Only four days into the New Year and the first four exoplanets of 2012 have been spotted orbiting four distant stars.

All four alien worlds are known as “hot Jupiters” — large gas giant planets orbiting very close to their stars. Their orbits are aligned just right with the Earth so that when they pass in front of their parent stars, they slightly dim the starlight from view.

Only 4 days into 2012 and already 4 new Hot Jupiters: HAT-P-34, HAT-P-35, HAT-P-36, HAT-P-37.

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As exoplanets pass in front of their stars, a small dip in star brightness may be detected. This detection method is known as the “transit method.” This is in addition to the “radial velocity method,” when the gravitational pull of an exoplanet causes its parent star to wobble slightly.*

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However, this most recent discovery doesn’t come from NASA’s Kepler space telescope team or any other space telescope, it comes from a ground-based telescope system maintained by the Harvard-Smithsonian Center for Astrophysics.

The Hungarian-made Automated Telescope Network (HATNet) Project consists of six small (11-cm diameter), wide-field automated telescopes based at the Fred Lawrence Whipple Observatory in Arizona and The Submillimeter Array atop Mauna Kea, Hawaii.

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Follow-up observations were made by Keck Observatory (also on Mauna Kea), the KeplerCam CCD camera (at FLWO) and Faulkes Telescope North at Haleakala Observatory in Hawaii.

The HATNet telescopes were established in 2003, and the system announced their first exoplanet discovery in 2006 (called HAT-P-1b). Now they have another four exoplanets, orbiting four different stars, to add to their growing list.

HAT-P-34b, HAT-P-35b, HAT-P-36b and HAT-P-37b have very tight orbits around their stars, completing a “year” in only 5.5-, 3.6-, 1.3- and 2.8-days respectively. Remember, the Earth orbits the sun every 365 days.

Apart from having breakneck orbital speeds, one of the exoplanets (HAT-P-34b) is notable for having a very elongated — or “eccentric” — orbit. Only four other transiting exoplanets are known to have more eccentric orbits.

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Although many “hot Jupiter” exoplanets are known to exist, this marks the start of a very exciting year of extrasolar planet-hunting.

Not only do we have the Kepler space telescope turning up near-Earth-sized worlds and multi-planetary systems on a regular basis, we also have ground-based telescopes with increasing sophistication tracking exoplanetary transits and wobbling stars.

Publication: “HAT-P-34b — HAT-P-37b: Four Transiting Planets More Massive Than Jupiter Orbiting Moderately Bright Stars,” Bakos et al., 2012. arXiv:1201.0659v1 [astro-ph.EP]

*Exoplanets may also be discovered via direct imaging of stars and microlensing, but the transit and radial velocity methods are the most widely used.

Image credit: NASA, ESA and G. Bacon (STScI)