The exoplanet waltz

For the first time astronomers have found a multi-planet system orbiting another star using gravitational microlensing, today's Science reports. The international team - which includes Oxford physicist Alison Crocker - observed two stars: making use of the effect that the nearer star's gravity bent the light of the more distant one, magnifying it. Using 11 telescopes they watched for a week as the merged images of the stars brightened and dimmed. From the light curve charting these changes in brightness they were able to detect the influence of the two planets. The planetary partners they found are like  'scaled down' versions of our own Jupiter and Saturn (approximately 70 per cent and 27 per cent of the mass of Jupiter respectively) and could not have been detected using standard techniques. Alison's involvement in the project came about in an unusual way: 'I was observing at the MDM observatory on Kitt Peak when I got a telephone call around four in the morning asking whether I would be willing to observe this microlensing event,' she said. At the time she was an undergraduate at Dartmouth College USA: 'I didn't feel qualified to make this decision myself, so I woke up my supervisor, Brian Chaboyer, to check if it would be okay to stop our observations and look at the microlensing event. We were able to observe the event that morning and one additional morning, contributing some of the light blue points to the light curve.' The finding suggests that many more multi-planet systems are out there, waiting to be discovered using the new technique. Alison describes her role in the work as 'very minor' but said that she's thrilled to be part of such an important discovery. At Oxford she is now back to her original research interest; studying star formation in galaxies.