Habitable planets may orbit billions of stars in the Milky Way, a study suggests.
...while we may not see all the planets, wherever we look in the sky, they are there
Astronomers came to the conclusion after a six-year star survey which argues that planets are commonplace in our galaxy.
Scientists estimate as many as 10 billion stars in the Milky Way may host planets in the “habitable”, or “Goldilocks”, zone.
This is the orbital band within which conditions are not too cold and not too hot but “just right” to allow surface liquid water and, potentially, life.
The discovery raises the possibility of a universe teeming with life, as depicted in popular sci-fi movies and TV series such as Star Wars and Star Trek.
However, scientists stress that just because a planet has conditions suitable for life it does not follow that life has evolved there.
Over the past 16 years, astronomers have made more than 700 confirmed detections of “exoplanets” orbiting distant stars.
The vast majority have been Jupiter-like gas giants or scalding hot planets hugging close to their stars. Both offer little hope of finding life.
In those cases astronomers relied on spotting tiny “wobbles” in the host star caused by a planet’s gravitational pull, or the minute dimming of starlight as a planet crossed in front of its star.
Both techniques are not suited to finding small rocky planets like the Earth in the habitable zone.
The new survey employed a radically different method called “gravitational microlensing”.
This involves a foreground star’s gravity acting like a “magnifying glass” to bend and amplify light from a background star.
If there is a planet orbiting the foreground star, a small extra “bump” might be seen in the light signal.
However, very special conditions are needed to detect planets by gravitational microlensing.
The background and foreground stars have to be lined up, and an additional chance alignment of the planet’s orbit is also needed.
Despite these obstacles, analysis of six years’ worth of microlensing data from telescopes around the world uncovered an unexpected number of exoplanets.
Dr Martin Dominik, who led a British team from the University of St Andrews involved in the research, said: “We do not know yet where all the planets are.”
“We also do not know how big, small, dense or fluffy they are, or whether they are home to life or not, but our latest results tell us that while we may not see all the planets, wherever we look in the sky, they are there.”