RAS: New Planet-Hunting Technique

[bystander]

Prospects for finding new Earths boosted by new planet-hunting technique
Royal Astronomical Society | 08 July 2010

A team of astronomers from Germany, Bulgaria and Poland have used a completely new technique to find an exotic extrasolar planet. The same approach is sensitive enough to find planets as small as the Earth in orbit around other stars. The group, led by Dr Gracjan Maciejewski of Jena University in Germany, used Transit Timing Variation to detect a planet with 15 times the mass of the Earth in the system WASP-3, 700 light years from the Sun in the constellation of Lyra. They publish their work in the journal Monthly Notices of the Royal Astronomical Society.

Transit Timing Variation (TTV) was suggested as a new technique for discovering planets a few years ago. Transits take place where a planet moves in front of the star it orbits, temporarily blocking some of the light from the star. So far this method has been used to detect a number of planets and is being deployed by the Kepler and Corot space missions in its search for planets similar to the Earth.

If a (typically large) planet is found, then the gravity of additional smaller planets will tug on the larger object, causing deviations in the regular cycle of transits. The TTV technique compares the deviations with predictions made by extensive computer-based calculations, allowing astronomers to deduce the makeup of the planetary system.
...
This is the first time that a new extra-solar planet has been discovered using this method. The new TTV approach is an indirect detection technique, like the previously successful transit method.
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The TTV method is very attractive, because it is particularly sensitive to small perturbing planets, even down to the mass of the Earth. For example, an Earth-mass planet will pull on a typical gas giant planet orbiting close to its star and cause deviations in the timing of the larger objects’ transits of up to 1 minute.

This is a big enough effect to be detected with relatively small 1-m diameter telescopes and discoveries can be followed up with larger instruments.

Transit timing variation in exoplanet WASP-3b

• lanl.arXiv.org > astro-ph > arXiv:1006.1348 > 07 June 2010
  Monthly Notices of the Royal Astronomical Society, in press

[bystander]

Perturbing Discovery: Does an Exoplanet's Orbital Oddity Reveal a Neighboring World?
Scientific American | 13 July 2010

Subtle changes in the observed orbit of a massive planet 700 light-years away may point to the gravitational influence of another object

Astronomers are uncovering newfound planets in orbit around other stars at a meteoric rate these days. The tally of known planets outside the solar system now stands at more than 450, of which about 50 have been discovered just this year. That pace promises to increase as NASA's Kepler mission carries out its multiyear survey of a large patch of stars; the campaign has already located several hundred planetary candidates for follow-up study and confirmation.

At the same time that missions such as Kepler are hard at work using proved detection methods, researchers are looking to expand the exoplanetary tool kit by demonstrating new ways of locating distant worlds. One method that has been discussed for years but has yet to bear fruit is known as transit timing—if a planet passes in front of its host star so that it blocks out a small but detectable fraction of the star's light, researchers can time the arrival of that partial eclipse, known as a planetary transit. An ordinary, unperturbed orbit will bring the planet around at regular intervals, but the presence of an additional unseen planet can disrupt an exoplanet's orbit, leading to slight variations in the timing of its transit.

In a new study a team of researchers in Germany, Poland and Bulgaria has used transit timing of a known massive exoplanet to identify a hypothetical, much smaller companion. If the hypothetical planet could be confirmed—by no means a sure thing—it would be the first exoplanet to be located by variations in transit timing. The paper, which is available at the online preprint repository arXiv.org, has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

... some researchers in the field remain unconvinced by the new research. "Unfortunately, my opinion is basically that it is another candidate that will need confirming rather than a solid result that you can hang your hat on," says Jacob Bean, an astronomer at the Harvard–Smithsonian Center for Astrophysics. Estimating the errors inherent in the kind of measurements used by Maciejewski and his co-authors is a tough thing to do, Bean says; if the actual errors in the data were larger than the researchers had accounted for, the variations in the observed transit times could vanish. And even if the accounting is solid, he adds, a 15-Earth-mass planet may not be the cause of the orbital disruption. "They don't have nearly enough data points to identify a unique solution," he says. "So it could be a planet like the one they propose, but I suspect there are other possible solutions as well."

One of the early proposers of using transit timing to discover new worlds remains similarly skeptical. "I'm not too hopeful that this is a planet," says astronomer Eric Agol of the University of Washington in Seattle. Given that transit timing is an unproved method for discovering exoplanets, Agol would like to see a signal-to-noise ratio much higher than that found by the European group as well as confirmation by another observational technique. "Maybe more data will turn something up—maybe I'm wrong," Agol says. "Mainly, this is a study that calls for more study."

[The Code]

July 13, 2010 | 1 comments
Perturbing Discovery: Does an Exoplanet's Orbital Oddity Reveal a Neighboring World?
Subtle changes in the observed orbit of a massive planet 700 light-years away may point to the gravitational influence of another object.

http://www.scientificamerican.com/artic ... wasp-3-ttv

tc