New Planet-Hunting Method Could Find Earth-Like Alien Worlds
This image shows the faint star WASP-3 (magnitude 10.5 or about 60 times fainter than can be seen with the unaided eye) in the center of the image, made using the 90-cm telescope of the University Observatory Jena. The star is enlarged with better sensitivity and resolution in the inset in the lower left. WASP-3 is at a distance of 700 light years from Earth and is located in the constellation Lyra. North is up, east to the left. The large image is a composite of three images taken using different filters (blue, visual and red) and the small inset only uses a red filter.
Credit: Gracan Maciejewski, Dinko Dimitrov, Ralph Neuhäuser, Andrzej Niedzielski et al.

A new planet-hunting technique that was used to detect an exotic alien world may be sensitive enough to help astronomers search for Earth-sized planets that orbit other stars, according to a new study.

The new approach, called Transit Timing Variation, was developed by a team of European astronomers led by Gracjan Maciejewski of Jena University in Germany.

The technique was used to pinpoint a planet that is 15 times the mass of Earth, located in the star system WASP-3, which is 700 light-years away from the sun in the constellation Lyra.

The method's high degree of sensitivity, however, could also make it a valuable tool for locating small planets with similar masses to Earth, the researchers said.

The results of the study have been accepted for publication in an upcoming issue of the journal Monthly Notices of the Royal Astronomical Society.

What is Transit Timing Variation?

The Transit Timing Variation (TTV) technique was suggested as a viable approach for discovering alien planets ? or exoplanets ? a few years ago. It built on the existing transiting method, which has been employed for years to detect a number of exoplanets, and is widely used by the Kepler and CoRoT space missions that scour the cosmos for Earth-like planets.

Transits occur when a planet passes in front of its parent star, temporarily blocking some of the star's light as seen from Earth. During these transits, astronomers can measure a drop in the host star's light, telling them that a planet has moved in front.

The new method allows astronomers to further identify smaller planets whose own transits might not be enough to significantly dent their star's light output. However, if smaller planets exist in addition to a large planet, the lesser siblings will exert a gravitational tug on the larger planet that changes its orbit, causing deviations in the regular cycle of transits.

The TTV technique compares these deviations with predictions that are made from extensive computer-based calculations. The estimates allow astronomers to infer the preliminary makeup of the planetary system being studied ? including the presence of possible Earth-like planets.

Combing the WASP-3 system

For their study, Maciejewski and his team of researchers used the 35-inch (90-centimeter) diameter telescopes at the University Observatory Jena and the 24-inch (60-centimeter) diameter telescope at the Rohzen National Astronomical Observatory in Bulgaria to study the transits of WASP-3b, a large planet that has a mass 630 times that of Earth.

Their observations led to an unexpected finding.

"We detected periodic variations in the transit timing of WASP-3b," Maciejewski said in a statement. "These variations can be explained by an additional planet in the system, with a mass of 15 Earth-mass (i.e. one Uranus mass) and a period of 3.75 days."

This newly discovered planet was named WASP-3c, and is among the smallest exoplanets found to date. It is also one of the least massive planets known to orbit a star that is more massive than our sun.

Using TTV for future searches

This finding marks the first time that a new extrasolar planet has been discovered using the TTV method.

The detection of the smaller 15 Earth-mass planet makes the WASP-3 system very intriguing, the researchers said.

The new planet's orbit is twice as long as the orbit of the more massive planet. Such a configuration is likely a result of the early evolution of the planetary system.

The TTV method's ability to detect small perturbing planets could help astronomers locate more of these Earth-like exoplanets in the future, the researchers said.

For instance, 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 one minute. This effect is significant enough to be detected with relatively small 1-meter diameter telescopes. Any potential discoveries can then be followed up with larger ground-based instruments.