Sunday, December 18, 2011

Weird Worlds: Kepler 22b

It's what all the cool kids are (still) talking about, so why not a post on it? In the glut of Kepler mission transiting planets, a new planet has risen to the fore as the possibly most Earthlike extrasolar planet. Huzzah! (And in a few months yet another new planet will take its place. Just watch).

Credit: NASA/Ames/JPL-Caltech

What we know

Kepler 22 is a star very similar to our sun. It is slightly smaller (0.98 times the radius of the sun) and slightly smaller (0.97 times the mass of the sun). It is 587.1 light years away, so it's not something we're going to be visiting soon.

So far, it only has one known planet, dubbed -- as these things go -- Kepler 22b. This planet is smack bang in the habitable zone ...on the inner edge, so OK, maybe not that smack bang... BUT. The part people are getting exciting about is that it's the smallest planet we've found in the habitable zone thus far.

How small? 2.38 Earth radii. For comparison, Neptune, the next biggest solar planet after Earth, is 3.88 times Earth's radius. That puts Kepler 22b just on the smaller side of halfway between Earth and Neptune. In terms of size.

What we don't know is how massive it is. The way the Kepler satellite detects exoplanets is by looking at stars and measuring how much dimmer they get when (if) a planet passes between the star and us. By knowing how much light the star gives out usually, and how far away it is, it's possible to work out how large the planet is. (And, actually, even if you don't know how far away the star is, you could still work out how big the planet has to be as a fraction of the size of the star.)

We know how long its year is, basically by measuring how often it passes in front of the star. Yeah. It's that simple (particularly since there seems to be just one planet in this system at the moment). So Kepler 22b's year is 290 days long, not drastically different to Earth's. That and its position in the habitable zone have lead people to suppose that maybe it's not so different to Earth.

Based on how far it is from its star etc, the average surface temperature would be about -11º Celsius if it had no atmosphere. However, if it had an atmosphere like Earth's average temperature would be about 22º C. Perhaps a slightly less insulating atmosphere would be in order, however, since Earth's mean surface temperature is actually 14º C. (Because we have to take global lows and highs into account, you see, and average over the whole planet, never mind that 22º is just about room temperature.)

Harping on what we don't know

It's that mass. And the fact that we don't have a planet of that size in our solar system. It's in the transitional zone, as I said, between rocky terrestrial planet and mini gas giant. If it's rocky, it's likely that the gravity will be stronger than Earth's, thanks to it's larger size. In fact, if it's the same density as Earth, the surface gravity will be about 2.4 times Earth. Which isn't long-term viable. At Neptune's density, we get a ball of gas with surface gravity 0.72 times Earth. A ball of ice would result in gravity 4.3 times Earth. The least dense terrestrial planet in our solar system is Mars and at Mars' density, Kepler 22b would have gravity 1.7 Earth's.

So there's quite a spectrum of possibilities there. We really don't know enough to make any definitive judgements at this stage. That doesn't make it less exciting, of course, and it's true that there might be oceans and continents there. Or it could be a small dense ball with a thick gaseous atmosphere inhabited by dragons (perhaps even fire-breathing ones, if there's methane in the atmosphere and breathing fire is a viable way to catch prey). Which would also be cool. Arguably, cooler.

Saturday, December 10, 2011

Australian Women Writers Challenge

Next year, I am going to take on the Australian Women Writers Challenge. To make it particularly challenging and to tie in better with the contents of my blog, I am going to try to read only science fictional books by female Australians.

The specifics of my challenge:

Genre challenge: Purist: one genre only

Challenge level: Miles (read 6 and review at least 3*)

* Should include at least one substantial length review

I'm excited! But also kind of glad that there are still a few weeks left in 2011 to finish the Vorkorsigan Saga which I'm in the grips of. (Only, um, 4-5 books to go...)

Book list

And here is my preliminary list of books/authors that I plan to read. The order I've listed them is more or less the order they occurred to me / were suggested to me on Twitter / I saw them on past Aurealis Awards short lists. Also, I think some of these will be difficult to acquire, so that will definitely affect my ability to get through them all.
  • Marianne de Pierres (definitely Angel Arias which is sitting on my bookshelf, quite possibly others)
  • Patty Jansen (Watchers Web / The Far Horison)
  • Kim Westwood (Courier's New Bicycle)
  • Maria Quinn (Gene Thieves)
Sara Creasy (Song of Scarabaeus)
  • Sonny Whitelaw (Rhesus Factor)
  • Claire Corbett (When We Have Wings)
  • Sue Isle (Nightsiders)
  • Maxine McArthur (Less Than Human / Time Future)
  • Michelle Marquardt (Blue Silence -- seems very hard to find though)
  • Tess Williams (Sea as Mirror)
  • Sally Rogers-Davidson (Spare Parts)
 I've put a link along the top bar thingy under the banner to a page where I'll be collating reviews and keeping track of the books I've read.

Wednesday, December 7, 2011

Measuring distances: the furthest away objects

[First up, apologies for the unscheduled hiatus. Being sick and moving house (mercifully not simultaneously) sort of quashed any blogging plans I may have had. OK, so I don't mean so much quashed as put out of my mind entirely, but whatever.

Also, thanks to changing life routines, I think I'll be changing my update schedule from Wednesday nights to weekends. For the time being it seems more manageable.]

This week I thought I'd talk about something a little bit outside the realms of foreseeable future SF: extragalactic distances. I say outside in the sense that there is currently no plausible way to travel to neighbouring galaxies, let alone galaxies at the edges of the observable universe.

How far is far?

The thing to understand here is that the universe is really big. Like, amazingly, mind-blowingly large. Douglas Adams said it well:
Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.
Light travels 300 000 km in one second (in a vacuum). It takes about eight minutes for light to travel from the sun to Earth. About five and a half hours from light to travel from the sun to Pluto. It takes a hundred thousand years for light to travel from one edge of our galaxy to the far edge (along the disc). By this stage, I'm sure you've heard the term light year. It's the distance that light can travel in one year and is about 9 460 000 000 000 kilometers (about 1013 km or ten trillion kilometres). The nearest galaxy is two and a half million light years away. See how all these distances stack up?

Most astronomers don't actually measure or think about distances in light years. They're somewhat useful for conceptualising things, but parsecs (abbreviated to pc) are more common. One parsec is 3.26 light years. That puts the nearest galaxy, Andromeda almost 800 kpc away (kpc is kiloparsec where the kilo indicates a factor of 1000). Mostly galaxy distances are measured in megaparsecs (Mpc) where one megaparsec is a million parsecs.

Even larger distances are measured using a scale called redshift. The universe is expanding. When light leaves a distant galaxy and travels towards us, it takes time. Possibly millions or billions of years, depending on just how distant that galaxy is. In all that time while it's travelling, the universe continues expanding. The expansion stretches out the light so by the time it gets to us, it has a longer wavelength. Longer wavelength means redder (on the visible spectrum, although in reality this light could have started at any wavelength, depending on what emitted it, and could finish up stretched out all the way into the radio region). Hence the term "redshift".

Doing the Measuring

I touched upon spectroscopy when I talked about the Doppler effect in this astronavigation post. Basically, you look for some known lines (often hydrogen lines) and see how far they've shifted towards the red end of the spectrum.

So we should just be able to use this to measure distances, since we know how fast the universe is expanding, right? Not quite. In the post I linked above, I talked about Doppler shift. This is different to redshift but it can look very similar. Far away galaxies can be moving relative to their neighbours (galaxies in a cluster orbiting a central galaxy, for example). These local motions are called peculiar velocites. This means that you could work out spectroscopic redshifts for galaxies in a cluster, which are all around the same distance from us, but get different results because of their peculiar velocities.

Instead we have to use a combination of different methods, two of which I'll talk about now. The same principle underlies both. Basicaly, in the 70s and 80s, it was discovered that there are a few "scaling relations" which galaxies obey. For example the Tully-Fisher relation relates a spiral galaxy's luminosity (how much light it gives out in total) and the rotational velocity of it's stars (how quickly they orbit the centre).

Spiral Galaxy M101
A spiral galaxy. Although, for a Tully-Fisher measurement, you'd
want it to be side-on, not face-on. But face-on looks prettier.
We can measure the rotational velocity of the stars in a spiral galaxy using the Doppler effect (even though the galaxy is moving away, the stars on one side will be moving towards us and on the other side away from us -- the difference between the two sides can be used to work out the rotational velocity). Once we know that, we get a prediction for the luminosity of the galaxy. However, the galaxy is far away and looks dim, much like a light in a high-ceilinged hall that isn't too bright too look at although it would hurt your eyes if you were up close. Exactly how dim a galaxy looks depends exactly on how far away it is. So if we know how bright it should be, we can compare with how bright it appears and work out how far away it is. Huzzah.

There is a similar, albeit slightly more complicated, relationship for elliptical galaxies called the Fundamental Plane.

Both the Tully-Fisher relation and the Fundamental Plane are constantly being improved upon as we build better telescopes that give more precise measurements and also as we understand the underlying physics governing them better. (At the moment, we're not super sure why they exist.) However, we're still able to use them to measure things like Hubble's constant. Who knows, maybe there are super advanced aliens out there who can set up extragalactic wormholes and need to know how far away to place them.

Probably not, though. I did say this post was outside the realm of plausibility.


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