Common kitchen atom found in air of distant planet
If a picture is worth a thousand words, a smidgen of light can be worth even more to an astronomer. Such a smidgen, which the reader can partially duplicate by some kitchen chemistry, recently revealed something interesting about a planet circling a star in the constellation Pegasus.
Without a star to light them, planets are dark. We can see Jupiter and Saturn this evening only because they are lit by the sun. From a distance, a planet orbiting another star is thousands of times dimmer than the star itself and impossible to see with our present telescopes.
Each of the 80 or so extra-solar planets discovered so far has been found by the way it makes its central star wobble through space, like a beach ball with a wad of gum stuck to one side.
By luck, the star system HD 209458 is oriented edge-on to our line of sight. Every 31/2 days, HD 209458 suffers an eclipse by a large planet that circles it. As the planet comes between the star and the Earth, the star’s light dims just a bit.
And one particular color, a hue of yellow-orange, dims a bit more than the rest.
Careering through a neon light at thousands of miles per second, electrons plow into atoms of neon, “exciting” other electrons within the atoms. Excited electrons are energized electrons, and they jump outward. A moment later, the electrons “relax” and jump back down – not any old way, but by a very specific amount. They make a “quantum jump.” The size of the jump corresponds to a specific (“quantized”) amount of energy, which the electron emits as a specific color of light.
Different atoms emit different colors (neon, for instance, an orangey-red). Astronomers use such spectra as atomic “fingerprints” to identify what the stars are made of.
If you hit the right note as you speak, you can make a piano string “sing.” Your voice puts energy into the air, making it vibrate; the string absorbs some of that energy and vibrates “sympathetically.” If you could measure it, you’d find your voice wasn’t quite as loud as it had been; its energy has been reduced by the amount absorbed by the piano string.
When starlight passes through a planetary atmosphere, atoms in the air pull energy from it. The energy they pull out is of the same amount – the same color – that they emit when they become excited then relax.
Sprinkle a bit of table salt – sodium chloride – into the dark blue flame of a kitchen range. The flame emits the yellow-orange signature of sodium.
Using the Hubble Space Telescope, David Charbonneau of CalTech examined the spectrum of HD 209458 in eclipse. He and his colleagues found the light to be dimmed a bit more in just that signature hue of yellow-orange. They discovered atoms of sodium floating in the planet’s atmosphere.
Earth’s atmosphere is anomalous. The huge amount of oxygen it contains should, by rights, quickly combine with the rocks and disappear. Oxygen remains in our atmosphere only because our planet is alive: Green plants and microorganisms continually replace the oxygen that’s used up. Using the same techniques that were used to detect sodium, we should be able, in the not-too-distant future, to search for other planets whose atmospheres are, like Earth’s, out of balance. If we find one, we may conclude that we have also found extraterrestrial life.
Trained as a biologist, Alan Stahler is also an amateur astronomer. He teaches biology and geology at Bitney Springs Charter High School. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).
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