Archive for the Space Category

L and T and OBAFGKM and Oh My!

Posted in Astronomy, Science, Space with tags , , , on April 4, 2012 by davidnm2009

As regular readers might have noticed, I’ve recently discovered the ‘Mass Effect’ series of games (yes, I know, late to the party, as usual!). I’ve recently started on Mass Effect 2 – I think I’m now about halfway through it, as best I can tell. So far I can honestly say that the entire thing is made of pure awesome, from an interesting storyline to well-drawn and entertaining characters. Also, it’s quite refreshing to come across a game series where I don’t have to simply turn off the science-nitpicking part of my brain, as the series is actually rather well-researched. (We’ll take the plot-devicium oxide that is Element Zero as a given for the time being, of course.)

Anyway, imagine my surprise when I discovered that one of the first missions in ME2 involves a star system that contains a brown dwarf! Obviously this got my attention, as I have more than a passing interest in these failed stars…

Continue reading

Advertisements

Astronomical Mystery #5: Revenge of the Mascons

Posted in Astronomy, Science, Space with tags , , , on February 7, 2012 by davidnm2009

The Moon. Astronomically, it’s quite nearby; close enough that it shows a disk even with the naked eye. Close enough that you can just about read a book by it at night, at least when it’s full. Close enough that its nature has been debated throughout history. Close enough that’s it’s even been physically-travelled to by actual, living human beings – the only celestial body for which this is true, aside from the Earth!

So, given all this closeness, you’d think we know the Moon pretty well, wouldn’t you?

Well, no, actually. We don’t. The Moon has its mysteries and some of them are rather baffling. In fact, the Moon’s mysteries are made all the more frustrating by the fact that it’s so nearby. One particular case is that of the ‘mascons’, or ‘mass concentrations’.

Basically, the Moon’s shape is broadly spherical, but its structure is lumpy. There is, in fact, some evidence that’s visible to the naked eye; the Moon’s so-called ‘seas’, the maria, are mainly located on the Earth-facing hemisphere. The maria, of course, aren’t bodies of water but are plains of frozen lava, darker in colour than the relatively-brighter, heavily-cratered lunar highlands. At some point billions of years in the past, the maria would have been true seas of a sort, albeit seas composed of red-hot molten rock. Those oceans of magma, however, quickly froze as they radiated their heat into space. These vast, volcanic outpourings were only a temporary phenomenon. The Moon is too small to have held much of its internal heat, and its mantle is solid and frozen. (Thanks to seismic data returned by remote landers and the Apollo missions, we actually have a relatively good knowledge of the Moon’s interior – although the keyword is ‘relatively’!)

Now, the side of the Moon that faces away from the Earth has far fewer maria. The ones that it does have are much smaller, and they seem to be confined mainly to the floors of big craters. It’s as if the far-side maria were actually produced when big impacts punched through the lunar crust, rather than through volcanic eruption. The reason for this appears to be partly that the Moon’s crust is thicker on the far side – it’s almost as if the entire Moon was actually several miles off-centre. In numbers, around 1% of the far side of the Moon is covered by maria, whereas 31.2% of the near side is covered in maria. The hemispheres have a clear, geological difference between them.

Yes, the Moon is weird.

But what, you may ask, does this have to do with the mascons? And what are they?

Well, in April 1972, Apollo 16 placed a small satellite in a close orbit around the Moon. This satellite, unromantically dubbed PSF-2, was intended to study the local environment around the Moon – charged particles, magnetic fields, that sort of thing. But the little satellite’s mission didn’t go to plan. The satellite’s orbit rapidly became unstable. It was originally meant to get no closer than 52 miles above the lunar surface. Instead, within two and a half weeks, PSF-2 was descending within six miles of the lunar surface. Six miles – that’s getting uncomfortably close to the height of some of the Moon’s bigger mountains! And all this instability developed in such a short space of time.

Needless to say, it didn’t take much longer for PSF-2 to crash headlong into the Moon’s rocky surface.

It turns out that the Moon’s crust contains some remarkable concentrations of matter. These dense lumps – the ‘mascons’ – also make the Moon’s gravitational field lumpy and uneven. The variance is surprisingly big, as much as half a percent. (For a gravitational field, this is a huge variation – for comparison, the Earth’s varies by less than one part in a thousand.) It would actually be easily-measurable to human astronauts, were any to land close to the relevant regions. Near the edge of a mascon, a pendulum or plumb-line would hang about a third of a degree off of vertical, with the tilt being oriented toward the mascon.

The biggest mascons are also located in the same area as the centres of the bigger lunar seas, so they are evidently related in some manner. That much at least, we do know. The positions of the mascons have been determined quite reliably, from measurements of satellite orbits. They have the effect of making low lunar orbits unstable, hence the unfortunate end of poor PSF-2. (The Apollo modules were sufficiently high so as not to be greatly-affected, thank heavens.) The mascons are presumably also much denser than normal lunar material, since they are massive enough to distort the Moon’s gravitational field. There is also a strong suspicion amongst planetary scientists that they were formed either through the volcanic upwellings of the maria themselves, or through large impact-events that ‘injected’ pockets of denser matter into the lunar crust, or some mix of both processes.

However, the truth is that we don’t really know.

Even within the above model, there are a lot of unknowns. For instance, there are demonstrably fewer mascons on the Moon’s far side, and those that exist are generally weaker too, despite the greater rate of impact on the far side. (The near face is shielded to an extent from impactors by the Earth.) Also, there do exist some mascons that aren’t obviously associated with maria. So, although we know of their existence, and we understand some of their properties, their full nature remains very much a mystery.

The Moon, it seems, guards her secrets closely.

Old Mars

Posted in Astronomy, Science, Space with tags , , , on December 31, 2011 by davidnm2009

“…Yet across the gulf of space, intellects vast and cool and unsympathetic, regarded our planet with envious eyes, and slowly and surely drew their plans against us….”

Yes, I’m listening to Jeff Wayne’s version on ‘War of the Worlds’.

Wells’s opening narration has to be one of the most wonderfully chilling things I think I’ve ever read. On the face of it, it breaks every narrative rule in the book (third person, passive voice, no dialogue, pure exposition) and yet, I find it impossible to read without shivering.

Interestingly, for its day, ‘The War of the Worlds’ was also scientifically-plausible. The Victorian Mars was believed to be a living world, if likely rather a dry and desolate one. Indeed there was even some evidence of supposed activity on the surface – the infamous ‘cannali’. (Actually ‘channels’ – the word was mistranslated into English as ‘canals’, which are a rather different entity from that which Schiapperelli meant to imply!)

Of course, Science Has Marched On (as it’s rather prone to). Our Mars is a nearly-airless, lifeless world. If anything does live on it – and there can’t be very much, else we would long since have known of it – then it couldn’t be more than a few microbes, perhaps huddling in some warm, wet reservoir beneath the surface. Our Mars almost certainly did have liquid water, warmth and air, but that phase was billions of years ago.

Our Mars is just too small.

Its core cooled and froze out aeons ago, stilling the planet’s internal dynamo. With no global magnetic field, there was nothing to shield it from the solar wind, and the storms of the Sun slowly stripped away its air. In addition, without plate tectonics, the atmospheric cycle slowly ground to a holt. Mar’s air was gradually lost to sediments deposited at the beds of the Noachian oceans. Then those oceans themselves gradually evaporated, their vapour rising into the stratosphere, where solar ultraviolet broke apart the heavy water molecules. The light hydrogen atoms would simply have escaped into space, Mars’s low gravity being too weak to hold them. The oxygen would have been lost into compounds by reaction with other materials in the Marian crust and air – oxygen is a notably reactive gas! (And as well it is – if it were any less reactive, our entire human metabolic system would be quite impossible.)

Over the millennia, these processes ran their course. Mars was left dry, desolate and lifeless. If there ever was anything living there, it does not seem to have been able to survive the transition from Blue Mars to Red Mars. Today, Mars averages something like -60 Celsius and it has a surface air pressure of a mere 7.6 millibars, or less than 1% that of the Earth. The only remaining water are some suspected permafrosts and the two small, bright caps of ice at either pole. There is also a breath or so of water vapour in the thin atmosphere, but not enough to form more than a single pond. Our Mars is a cold, cratered orb, staring blindly into the heavens.

Still, one has to wonder.

“…The chances of anything coming from Mars, he said, were a million to one…”

Image credit: NASA, via Wikimedia Commons

Moon of the Day (3)

Posted in Astronomy, Space with tags , , on August 9, 2011 by davidnm2009

Today’s pick comes from the Jovian system:

Image via: Wikipedia and the Galileo orbiter.

Ganymede is hard to miss. It’s sufficiently prominent that it was originally discovered by Galileo on the 7th of January, 1610 – in fact, it may well have been the first object ever discovered via a telescope. (We just don’t know precisely which of the Galilean Moons Galileo saw first; we do know that he saw all four of them on the same night!) Ganymede is actually fairly bright, for an outer-system object. At magnitude 4.5ish, it would actually be a naked-eye object, except for the glare from Jupiter.

Continue reading

Dione

Posted in Astronomy, Space with tags , on August 5, 2011 by davidnm2009

Saturn, I have to admit, is a bit of an easy target for this sort of thing, given that it has something like 60 or so moons. With that many satellites, it’s pretty much inevitable that you’ll find some interesting oddballs. Dione is another such moon of Saturn.


Credit: Cassini/NASA, via Wikipedia

Dione was first observed in 1684 by Giovanni Cassini, who also discovered three others of Saturn’s satellites[0]. Dione wasn’t actually formally named until 1847; Cassini called his discoveries the ‘Sidera Lodoicea’ (‘Stars of Louis’) after his patron, the French king Louis XIV. (This sort of fawning was entirely normal at that point in history … luckily, it’s one practise we seem to have left behind!)

Continue reading

Gravity, Part. 2

Posted in Space, Speculation with tags , , , on March 31, 2011 by davidnm2009

It’s all about the bones.

Your bones are a central part of your physiology. They hold your body up. They also help you to move, by giving your muscles something to push against. They also house the marrow that amkes your red blood cells. And, like all systems in the human body, evolution has optimised them for 1 g of gravity. How are they going to react to a hypothetical colony planet, with g=0.68? or 1.3? or 0.17 (if we’re talking about a Moon colony)?

I’ll be clear about one thing; at the moment, we don’t know for an absolute fact. But there is some evidence to suggest that there could be tears before bedtime…

Continue reading

Air Pressure

Posted in SF, Space, Speculation with tags , on February 12, 2011 by davidnm2009


Feeling the pressure…

Recently, I’ve been attempting to re-read a book. I first read it back in ’90s, and didn’t get that much from it. I thought I might enjoy it more now – unfortunately, though, I’m actually liking it even less. Without naming the guilty, it’s sort-of a space colonisation story. You could sum the plot up as Rugged Libertarian Authority Figure(tm) is forced to Take Control and show a bunch of useless strawman liberals what’s good for them. (The authors do not appear to notice the inherent irony of a libertarian authority figure, either.) Few of the characters are at all sympathetic – the only one who is has severe brain damage and thus the IQ of a 10-year old. Also, we’re repeatedly assured that the colonists are a special elite, selected for their inherent genetic superior-ness to ordinary, scummy, untermensch humans. (That is, you and me. Just so we’re clear on this.)

Given my current politics, I found all of this utterly irritating.

I don’t think I’ll bother to finish the book. But there’s actually worse, though. You see, it’s supposedly hard SF. Now, I like hard SF. But what I don’t like is schoolboy research errors. (For instance, in this book, the authors seem to think that Tau Ceti is an F-class star – it’s really, really not). Also, the book is supposedly about the impact of an alien environment on the colonists. (I say ‘suppposedly’ what it actually seems to be about is an excuse for their uber-manly Heinleinian poster-boy to flex his manly Marty Stuish pecs at the readers.) However, the environment makes a surprisingly small impact on the characters. In particular, two critical world-building factors are entirely ignored.

These are surface gravity and air pressure.

I’ll deal with gravity some other time, but let’s talk about air pressure.

Continue reading