The Tau Ceti Diversion

The twin Earth almost had

Posted on by Chris McMahon

It’s hard to imagine Mars as a wet place, but that’s exactly what the data and images coming in from the Curiosity rover in Gale Crater are telling us. In fact, Mars is the twin Earth almost had.

Wet Mars.

3.5 billion years ago Gale Crater was filled with ponds of water, with streams cascading down the ancient basin’s walls, down to its wet centre. Eventually these watercourses dried up, but then perhaps the whole cycle repeated numerous times. Of course the water did eventually go for good.

Why?

Unlike Earth, which has a powerful magnetic field protecting its atmosphere, Mars has no such advantage. The solar wind — all those energised particles — just ram straight into it, knocking molecules right out of its atmosphere into space. Which molecules go first? The lightest ones. The hydrogen, the water, the oxygen. What is left is the heavier molecules like carbon dioxide, purely by virtue of the balance between gravitational attraction and the applied force of that solar wind. But that’s planet formation!

How do scientists conclude that there may have been these super wet and dry periods from the geology? By evidence left in the rocks, specifically high concentrations of mineral salts, deposited during periods of evaporation. This is not the first time Curiosity has found evidence of water here. The rover has also unearthed evidence of freshwater lakes.

Gale Crater: Source NASA JPL

The Gale crater itself started life with a bang, and is thought to have been formed by one massive impact. Sediment on the floor of the crater was built in layer upon layer of alluvial deposits, drying into a substantial formation over time. This layered rock was later wind-eroded to form the current Mount Sharp, which Curiosity is busily climbing.

So, we know there was water there, and likely there for long periods of time. The 64 million dollar question is, was this wet environment capable of supporting microbial life at the surface, and if so, for how long? How long were evolution’s engines allowed to turn, working to transform that life? And is that life still present?

If not for the weak magnetic field of Mars, we could have had a celestial twin. A planet in our own solar system with water-based life. Now that is something to think about!

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

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 . . .

Get it now on Amazon!

Space Lasers Fired at the Moon!

Posted on by Chris McMahon

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!

SpaceX Claims the Title of World’s Most Powerful Rocket

Posted on by Chris McMahon

This week’s launch of the Falcon Heavy Booster on Tuesday (February 6) means that Elon Musk’s SpaceX claims the title of world’s most powerful rocket. The Falcon Heavy can carry twice the payload as its nearest competitor, the United Launch Alliances Delta IV Heavy – and at a lower cost.

Every time I see footage of the SpaceX boosters touching down on reentry I get a shiver down my spine. This is really some revolutionary technology, driven by revolutionary thinking. All based on the simple premise that the most expensive thing about spaceflight is the hardware – not the fuel. If you can reuse the booster that gets you to orbit, then the whole ball game changes.

Watch the Falcon Heavy launch footage here.

 

The two smaller side-boosters completed their vertical reentry landing without a hitch, but the much larger central booster missed its drone-ship landing and crashed into the ocean. Still, the test is considered a success.

Falcon Heavy can lift an impressive 64 metric tons, certainly more than adequate for the astronaut-come-space-dummy and Tesla Roadster that Musk send into orbit around the sun, which is expected to orbit for hundred’s of millions of years! That’s a hell of a time capsule!

Falcon Heavy launches come at an estimated cost of $90 million, with the Delta IV launching 29 metric tons for between $300 and $500 million per flight. It’s easy to see how SpaceX’s paradigm is changing the future of space travel.

 

There are two more Falcon Heavy launches scheduled for this year. The first is a communications satellite, and the second a Space Test Program for the US Air Force that will also launch a solar sail for the Planetary Society. As well as the possible launch of two passengers in a trip around the moon. To apply for a ticket, click here – no, just kidding! – but wouldn’t that be awesome?

And this isn’t the end for the development of SpaceX’s reusable launch systems. SpaceX’s BFR (Big F- Rocket), a megarocket capable of a single-stage to orbit fully fuelled, will potentially launch a spaceship carrying up to 100 passengers, taking us further on a development path that might lead to the establishment of a city on Mars – one of Musk’s ultimate goals.

Space exploration is at the heart of my novel The Tau Ceti Diversion! But they got a little further than the asteroid belt!

Read it now on Amazon!

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Estimating Surface Gravity on a Fictional Planet

Posted on by Chris McMahon

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).

WARNING: MATHS CONTENT!!!

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!

 

 

 

 

 

 

 

 

ADDENDUM

For those interested in the maths. . .

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

Where:

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

 

Tau Ceti – One of Our Celestial Neighbours

Posted on by Chris McMahon

The Tau Ceti system is indeed one of our close cosmic neighbours. At less than 12 lightyears away, it is one of the closest systems to Earth’s own solar system – along with others such as the Centauri system and Epsilon Eridani. Because of its nearness to our own solar system, it has been a favourite in science fiction for decades. A likely first or second step for any intrepid interstellar explorers.

I first started toying with the idea of a novel set in the Tau Ceti system more than twenty years ago. And as these things go, the story developed in fits and starts as I bounced between novel projects and other stories. One of the things about writing science fiction, particularly near-future SF, is that the science never stands still. And particularly, in the last few decades, the developments in astronomy and the identification of planets outside our solar system, called exoplanets, has been almost exponential!

When I wrote the first draft of The Tau Ceti Diversion, there was not a single confirmed planet identified outside Earth’s solar system. Now, thanks largely to the latest Kepler space-based telescope discoveries, there are more than 3000! Not only that, but there have been five identified in the Tau Ceti system itself, with one – and possibly two – in the habitable zone around that star.

What did this mean for me? It meant a ton of research, and lot of very careful rewriting!

In my very early drafts of The Tau Ceti Diversion, I was free to imagine an Earth-like solar system of planets and shape them as I saw fit for the story. But by the time the last draft was completed, only months ago, I had very specific information about what those planets might be. I knew their approximate mass, their orbits, even their eccentricity. I had to go back to the drawing board – and my excel spreadsheets – to try and work out how these known planets would fit within the very specific constraints of my story. Not the least of which was that my story included a tidally locked planet!

It’s no accident that the Tau Ceti system has been popular as a setting for science fiction. Even before the identification of its family of planets, Tau Ceti, in the constellation of Cetus, was known to be very similar to our own Sun. It is smaller, about 78% of the Sun’s mass, and is the closest solitary G-class star (the same spectral class as the Sun). That’s enough to make it seem like our cousin. Add to that Tau Ceti’s stability, and lack of stellar variation, and you already feel like moving in. The only hitch is the presence of a debris disk, which means that any planet orbiting Tau Ceti is likely to face more impact events than planets in our own solar system.

Seen from Tau Ceti, the Sun would appear much like Tau Ceti does to us – a third magnitude star visible to the naked eye.

The composition of Tau Ceti, as measured by the ratio of its iron to hydrogen content, or metallicity, is lower than our Sun, indicating that it is older: its makeup derived from earlier stars yet to manufacture the same amount of heavy elements in their internal fusion factories.

So similar to our own Sun, and so close, it’s no wonder that it is also a target for the SETI (Search for Extra-Terrestrial Intelligence) program.

As readers of my novel The Tau Ceti Diversion will discover, the explorers in my novel certainly find some intelligent life there!

Read it now on Amazon!

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Laser Communication with Spacecraft

Posted on by Chris McMahon

New technology promises to take laser communication with spacecraft from science fiction to science fact. This technology offers a new answer to a 60-year-old problem: you have had your launch and your shiny new space probe has made it to orbit without being ripped to shreds by tons of exploding chemical fuel, but once it’s up there, how do you talk to it?

The conventional answer is radio waves, but the rate of information transfer is woefully slow – just ask any NASA scientist who has tried to distill usable data out of probe transmissions. There are no ‘subspace’ communications in the real world, just lots of waiting while the precious data rolls in at the same old pace.

But, thanks to new laser technology, this is about to change.

Radio waves have been the standard since the dawn of spaceflight, but the new optical communications has the potential to increase that rate by as much as 10 to 100 times. That means instead of painstakingly assembling still photographs, we could actually get high-res photos or even video from the surface of other planets, or moons like Titan. How cool is that!

This new communication system will also be crucial as spacecraft are sent further into the solar system, stretching conventional radio transmissions to the limit.

The key factor is that while both radio and lasers travel at the speed of light, lasers use a higher-frequency bandwidth, allowing the transmission of much more data. The typical rate of information transfer might around a few megabits per second (Mbps). For example, NASA’s Mars Reconnaissance Orbiter sends data at a maximum rate of around of 6 Mbps. Using laser technology of equivalent size and power rating would probably increase this to 250 Mbps – a huge improvement.

There are some possible wrinkles though. Clouds and atmospheric conditions can cause interference in laser transmissions. And receiving those transmission will require a whole new Earth-based infrastructure – preferably in areas with clear skies.

Radio’s reliability will ensure it will endure as a communication method, but the new technology will continue to step closer to widespread application. The Laser Communications Relay Demonstration (LCRD), led by NASA’s Goddard Space Flight Center, will launch in 2019. This probe will test signals between two new ground-based stations and geostationary orbit, a distance of 40,000 km. This will be followed by the Deep Space Optical Communications (DSOC) probe, led by JPL, in 2023, which, along with other science goals, will test transmissions between Earth and its target, a nearby metallic asteroid.

In my novel, The Tau Ceti Diversion, the explorers use laser communications to stay in contact with Earth – well at least until an unnamed saboteur puts the beam out of alignment:) Read more about the story and check out the free sample chapters on Amazon!

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Our Closest Earth-like Planet

Posted on by Chris McMahon

In an amazing stroke of cosmic luck, our closest Earth-like planet Proxima b turns out to be orbiting our closest star, Proxima Centauri, only 4.2 lightyears away!

The Kepler space telescope has been expanding our knowledge of exoplanets – planets outside the solar system – for years now. The number of confirmed exoplanets from Kepler now exceeds 3000, and the rate at which our knowledge of these planets is increasing is truly amazing. Kepler is able to give us data on planets thousand of lightyears from our own little corner of the universe.

So it came as a surprise, a number of months ago, when the very closest potentially Earth-like, habitable planet, turned out to be so close. Unlike its very bright neighbours, Alpha and Beta Centauri, which can easily be seen with the naked eye, you need special equipment just to see Proxima Centauri!

proxima-centauri-b-planet

Photo: space.com

Proxima Centauri is a red dwarf, one of the most common stars in the universe. In a bit of stellar Karma, it turns out that little stars like Proxima have much longer lifetimes that the bigger, brighter white or blue stars, or even our own yellow star, surviving for trillions of years – plenty of time for life to take hold if the conditions are right.

Astronomers have been trying to unlock Proxima Centauri’s secrets for more than 15 years, using two instruments from the European Southern Observatory in Chile – the Ultraviolet and Visual Echelle Spectrograph (UVES) and the High Accuracy Radial velocity Planet Searcher (HARPS). Both instruments focus on deciphering the star’s ‘wobbles’. So why did it take so long? The detection was made more difficult by sparse data, and the long-term variability of the star itself, which masked the presence of the planet. With new, key observations made in 2016, the astronomers were able to confirm not only Proxima b, but also reveal indications of a possible second planet with an orbital period of between 60 and 500 days also orbiting around Proxima Centauri.

Observations indicate Proxima b is around 1.3 times heavier than Earth, putting it into the rocky planet category. Although the planet is in the habitable zone, it orbits at only around 7.5 million kilometres, completing an orbit every 11.2 Earth days. Due to the closeness to its host planet, astronomers consider it likely that the planet is tidally locked, divided into halves of night and day, and always showing the same face to Proxima Centauri. Earth orbits at 150 million kilometres, much further out from our brighter, hotter sun, but still in our habitable zone. The temperature is right on the planet for surface water to exist, but much depends on the planet’s history. If its star was very active, the water may have been blown away in its early formation, whereas if the planet migrated inward at a later stage, it might be water rich.

So Proxima b’s in the habitable zone, which means it may have surface water, but will it have life? On the pessimistic side, it turns out that Proxima Centauri emits powerful flares and X-ray radiation. That may work to erode the atmosphere of the planet, although we don’t know how much because we don’t know if the exoplanet has a nice, strong magnetic field like Earth that would help to preserve the atmosphere and protect any developing life.

We need to go and have a look. But how to get there?

If we could shrink down to about two inches tall, we could hitch a ride on something like NASA’s New Horizon’s probe, which managed its trip to Pluto in around 9.5 years at around 84,000 km/h. That would get us a sneak peek of Proxima b in around 54,400 years. Hmmn. Or maybe the hotshot Juno probe that reached a whopping 265,000 km/h? That would cut the trip to 17,157 years.

One option is to accelerate a small probe with solar sails to relativistic speeds using a high powered laser. Just such a thing has been proposed by the Breakthrough Starshot initiative. For around $18 billion we could build a system that would send wafer-thin probes to Proxima Centauri. The Earth-based laser would accelerate the probes to around 20 percent the speed of light (215.85 million km/h). That would get the tiny probes to Proxima Centauri in 20 to 25 years. What these small probes could tell us will rely very much on how powerful their miniaturized instruments were, and of course scientists being able to conceive a way for a targeted message to reach Earth with the data.

It’s exciting that we have an Earth-like planet so close to our solar system. How we get there is one thing, but if human history tells us anything, once we want to go there – we will find a way.

My novel, The Tau Ceti Diversion, a story about our search for new planets to colonise outside our solar system, and is now available on Amazon! Read more about what happens in the story here!

Check out the free chapter download!

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