The entrance to Stardome Planetarium and Observatory in Auckland photographed on 28 April 2012. Image and copyright Nick Lomb ©, all rights reserved
Last weekend, 28-29 April 2012, I attended the annual meeting of the Australasian Planetarium Society at Auckland Stardome Planetarium and Observatory in New Zealand. The agenda for the meeting included the showing of many exciting planetarium shows and two talks to which members of the Auckland Astronomical Society (AAS) were also invited. One was a talk by me on the forthcoming transit of Venus and the other was by Dr Grant Christie of Stardome and the president of the AAS on the detection of exoplanets, that is, planets around distant stars.
Here I report on Dr Christie’s fascinating talk that was held in the very comfortable surroundings of the planetarium dome. Of course, any errors in the report are my own and possibly due to those comfortable surroundings.
Astronomers, like almost everyone, else are curious to know if there is life elsewhere in the Universe. Judging by our own situation on Earth, good places to search are on planets around stars other than the Sun. The first step in this quest is to find those planets. Since the mid 1990s many exoplanets have been discovered, initially by looking for a small wobble in the motion of stars due to planets circling around them. More recently, the Kepler spacecraft has been finding numerous candidate planets with the transit method, which is looking for the slight dimming due to a planet moving in front of a star.
There is, however, a third method involving gravitational microlensing, which is particularly useful in finding planets in the Goldilocks or habitable zone, that is, at a distance from its parent star that is neither too hot or too cold for water to exist in liquid form. Liquid water is likely a necessity for life.
Any star can act like a lens increasing the brightness of another star that happens to pass behind it. Such events are, of course, so rare that calculations suggest that the probability of it happening for any star is one in a million. In spite of this low probability, astronomers are finding hundreds of such events a year by monitoring areas near the centre of the galaxy where many millions of stars are bunched together.
If the lensing star is a single star it forms is a symmetrical lens so that it appears to brighten and then fade smoothly. If, however, the lensing star has an orbiting planet there are distortions in the shape of the lens and in the brightness curve as the source star passes behind. Auckland Observatory is part of an international collaboration called MicroFun – Micro Lensing Follow-Up Network – that picks out microlensing events that could be suitable for detecting a planet and then arranges for intensive 24-hour coverage through the various observatories that are part of the network.
The research telescope at Auckland Stardome is a Meade 40-cm telescope. Stardome also has another, larger telescope for public use. Image and copyright Nick Lomb ©, all rights reserved
Auckland Observatory uses a Meade 40-cm telescope on a solid Paramount mount. Once the observatory receives a request it uses the telescope on every available clear night to continually take images of the target star. At the end of each night of observing the images are sent to Ohio State University, the headquarters of MicroFun, where the images are processed to yield brightness measurements, merged with data from other observatories and the brightness curve is put together.
MicroFun has now detected a number of planets including one in April 2005 with a mass three times that of Jupiter and soon afterwards another with a mass similar to Neptune. This is cutting edge science and it is highly admirable for a small institution like Auckland Stardome, with its relatively small telescope, to have a major involvement.