On February 2, a team of astronomers detected an exoplanet (short for extrasolar planet) located in the habitable zone, a slim area in which a planet must be located, so that it is not too close nor too far away from the star it orbits, thus having a surface temperature that can sustain liquid. This newly discovered exoplanet may be able to sustain water and even life.

Using data from the European Southern Observatory, the W.M. Keck Observatory in Hawaii, and the Carnegie Planet Finder Spectograph at the Magellan II Telescope in Chile, the astronomers – from the University of California in Santa Cruz and the private research organization Carnegie Institution for Science in Washington, DC – found the exoplanet through discerning the gravitational tug it and its parent star impose on each other. The system lies 22 light-years away in the constellation Scorpius.

“This is basically our next-door neighbor,” Steven Vogt tells Space.com. Vogt, one of the members of the team, is an astronomer at the University of California. “It’s very nearby. There are only about 100 stars closer to us than this one.”

“We’ve been explicitly focusing on very nearby stars,” he adds, “because with today’s technology, we could send a robotic probe out there, and within a few hundred years, it could be sending back picture postcards.”

The star, dubbed GJ 667C, is a part of a triple star system. Unlike its companion stars, which are orange K dwarfs, GJ 667C is an M-class dwarf: it is much smaller and less luminous than the Sun and emits infrared light, which is less intense in light and temperature. GJ 667C’s composition is very different from that of the Sun’s, lacking elements heavier than hydrogen and helium such as carbon, iron, and silicon that are needed to form planets.

“We shouldn’t have really expected this star to be a likely case for harboring planets,” says Vogt.

The exoplanet, named GJ 667Cc, is a super-Earth, roughly 4.5 times the size of the Earth. Because of the absence of heavy elements, much of GJ 667Cc’s mass comes from ice and gas. The orbital period of GJ 667Cc measures 28 days, which would seem dauntingly close to us compared to the Earth’s orbital period.

A planet that takes the same amount of time to orbit the Sun (for instance) would roast; however, GJ 667C’s weak temperature and light, and the fact that GJ 667Cc receives 10 percent of the light the Earth receives from the Sun, counterbalance the closeness of the exoplanet, creating a comfortable region in which to dwell.

Furthermore, GJ 667Cc is in the right spot to absorb the same amount of energy that the Earth absorbs from the Sun to have an atmosphere. In the Carnegie Institution for Science press release, Guillem Anglada-Escudé – co-leader of the study and lead writer of the team’s paper that will soon be published in The Astrophysical Journal Letters – states, “This planet is the new best candidate to support liquid water and, perhaps, life as we know it.”

GJ 667Cc has a sibling, GJ 667Cb, which is around the size of the Earth. Unlike GJ 667Cc, GJ 667Cb has a much smaller orbital period. Hence, it is too close and has too high a temperature to sustain liquid.

Only one other exoplanet located in the habitable zone has been discovered before, Kepler-22b, which was detected by the NASA spacecraft Kepler on December 5, 2011. Astronomers believe that Kepler-22b, which is 2.4 times the Earth’s size, may also maintain water and life.

Image Courtesy of  http://www.esa.int

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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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Earlier this week, the spacecraft, Kepler, discovered two exoplanets around the size of the earth – the first of their kind – orbiting a sun-like star. Named Kepler-20e and Kepler-20f, these exoplanets are a part of the star system, Kepler-20, which lies 950 light years away from Earth near the constellation, Lyra.

“This discovery demonstrates for the first time that Earth-size planets exist around other stars and that we are able to detect them,” says Dr. Francois Fressin, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Launched in 2009, Kepler is a space telescope built and sent by NASA to detect Earth-like exoplanets (also known as extrasolar planets, which are planets that exist outside our solar system) orbiting stars in habitable zones. Its most recent, significant discovery occurred in early December, when it detected the Neptune-sized Kepler-22b, the first of its kind that has been seen orbiting in the “Goldilocks zone” and that might possibly have water and life.

Kepler took a step closer in accomplishing its mission when it detected Kepler-20, Kepler-20e, and Kepler-20f. Kepler-20 is similar to the sun, in that it is a G-type star. It is yellowish, though a bit smaller and cooler. The star contains five planets in total, all of which orbit it closer than Mercury orbits the sun. The three other planets are gas giants, which are about the size of Neptune, and each planet orbits alternating in size.

These newly discovered exoplanets are only Earth-like in their sizes and rocky composition. Kepler-20e orbits its star every 6.1 days, and its temperature is 1400° F. Its diameter, 6900 miles, is 0.87 times the diameter of the Earth’s. Kepler-20f has an orbit of 19.6 days. It has the temperature of 800° F, and it is 1.03 times Earth’s diameter, being 8,200 miles.

Because of their close orbits and high temperatures, these two exoplanets are not able to sustain water, let alone life. For them to have water and life, they have to lie in the “Goldilocks zone,” or the habitable zone, in which a planet cannot be too close or too far (hence, too hot or too cold) from the star it orbits.

Ever since its launch in 2009, Kepler has been detecting hundreds of exoplanets, many of which are not Earth-like, being hostile and sometimes lonely, not orbiting any stars. With its most recent detection of Kepler-22b and of Kepler-20′s two Earth-like planets, Kepler has reached a new landmark, not just in its journey, but in our knowledge of the various kinds of planets that exist in the observable universe.

“This could be an important milestone,” Dr. Fressin states. “I think 10 years, or maybe even 100 years, from now people will look back and ask when was the first Earth-sized planet found. It is very exciting.”

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