The Guardian carried an article today about the Habitable Planets Catalog,a directory which lists those exoplanets and moons that are believed to have the potential to bear life.
Launched on Monday the scientists behind this database that it will help astronomers, and others with an interest, to compare faraway worlds and keep tabs on the most habitable ones as researchers discover them.
More than 700 exoplanets have been spotted and verified outside our own solar system in recent decades (as at 2 December the total is 707), while thousands more await confirmation by missions such as Nasa's Kepler space telescope.
The Habitable Exoplanets Catalogue in essence ranks the habitability of planets and moons according to three criteria: their surface temperature, similarity to Earth, and capacity to sustain organisms at the bottom of the food chain.
"One important outcome of these rankings is the ability to compare exoplanets from best to worst candidates for life," said Abel Méndez, director of the planetary habitability laboratory at the University of Puerto Rico in Arecibo.
Only a small proportion of alien worlds appear ripe for life as we know it. The catalogue suggests that among hundreds of candidates, 15 or more planets and 30 moons are potentially habitable.
The catalogue gives high scores for habitability to two confirmed planets. The first, Gliese 581d, is among several that circle one of Earth's nearest stars, a cool red dwarf around 20 light years away. The planet is about six times as massive as Earth.
The second planet, HD85512b, orbits a star 36 light years away in the constellation Vela. It is more than three times as heavy as our own planet. Most of the planets astronomers have found are gas giants like Jupiter that are in close orbits around their stars.
Astronomers rank the planets by scoring them on three different scales. The first is called the habitable zone distance, which reflects the planet's position in the Goldilocks region of space around a star, where the conditions are neither too hot nor too cold for liquid water to form. Many astrobiologists consider liquid water essential for life to flourish.
The second scale is called the Earth similarity index, which ranks planets according to how closely their mass, radius, temperature and probability of having an atmosphere matches our own planet.
The third scale ranks planets according to their "global primary habitability", which reflects whether the estimated surface temperatures are suitable for life like plants and phytoplankton to grow. Earth scores quite low on this scale, because some basic organisms would fare better at warmer temperatures.
It is less than 20 years since the first exoplanets were discovered. planets were found orbiting a pulsar in 1992. The first star found to have a planet was 51 Pegasi in 1995. It is a new discipline and the tools available are crude. Most of the planets found so far are super giants orbiting their stars and astonishing ly snort distances.
But this will change. Thousands if not millions of planets are going to be found and a fair few will be capable of supporting life. How we can verify this by visiting them is the big question though
Launched on Monday the scientists behind this database that it will help astronomers, and others with an interest, to compare faraway worlds and keep tabs on the most habitable ones as researchers discover them.
More than 700 exoplanets have been spotted and verified outside our own solar system in recent decades (as at 2 December the total is 707), while thousands more await confirmation by missions such as Nasa's Kepler space telescope.
The Habitable Exoplanets Catalogue in essence ranks the habitability of planets and moons according to three criteria: their surface temperature, similarity to Earth, and capacity to sustain organisms at the bottom of the food chain.
"One important outcome of these rankings is the ability to compare exoplanets from best to worst candidates for life," said Abel Méndez, director of the planetary habitability laboratory at the University of Puerto Rico in Arecibo.
Only a small proportion of alien worlds appear ripe for life as we know it. The catalogue suggests that among hundreds of candidates, 15 or more planets and 30 moons are potentially habitable.
The catalogue gives high scores for habitability to two confirmed planets. The first, Gliese 581d, is among several that circle one of Earth's nearest stars, a cool red dwarf around 20 light years away. The planet is about six times as massive as Earth.
The second planet, HD85512b, orbits a star 36 light years away in the constellation Vela. It is more than three times as heavy as our own planet. Most of the planets astronomers have found are gas giants like Jupiter that are in close orbits around their stars.
Astronomers rank the planets by scoring them on three different scales. The first is called the habitable zone distance, which reflects the planet's position in the Goldilocks region of space around a star, where the conditions are neither too hot nor too cold for liquid water to form. Many astrobiologists consider liquid water essential for life to flourish.
The second scale is called the Earth similarity index, which ranks planets according to how closely their mass, radius, temperature and probability of having an atmosphere matches our own planet.
The third scale ranks planets according to their "global primary habitability", which reflects whether the estimated surface temperatures are suitable for life like plants and phytoplankton to grow. Earth scores quite low on this scale, because some basic organisms would fare better at warmer temperatures.
It is less than 20 years since the first exoplanets were discovered. planets were found orbiting a pulsar in 1992. The first star found to have a planet was 51 Pegasi in 1995. It is a new discipline and the tools available are crude. Most of the planets found so far are super giants orbiting their stars and astonishing ly snort distances.
But this will change. Thousands if not millions of planets are going to be found and a fair few will be capable of supporting life. How we can verify this by visiting them is the big question though
