Archive for February, 2011

Mauna Kea

Posted in Astronomy with tags , on February 24, 2011 by davidnm2009

I don’t think I ever actually posted this, back in last April. This is a photo I took, from the summit of Mauna Kea. You can see the Sub-Millimete Array. down there. Those dishes are a bit spooky – they all move together, in total silence.

Also, you can see a bit of the local scenery. The thing that struck me about the summit was just how Mars-like it looks. Aside from the blue sky and the clouds, it really does have a Mars-like feel to it.

More Brown Dwarfs

Posted in Art with tags on February 19, 2011 by davidnm2009

Hmm. I can’t say I feel particularly happy with this one.

The idea was a brown dwarfs binary, with a mid-T dwarf (the big one in the middle) and a very much cooler, late-T companion. The late-T companion is so faint in the optical that you can only really see it where its surface reflects the meagre light from its companion.

But it just looks like a picture of some round, swirly things. Oh well. You don’t win them all, I guess.

Larger version here, should anyone want it.

We’re Living In The Future

Posted in Astronomy, Personal with tags , on February 17, 2011 by davidnm2009

What else can you say when one of the headline news articles on the BBC news concerns a flare on the Sun?*

By the way, in case anyone’s concerned, I don’t really think there’s much to be worried about with this one. It might cause some aurorae and possibly make a few satellites glitch a bit, but I don’t think we’re going to wake up to widespread disruption tomorrow.

Of course, if a repeat of the Carrington Event were to happen today, that would be quite a different conclusion.
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*There’s also the point that my main source for news these days is a decentralised, global, electronic computer network … which I would have regarded as downright bizarre/unlikely as recently as 1995.

Failure Points

Posted in Astronomy, SETI, Speculation with tags , , , , on February 15, 2011 by davidnm2009

I had an odd thought earlier, whilst typing an e-mail.

Just what is the average metallicity of the galactic disk?

I’m not sure, but I have a suspicion that it might be at least a little bit subsolar. Why is this bothering me? Well, I have a suspicion this could impact on the Fermi Paradox. My thought goes something like this…

Consider a somewhat metal-poor star, say [Fe/H] = -0.3 – that is, about 50% the heavy-element abundance of the Sun [1]. Let’s assume its protostellar disk shares the same composition – not wholly unreasonable, since they formed in the same place! Presumably, the star’s relative lack of heavy elements will be reflected in the planets that it forms.

Now, first off, you won’t get as many planets around metal-poor stars; planet-formation seems to correlate with stellar metallicity. That said, you do get at least some planets around low-Z stars. But, until relatively recently in galactic history, most stars will have been ‘low’ metallicity. The interstellar medium didn’t originally contain metals; heavy atoms got there as a result of pollution by supernovae and red giants, and that process takes time. And the galactic disk still contains plenty of metal-poor regions even now. (A star having a subsolar metallicity is not a guarantee that it’s older than our Sun – something that’s irritatingly inconvenient for my own research!)

Anyway, I can imagine terrestrial planets existing around our [Fe/H] = -0.3 star. I can even imagine them having a reasonable amount of carbon, oxygen, nitrogen and hydrogen, so the absolute-minimum basis for CHON life is there. Probably there’s at least a dash of other stuff too. But what I imagine it particularly lacking is big, heavy atoms – like rare-earth elements and so on.

Supposing life gets started on such a planet. Suppose even some sort of civilisation gets going. But presumably you’re not going to be able to have much of an electronics industry without metals or rare-earth elements? And if building even just a radio is difficult – let alone TVs, radar etc. – then you’re not going to be leaking much EM radiation into space. And without much leakage, you’re certainly not going to be detectable at interstellar distances.

And if the galaxy as a whole is, on average, metal-poor relative to our Sun, does this also mean that advanced electronics industries are also rare? Food for thought…

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[1] In astronomy, a ‘metal’ is anything heavier than helium – i.e., something that couldn’t have been formed during the Big Bang. The [Fe/H] scale is a logarithmic scale, based on the relative levels of iron[2] as compared to hydrogen; [Fe/H] = 0.0 is 100% solar, i.e. 10^0 = 1. [Fe/H] = -1.0 is 10% of solar and [Fe/H] = +1.0 would be 10x the solar content of metals. In practise, the highest values of [Fe/H] seem to be about +0.5ish. The record object for lowest metallicity, however, is HE 0107-5240, with a breathtakingly-low metallicity of [Fe/H] = -5.2.
[2] In stars with so-called ‘solar’ abundances, you can use the amount of iron as a sort of standard calibrator for other elements. In less well-behaved stars, those with non-solar abundances, this breaks down, and you have to be a bit careful. In these cases it can be more useful to use [M/H], which is exactly the same logic as Fe, except that M is the total amount of metals against the total amount of hydrogen.

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

Beware The Dawn

Posted in Art with tags , on February 8, 2011 by davidnm2009

New painting:

I’ve been slowly making my way through Tolkien’s Ring trilogy. This is for the second time – I read it once before, in the mid-’90s, and didn’t get that much out of it that time. I’m enjoying it more now. That said, the focus on all the ‘hero’ characters did get me to wonder about the ‘non-hero’ pople who live in its world, whom we never really get to see. And this is a common issue with high fantasy – a lot of minor or even non-characters who are just there to be Orc-fodder.

So this picture is about them – the people for whom sunrise probably isn’t good news.

(Higher-res version over here.)

Odds and Ends

Posted in Astronomy, Speculation with tags , on February 6, 2011 by davidnm2009

On the bus home on Friday, I was grinning like a maniac. Goodness knows how much I must have worried the other passengers! I really was atypically cheerful.

You see, I finally had a chance to start to read Borucki et al. 2011 in detail – this being, of course, the one of the Kepler papers that deals with (amongst other things) the candidate-terrestrial exoplanets. Actual data on credible, habitable-zone planet-candidates … this is something I’ve wanted to see for years, and at one point didn’t think I ever would.

In particular, I was looking at Table 6 of Borucki et al. This is the table where the habitable zone candidate-planets are listed.

And there are some interesting things in there. First off, the smallest detected object is KOI 326.01, with an estimated radius of 0.85 Earths. (This makes it a bit smaller than Venus, but rather bigger than Mars.) This object is in a ~13-day orbit around an M dwarf. It presumably has a lower mass than Earth as well and presumably a lower surface gravity.

There are six HZ-objects with radii < 2 Earths (KOIs 1026.01, 854.01, 701.03, 268.01, the aforementioned 326.01 and also 70.03). Of these all but 326 are larger than 1.7 R_Earth – this is at least partly an artifact of the methodology, which makes it easier to detect bigger planets. (You get a bigger dip in the star’s light – a ‘fatter’ planet blocks more of it!) However, it does appear that there are more planets larger than Earth than smaller than Earth. As the paper points out there seems to be some evidence that the size distribution of planets peaks at about 2-3 times the size of Earth, then the numbers start declining again.

As well as small HZ-planets, there are also some very, very big ones. KOI 1375.01 caught my eye in particular – R_p = 17.88 Earths, implying a diameter of ~228,000 Km. By contrast, Jupiter has a diameter of ~142,000 Km. And Jupiter is about as big as planets can get – beyond something like 1.3 Jupiter radii, electron degeneracy pressure starts taking over in the core, and as you add mass to the object, it actually shrinks a bit. (In other words, you enter the brown dwarf regime somewhere around here.)

Now, if KOI 1375.01 was a hot Jupiter, there wouldn’t be a problem – possibly it was bloating up due to the star’s intense heat. However, it orbits in a 321-day period with an estimated temperature of 300 K (or about 27 degrees C). That’s warm, but hardly roasting – in fact it’s not that much warmer than we are. So it can’t be bloated due to irradiation – there’s just not enough heat!

But, its radius would be about right for a mid-M red dwarf. So I suspect KOI 1375.01 will turn out to actually be a small star, not a planet. This might be relatively easy to test – M dwarfs are proportionately a lot brighter in the near-infrared than F, G or K stars, and KOI 1375 appears to be either late-F or early-G type. (It has a temperature of ~6,200 K listed, which would be consistent with that sort of range.) So if the star shows an unusual NIR excess – i.e. it’s unsually-bright in the infrared – then you’ve got some evidence straight away for an M-dwarf companion. Better yet, the system will very probably be a spectroscopic binary. (And this, in addition, is another use for Kepler – binary stars are extremely important as a test of theoretical models.)

Before I sign off, one more intriguing object. KOI 211.01 has an orbital period of 372.1 days around a star with T = 6072 K, leading to an estimated temperature of exactly 0 degrees C*. This is in fact probably the most ‘Earthlike’ combination of temperature, star and orbit on the list. 211.01 itself is not Earthlike – it has a radius of 14.99 R_Earth, so in fact it’s bigger than Jupiter. But, in fact, it’s almost exactly 1.3 times bigger than Jupiter – a brown dwarf, I wonder?

And if a brown dwarf orbiting in a star’s habitable zone had a terrestrial-sized moon – well, that would make me doubly happy. More crazed beaming on the bus would be in order!
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*Note that the Earth’s equilibrium temperature is actually about -19 C – the additional 34 degrees comes from the greenhouse effect of our atmosphere.) If we assume an exactly Earthlike greenhouse effect for a satellite of 211.01, then an equilibrium of 0 would imply a surface temperature averaging 34 C – rather on the warm side, and the tropics would be miserable, but the polar/temperate regions would presumably tend toward our Meditarranean.