Everything Else Is Speculation…

…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.


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