Spot the planet

FOR AS long as humans have looked at the night sky we have speculated on the possibility that other planets harbour intelligent life. Now that we are capable of sophisticated scientific probing of the universe, the search for such planets is on in earnest. Nasa launched the Kepler telescope in March 2009 to search for potential life-supporting Earth-sized planets around other stars (kepler.nasa.gov).

The Kepler telescope orbits the sun in an Earth-trailing orbit so that its view of the stars is not blocked periodically by the Earth, moon or sun. The telescope looks fixedly at a star field in our region of the Milky Way in an effort to detect associated planets that are one-half to twice the size of Earth, particularly planets that orbit their stars in the “habitable zone”, where liquid water could exist and where life as we know it might reside.

The Kepler telescope is a special 0.95m-diameter light-meter called a photometer. It has a very large field of view (105 sq degrees) for an astronomical telescope – most telescopes have a field of view of less than one sq degree. Kepler needs to be this big in order to look at a large number of stars simultaneously. It will stare at the same star field for the duration of its entire mission (at least 3.5 years), monitoring the brightness of more than 100,000 stars.

Kepler will use the transit method to detect planets. When a planet passes (“transits”) in front of its star, it prevents a small fraction of light from reaching Kepler. Transits by Earth-sized planets will dim a planet’s detected brightness by one part in 10,000, over a period of two to 16 hours. For a signal to be attributed to a planet, it must be absolutely periodic, it must cause the same change in brightness each time and last the same length of time. In order to achieve reliability, four observations must be made. The time between transits for habitable-zone planets will be about one year and so the mission must last at least 3.5 years in order to make four transit measurements.

The Kepler telescope is fantastically sensitive. Detection of the transit of an Earth-sized planet is a feat equivalent to detecting the dimming effect of a fly crawling across a car headlamp on full beam when observed from a distance of many kilometres. In order to achieve this power and precision, the telescope must be based in space. Earth-based observations would be degraded by atmospheric perturbations, the effects of day and night cycles, and so on. Once detected, the planet’s size can be determined from the extent of the brightness change. The size of the planet’s orbit and its temperature can be determined from the time between transits. This data will tell whether or not life is possible on the planet. Assuming that planets are common around stars such as our sun, Nasa expects that Kepler will detect about 50 Earth-sized planets.

Science takes the possibility of life elsewhere in the universe very seriously. It would be surprising if microbiological life-forms did not exist elsewhere, and we may yet discover them in our own solar system, on Mars, Europa or Titan. But the really exciting prospect is that intelligent self-conscious aliens live elsewhere in the universe and that, some day, we will contact them. The possibility of intelligent alien life has important philosophical and theological implications.

This time around the Vatican, mindful of the Galileo affair and public perceptions about Giordano Bruno, is not going to be caught napping. The church held a five-day conference in Rome in early November to hear scientific experts discussing the possibility of extraterrestrial life and to ponder its implications for the church. In an article in the official Vatican newspaper entitled “Aliens are my brother”, Fr Gabriel Funes, director of the Vatican Observatory, said that the existence of extraterrestrial life does not contradict belief in God. Some witty reporters entitled their covering pieces “ET phone Rome”.

Incidentally, the Catholic Church is often accused of burning Giordano Bruno (1548-1600) at the stake because he taught that the universe is teeming with planets that harbour alien intelligent life. But, according to the Catholic Encyclopaedia, this was not the charge on which Bruno was convicted by the Inquisition. He was convicted for preaching theological errors, such as denying the divinity of Jesus, claiming that the Devil can be saved, and more. Now, don't get me wrong. I am not defending the burning of the unfortunate Bruno, just trying to present an accurate record. Burning for either reason would be equally wrong and horrible.

William Reville is associate professor of biochemistry and public awareness of science officer at University College Cork