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Exoplanets
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Do you see it? That tiny spark, that wee blip of light? It may not look like much, but it is in fact a normal planet orbiting a normal star, 250 trillion kilometers from Earth.
Holy Haleakala.
The picture as a whole needs some splainin’. The star in question is Fomalhaut, a star easily visible to the unaided eye; it’s the brightest star in the constellation of Piscis Austrinus, the 18th brightest in the sky, and only 25 light years away. It’s literally millions of times brighter than the planet, so the Hubble camera uses an occulting bar, a small piece of metal that blocks the brightest part of the star’s image. The blacked-out area in the center of the picture is where Fomalhaut is (also, the star’s image has been digitally subtracted using an image of another star as a template; that further reduces the amount of unwanted light). The radial lines are not real; they are an optical effect of the very bright star. The ring is real; it’s dust leftover from the formation of the star and the planet. In fact, the thinness of the ring was a big factor in assuming a planet was lurking there; the planet’s gravity sculpts the ring, keeping it narrowly confined. Also, the ring is off-center from the star, and a planet in an elliptical orbit would explain that nicely.
The planet itself is just that small dot, almost lost in the noise from the star and the light from the ring. I’ll be honest; had I been analyzing the image, I might have missed it at first. But it’s there, and it’s real. Images taken almost two years apart show that the planet is moving with the star, and is consistent with it orbiting Fomalhaut at a distance of about 18 billion km (11 billion miles). That’s four times the distance of Neptune from the Sun. It takes 872 years to make one complete orbit. The mass is not easy to determine, and is estimated using its effect on the ring; it’s likely to be about the same size and mass as Jupiter.
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This is huge news.
And it gets even huger. Because there’s more:
That image is the first to directly show two planets orbiting another star! It’s a near-infrared image using the giant Gemini North 8 meter telescope. Like in the Hubble image, the star’s light has been blocked, allowing the two planets to be seen (labeled b and c).
The star is called HR 8799. It’s a bit more massive (1.5 times) and more luminous (5x) than the Sun, and lies about 130 light years from Earth. The planets in this picture orbit it at distances of 6 billion km (3.6 billion miles) and 10.5 billion km (6.3 billion miles). A third planet, not seen in this image but discovered later using the Keck 10 meter telescope, orbits the star closer in at a distance of 3.8 billion km (2.3 billion miles).
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How long before we see the Holy Grail, the first image of a terrestrial planet, orbiting a star like the Sun at just the right distance for liquid water to bathe its surface? It may not be for a decade or two, but mark my words: that day will arrive. And when it does, well, we’ll just have to rewrite the history books again, won’t we?
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