In 2007, two super-Earths known as Gliese 667 C and Gliese 581d were discovered orbiting red dwarfs in the habitable zone, an area in which a planet is able to have surface temperature in order to liquid water. Recently, results from a study suggest these planets plus smaller, rocky ones are quite common in our galaxy and orbit red dwarfs by the tens of billions.

The study was conducted by an international team of scientists a part of the HARPS (High Accuracy Radial velocity Planet Search), ESO’s (European Southern Observatory) planet finder. HARPS’s mission is to detect planets beyond the solar system. HARPS especially aims to discover planets that are in the habitable zone.

In order to calculate the largest amount of Earth-like planets that could exist in the Milky Way, HARPS studied the most common type of star in the galaxy: red dwarfs. Red dwarfs are small, cool, and faint in luminosity in comparison to the Sun. Because they spend less energy than other types of stars, they are long-lived and, therefore, are the most common. Approximately 160 billion exist in the galaxy alone, making up a whopping 80% of the total number of stars.

Using a spectrograph from a 3.6-meter telescope from La Silla Observatory in Chile, HARPS chose a sample of 102 red dwarfs from the southern portion of the sky and studied them for six days. HARPS detected nine super-Earths (planets up to ten times the size of the Earth), two of which were inside the habitable zone. Furthermore, 40% of red dwarfs contain super-Earths that are able to sustain water on their surfaces.

Combining their data and the number of stars without planets, and an estimate of how many planets could be discovered, HARPS was then able to calculate the total number of planets orbiting red dwarfs and the different types of these planets. In the end, their results illustrated that tens of billions of smaller rocky planets exist in the Milky Way.

100 of these hypothesized planets should exist in the immediate vicinity – around 30 light-years – of the Sun (smaller planets are difficult to detect). Massive gassy planets (around the size of Jupiter and Saturn), on the other hand, were calculated to be rare when it came to orbiting red dwarfs.

Although it is exciting knowing that so many Earth-sized orbit stars in the habitable zone, astronomers are not getting their hopes up of finding life. It would be difficult for life to thrive on planets that orbit red dwarfs: because red dwarfs are cool, the habitable zone is rather close, leaving any planets close to the red dwarf to be bombarded with flares of ultraviolet rays and X-rays, making the planets not habitable after all. But that does not daunt astronomers of thinking that any of these small worlds could harbor life.

“Now that we know that there are many super-Earths around nearby red dwarfs,” Xaiver Delfosse, a member of the team tells ESO, “we need to identify more of them using both HARPS and future instruments. Some of these planets are expected to pass in front of their parent star as they orbit — this will open up the exciting possibility of studying the planet’s atmosphere and searching for signs of life.”

A detailed report of HARPS experiment and results can be found here.

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On February 27, the team of astronomers involved with NASA’s spacecraft Kepler published their most recent catalog of exoplanets (short for extrasolar planets, which are planets beyond our solar system) that Kepler has detected.

Data from the newest catalog is cumulative and includes information from the two catalogues created in June 2010 and February 2011. As of now, the total number of exoplanets Kepler has detected is 2,321, which orbit 1,790 stars. A full 93% are smaller than Neptune, the smallest of the gas giants in the solar system. Over 200 are Earth-sized and more than 900 are smaller than twice the size of the Earth’s diameter. There are 46 exoplanets located in the habitable zone, 10 of which are Earth-sized.

“With each new catalog release a clear progression toward smaller planets at longer orbital periods is emerging,” Natalie Batalha, Kepler deputy science team lead at San Jose State University in California, states in NASA’s press release. “This suggests that Earth-size planets in the habitable zone are forthcoming if, indeed, such planets are abundant.”

Furthermore, the percent for more than one planet orbiting a star has increased to 20 percent from last year’s 17 percent (many other planets are rogue, unattached to a parent star, twirling alone in space). More and detailed statistics can be found here.

Three methods can be utilized to find exoplanets: gravitational lensing, radial-velocity, and transiting. Kepler largely uses the latter method, using the software Transiting Planet Search (TPS) pipeline module, because it has proven to produce more results compared to the former two. Transiting works as thus: one measures a star’s periodic drop in brightness due to an object – in the most hopeful scenario, a planet – passing in front of the star.

Sifting through 150,000 stars, Kepler detected around 5,000 transit signals, through which the spacecraft had more to sort. One can easily misidentify an object to be an exoplanet when using the transiting method; one may instead find a binary star system, which contains two stars that orbit and eclipse one another. To confirm its detection of a planet, Kepler has to record the transit at least three times.

Kepler was launched in mid-2009 to find Earth-like exoplanets that are able to sustain water and life. These planets would have to be located in the habitable zone, an area in which a planet must orbit a star in order for liquid water to exist on its surface. Kepler goes about attempting to detect exoplanets by looking at their parent stars first, largely searching for G-type stars, or Sun-like stars (or at least stars a part of the Main Sequence), which astronomers believe to be ideal parent stars.

For much of the time Kepler began exploring, it mostly detected gas giants tens of times larger than Jupiter. As the spacecraft endured, it began, recently, to find numerous smaller rocky planets. Soon after, astronomers working with Kepler have calculated that there are more of these kinds of planets than there are gas giants.

Kepler’s latest milestone includes Kepler-20e and Kepler-20f, which were detected this January and are the first Earth-sized planets known to exist. Another milestone occurred in December 2011, when Kepler discovered super-Earth Kepler-22b, the first known exoplanet in the habitable zone.

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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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This week, the National Aeronautics and Space Administration’s (NASA) spacecraft, Kepler, detected eleven planetary systems, which, overall, contain 26 new exoplanets (short for extrasolar planets, which exist beyond out solar system). Located in the Lyra and Cygnus constellations, each system contains two to five planets. The systems have been dubbed Kepler-23, Kepler-24, Kepler-25, Kepler-26, Kepler-27, Kepler-28, Kepler-29, Kepler-30, Kepler-31, Kepler-32, and Kepler-33.

The sizes of the exoplanets range from 1.5 to 5 times the size of Earth to larger than Jupiter. All of them orbit their parent stars closely; none of them lie in the habitable zone, an area in which a planet is not too close or too far away from a star so that it can sustain water and life. Each of their orbits is closer than that of Venus. The farthest exoplanet has years that last fewer than 200 days and the surface temperature of hundreds of degrees.

Kepler primarily detects planets through a process known as transiting, in which it measures a star’s periodic change in brightness generated by a planet crossing its parent star, causing the star’s light to drop a bit in brightness.

The NASA spacecraft was able to find these newer exoplanets by means of measuring Transit Timing Variations (TTVs). With this method, Kepler calculates changes in the acceleration of planets due to the gravitational pull on one another from being so close together. TTVs help Kepler find the more distant – hence fainter – star systems.

“Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky,” said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington, in the press release on NASA’s Kepler website.

“Now,” Hudgins continues, “in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits.”

Kepler has been in space for nearly three years. Its mission is to search for Earth-like exoplanets that orbit stars in the habitable zone. Ever since its launch in March 2009, Kepler has made numerous momentous findings, especially in the last couple of months.

On December 5, the spacecraft detected Kepler-22b, the first planet to be found in a habitable zone, and on December 20, it discovered the first two Earth-sized exoplanets, Kepler-20e and Kepler-20f. Kepler’s most recent significant detection occurred earlier this month: exoplanets KOI-961.01, KOI-961.02, and KOI-961.03, the tiniest exoplanets thus far.

Based on the diversity of the types of exoplanets, astronomers believe they will attain a better understanding of how planets form.

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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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