What is a Realm?

My new novel, Warriors of the Blessed Realms is out into the world, but what is a Realm?

In the exact sense, a “realm” is a community or territory over which a sovereign, such as a king, rules. Or an area or sphere of certain knowledge or activity.

In the case of Warriors, a Realm is a world. A planet.

And there are many worlds in this epic tale. One of them is Earth itself, where the story starts with central character Liam Durrow.

The Vaults of Sheol are fifty-eight planets ruled by a ruthless mind-controlling alien warlord, VoYannan, one of a solitary species called a krell that can dominate millions, growing in strength with each new mind that falls under their sway.

The Vaults are dystopian SF worlds. The enslaved populations are kept in check by legions of laser-wielding brutes called Siithe. Here desperation breeds under leaden, cloud-filled skies, which lower over vast ruined cities, while factories manned by slaves from a dozen conquered species churn out weapons of destruction.

Standing against VoYannan is The Blessed Realms, a coalition of six worlds with benign technology that is dedicated to preserving life, with magic that can stop Vault technology in its tracks. The Realms have fought VoYannan for thousands of years, containing him with steel and magic.

VoYannan plots to unleash a devastating assault on the Blessed Realms. He uses an ancient Gateway on Earth to strike. His Vault forces capture the priestess Sephany, crucial to his plans, and escape.

Realm warrior Finn Evenstone sets off in pursuit, but cannot pass the Gateway used by the Vault.

Liam Durrow, sole survivor of an ancient Earth lineage, is led to Fraser Island by a vision, and uses his unique magical abilities as Keeper to open the Gateway.

Both Finn and Liam are soon battling the Vault on Earth, and in the Shadow Worlds, planets already ruined by the krell. They need all the help they can get. They are joined by tenacious Federal Agent Yolinda Paris, who has her own score to settle.

That that’s Warriors! An epic tale spanning multiple worlds and multiple genres — fantasy, urban fantasy, and SF — where magic and high-technology go head-to-head!

Check it out! Grab a copy of the book! Available at selected bookstores and these online retailers!

Amazon – Print and kindle

Barnes & Noble – Print and Nook

Google Books – Print

Booktopia – Print

Bookdepository – Print

Fishpond – Print

Waterstones – Print

Kobo – ebook

Walmart – ebook

eBay – Print

itsi – epub

Warriors of the Blessed Realms Launches September 4 2020

The launch of Warriors of the Blessed Realms is finally here!

The online launch of the Warriors’ ebook will be on Facebook on Friday September 4 2020. Click on this link to join the online event!

There will be games and heaps of giveaways. I have prize packs of signed Jakirian Cycle books, and copies of the latest Lanedd Press edition of my SF book The Tau Ceti Diversion to give away, as well as rare editions of other collections with my stories inside to gift as prizes. The last Facebook launch, for the Lanedd Press edition of The Tau Ceti Diversion, was a great event, and I’m looking forward to sending Warriors’ off into the world in style.

Warriors’ is an epic tale, spanning multiple worlds and multiple genres — fantasy, urban fantasy, and SF. At its heart it is Heroic Fantasy, for which the works of David Gemmell gave me a life-long love.

The novel has both traditional fantasy settings as well as urban fantasy based in Brisbane and Sydney in Australia, as well as strong elements of both SF and horror. That’s quite a landscape, and a lot to balance, but readers can expected one Hell of a ride!

And the story . . .

The immortal krell lord VoYannan rules one of the Vault empires, dominating millions with the mind-powers of the solitary krell, drinking the souls of his thralls to fuel his talent. A prophecy foretells that he will leash the power of his Spawn if he can implant it in one special priestess — Sephany — and ensure it feeds on her broken spirit. 

In the Blessed Realms, Finn Evenstone, last surviving son of a once elite clan, waits for the attack. The talented Realm noble knows that the Vault will emerge through the Stonelake Gateway.

In Brisbane, Australia, Liam Durrow struggles to come to terms with strange visions. When his uncle and guardian dies in an accident, he learns he is the sole survivor of an ancient lineage. As Keeper he inherits unique magical abilities.

Using Earth as a stepping-stone, the forces of the Vault strike the Stonelake Temple and capture Sephany. A fierce battle ensues, but they escape with the priestess through the Gateway.

From Earth, Liam opens the Gateway for Finn, allowing him to continue the pursuit. They are joined by Federal Agent Yolinda Paris, who has her own score to settle with the Vault.

Their journey leads them through the Blessed Realms and other darker worlds ruined by the krell, until it reaches its climax in the court of krell lord VoYannan.

Want to read the story? Don’t forget to join the online event!

Space Lasers Fired at the Moon!

Space lasers fired at the Moon! It sounds like something from an Austin Powers movie – do you mean a “Space Laser” <air quotes> 🙂

The truth is even more interesting. Astronomers at observatories in new Mexico, Italy and Germany have been firing lasers at the Moon for 50 years as part of a long-ranging experiment that has yielded data on the tidal behaviour of Earth’s oceans, the surprising flex of the elastic lunar surface (up to 15 cms), the gradual movement of the Moon away from the Earth, and confirmation of Einstein’s gravitational theories.

Mercury's Tidally Locked Orbit
Apollo legacy lives on – through prisms

Arrays of hundreds of prisms left on the lunar surface by Apollo missions receive the incoming laser beams and bounce them back to Earth. The Apollo 11 and 14 arrays have 100 quartz glass prisms each, while the array left by Apollo 15’s astronauts has 300! The accuracy in measurement these prism arrays allow is stunning — and the experiment just keeps yielding data year after year because the arrays require no power or maintenance.

The returning signals have allowed the orbit, rotation and orientation of the Moon to be very accurately determined, and have confirmed that he the distance between the Earth and Moon is increasing by around 4 cm a year.

The experiment has highlighted the behaviour of Earth’s ocean tides, but also has shown that the lunar crust also rises and falls in a solid lunar “tide”. It has also confirmed that the Moon has a fluid core! This really surprised me, having thought (like many others) that the Moon was a “dead” rock. In fact the prevailing theory, even among scientists, was that the core would be cool and solid. The Moon’s fluid core affects the position of its north and south poles, which the experiment was sensitive to pinpoint.

The experiment has also confirmed Einstein’s theory of gravity, which assumes that the attraction between bodies is independent of their composition – proven true for the gravitational affects between the Sun and Moon, and Sun and Earth, despite the higher iron content of the Earth.

And that’s not the end for lunar reflectors. NASA has recently approved a new generation of reflectors to be positioned within the next ten years. These would be spread over a larger area, allowing more extensive analysis of lunar geography and further verification of Einstein’s gravitational theory.

Cool, huh?

Studies like this are invaluable in understanding new worlds. As a SF writer, they provide invaluable insights when it comes to building your own planets. Check out my own world-building in my SF novel, The Tau Ceti Diversion.

With the crew dead, and the starship’s jury-rigged fusion threatening a lethal explosion, Karic and the surviving officers finally reach a habitable planet. It’s a miracle, but the last thing they expected was to find that planet already occupied . . .

Get it now!

Near Future SF

Try some Near Future SF! With the crew dead, and the starship’s fusion drive held back from a lethal explosion, Karic and the surviving officers reach a habitable planet – the last thing they expected was to find it already occupied . . . #TheTauCetiDiversion @ChrisMcMahon111 #ScienceFiction #NearFuture Check it out on Amazon!

Near Future SF

Try some Near Future SF! With the crew dead, and the starship’s fusion drive held back from a lethal explosion, Karic and the surviving officers reach a habitable planet – the last thing they expected was to find it already occupied . . . #TheTauCetiDiversion @ChrisMcMahon111 #ScienceFiction #NearFuture https://amzn.to/2k8k1Vx

Atmosphere on a Fictional Planet

So you’ve got your story working, but how do you sketch out the atmosphere on a fictional planet? Maybe you have some idea of the mass, radius and gravity and you’ve got the orbit in the ‘sweet spot’ goldilocks zone where liquid water can be present on the surface, but what will conditions on the surface actually be like?

What sort of factors go into whether that planet, presumably an Earth-like rocky world, will have an atmosphere that can support terrestrial life?

Planets above a blue planet

The gravity of the planet is one key variable, along with surface temperature, and the strength of the planet’s magnetosphere, which can protect against atmospheric stripping due to solar wind.

The surface temperature of a planet will determine how much kinetic energy, and so velocity, the gas particles will have. If that temperature, and velocity, is high enough it will exceed the planet’s escape velocity and the molecules will fly off into space like tiny spaceship explorers. Earth has lost most of its very light gases like hydrogen and helium in this way, whereas the gas giants have enough gravity to retain them. We kept our water, and we’ve got a lot of it! If Earth was sitting where Venus is things would be different, the additional temperature would give those lighter gases like water vapour enough energy to escape, and also prevent any being trapped on the planet’s surface itself (whereas some is ‘sequestered’ on Earth as water and ice at our lower surface temperature). But beyond the early, settling down period where the lighter gases are lost, any world larger than Earth, orbiting in that goldilocks zone, will not continue to lose a significant proportion of its atmosphere through thermal processes.

Here’s a cool pictorial on thermal escape (source: Wikipedia).


Beyond that thermal stripping process, is where the magnetosphere comes into its own, deflecting the solar wind – one of the main non-thermal processes leading to atmospheric loss. The very thickness of a planet’s atmosphere (retained due to its gravity, and as a function of surface temperature), will also protect a planet from the solar wind, even in the absence of a magnetosphere. It’s thought that Venus’ thick atmosphere, ionized by solar radiation and the solar wind, produces magnetic moments that act out to 1.2-1.5 planetary radii away from the planet to deflect the solar wind, much like a magnetosphere (but an order of magnitude closer to the planet). In fact, it’s thought the dominant non-thermal atmospheric loss process on Venus is actually from a type of naturally induced electrical acceleration. On Venus, the stripping of the lighter electrons from the atmosphere causes an excess of positive charges, accelerating ions like H+ out of its atmosphere.

Our explorers need a breathable atmosphere, but they also need an atmospheric pressure like our own Earth’s.

My fictional planet of Cru, in the Tau Ceti Diversion, has comparable surface temperatures to Earth, but a higher surface gravity. The higher surface gravity, and its lower density, allowed me to assume a lighter atmospheric composition, and allow an atmospheric pressure, or weight of atmosphere, close to surface much like Earth’s. That atmospheric composition is crucial to having a reasonable atmospheric pressure – its not just the gravity of the planet. Venus, even though it has slighter lower gravity than Earth, has a crushing atmospheric pressure of 90 times Earth’s due to its heavier  atmosphere of CO2.

Check out what my my intrepid explorers found in my novel The Tau Ceti Diversion when they touched down on the planet!

Read it now on Amazon!

Tau-Ceti-Diversion-severed-ebook-cover (Medium)

Estimating Surface Gravity on a Fictional Planet

So you want to estimate surface gravity on a fictional planet? Easy!

One of the things I had to do as part of the rework of my novel The Tau Ceti Diversion, is to try and work out the surface gravity of my fictional planets. From the Kepler data, there are two exoplanets located in the Tau Ceti system that are likely to be in the system’s habitable zone, or where there is the possibility of liquid water on the surface, and perhaps life as we know it.

To play around with my estimates of gravity, I used ratioed rearrangements of Newton’s law of gravity (law of universal gravitation) and a simple formula relating the density of a spherical planet to its mass and radius (these are at the bottom of the post in the ADDENDUM).


Here’s Newtons famous law:)

law of gravity

The two planets thought to be in Tau Ceti’s habitable zone are denoted Tau Ceti e and Tau Ceti f. What is known about these two planets is their likely orbit, eccentricity, and their mass. All of these properties have been derived by calculation, based on observed data, so are all known to within appropriate error bounds, but I’m leaving the error off my scribblings so things don’t get too messy.

Tau Ceti e is thought to be around 4.3 Earth Masses, or Me (i.e. 4.3 times as heavy as Earth), while Tau Ceti f, the planet that orbits a bit further out, is thought to be around 6.67 Me. For the astronomically minded, these two planets orbit at around 0.55 and 1.35 AU from Tau Ceti respectively.

So, here’s where I cheated a bit, like any good engineer. I started with the answer I wanted and calculated backwards to see if the answer I wanted led to reasonable base assumptions. This is not as cheeky as it sounds, because when you have an insoluble problem (i.e. not enough data is known for an explicit result), an iterative approach is often used.

For my story to work, I needed a surface gravity on my planet of no more than 1.2g – that’s twenty percent higher than Earth’s. But how could I get a gravity that low on a planet that was over 4 times the mass of Earth? The answer is that surface gravity is a function of mass and radius, or going a step further along the calculation path, mass and density.

I used a ratioed form of Newton’s law that allowed me to relate the ratio of two planets gravitational forces to the ratios of their masses and radii. I already knew the ratio of the gravities ( assumed at gTCe/gE= 1.2) and the ratio of the masses (MTCe/ME =  4.3), so could calculate the ratio of radii (rE/rTCe) at 1.89.  Using another formula that related the ratio of the two planet’s densities to their ratioed mass and radii, I could then calculate their ratioed densities (dens TCe/ densE) at 0.63. So at the end of all that, to have a surface gravity of 1.2 g, Tau Ceti e would have to have a density of 63% of Earth’s. Is that reasonable?

The density of Earth is 5.514 g/cm3, not too much different from the density of a rocky planet like Mercury (5.427 g/cm3), but a lot higher than other solar system planets like Jupiter and Uranus (1.326 g/cm3 and 1.27 g/cm3 respectively), comprised of lighter materials. A surface gravity of 1.2g on Tau Ceti e would put its density at around 3.5 g/cm3, less dense than our own rocky planets, but certainly in a feasible range.

So what sort of densities would you expect for the Tau Ceti system? One clue is the metallicity of the system, which is a measure of the ratio of iron to hydrogen in the star’s makeup. In the case of Tau Ceti, this is estimated to be around one third of our own sun. This indicates the star is likely to be older than the Sun, made up of stellar remnants left over from less evolved stars that have not had time to form as much of the heavier elements in their internal fusion factories.

So Tau Ceti is made up of lighter elements. Based on this, it was reasonable to assume that the planets in the Tau Ceti system would also be made up of proportionally lighter elements, and quite possibly in the range I had estimated. Tau Ceti e and Tau Ceti f are also large planets – much larger than our own Earth – so having a density in between Earth and our own gas giants also made sense to me.

Using the same planetary density I had calculated for Tau Ceti e, for the larger Tau Ceti f, gave me a surface density of around 1.4g for the bigger planet – just a little too high for feasible human colonisation – and that fit nicely with my story as well.

It was a lot of fun playing with these calculations, and thankfully the known science fit with my story, at least with some comfortable wiggle room!

Check out what challenges that increased gravity provided for my intrepid explorers in my novel The Tau Ceti Diversion!

Read it now on Amazon!










For those interested in the maths. . .

Density formula:  densp= Mp / (4/3*pi()*rp^3)


densp= Density of Planet (kg/m3)

Mp = mass of planet (kg)

rp = radius of planet (m)

In ratio form: densp1/densp2= Mp1/Mp2 *(rp2/rp1)^3


Ratio of Newtons law relating gravity, mass and radius of two planets:

gp1/gp2= Mp1/Mp2 *(rp2/rp1)^2