New planets discovered from old data

By on November 13, 2012

Digging through old data, astrophysicists have found a gold nugget that had previously slipped through the sieves. By simply reanalyzing the old data, scientists discovered three new exoplanets, one of which could potentially support life.

The star HD 40307, 42 light years away in the obscure, southern constellation of Pictor, is a Sun-like star that had been observed by the HARPS instrument at the European Southern Observatory. The HARPS instrument detects planets by measuring the Doppler shifts in the light from the star. As a planet orbits, it tugs the star with it, causing the star to wobble periodically. The wobble introduces minute, yet measurable, shift to the star’s light.

Depication of close orbiting exoplanet being devoured by its star. fotopedia.com

Previous measurements have indicated that three planets orbited the HD 40307, with periods of 4, 9, and 20 Earth days. After updating the data by eliminating possible errors from the HARPS instrument and the development of better analysis software, scientists re-examined the data. After subtracting the signatures of the three known planets, the team found signatures of three more planets, orbiting at 34, 51, and 320 days. Upon further scrutiny, the 320-day signal was corrected down to 200 days.

The first five planets of this crowded system are not of much interest, as they orbit so close to the star that they are quite literally scorched by the blazing heat. The orbital period of the sixth planet, HD 40307 g, however, places it square in the Goldilocks Zone of HD 40307.

The Goldilocks Zone of a star is a range of orbits in which liquid water could exist on the surface of a planet. Liquid water is indispensable to all life as we know it. Too close to the star, and the intense heat evaporates the water; too far, and the water freezes. Since HD 40307 g is in this zone, it just might be able to support life.

The astronomers peg this new planet at an awkward size between a super-Earth and a Neptune. Super-Earths are large, rocky planets several times the mass of the Earth. Neptunes, on the other hand, are much larger, and have no solid surface. A thick atmosphere would surround a high-pressure liquid core. It would be much easier for life to arise on a super-Earth.

Without any further data, however, it would be very hard to determine what exactly HD 40307 is. The scientists note that, since this new planet is so close Earth, we may be able to glean more information into its nature in the near future. If HD 40307 g transits its parent star, we would be able to determine is size and density and possibly its atmospheric composition. Powerful future telescopes may even be able to directly image the planet, searching for telltale signatures of life. With any chance, we may finally begin to settle the age-old question of whether we are alone in the universe.

Tianjiao Zhang
Staff Writer
tzhang@uab.edu

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