Many of the planets discovered elsewhere in our galaxy are not like Earth , but rather more like Jupiter . Such gas giants , as far as we know , are not hospitable to life , but now it has been suggested that the moons of these planets could be habitable . If confirmed , it would suggest these locations could be the predominant sources for life in the universe , not worlds like our own Earth . The idea was discussed by Dr Sarah Ballard of the University of Washington in Seattle , on the Public Radio International 's ( PRI ) show The Takeaway . Scroll down for audio . Dr Sarah Ballard of the University of Washington was speaking to PRI . She said exomoons could be the 'predominant sites of life in the universe ' . Shown is an illustration of Upsilon Andromedae d , the large world in the distance , orbiting the gas giant in the foreground , which could have habitable moons . She explained how Jupiter-sized planets in the habitable zones of stars - where conditions are ideal for water , and perhaps life - are more common than single rocky worlds like Earth . Hot exomoons . Too close to a star and an exomoon may have an average temperature above the boiling point of water , making it highly unsuitable for any form of life . Habitable exomoons . Exoplanets orbiting in a system ’ s habitable zone ( where liquid water can persist on a planet ’ s surface ) still need sufficient gravity to trap an atmosphere that regulates their temperature . If these conditions are met , however , the prospects for life are promising . Snowball exomoons . Moons formed in the outer reaches of an alien solar system are likely to be dominated by ice . They will remain deep-frozen unless heated by tides from their parent planet - again these are unlikely to be habitats for life . Transient exomoons . Moons of planets with elliptical orbits might be habitable for most of their planet ’ s year , but can experience hot or snowball periods as they venture too close to their star , or too far from its life-giving heat . Source : All About Space magazine . ‘ If even some of these Jupiter-sized planets have moons , they might be the predominant sites of life in the universe , ’ she said . In particular , she focused on the world of Upsilon Andromedae d , a gas giant exoplanet about 10 times the mass of Jupiter , located 44 light-years from Earth . While the planet itself is not thought to be habitable , it is possible that a moon in its orbit - known as an exomoon - could be . And if you were to step on the surface of the moon , you would see ‘ beautiful tumultuous clouds on the Jovian planet ’ and ‘ incredibly complex cloud activity , ’ according to Dr Ballard . So far , no exomoons have been discovered , but given that six of the eight planets in our solar system have moons , most astronomers regard it as an inevitability rather than a possibility that one will be found . It might be possible to find one in data collected by Nasa ’ s Kepler space telescope , or it may be necessary to wait for a more powerful planet-hunter to come online , such as the Transiting Exoplanet Survey Satellite ( Tess ) , due to launch in 2017 . Finding exomoons is a bit of a problem though , as their mass and size is so much less than their host planet . One technique to find them that may prove successful is gravitational microlensing , which uses a foreground star to magnify a more distant one . The chance alignment can reveal exoplanets around a star , and could possibly even be used to spot a moon in orbit . So far , no exomoon has been discovered , but given that six of the eight planets in our solar system have moons , most astronomers regard it as an inevitability rather than a possibility that one will be found . It might be possible to find one in data collected by Nasa ’ s Kepler space telescope ( illustration shown ) And we are able to rule certain planets out - ones that are too close to their host star , like Mercury and Venus in our own solar system , are unable to cling on to natural satellites . But finding out if moons are common in our galaxy will be key for the search for life , and could signal a change in goals for planet-hunters in the near future . ‘ The fact we reside on a single rocky hunk of rock , orbiting without a big brother planet , might be relatively unusual , ’ added Dr Ballard . One technique to find moons could be gravitational microlensing , which uses a foreground star to magnify a more distant one , as shown in this diagram . The chance alignment can reveal exoplanets around a star , and could possibly even be used to spot a moon in orbit .
Dr Sarah Ballard of PRI was speaking to the University of Washington . She said exomoons could be the 'predominant sites of life in the universe ' Many planets discovered outside the solar system are Jupiter-sized worlds . It suggests habitable Earth-like planets may not be that common . Instead , moons orbiting larger planets could be the best bet for life .