The New Blue Planet

KOMPAS.com - Astronomers have discovered the first habitable blue planet orbiting in the habitable zone of a star similar to the Sun.

NASA’s Kepler Mission has been finding new worlds at an incredible rate over the past year but this is the first discovery of what could be a habitable super-earth as it appears to be large, rocky planet with a surface temperature of about 72 degrees Fahrenheit, similar to spring day on Earth.

A team of researchers, including Carnegie Institute's Alan Boss, made the discovery which will be published in The Astrophysical Journal.

The discovery team, led by William Borucki of the NASA Ames Research Center, used photometric data from the NASA Kepler space telescope, which monitors the brightness of 155,000 stars.

Earth-size planets whose orbital planes are aligned such that they periodically pass in front of their stars result in tiny dimmings of their host star’s light, dimmings that can only be measured by a highly specialized space telescope like Kepler.

This discovery is the first detection of a possibly habitable world in orbit around a Sun-like star.
The host star lies about 600 light-years away from us toward the constellations of Lyra and Cygnus.

The star, a G5 star, has a mass and a radius only slightly smaller than that of our Sun. As a result, the host star is about 25 per cent less luminous than the Sun.

The planet orbits the G5 star with an orbital period of 290 days, compared to 365 days for the Earth, at a distance about 15 per cent closer to its star than the Earth from the Sun. This results in the planet’s balmy temperature.

It orbits in the middle of the star’s habitable zone, where liquid water is expected to be able to exist on the surface of the planet. Liquid water is necessary for life as we know it, and this new planet might well be not only habitable, perhaps even inhabited.

Numerous large, massive gas giant planets have been detected previously in habitable-zone orbits around solar-type stars, but gas giants are not thought to be capable of supporting life.

This new exoplanet is the smallest-radius planet discovered in the habitable zone of any star to date. It is about 2.4 times larger than that of the Earth, putting it in the class of exoplanets known as super-Earths.

While the mass of this new planet is not known, it must be less than about 36 times that of the Earth, based on the absence of a measurable Doppler (radial velocity) wobble in the host star.

The masses of several other super-Earths have been measured with the Doppler technique and determined to lie in the range of about 5 to 10 times that of the Earth.

Some appear to be rocky, while others probably contain major fractions of ice and water.  Either way, the new planet appears to be habitable.

'This discovery supports the growing belief that we live in a universe crowded with life,' Boss said. 'Kepler is on the verge of determining the actual abundance of habitable, Earth-like planets in our galaxy'.

Meanwhile scientists have started a systematic 'index' to categorise which planets might be 'habitable' - and so far, we've found 47 planets and moons that might fit the bill.

The Planetary Habitability Laboratory (PHL) of the University of Puerto Rico at Arecibo (UPR Arecibo) judges candidates by where they sit in their solar system, and what type they are. Most of the 700 planets so far detected are no-go zones - but 47 look promising.

Over 700 exoplanets have been detected and confirmed with thousands more still waiting further confirmation by missions such as NASA Kepler.

Most of these are gas giants, similar to Jupiter and Neptune, but orbiting very dangerously close to their stars. Only a few have the right size and orbit to be considered suitable for any life.

'One important outcome of these rankings is the ability to compare exoplanets from best to worst candidates for life,' says Abel Méndez, Director of the PHL and principal investigator of the project.

The catalogue uses new habitability assessments like the Earth Similarity Index (ESI), the Habitable Zones Distance (HZD), the Global Primary Habitability (GPH), classification systems, and comparisons with Earth past and present.

According to Méndez, 'New observations with ground and orbital observatories will discover thousands of exoplanets in the coming years. We expect that the analyses contained in our catalogue will help to identify, organize, and compare the life potential of these discoveries.'

The catalogue lists and categorizes exoplanets discoveries using various classification systems, including tables of planetary and stellar properties.

ne of the classifications divides them into eighteen mass and thermal categories, creating a table similar to a periodic table for exoplanets. Additional resources of the catalogue will include scientific visualizations and stellar maps of exoplanets.

Only two confirmed exoplanets so far match the criteria for habitability in the catalogue, Gliese 581d and HD 85512b - both of which are Earthlike. However, the catalogue identifies over 15 exoplanets and 30 exomoons as potential habitable candidates.

Future observations with new instruments, such as the proposed NASA Terrestrial Planet Finder, will be necessary to confirm the suitability for life of any of these candidates.

'I hope this database will help increase interest in building a big space-based telescope to observe exoplanets directly and look for possible signatures of life,' says Jim Kasting, an expert on planetary habitability science from Penn State.