Archive for science

Hot Earth Dreams, by Frank Landis

Posted in Books, Reviews, Science, Social Concern with tags , on December 1, 2015 by davidnm2009

Unfortunately, climate change is something that matters to all of us, and is going to matter even more as this century wears on. With this grim fact in mind, Hot Earth Dreams is a serious work of speculation on what the Earth’s warm, storm-ridden and wet future might be like.

The short version is, we’re completely and nightmarishly fucked. Things aren’t quite as bad as is conceivable, but there aren’t many grounds for optimism either.

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The Eocene in Antarctica

Posted in Science with tags , , on August 2, 2012 by davidnm2009

I’ve just become aware of what I think is a very interesting paper, albeit one from outside of my field: Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch (Pross et al 2012).

The executive summary, as it were, is that Eocene-era Antarctica (55-48 million years ago) may have been a lot warmer than is generally reckoned. It’s been known for quite a while that the southern-polar continent hasn’t always been glaciated, and certainly has been forested in the distant past. However, the impression I’d got (from what I’ve read, here and there) was that the general opinion was that non-glaciated Antarctica was still a fairly cold place. Intuitively, given its extreme latitude, that would seem to make sense.

This study is arguing that simple intuition is wrong in this case.

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Meta – Vague Direction

Posted in Personal with tags , , , on May 29, 2012 by davidnm2009

I have to admit, I don’t use this place as effectively as I used to

It was originally an at least semi-serious blog, with a vague emphasis on entertaining, odd and weird things from the world of astronomy. (And, to a lesser extent, that of physics.) And I still occasionally do science posts, of course, and have no intention of completely stopping. However, these days I seem to be using this place more as a repository for various personal projects, essentially as a way of buying off that weird urge to make everything public. (It is strange – objectively, I’m well aware that the world does not and has no reason to care about my various artistic attempts, but there’s still this strange urge to push stuff out there. I’m not by nature an attention-seeker of any sort, so it really is out of character for me. I wish I understood it, but I really don’t!)

I also tried using this place as somewhere to discuss serious issues like current affairs and politics. Unfortunately, there’s a lot to feel annoyed about at the moment, and consequently most of those posts tended to decay into rants. Then I found I ran out of emotional energy to engage properly with these things – the last few years haven’t been good for my sense of optimism, unfortunately. I still have opinions, of course, but these days I’m wondering if I’m better off keeping them for the pub, not the internet. Then there’s the depressing fact that I’m increasingly doubtful as to whether my analysis is actually worth anything (I’m still cringing from my big mistake of 2010). Certainly I doubt there’s anything I’m saying that lots of other people haven’t already, so it’s not like I’m adding to the debate in any way. On that basis I don’t see this place going down a more overtly political route.

So, I suppose what I’m saying is that I no longer have a really clear sense of purpose for this project anymore. Probably I’ll carry on posting the occasional painting and the occasional bit of fiction. I’ll probably even write the occasional science post, now and again. But other than that, who knows?

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 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

Everything Else Is Speculation…

Posted in Astronomy, Personal, Science, Social Concern with tags , , on December 8, 2011 by davidnm2009

…I did promise I’d break my silence if anything interesting comes up, and I guess Kepler-22b counts. It’s just a pity that the news has already been enveloped in a fog of the worst sort of pseudo-scientific disinformation.

I think Kepler-22b is an exciting and significant result, and I’m enjoying watching the Kepler candidates followed up. However, I’m depressed to see that the press coverage here has been even more woeful than usual.

Here’s the TL;DR version; the relevant paper is right here. It’s a planet, it exists, it’s ‘Earthlike’ in the sense that it’s probably-but-not-certainly a terrestrial, and it orbits inside a star’s habitable zone. Other than that, we don’t know that much about it.

Longer version … there’s a lot of crap floating around about this object. Allow me to cut through the haze by listing the details that aren’t speculative:

  • The star (Kepler 22) is a type G5, so somewhat solar-like, but also somewhat cooler and fainter (K-22 has an effective temperature of 5518 K, against 5578 K for the Sun).
  • The planet has a radius of 2.38 times that of the Earth, with an error range of 0.13. Or to put it another way, it’s somewhere between 28,700 Km and 32,000 Km in diameter. (I’m rounding to the nearest ~100 Km there, incidentally.)
  • Based on the (lack of) Doppler shifting in the star’s light, the planet must weigh less than 124 Earth masses. By contrast, Jupiter weighs 317.7 Earth masses, so K-22b is definitely a planet and not a star or brown dwarf.
  • The orbital period is 290 days.
  • The blackbody temperature for 22b – assuming a terrestrial reflectivity! – is 262 K, or -11 degrees Celsius.

And, umm, that’s it.

The temperature figures that are getting a lot of attention are somewhat inferential. First off, the orbital period has been used to infer an orbital radius; this isn’t a problem, incidentally. (Although note that it tells us little about the temperature on K-22b today, as the number you’ll get out from this won’t tell you anything about eccentricity, inclination and so on, and these could all impact on surface temperature.)

The real issue is that this number doesn’t include any atmospheric effects – the number of 22 degrees was arrived at by assuming an exactly Earthlike reflectivity and an exactly Earthlike atmosphere. (The blackbody temperature for Earth is -19 degrees Celsius; the atmosphere adds another 30 or so degrees in greenhouse heating.) Neither of these is likely at all for K-22b. The combination is particularly unlikely.

The paper-writers, I want to note, make no bones about the limitations of this calculation:

  • …Using Equation 2, and assuming a planet with a surface and an atmosphere with thermal properties similar to that of the Earth (which is unlikely) and a Bond albedo of 0.29, the surface temperature of Kepler-22b would be approximately 295 K. [295 K = 22 Celsius. Emboldening added by me]

Needless to say, the press are conveniently ignoring that bit. If they even noticed that it was there in the first place, that is.

Depressingly, the press coverage about this object seems to be telling us a lot more about the media than it is about exoplanets. It’s almost a classic case of ‘churnalism‘, where lazy and/or time-pressed journalists simply regurgitate press releases, with neither fact-checking nor criticism. It’s also one of the reasons why more and more people are abandoning the mainstream media – if all you get is a mix of rented-mouth propaganda and stale churnalism, one has to wonder what the point of the media actually is?

Ahem. Yes, as it happens, I do feel strongly about factual accuracy in science-related articles (note that I’m not linking to any of the offending articles – if you must find them, Google is your friend). Anyway, ranting about press releases and dodgy newspapers aside, I think the point I’m trying to make is that Kepler-22b and their ilk are interesting and exciting objects, and as such they deserve to be considered on their own, factual merits, not on the basis of vague, ill-informed, emotive guff.

Also, there is a further problem with this. Declaring each new planet ‘habitable’ could have the effect of raising the public’s expectations – only to dash them down again. First off, it’s not a fair way to treat people, secondly it’s bad for public understanding of science and thirdly, it could backfire on the world of astronomy. Do we want the taxpaying public to be conditioned into a cynical expectation of disappointment? I think not!

Anyway, I would write more, but I don’t wish to add any more idle speculation to an already ill-informed debate.