An international team of scientists led by astronomers based in Warsaw and working within OGLE project has announced a discovery of an extrasolar planetary system, which - after rescaling - resembles our own Solar System. An article on the discovery will appear in tomorrow's issue of Science magazine.
The system, designated OGLE-2006-BLG-109, is situated 4,500 light years away from Earth. It is composed of two massive planets which resemble Jupiter and Saturn, and which revolve around a star similar to our own Sun.
The planets were discovered with the use of gravitational microlensing method. Gravitational microlensing happens when a mass-endowed celestial body (for example a planet or a black hole) transits close to the line-of-sight between a star and the Earth (observer), resulting in a noticeable brightening of the light from the star.
Such events are extremely rare. For example, the frequency of the event measured for the centre of our Galaxy, which is occupied by a great number of objects, does not exceed one event per one million stars. Additional changes in the light curve caused by the presence of planets in the system are even less frequent. The effect caused by a planet lasts from only a couple of hours to 1-5 days in case of the most massive planets.
While monitoring the light from 120 million stars from the vicinity of our galactic centre, OGLE astronomers discovered a new gravitational lens. On 26 March 2006 scientists observed that the brightness of one of the stars increased in a manner characteristic of gravitational microlensing. The object was designated OGLE-2006-BLG-109 (109th lens discovered by OGLE in the year 2006).
However, only two days later, i.e. on 28th March 2006, OGLE software found that the microlens did not 'behave' exactly as predicted by the model. Professor Michal Szymanski who was operating the telescope at that time immediately decided to take additional measurements, since such deviation from the model may be indicative of the existence of a planet in the system. The information was also forwarded to other teams dealing with gravitational microlensing.
A peak of the OGLE-2006-BLG-109 occurred on 5th April 2006. Yet, Subsequent observations demonstrated that the light curve had not behaved typically, prompting the existence of a more complicated planetary system, as opposed to an individual planet.
The collaboration between OGLE and the Americal microFun, New Zealand MOA and the international PLANET/ROBONET teams resulted in a precise coverage of the event with observational points.
Both Dr Scott Gaudi from Ohio State University and Dr David Bennet from the University of Notre Dame (USA) played a key role in the interpretation of this unusual event. The models put forward by the scientists assume the existence of two planets. The first of the planets has a mass equal to 0.71 that of the Jupiter and revolves around the parent star in the distance equal to 2.3 Astronomical Units (AU), while its second sibling has a mass of 0.27 Jupiter mass and orbits the star in the distance of 4.6 AU. After rescaling, the planets correspond to Jupiter and Saturn respectively, while the star is half as massive as our Sun. It is also cooler than our nearest stellar object.
Scientists discover around 600 gravitational lensing events every year within the OGLE project, which positions them as world leaders in this field. The project, based at Warsaw University, uses a dedicated 1.3-metre telescope mounted in Las Campanas in Chile. The undertaking is partially financed by the Ministry of Science and Higher Education, the Foundation for Polish Science, and the Foundation for Polish Astronomy. The OGLE Web Site is available at
ogle.astrouw.edu.pl.
The OGLE team includes: Professor Andrzej Udalski, Professor Marcin Kubiak, Professor Michał Szymanski, Professor Grzegorz Pietrzynski, Dr Igor Soszynski, Dr Lukasz Wyrzykowski, Dr Olaf Szewczyk and Krzysztof Ulaczyk from Warsaw University Astronomical Observatory.
Almost 300 extrasolar planets have been discovered so far, with as many as 13 objects by the OGLE team. Also other Polish astronomers made notable planetary discoveries, namely Aleksander Wolszczan (the first ever extrasolar planets), Maciej Konacki (a planet in a triple star system), Andrzej Niedzielski (a planet around a red giant) or Krzysztof Gozdziewski (who, by means of theoretical calculations, found a fourth planet in a system where other observers had seen only three objects).
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