Giant planets do not come as lonely hearts

Dr Dominik concludes: "While most planetary systems around other stars substantially differ from the Solar system, a series of recent detections have brought us closer and closer to home. Sooner rather than later, someone can be expected to discover an Earth-mass planet orbiting a star other than the Sun - and it could be us."

Prof Horne adds, "Apart from individual spectacular discoveries, the technique of gravitational microlensing allows to infer a census of planets within the Milky Way. Once we know that planets similar to Earth are common, it is straightforward to go ahead on finding them and investigating whether these harbour any forms of life."

Timeline of a global discovery

26 March 2006:

• the OGLE (Optical Gravitational Lens Experiment) team, led by Prof Andrzej Udalski from Warsaw University (Poland), gave notice of the event OGLE-2006-BLG-109 being in progress
  
  

28 March 2006:

• the OGLE team found an unexpected brightening by about 10 per cent, which could have been the signature of a planetary companion to the lens star

• other teams started follow-up observations on OGLE-2006-BLG-109.

  For the UK-based RoboNet microlensing programme, led by Prof Keith Horne at the University of St Andrews, Dr Martin Dominik from the same institution, devised a sampling strategy and passed it on to Dr Martin Burgdorf, the RoboNet project scientist at the Astrophysics Research Institute (ARI) of Liverpool John Moores University (LJMU), who entered the respective observing requests into the scheduler.

5 April 2006:

• OGLE-2006-BLG-109 shows a deviation from the predicted light curve.

• A preliminary model obtained within 12 hours by Dr Scott Gaudi, from Ohio State University, the lead author of the publication and member of the MicroFUN team, indicates a Jovian-class planet and predicts an additional peak on 8 April
  
  

6 April 2006:

• Surprisingly, a further peak was observed, which later turned out to be the signature of OGLE-2006-BLG-109Lb, the more massive planet being closer to the lens star
  
  

8 April 2006:

• The earlier predicted peak occurs, and confirms OGLE-2006-BLG-109Lc with a mass similar to that of Saturn
  
  

Summary of Planet Properties

OGLE-2006-BLG-109Lb OGLE-2006-BLG-109Lc Jupiter Saturn Mass 0.71 Jupiter mass 0.27 Jupiter mass 1 Jupiter mass 0.30 Jupiter mass
Orbital distance from parent star 2.3 AU 4.6 AU 5.2 AU 9.6 AU Orbital period 5 years 14 years 12 Years 30 Years

Where AU = Astronomical Unit, the distance from the Earth to the Sun.