that sounded profound, but which he himself had no personal stake in. His own beliefs and thoughts remain unstated. Basically, these extended sections of dialogue were literary smoke and mirrors. I concluded that this is in effect a form of delayed resolution to draw the reader on, where many questions are raised, yet no conclusion is ever delivered. And no truth.

The main focus of Dune’s narrative is the inner experience and transformation of Paul. I was impatient with this when I first read Dune. On this second read, may years later, I appreciated Herbert’s prose expression, yet felt he failed to convey a true transformative experience, falling back into word-puzzles and a philosophical mish-mass that implied significance without delivering.

The fact of genetic memory is a central premise of this world. I cannot accept this as a credible basis. This does not make sense to me from a scientific point of view.

Herbert’s novel implies telepathy through contact in the spice ritual that creates the Reverend Mothers, yet the mechanism or actuality is unclear.

The idea of a Mentat is sound, yet Thufur fails to convince me as a character. We are told he is a master assassin and mentat, yet he never actually shows us anything to convince us of this. And believe me — I wanted to believe it! I wanted to see it!

The Bene Gesserit are done well – you can see directly how their training gives them advantages. You can credit this, and it is shown directly through Jessica as a character. The Bene Tleilaxu are vaguely presented in this first book, but intriguing.

All up I enjoyed the return to the world of Dune, and enjoyed Herbert’s prose. He has created a in-depth and convincing world that has remarkable texture and is a pleasure to visit.

My SF Short Time Pump Just Published in Dimension6

I’m very excited to announce my SF short Time Pump has just been published in Keith Stevenson’s Dimension6 ezine! Click here to download a free, DRM-free epub or here to download a mobi file!


The story was born from an intriguing SF idea and gradually took shape through various edits and critique sessions. I’m sure quite a few of my former Vision and Edge writing group partners will remember this one.

Time Pump has always been one of my favourite stories. I don’t want to give too much away, but suffice to say it raises some interesting questions about time travel. Time Pump was great fun to write, and the SF idea aside, it is a classic survival story set on a frigid ice-world. Originally it had a lot more backstory about the central character MacPherson and why he ended up on the planet like that (and who betrayed him), but various critique partners encouraged me to focus and shorten the story. So if you’re wondering about that deeper mystery . . . blame them for never finding out:)

The prequel novella to my three-book Heroic Fantasy series Jakirian Cycle, Flight of the Phoenix, is also available as a free download from my website. Haunted by terrible visions, and battling his own fear of Sorcery, the aging weaponmaster Belin must face the magical assassins that stalk the capital Raynor and bring the newborn son of the fallen Emperor — the last of the Cinanac line — to safety. Check it out — it’s a great way to get a taste for the series.

Here is the cool cover by Daryl Linquist


The Jakirian Cycle is Heroic Fantasy in a world of ceramic weapons, where all metal is magical. It’s had some great reviews and is available through my website in either print versions or in a variety of electronic formats and platforms. My favourite review tag line is ‘Think Kill Bill meets Dune!’ – I mean, how cool is that? Here are the covers, also by Daryl.

Calvanni front cover (Small)Scytheman front cover (Small)Sorcerer front cover (Small)