Archive for the Astronomy Category

Unintended Extra Travels…

Posted in Astronomy, Science, SF with tags , on October 31, 2015 by davidnm2009

Just for once, I’d love to see a time travel story where the protagonists know their probe has worked because they see a starfield when it drops backward to 9,000 BC (or whenever).

This is a minor point that often annoys me with time travel stories: if you actually had a time machine or viewer, you’d better hope it’s a space machine as well. Why? Because the Earth (and the Sun) move.

And they’re actually quite fast.

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Pluto and Charon

Posted in Astronomy with tags , , , on July 11, 2015 by davidnm2009

Pluto and Charon from New Horizons

The New Horizons space probe will fly by the Pluto-Charon binary on next Tuesday.

The above is a composite colour image that was released a couple of days ago. Both objects are visible. The close flyby images will be much better.

A lot to look forward to, needless to say! 2015 has been a good year for space probes.

Splat!

Posted in Astronomy with tags , , , on June 1, 2012 by davidnm2009


Image credit: www.hubblesite.org

My eye was caught by this article on the BBC earlier. That said, I couldn’t help but notice that they immediately tried to sensationalise the subject-matter:

    Our Sun’s position will be disturbed but the star and its planets are in little danger of being destroyed.

Note the ominous subsection there: ‘…little danger of…’, that is, implying that there is indeed some ‘danger of’, not ‘no’ danger of.

Actually, the planet’s not in any danger at all. And we human beings are in none whatsoever – by the time this happens, something else will certainly have finished us off long beforehand. The Milky Way/Andromeda collision is interesting, but it’s not really our problem in any direct sense.

That said, what is happening? And why?

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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…

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Astronomical Mysteries Summary

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

Here is a quick summary-page for the posts in the mysteries series:

Mystery #5: Mascons on the Moon.

Admittedly this is, what, 18 months late? But never mind that!

Here’s a list of the previous posts:

#4: What is KOI-74b? – Note that this has been subsequently solved! It was indeed a small white dwarf.

#3: Where do cosmic rays originate?

#3: Just what exactly is going on with Epsilon Aurigae?

#1: Is the Sun binary? – since I wrote this, we’ve had nearly a year of the WISE survey, and no-one’s pulled a solar companion out of it yet. However, there is still 43% of sky-coverage yet to be released (not that it’s likely one will be found, but you never know).

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