The discovery of two extrasolar planets orbiting the star HAT-P-13 will allow scientists to use one of them to "x-ray" the other to determine if it's got a rocky core.
Astronomers plan to use a large outer planet, HAT-P-13c, that transits the face of its sun, to probe the internal structure of the smaller HAT-P-13b.
As the two planets pull on each other, they warp each other's orbits. By measuring how eccentric the orbits of the planets are, they can use some fancy, old-school math to determine how much of the interior planet's mass is located at its center. It's like a planetary laboratory 700 light-years away.
"C is allowing us to look inside B," said Greg Loughlin, an astronomer at University of California, Santa Cruz, and co-author of the paper submitted to the journal Astrophysical Journal Letters. "X-raying the planet taps into these esoteric theories that were worked out in the 1930s, but hadn't been picked up by the extrasolar planet community."
The new system, and the technique for analyzing it, reflect a growing trend in exoplanetology towards looking at extrasolar planetary systems, not just individual planets. Just this week, astronomers reported the first tentative sighting of an exomoon. Astronomers are excited about those because although we know 374 exoplanets, all 30 of the planets in the habitable zones around their stars are uninhabitable gas giants. But the moons encircling these planets could, like Jupiter's moon Titan or Saturn's Enceladus, be good candidates for some form of life.
More and better observations of exoplanet-bearing stars combined with creative techniques for analyzing those systems are yielding fascinating new results. Each discovery tells us more about solar systems in general, which lets us understand how our own remote outpost of the Milky Way is special (or not so special).
Even planets that we know relatively well, like WASP-17b and HAT-P-7b, hold surprises. Both planets are actually orbiting against the direction of their stars' spin. Scientists call that retrograde orbit, and the idea that a planet could do it is kind of shocking. Generally, it had been assumed that solar systems were like ours, forming from a single rotating disc of dust and gas, until gravity sorted things into their present configuration.
"Right now, we have an extremely interesting observation to explain," Gaspar Bakos, who studies exoplanets at the Harvard-Smithsonian Center for Astrophysics, said of HAT-P-7b.
Bakos, himself, is responsible for the recent observation of HAT-P-13, and many others. He is one of the next generation of planet hunters that is following up on the work of pioneers like Geoff Marcy of the University of California, Berkeley. They are redesigning the tools of the astronomical trade for a pursuit that's very different from the search for dark matter or the first structures in the universe.
While Marcy used the "wobble" in a star's orbit caused by its orbiting planets, Bakos has been looking for planets that we can see pass in front of their stars. While it's tougher to find these planets because they have to be precisely aligned with us earthlings, researchers can determine a lot about the stars once they've been spotted. Most fundamentally, because Bakos is measuring the dimming of the star's light when the planet crosses its face, they can figure out the surface area of the planet. The bigger the planet, the more dimming that occurs.
He's built a fleet of six small, robotic telescopes, four of which he's deployed in Arizona and two in Hawaii. They were developed based on a telescope concept from Polish astronomer, Greg Pojmanski, and advanced to their current state with the help of three amateur astronomers Bakos met at the Hungarian Amateur Astronomer Association.
The HATNet telescopes — HAT stands for Hungarian-made Automated Telescopes — are about the size of a doghouse and, Bakos said, "would fit in the trunk of a car." (One installation is pictured at the top of this article.)
The doghouse telescopes are a far cry from existing monster telescopes like Keck, or any of the planned extremely large telescopes. Their dimensions and costs are modest.
"To look at and examine many bright stars in the sky, there is a suitable instrument and it's not necessarily big. There was a black period — the medieval ages of the '90s — when they used to shut down everything that was a small telescope, " Bakos said. "They were blinded by the science that big science and big telescopes bring, like detecting a quasar."
The study of exoplanets, in bringing exciting science back from the edges of the universe, is allowing scientists to put a greater variety of tools to use. But it's not just what the telescopes are looking at that's changed. What the robotic HATNet lacks in hardware size, it makes up for with software intelligence.
"You need very intense software work that probably does not differ from that of the big telescopes," he said. "We have a fairly good software pipeline. It's a lot of extraordinary-type work."
And that's exactly what you'd expect in the search for extrasolar planets.
Images: 1. A HATNet telescope being installed at FLWO/Gaspar Bakos. 2. A moonlit night at a HATNet installation/Gaspar Bakos.
See Also:
- Aack, No Brakes! Giant New Exoplanet Goes the Wrong Way
- Kepler Shows Exoplanet Is Unlike Anything in Our Solar System
- Smallest Exoplanet Is Most Earth-like Yet
- Extreme Exoplanet's Wild Ride
- Astronomers Find Hidden Exoplanet in Hubble's Dustbin
- Astronomers Closer to Exoplanet 'Holy Grail'
- Hubble Detects First Organic Molecule Around Exoplanet
- Ground-Based Telescope Measures Exoplanet Atmosphere For First ...
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