Locklin on science

What is wrong with this picture?

Posted in astronomy by Scott Locklin on October 2, 2010

An “artists rendering” of a potentially habitable planet recently discovered.

This kind of thing really gives you hope, doesn’t it? Makes you think we’re about to go land in a nice, green planet, or at least peering at one through a telescope.

Well, the first thing wrong with this is, nobody has actually seen a planet here. The way these exo-solar planetary discoveries work is by very painstaking examinations of the spectra of stars shifting over years. You see, if you pass the light from a star through a spectroscopic instrument (a prism, or the little rainbow like holograms on your credit card), you’ll see certain lines. These lines come from atoms in the star. If you see them shift in wavelength, it is because the thing producing the lines is moving. This is the Doppler shift; anything which makes waves shifts in frequency when it moves towards or away from you. When the train is approaching, the sound is high pitched, and when it moves past you and away, the sound is lower pitched. Same thing with light; it gets bluer and redder depending if it moves towards or away from you. If this shift varies periodically over time, that’s probably because it is orbiting around something. Granted, we don’t know this with 100% certainty, but it is something generally assumed to be true in Astronomy. So, in all actuality, the dude didn’t see a planet in his telescope; he looked at some spectral line jiggling around for 11 years -long enough to collect good statistics on this star, and to take a Fourier transform of the time series of the spectral shifts.

What else is wrong with this picture? Well, it’s a red dwarf star: that’s correct in the picture. So, what happens when you put a red light bulb in your house and draw all the shades? Kind of hard to see green and blue reflected in red light, isn’t it? Really, the whole planet will look pretty damn red, even if it is covered in oxygenated water and green plant life.

What else is wrong with this picture? Well, why are plants green? As it happens, they’re green in part due to the spectral composition of our sunlight, and also because of some accidents of fate which produced chlorophyl. No reason for plants going around a red star to have green leaves, even if you had a white light bulb nearby. In fact, photosynthesis is arguably a blue-light phenomenon … maybe a red dwarf couldn’t support vigorous plant life? Planck’s law and the back of my envelope say there is at least a factor of 10 less blue light coming from a red dwarf (3500K) than from a sol like sun (5500K)

What else? Well, this planet seems to have an enormous atmosphere. In all actuality, we don’t know if it really has one at all, and if it does, it’s likely to be thinner than ours in extent/height, so you really wouldn’t see it extending out by hundreds of miles like in the photo, and the terminator lines separating night from day would be much cleaner.

OK, this is pure science nerdery, like complaining about space ship explosions making noise in a vacuum, but the upshot is: don’t trust stuff in press releases, even in a respectable science like astronomy. Most of what they are telling you is lies. I really hope some way can be found to discover life on other worlds, and I think this kind of science is one of the few modern ones likely to produce interesting results in coming years, but … press releases … they tell lies.


9 Responses

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  1. wburzyns said, on October 3, 2010 at 9:32 am

    I remember reading an interesting article related to the topic: http://www.scientificamerican.com/article.cfm?id=the-color-of-plants-on-other-worlds
    Unfortunately it’s no longer freely available.

  2. jay said, on October 5, 2010 at 2:03 am

    I’ve been seeing a lot of somewhat panicky articles related to NASA in the media as of late. I think the dudes who get the funding are rapidly realizing that it is going to dry up unless they fake some immediate practical use for whatever it is they’re fucking around with at the moment.


    Rather fortunate that they noticed that they had a “problem” right about after the collapse of the Soviet Union, don’t you think? Or maybe I just have an unhealthy dose of apophenia.

    • Scott Locklin said, on October 5, 2010 at 4:32 am

      Wait a minute; you mean it ain’t an outreach program to make the Muslims love us?

      Nasa is an important pork barrel for Southerners, so they’ll probably survive if they make it past November, but … they do need to demonstrate some relevance eventually. No shuttle. No space ships. No Buck Rogers: no bucks.

  3. William O. B'Livion said, on October 8, 2010 at 4:29 pm

    Also the reflections off the other planets or moons, shouldn’t those be considerably more red?

    NASA isn’t (just) pork barrel for Southerners, it’s a jobs program for people with doctorates. There is a **LOT** of NASA money flowing into California and college campii all across the country.

    • Scott Locklin said, on October 8, 2010 at 4:47 pm

      Sharp eyes; probably so.
      Well, NASA was originally conceived of by Johnson as pork for the South (Texas specifically), but it has certainly evolved into welfare for Ph.D.’s. Sort of like the college system in general. Why does that pork barrel continue growing anyway? I mean, it’s nice we’re teaching the world, since we have too many schools for our own citizens … but why should anyone subsidize this?

  4. Chris Laurel said, on December 9, 2010 at 7:42 pm

    The temperature of the star GJ 581 is greater than that of many incandescent light bulbs, and we certainly have no trouble perceiving reflected blue and green lights indoors. In this image, it’s the star more than the planet that is unrealistically colored. The red light bulb appearance is misleading, though I sort of understand the artist’s desire to emphasize that that the star is a red dwarf (I’ve been guilty of such color exaggerations in my own work.)

  5. foxyquant said, on December 30, 2011 at 6:30 pm

    This is by far my favorite post of yours.

    • Scott Locklin said, on December 30, 2011 at 7:35 pm

      Nobody seems to read ’em unless I’m making fun of windbags. This was probably the nerdiest.

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