[ENGLISH VERSION]
SOURCE/LINK: http://astronomynow.com/2015/07/23/new-kepler-planet-could-be-earths-closest-cousin-yet/
New Kepler planet could be Earth’s closest cousin
yet
An artist’s impression of what Kepler-452b
might look like. Image: NASA Ames/JPL–Caltecg/T Pyle.
A super-earth
discovered by NASA’s Kepler Space Telescope and orbiting an older version of
our Sun, is tantalising astronomers as potentially being the closest thing to a
world like Earth.
“Kepler-452b is
the first small planet [we have found] in the habitable zone of a star like our
own Sun,” says Jon Jenkins, Kepler’s lead data analysis scientist at NASA’s
Ames Research Center.
The
newly-discovered exoplanet orbits its star, which is 1,400 light years away,
every 385 days, meaning that its year is only 20 days longer than our own. This
orbital period places it at only five percent further from its star than Earth
is from the Sun, slap bang in the middle of its star’s habitable zone, where
temperatures should be suitable for liquid water to exist, on the condition
that an atmosphere is present around the planet.
This size and scale of the Kepler-452 system
compared alongside the Kepler-186 system and the solar system. Image:
NASA/JPL-CalTech/R. Hurt.
Interestingly,
Kepler-452b provides a look into the future of our own Earth. Its star is a
‘G2-type’ star, which is nearly identical to our own Sun, but because it is 1.5
billion years older, there are a couple of critical differences. As stars age
they grow hotter and brighter and, in 1.5 billion years, our Sun will have
grown so hot that it will instigate a runaway greenhouse effect in Earth’s
atmosphere, evaporating the oceans and rendering our planet an inhospitable
desert. If Kepler-452b is rocky and has oceans, it could be in danger of being
about to enter this runaway greenhouse stage.
“It’s maybe
good that this planet is a bit further from its star than we are,” says
Jenkins. The extra distance – it orbits 157.1 million kilometres from its star,
compared to Earth’s 149.6 million kilometres – will reduce the heat it
receives, perhaps staving off the runaway greenhouse stage for another 500
million years.
Unfortunately,
there are two caveats to this story. The first is that we have no way of
knowing for sure what Kepler-452b is like. Its mass is an estimated five times
the mass of Earth, which would make Kepler-452b a ‘super-earth’, but we have no
example of a super-earth in our Solar System and geologists are still
struggling to model what their interiors are like. For example, would such a
world contain too much internal heat for plate tectonics to occur, which are
vital for the carbon-silicate cycle that helps regulate the ice ages, warm
periods and long-term climate in general on Earth? The Kepler team consulted
with planetary geologist Bill Moore of Hampton University who, based on
geological models, predicted that Kepler-452b could be covered with copious
volcanism. At this stage, however, this is just an educated guess. Even
confirming its mass from observations of the Doppler shift its gravity incurs
in its parent star is impossible with current technology because the star is
too faint.
Similarly, we
have no way of knowing yet if Kepler-452b has an atmosphere or water. Future
missions that could study exoplanet atmospheres, such as the James Webb Space
Telescope and the Ariel mission (http://ariel-spacemission.eu), which is under consideration by the
European Space Agency, will look to make Kepler-452b a priority target.
The other
problem is the true nature of Kepler-452b. “There’s a better than even chance
that Kepler-452b is rocky,” says Jenkins, but not all planetary scientists
agree. Some suspect that, when a planet’s mass is over one and a half times the
diameter of Earth, it is more likely to be a gaseous, water-rich ‘mini-neptune’
(see the pre-print of a new paper by Leslie Rogers of the California Institute
of Technology that describes this hypothesis http://arxiv.org/abs/1407.4457). Again, follow-up observations with the
next generation of planet-studying telescopes will be required to determine
whether this is the case.
Kepler-452b is
just one of more than 500 potential new planets just announced by the Kepler
team to add to the 4,175 planetary candidates already found by the
planet-hunting space telescope.
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[PORTUGUESE VERSION]
Nasa dá
detalhes de exoplaneta que pode abrigar a raça humana
·
·
·
Montagem compara o planeta Terra (esquerda) e seu Sol com o novo
exoplaneta
A Nasa divulgou nesta quinta-feira (23) detalhes do exoplaneta “gêmeo” da Terra. Segundo a agência espacial dos Estados Unidos, o “primo distante”, que é 60% maior que o nosso planeta, realmente teria condições de abrigar a raça humana.
“Devem existir todos os ingredientes e as condições necessárias para a vida existir nesse planeta. É inspirador considerar que ele já vive há 6 bilhões de anos na área habitável de uma estrela, mais do que a própria Terra”, afirmou Jon Jonkins, responsável pelo projeto que captou o exoplaneta.
O exoplaneta em questão é o Kepler-452b, que está no sistema solar da Kepler-452. Essa estrela, aliás, é extremamente semelhante ao nosso Sol. Tem a mesma temperatura, é 20% mais brilhante e tem um diâmetro 10% maior.
O satélite Kepler, responsável pela descoberta, ainda mapeou outros 11 candidatos a planetas que estão em zonas habitáveis. No total, o equipamento já encontrou nada menos do que 521 exoplanetas desde que foi lançado.
