Adjective
coming from or existing outside the planet Earth
extra-terrestrial
Humans have long been fascinated by the possibility of extra-terrestrial life. Novels, films, and folk tales have encouraged curiosity and speculation about what might be 'out there' in space.
Verb
to travel around something, such as a planet or moon, in a curved path
orbit
Gliese 581g is part of a string of planets in the Gliese 581 solar system. Two of Gliese 581g's siblings - Gliese 581e and Gliese 581b - orbit too close to their parent star to support any kind of life on them.
Noun
the basic structures that are needed for something to function properly
infrastructure
Gliese 581c skims the near side of the habitable zone, but scientists suggest that it does not have enough of a toehold in this zone to provide a stable infrastructure for organic formations.
wonderment
More recently, scientists have joined in on the collective wonderment after the first discovery by astronomers of a new planet - Gliese 581g - that could almost certainly support extra-terrestrial organisms.
Verb
to give honor or recognition to someone for doing something or for making something happen
credited
Steven Vogt - one of the two astronomers credited with discovering Gliese 581g - has declared that 'the chances of life on this planet are 100 per cent' and that he has 'almost no doubt about it'.
Noun
an area that is different from other areas in a particular way
zone
Roughly the same goes for Gliese 581d, which has a stronger presence in the habitable zone on its far side, but may not be hot enough for liquid water - opinion is not 'completely settled' on this matter.
Noun
an opportunity for something to happen or be successful
prospect
Professor James Kasting suggests that Gliese 581g is 'smack dab in the middle' of the zone which, along with its size and composition, makes it the most exciting and realistic prospect for extra-terrestrial life yet.
harbor
Although we currently know very little about Gliese 581g, a couple of its features strongly indicate that this planet might harbor the existence of organisms.
Verb
to provide what is needed for something or someone to exist, continue, etc.
sustain
Firstly, Gliese 581g is located at almost exactly the right distance from its red dwarf parent star (Gliese 581) in order to sustain liquid water, which is the only known criterion for organic formation.
Verb
to say that (something) is larger or greater than it really is
overstated
The comparisons between the Earth and Gliese 581g should not be overstated, however. Even if Gliese 581g can sustain organisms, it would be a very different place to live.
Noun
the force of attraction that bodies exert on one another as a result of their mass
gravitational pulls
Because Gliese 581 is only 1% as bright as the Sun, it exudes little warmth, and its habitable zone lies much closer. At this distance, planets get locked into strong gravitational pulls that tend to slow their rotation.
Adjective
having the qualities that are right, needed, or appropriate for something
suitable
Planets that orbit too close to or too far away from their stars do not have a suitable climate; this can only be found in a slender strip of solar space around each star known to astronomers as a 'habitable zone'.
Adjective
lasting or continuing without interruption
permanent
Planets become stuck with one side always facing the star, just like the Moon and the Earth. Because of this, it is likely that Gliese 581g has permanent daytime on the side facing the star and permanent shadow on the other.
Verb
to give or form a general idea about the value, size, or cost of something
estimate
Astronomers estimate that average temperatures on Gliese 581g's star side would be about 71°C and average temperatures on the other much chillier: -34°C.
mass
Like the Earth, Gliese 581g is also the right size for organic life. It is about 3.1 to 4.3 times the size of the Earth, and this relatively low mass means it should be made mostly of rock.
uninhabitable
Planets that grow beyond 10 times the size of the Earth tend to become gaseous and uninhabitable, without the solid or liquid infrastructure necessary for organisms.
Noun
the line where the earth or sea seems to meet the sky
horizon
Steven Vogt suggests that Gliese 581g probably has a comfortable area along the midpoint, called the terminator. Any life here would always see the star sitting on the horizon and thus experience eternal sunrise or sunset.
boasting
Even if there is no life on Gliese 581g, its discovery reveals that habitable planets are quite common, with around 10 to 20 per cent of red dwarves and sun-like stars boasting them.
precision
Gliese 581 is one of just nine stars at that particular distance which astronomers have searched with high enough precision to uncover a planet in the habitable zone.
overwhelming
Even at 10%, the high possibility of life is overwhelming. There are at least a few hundred billion stars in our galaxy, which means that around 20 to 40 billion planets have the potential for the development of organisms.
Noun
the group of colors that a ray of light can be separated into
spectrum
The next step in finding out the chances of life on the planet would be to measure its light spectrum, a process that would reveal molecular oxygen if it exists. The glare from Gliese 581 makes this impossible, however.
Noun
a unit of distance equal to the distance that light travels in one year
light years
Another way to gather information would be to transport a vessel to and from the planet. The technology exists to do this, but at 20 light years from the Earth, it would take 200 years for astronomers to receive the result.
platform
Astronomers suggest that many rocky planets are likely to be found in habitable zones during the coming years, and some of these will provide a better platform for research with current instruments.