Marsquakes

One of the more interesting aspects of the latest NASA landing on Mars is that the rover has dug into the surface, inserted a seismometer, and is looking for marsquakes. On Earth, earthquakes are fairly common, especially where I live, and they are generated through the fact that our continents are gigantic lumps of rock moving around over the mantle. They can slide past each other or pull themselves down under another plate, to disappear deep into the mantle, while at other places, new rock emerges to take their place, such as at the mid-Atlantic ridge. Apparently the edges of these plates move about 5 – 10 cm each year. You probably do not notice this because the topsoil, by and large, does not move with the underlying crust. However, every now and again these plates lock and stop moving there. The problem is, the rest of the rock is moving, so considerable strain energy is built up, the lock gives way, very large amounts of energy are released, and the rock moves, sometimes be several meters. The energy is given out as waves, similar in many ways as sound waves, through the rock. If you see waves in the sea, you will note that while the water itself stays more or less in the same place on average, in detail something on the surface, like a surfer, goes up and down, and in fact describes what is essentially a circle if far enough out. Earthquake waves do the same thing. The rock moves, and the shaking can be quite violent. Of course, the rock moves where the actual event occurred, and sometimes the waves trigger a further shift somewhere else.

Such waves travel out in all directions through the rock. Now another feature of all waves is that when they strike a medium through which they will travel with a different velocity, they undergo partial reflection and refraction. There is an angle of incidence when only reflection occurs, and of course, on a curved surface, the reflected waves start spreading as the angles of incidence vary. A second point is that the bigger the difference in wave speed between the two media, the more reflection there is. On Earth, this has permitted us to gather information on what is going on inside the Earth. Of course Earth has some big advantages. We can record seismic events from a number of different places, and even then the results are difficult to interpret.

The problem for Mars is there will be one seismometer that will measure wave frequency, amplitude, and the timing. The timing will give a good picture of the route taken by various waves. Thus the wave that is reflected off the core will come back much sooner than the wave that travels light through and is reflected off the other side, but it will have the same frequency pattern on arrival, so from such patterns and timing you can sort out, at least in principle, what route they took and from the reflection/refraction intensities, what different materials they passed through. It is like a CT scan of the planet. There are further complications because wave interference can spoil patterns, but waves are interesting that they only create that effect at the site where they interfere. Otherwise, they pass right through other waves and are unchanged when they emerge, apart from intensity changes if energy was absorbed by the medium. There is an obvious problem in that with only one seismometer it is much harder to work out where the source was but the scientists believe over the lifetime of the rover they will detect at least a couple of dozen quakes.

Which gets to the question, why do we expect quakes? Mars does not have plate tectonics, possibly because its high level of iron oxide means eclogite cannot form, and it is thought that the unusually high density of eclogite leads to pull subduction. Accordingly the absence of plate tectonics means we expect marsquakes to be of rather low amplitude. However, minor amplitude quakes are expected. One reason is that as the planet cools, there is contraction in volume. Accordingly, the crust becomes less well supported and tends to slip. A second cause could be magma moving below the surface. We know that Mars has a hot interior, thanks to nuclear decay going on inside, and while Mars will be cooler than Earth, the centre is thought to be only about 200 Centigrade degrees cooler than Earth’s centre. While Earth generates more heat, it also loses more through geothermal emissions. Finally, when meteors strike, they also generate shockwaves. Of course the amplitude of these waves is tiny compared with that of even modest earthquakes.

It is hard to know what we shall learn. The reliance on only one seismometer means the loss of directional analysis, and the origin of the quake will be unknown, unless it is possible to time reflections from various places. Thus if you get one isolated event, every wave that comes must have originated from that source, so from the various delays, paths can be assigned. The problem with this is that low energy events might not generate enough reflections of sufficient amplitude to be detected. The ideal method, of course, is to set off some very large explosions at known sites, but it is rather difficult to do that from here.

What do we expect? This is a bit of guesswork, but for me we believe the crust is fairly thick, so we would expect about 60 km of solid basalt. If we get significantly different amounts, this would mean we would have to adjust our thoughts on the Martian thermonuclear reactions. I expect a rather tiny (for a planet) iron core, the clue here being the overall density of Mars is 3.8, its surface is made of basalt, and basalt has a density of 3.1 – 3.8. There just is not room for a lot of iron in the form of the metal. It is what is in between that is of interest. Comments from some of the scientists say they think they will get clues on planetary formation, which could come from deep structures. Thus if planets really formed from the combination of planetesimals, which are objects of asteroid, size, then maybe we shall see the remains in the form of large objects of different sonic impedance. On the other hand, the major shocks to the system by events such as the Hellas impactor may mean that asymmetries were introduced by such shock waves melting parts. My guess is the observations will not be unambiguous in terms of their meaning, and it will be interesting to see how many different scenarios are considered.

Bloghop: Red Gold

I have been introduced to the “Bloghop” concept, where an author posts answers to ten standard questions, so here goes. Needless to say, some of my answers will hardly be standard! (I have also cheated a little by including a touch of the greater concept behind my writing, but then again, it is my blog so why not!)

1   What is the title of your book?

My latest is called Red Gold, and is set in 2075-76.It forms part of a “future history”, which starts in 2030 with Puppeteer, proceeds to the early 2050s with Troubles.

 Where did the idea come from for the book?

I started writing a futuristic novel in the 1990s, but it had far too much backstory, so I cut out some bits, and part of those cuttings led to the idea for Red Gold. The cuttings have actually provided material for five further books.

 3   What genre does your book fall under?

Science Fiction and Thriller, although the series itself will include two that would qualify as historical. The series goes to the 24th century before progressing back to the 1st as a “reboot”, and apart from two chapters, one in each book, they would be straight historical, dealing with the life of the main protagonist under the end of the Imperium of Tiberius, through Gaius Caesar, and the invasion of Britain under Claudius.

 4   Which actors would you choose to play your characters in a movie rendition?

I have no idea, but I would love Peter Jackson to direct, and Weta Workshops to do the special effects. With a bit of luck, they might let the author in to see some of what is going on. Part of “Lord of the Rings” was filmed opposite where I was working at the time, and I really wanted to see what was going on behind the huge “fence”.

 5   What is the one-sentence synopsis of your book?

Red Gold is about one man’s need to expose a fraud committed by his business partner during the colonization of Mars.

 6   Will your book be self-published or represented by an agency?

 It is self-published as an ebook.

 7.   How long did it take you to write the first draft of your manuscript?

About 8 months, I think. It was some time ago, because I abandoned it for a number of years.

 8   What other books would you compare this story to within your genre?

Obviously, nothing is exactly similar, but Kim Stanley Robinson’s Red Mars has a certain similarity in terms of genre.

 9.   Who or What inspired you to write this book?

The first of the futuristic novels was written to “see if I could make it”. To explain that, my first attempt at writing a novel was as an undergraduate in the 1960s. I was with a few female students who were going for a BA, and I could not resist saying that at least science was aimed at creating something, while all they were doing was criticizing. They should be doing, like writing novels. Their response was, I could not come up with a plot so . . My response to that was, of course I could; it was them who could not. So they challenged me, and I came up with one. They challenged me to write it, so I did. I posted it off, got four rejections and gave up. About 15 years later, I looked at it again, and the first twenty pages were awful, and nobody got past them. So I tried rewriting, and sent out query letters, but got no response. Then I tried self-publishing, on the basis that (a) I had some sort of platform because I was on nationwide TV from time to time, and (b) I was getting involved with an industrial venture, and I needed to clear the decks, so to speak. I did, but the venture also took off, and financiers forbade me to seek any publicity for anything. With no advertizing, no publicity, sales were only modest, so in the 1990s I decided to try again and see if I could make it.

 10.    What else about your book might pique the reader’s interest?

I got an agent, the book went to a major publisher, but the editor died and his replacement cleared his desk. According to this editor, my plot was too ridiculous. The book is about a fraud during the colonization of Mars, and it is exposed by an unexpected discovery, which involved where the atmosphere of Mars went. The colonization of Mars is hardly too ridiculous for SciFi, fraud is never ridiculous, which meant my science was ridiculous, and that was the prime insult. I then devoted myself to going deeper into this topic, and this ended up as my ebook “Planetary formation and biogenesis”. If Mars rovers ever find a deposit of nitrogen-rich organic material, this will be the first book to have predicted it.

Finally, something about Bloghop. To see more, go to http://www.colleensayre.blogspot.com