Humans are closer to finding an Earth-like inhabitable planet
According
to a new study, discovery of multi-planet systems is much more likely
than ever, hinting that one or more planets in those systems can be like
Earth
Jojo Puthuparampil
Astronomers
have always been intrigued by exoplanets (planets outside the solar
system) as they possibly offer a clue to finding an Earth-like planet in
the outer space that supports life. According to a new study, published
in Astrophysical Journal, humans are one step closer to finding an
‘inhabitable’ planet within the solar system. The study, based on data
from NASA’s Kepler spacecraft which envisions to discover Earth-like
planets orbiting other stars, says discovery of multi-planet systems is
much more likely than ever, hinting that one or more planets in those
systems can be like Earth.
The
spacecraft, named in honour of the 17th-century German astronomer
Johannes Kepler, has since its inception in March 2009 identified 1,235
planetary candidates in 997 host star systems. Of these candidates, 759
are confirmed exoplanets, including 54 that may be in the habitable
zone, the region around a star where liquid water, and thus life, can
exist. For instance, one of the newly discovered worlds, dubbed HD
85512b, lies at the edge of its star's habitable zone. According to the
study co-author Elisabeth Adams, an astronomer at the
Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge,
Massachusetts, of the 997 planetary systems, 170 have multiple planet
candidates, implying the chance of one or a few of them being
Earth-like, possibly with life-supporting elements like water.
Kepler
looks for Earth-size planets around Sun-like stars. It has an inbuilt
photometer that continually monitors the brightness of over 145,000 main
sequence stars which are known for longevity and stability. With the
help of this photometer, it spots potential alien worlds by staring at a
patch of sky and watching for dips in starlight caused by objects
transiting their stars, as seen from Earth. For instance, if a planet’s
orbital period is 10 days, it will pass in front of the parent star
every 10 days, resulting in a dip in the light emanating from the star.
This data is transmitted to Earth, then analysed to detect periodic
dimming caused by extrasolar planets that cross in front of their host
stars.
But
simply seeing a transit isn't enough to prove a planet is involved.
Some other phenomenon, such as a smaller star passing in front of its
much larger neighbour, could be causing the main star to dim
periodically. Therefore, astronomers rely on other methods such as
‘radial velocity’ and ‘transit timing variation’ to confirm that the
spotted body is indeed a planet. In the study, Adams and colleagues ran a
statistical analysis and found that, if a star system has multiple
planet candidates, the confirmation step can be skipped, as most planet
candidates in multi-planet systems are likely to be ‘real’ planets.
Discovery
of multi-planet systems also helps astronomers look at multiple worlds
that were born together to get a better understanding of planetary
transformations and hence deeper insights into Earth’s formative years
after the Big Bang.
Scientists
are enthused by Kepler’s recent discovery of Kepler-22b, a planet about
2.4 times the radius of Earth, in the habitable zone of its star. They
do not yet know if it has a rocky, gaseous or liquid composition, but
they feel its discovery is a step closer to finding Earth-like planets.
Kepler has also found two other planets with higher atmospheric
densities, suggesting they have atmospheres of mostly water, and
therefore conducive for life to sprout. Spotting water in any of the
Earth-like planets is the biggest leg-up astronomers are expecting in
their search of life elsewhere.
The
findings of Kepler are supplemented by data from High Accuracy Radial
Velocity Planet Searcher (HARPS) at the European Southern Observatory's
La Silla facility in Chile. HARPS recently found 50 new alien worlds,
including 16 ‘super Earths’. Astronomers use Doppler wobble technique
which involves searching for wobbles in a star's light that indicate the
gravitational pull of an orbiting planet. The method helps them find
massive planets that orbit close to their host stars. In 2007, HARPS
discovered a super-Earth, called Gliese 581d, that is believed to be
lying within the habitable zone of its star.
Scientists
plan to upgrade HARPS hardware and software and use the instrument to
conduct a more refined search of nearby Sun-like stars for rocky
Earth-like planets that could support life. They are encouraged by the
fact that there has been a significant increase in the number of rocky
exoplanets discovered by space missions, including Kepler and HARPS.
They expect that in 10 to 20 years, humans should have the first list of
potentially habitable planets in the Sun's neighborhood, according to
another study by Michel Mayor, an astronomer at the University of Geneva
in Switzerland. One of those would-be-discovered planets, they hope,
may splash chemical signs of life—such as oxygen—in their atmospheres,
helping unicellular organisms to evolve.
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