Using data from NASA's Kepler spacecraft on its K2 mission, an international team of astronomers has confirmed a treasure trove of new worlds with over 100 exoplanets, some of which may harbor life.
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Among the findings tallying 197 initial planet candidates, scientists have confirmed 104 planets outside our solar system. Among these is a planetary system comprising four promising planets that could be rocky.
The planets, all between 20 and 50 per cent larger than Earth by diameter, are orbiting the M dwarf star K2-72, ere found 181 light years away in the direction of the Aquarius constellation.
The host star is less than half the size of the Sun and less bright.
The planets' orbital periods range from five and a half to 24 days, and two of them may experience irradiation levels from their star comparable to those on Earth.
"The K2 mission allows us to increase the number of small, red stars by a factor of 20, significantly increasing the number of astronomical 'movie stars' that make the best systems for further study," said lead author Ian Crossfield from University of Arizona's Lunar and Planetary Laboratory.
Despite their tight orbits -- closer than Mercury's orbit around the Sun -- the possibility that life could arise on a planet around such a star cannot be ruled out, he added in a paper published in the Astrophysical Journal Supplement Series.
Both Kepler and its K2 mission discover new planets by measuring the subtle dip in a star's brightness caused by a planet passing in front of its star.
In the spacecraft's extended mission in 2013, it lost its ability to precisely stare at its original target area, but a brilliant fix created a second life for the telescope that is proving scientifically fruitful.
After the fix, Kepler started its K2 mission which has provided an ecliptic field of view with greater opportunities for Earth-based observatories in both the northern and southern hemispheres.
These observations represent a natural stepping stone from the K2 mission to NASA's other upcoming exoplanet missions such as the Transiting Exoplanet Survey Satellite and James Webb Space Telescope.
"This bountiful list of validated exoplanets from the K2 mission highlights the fact that the targeted examination of bright stars and nearby stars along the ecliptic is providing many interesting new planets," added Steve Howell, project scientist for the K2 mission at NASA's Ames Research Center in Moffett Field, California.
About the Kepler K2 Mission
Like its predecessor, K2 searches for planetary transits – the tiny, telltale dip in the brightness of a star as a planet crosses in front – and for the first time caught the rubble from a destroyed exoplanet transiting across the remains of a dead star known as a white dwarf. Exoplanets have long been thought to orbit these remnant stars, but not until K2 has the theory been confirmed.
K2 has fixed its gaze on regions of the sky with densely packed clusters of stars which has revealed the first transiting exoplanet in such an area, popularly known as the Hyades star cluster. Clusters are exciting places to find exoplanets because stars in a cluster all form around the same time, giving them all the same "born-on" date. This helps scientists understand the evolution of planetary systems.
Seventy days worth of solar system observations from K2 are highlighted in this sped-up movie. Neptune, in a dance with its moons, demonstrates the solar system in action. Neptune appears on day 15, followed by its moon Triton, which looks small and faint. Keen-eyed observers can also spot Neptune's tiny moon Nereid at day 24.
The repurposed spacecraft boasts discoveries beyond the realm of exoplanets. Mature stars – about the age of our sun and older – largely populated the original single Kepler field of view. In contrast, many K2 fields see stars still in the process of forming. In these early days, planets also are assembled and by looking at the timescales of star formation, scientists gain insight into how our own planet formed.
Studies of one star-forming region, called Upper Scorpius, compared the size of young stars observed by K2 with computational models. The result demonstrated fundamental imperfections in the models. While the reason for these discrepancies is still under debate, it likely shows that magnetic fields in stars do not arise as researchers expect.
Looking in the ecliptic – the orbital path traveled around the sun by the planets of our solar system and the location of the zodiac – K2 also is well equipped to observe small bodies within our own solar system such as comets, asteroids, dwarf planets, ice giants and moons. Last year, for instance, K2 observed Neptune in a dance with its two moons, Triton and Nereid. This was followed by observations of Pluto and Uranus.
“K2 can’t help but observe the dynamics of our planetary system, " said Barclay. "We all know that planets follow laws of motion but with K2 we can see it happen.”
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These initial accomplishments have come in the first year and a half since K2 began in May 2014, and have been carried off without a hitch. The spacecraft continues to perform nominally.