Astronomers part of the international collaboration Probing Lensing Anomalies NETwork (PLANET) calculated the approximate number of planets based on statistical analyses from multiple surveys gathered from observatories, institutions, and ground-based telescopes, including NASA’s spacecraft Kepler, the European Southern Observatory (ESO), the Niels Bohr Institute, the Optical Gravitational Lensing Experiment (OGLE), and the Microlensing Observations in Astrophysics (MOA).

PLANET has taken 16 years to find planets, and six to make a statistical hypothesis (from 2002 to 2007). It is estimated that there are at least 100 billion stars in the Milky Way and that each one has 1.6 planets in orbit on average, coming to a total of 160 billion hypothetical planets. This number is much, much higher than the number originally predicted.

Astronomers use three methods to search for planets. The first one is called transiting, in which one observes a stars’ level of brightness. If the level slightly drops, the dip acts as a signal that a planet is crossing the star during its orbit. The second method is the radial-velocity method. When planets orbit a star, the star does not remain stationary.

Rather, it moves in a small circular motion, causing the planet’s gravitational pull. Lastly, the third method is gravitational microlensing. In relation to an observer on Earth, two stars, one in front of the other, seem to form a straight line. The foreground star causes light from the background star to curve, thus magnifying the latter. If there is a slight temporary difference in the light curve from the foreground star, a planet is orbiting the star.

With the former two methods, astronomers can only find low-mass planets closely orbiting stars. They are what the Kepler spacecraft uses to hunt for planets. The third one, on the other hand, is more sensitive: astronomers can find planets of all sizes (from Mercury-sized to Jupiter-sized) and those that are near and far from their parent stars. In addition, planets’ masses can be determined.

“Together,” Uffe Gråe Jørgensen states in the Niels Bohr Institute press release, “the three methods are, for the first time, able to say something about how common our own solar system is.” Jørgensen is the head of the Astrophysics and Planetary Science research group at the Niels Bohr Institute at the University of Copenhagen.

Based on the collected data, astronomers predict that Earth-like planets (small and rocky) are much more common in the galaxy than gas giants like Jupiter. According to Stephen Kane – who is a part of NASA’s Exoplanet Science Institute at the California Institute of Technology in Pasadena, California – in the HubbleSite press release, “This is encouraging news for investigations into habitable planets.”

Ultimately, this new hypothesis significantly increases the probability of the existence of extraterrestrial life, even sentient life.

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Working with the Palomar Observatory near San Diego and the W.M. Keck Observatory in Hawaii and using NASA’s spacecraft Kepler, astronomers from the California Institute of Technology have found three teeny, rocky, extrasolar planets (otherwise known as exoplanets, which lie beyond our solar system).

NASA launched Kepler in 2009 to search for Earth-like planets that orbit stars in the habitable zone, a region colloquially called the “Goldilocks Zone”, in which a planet must not be too close or too far from a star, so that its temperature would be just right to be habitable for life. Kepler uses a method called transiting to accomplish its mission: it sees if any stars have slight dips in brightness caused by a planet, which eventually eclipses its parent star sometime during its orbit.

The freshly discovered planetary system’s star is named KOI-961 (KOI is an acronym for Kepler Object in Question). Approximately 130 light-years from the Earth, KOI-961 is a red dwarf – a pipsqueak of a star compared to the Sun, which is six times larger. KOI-961 is similar to a nearby star, Barnard’s Star, which is also a red dwarf. Astronomers used information about Barnard’s Star to determine KOI-961′s characteristics, which were then used to calculate its companion planets’ sizes.

The planets’ names are KOI-961.01, KOI-961.02, and KOI-961.03 and have the radii of 0.78, 0.73, and 0.57 times that of the Earth, respectively. The smallest, KOI-961.03, is about the size of Mars, and the other two are about the size of Venus. All three do not lie in habitable zones; they orbit their parent star too closely, and one year equals two days.

Due to their incredibly close orbits, they are too hot to form liquid, let alone for life to thrive. Temperatures are hundreds of degrees, with the closest, KOI-961.01, having a surface temperature of nearly 1,000 degrees Fahrenheit (500°C).

This planetary system is the tiniest known to astronomers. John Johnson, assistant professor of astronomy at Caltech and co-author of the team’s paper, states in the Caltech press release, “It’s actually more similar to Jupiter and its moons in scale than any other planetary system. The discovery is further proof of the diversity of planetary systems in our galaxy.”

Red dwarfs are the most common type of star in our home galaxy, the Milky Way, making up eight out of every ten stars. Because of their ubiquity, Kepler may find more planetary systems with red dwarfs as parent stars. “That boosts the chances of other life being in the universe – that’s the ultimate result here,” Johnson says.

In the past, Kepler has found numerous gas giants around the sizes of Jupiter and Neptune. Its most recent discoveries occurred in December 2011, when it detected Kepler-22b, the first planet discovered to orbit in the habitable zone, and Kepler-20e and Kepler-20f, the first Earth-sized exoplanets detected.

The more planets Kepler detects nowadays, the more they become smaller and rockier, it seems. Kepler’s last two discoveries increases the probability that there may be more rocky exoplanets than astronomers thought, thereby, boosting the chance of the existence of extraterrestrial life.

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