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This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone. CREDIT: ESO/L. Calçada Billions of Habitable Alien Planets Should Exist in Our Galaxyby Clara Moskowitz, SPACE.com Assistant Managing EditorDate: 28 March 2012 Time: 07:00 AM ET There should be billions of habitable, rocky planets around the faint red stars of our Milky Way galaxy, a new study suggests. Though these alien planets are difficult to detect, and only a few have been discovered so far, they should be ubiquitous, scientists say. And some of them could be good candidates to host extraterrestrial life. The findings are based on a survey of 102 stars in a class called red dwarfs, which are fainter, cooler, less massive and longer-lived than the sun, and are thought to make up about 80 percent of the stars in our galaxy. Finding super-Earths Using the HARPS spectrograph on the 3.6-metre telescope at the European Southern Observatory's La Silla Observatory in Chile, astronomers found nine planets slightly larger than Earth over a six-year period. These planets, called super-Earths, weigh between one and 10 times the mass of our own world, and two of the nine were discovered in the habitable zone of their parent star, where temperatures are right for liquid water to exist. Extrapolating from these findings, the researchers estimate that tens of billions of these planets are to be found in the Milky Way, and about 100 should lie in the immediate neighborhood of the sun. [Vote Now! Strangest Alien Planet Finds] "Our new observations with HARPS mean that about 40 percent of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet," team leader Xavier Bonfils of the Observatoire des Sciences de l'Univers de Grenoble in France said in a statement. "Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone." The two stars found inside the habitable zone were discovered around the stars Gliese 581 and Gliese 667 C. The latter planet is the second of three worlds orbiting its star, and seems to lie right in the middle of Gliese 667 C's habitable zone. Although the planet has four times the mass of Earth, it is considered the closest twin to Earth found so far. Search for life This and other planets are good candidates for follow-up studies that aim to analyze the atmospheres of these worlds for signs that organisms are living there. "Now that we know that there are many super-Earths around nearby red dwarfs, we need to identify more of them using both HARPS and future instruments," said team member Xavier Delfosse. "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." However, there are some issues with looking for life around red dwarfs. Since these stars are cooler than the sun, their habitable zones are much closer in than ours. That puts any planets there at risk of being hit with stellar eruptions or flares, which are common on red dwarfs. Such flares could release X-rays or ultraviolet radiation that could harm or inhibit the development of life, scientists say. The new findings will be described in a paper to be published in an upcoming issue of the journal Astronomy & Astrophysics. www.space.com... Originally posted by NewAgeMan Originally posted by NewAgeMan Originally posted by NewAgeMan Just watched this again and burst into tears for reasons that I cannot explain in words. Originally posted by NewAgeMan reply to post by itsJUSTzo There's no reason this planet cannot be funner.. Extrasolar PlanetFrom Wikipedia, the free encyclopedia An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of 763 such planets (in 611 planetary systems and 101 multiple planetary systems) have been identified as of April 14, 2012.[1] Estimates of the frequency of systems strongly suggest that more than 50% of Sun-like stars harbor at least one planet.[2] In a 2012 study, each star of the 100 billion or so in our Milky Way galaxy is estimated to host "on average ... at least 1.6 planets."[3][4] Accordingly, at least 160 billion star-bound planets may exist in the Milky Way Galaxy alone. Unbound free-floating planetary-mass bodies in the Milky Way may number in the trillions with 100,000 objects larger than Pluto for every main-sequence star.[5] For centuries, many philosophers and scientists supposed that extrasolar planets existed. But there was no way of knowing how common they were or how similar they might be to the planets of the Solar System. Various detection claims made starting in the nineteenth century were all eventually rejected by astronomers. The first confirmed detection came in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12.[6] The first confirmed detection of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi. Due to improved observational techniques, the rate of detections has increased rapidly since then.[1] Some exoplanets have been directly imaged by telescopes, but the vast majority have been detected through indirect methods such as radial velocity measurements.[1] Most known exoplanets are giant planets believed to resemble Jupiter or Neptune. That reflects a sampling bias, since massive planets are much easier to observe.[7] Some relatively lightweight exoplanets, only a few times more massive than Earth (now known by the term Super-Earth), are known as well; statistical studies now indicate that they actually outnumber giant planets[8] while recent discoveries have included Earth-sized and smaller planets and a handful that appear to exhibit other Earth-like properties.[9][10][11] There also exist planetary-mass objects that orbit brown dwarfs, and there exist others that "float free" in space not bound to any star, however the term "planet" isn't always applied to these objects. The discovery of extrasolar planets has intensified interest in the possibility of extraterrestrial life.[12] Several discoveries have been made in the habitable zone, a region around stars thought to be life bearing. Planetary habitability is the measure of a planetary body's potential to sustain life and considers a wide range of factors. files.abovetopsecret.com... History of detection Early speculations "This space we declare to be infinite... In it are an infinity of worlds of the same kind as our own." —Giordano Bruno In the sixteenth century the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. He was burned at the stake by the Roman Inquisition in 1600, though his views on astronomy were not the main reason for his condemnation.[14] In the eighteenth century the same possibility was mentioned by Isaac Newton in the "General Scholium" that concludes his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centers of similar systems, they will all be constructed according to a similar design and subject to the dominion of One." Discredited claims en.wikipedia.org... Confirmed discoveries Artists's "cartoon view" gives an impression of how common planets are around the stars in the Milky Way.[23]The first published discovery to receive subsequent confirmation was made in 1988 by the Canadian astronomers Bruce Campbell, G. A. H. Walker, and Stephenson Yang.[24] Although they were cautious about claiming a planetary detection, their radial-velocity observations suggested that a planet orbits the star Gamma Cephei. Partly because the observations were at the very limits of instrumental capabilities at the time, astronomers remained skeptical for several years about this and other similar observations. It was thought some of the apparent planets might instead have been brown dwarfs, objects intermediate in mass between planets and stars. In 1990 additional observations were published that supported the existence of the planet orbiting Gamma Cephei,[25] but subsequent work in 1992 again raised serious doubts.[26] Finally, in 2003, improved techniques allowed the planet's existence to be confirmed.[27] In early 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of two planets orbiting the pulsar PSR 1257+12.[6] This discovery was confirmed, and is generally considered to be the first definitive detection of exoplanets. These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation, or else to be the remaining rocky cores of gas giants that somehow survived the supernova and then decayed into their current orbits. On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting a main-sequence star, namely the nearby G-type star 51 Pegasi.[28] This discovery, made at the Observatoire de Haute-Provence, ushered in the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the rapid detection of many new exoplanets: astronomers could detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. More extrasolar planets were later detected by observing the variation in a star's apparent luminosity as an orbiting planet passed in front of it. Initially, most known exoplanets were massive planets that orbited very close to their parent stars. Astronomers were surprised by these "hot Jupiters," since theories of planetary formation had indicated that giant planets should only form at large distances from stars. But eventually more planets of other sorts were found, and it is now clear that hot Jupiters are a minority of exoplanets. In 1999, Upsilon Andromedae became the first main-sequence star known to have multiple planets.[29] Other multiple planetary systems were found subsequently. As of April 14, 2012, a total of 763 confirmed exoplanets are listed in the Extrasolar Planets Encyclopaedia, including a few that were confirmations of controversial claims from the late 1980s.[1] That count includes 611 planets in planetary systems and 101 planets within multiple planetary systems. A system has been discovered in which a planet orbits around two stars, which orbit around each other.[30] As of February 2012, NASA's Kepler mission had identified 2,321 unconfirmed planetary candidates associated with 1,790 host stars, based on the first sixteen months of data from the space-based telescope.[31] Detection methods Methods of detecting extrasolar planets Planets are extremely faint light sources compared to their parent stars. At visible wavelengths, they usually have less than a millionth of their parent star's brightness. It is difficult to detect such a faint light source, and furthermore the parent star causes a glare that tends to wash it out. It is necessary to block the light from the parent star in order to reduce the glare, while leaving the light from the planet detectable; doing so is a major technical challenge.[32] An infrared image of the HR 8799 system. The central blob is noise left over after light from the star has been largely removed. The three known planets can be seen: HR 8799d (bottom), HR 8799c (upper right), and HR 8799b (upper left). For the above reasons, telescopes have directly imaged no more than about thirty exoplanets as of November 2011. Several approaches have been studied for blocking the light from the parent star. One technique, recently demonstrated by a team of researchers from the Jet Propulsion Laboratory, uses a vector vortex coronagraph. The researchers are hopeful that many new planets may be imaged using this technique.[33][34] Another promising approach is nulling interferometry.[35] All exoplanets that have been directly imaged are both large (more massive than Jupiter) and widely separated from their parent star. Most of them are also very hot, so that they emit intense infrared radiation; the images have then been made at infrared rather than visible wavelengths, to reduce the problem of glare from the parent star. An exception is the exoplanet Fomalhaut b, observed at visible wavelengths by the Hubble Space Telescope. That planet was found to be surprisingly bright in visible light, possibly because it is surrounded by a large disk of reflective material that may be a satellite system in the process of formation. Though direct imaging may become more important in the future, the vast majority of known extrasolar planets have only been detected through indirect methods. The following are the indirect methods that have proven useful: Radial velocity or Doppler method As a planet orbits a star, the star also moves in its own small orbit around the system's center of mass. Variations in the star's radial velocity — that is, the speed with which it moves towards or away from Earth — can be detected from displacements in the star's spectral lines due to the Doppler effect. Extremely small radial-velocity variations can be observed, of 1 m/s or even somewhat less.[36] This has been by far the most productive method of discovering exoplanets. It has the advantage of being applicable to stars with a wide range of characteristics. One of its disadvantages is that it cannot determine a planet's true mass, but can only set a lower limit on that mass. Transit method If a planet crosses (or transits) in front of its parent star's disk, then the observed brightness of the star drops by a small amount. The amount by which the star dims depends on its size and on the size of the planet, among other factors. This has been the second most productive method of detection, though it suffers from a substantial rate of false positives and confirmation from another method is usually considered necessary. The transit method reveals the radius of a planet, and it has the benefit that it sometimes allows a planet's atmosphere to be investigated through spectroscopy. Transit Timing Variation (TTV) When multiple planets are present, each one slightly perturbs the others' orbits. Small variations in the times of transit for one planet can thus indicate the presence of another planet, which itself may or may not transit. For example, variations in the transits of the planet WASP-3b suggest the existence of a second planet in the system, the non-transiting WASP-3c.[37] If multiple transiting planets exist in one system, then this method can be used to confirm their existence.[38] In another form of the method, timing the eclipses in an eclipsing binary star can reveal an outer planet that orbits both stars; as of November 2011, five planets have been found in that way. Gravitational microlensing Microlensing occurs when the gravitational field of a star acts like a lens, magnifying the light of a distant background star. Planets orbiting the lensing star can cause detectable anomalies in the magnification as it varies over time. This method has resulted in only 13 detections as of June 2011, but it has the advantage of being especially sensitive to planets at large separations from their parent stars. Astrometry Astrometry consists of precisely measuring a star's position in the sky and observing the changes in that position over time. The motion of a star due to the gravitational influence of a planet may be observable. Because the motion is so small, however, this method has not yet been very productive. It has produced only a few disputed detections, though it has been successfully used to investigate the properties of planets found in other ways. Pulsar timing A pulsar (the small, ultradense remnant of a star that has exploded as a supernova) emits radio waves extremely regularly as it rotates. If planets orbit the pulsar, they will cause slight anomalies in the timing of its observed radio pulses. The first confirmed discovery of an extrasolar planet was made using this method. But as of 2011, it has not been very productive; five planets have been detected in this way, around three different pulsars. Circumstellar disks Disks of space dust surround many stars, believed to originate from collisions among asteroids and comets. The dust can be detected because it absorbs starlight and re-emits it as infrared radiation. Features in the disks may suggest the presence of planets, though this is not considered a definitive detection method. Most confirmed extrasolar planets have been found using ground-based telescopes. However, many of the methods can work more effectively with space-based telescopes that avoid atmospheric haze and turbulence. COROT (launched December 2006) and Kepler (launched March 2009) are the two currently active space missions dedicated to searching for extrasolar planets. Hubble Space Telescope and MOST have also found or confirmed a few planets. The Gaia mission, to be launched in March 2013, will use astrometry to determine the true masses of 1000 nearby exoplanets. Definition of "Planet" The official definition of "planet" used by the International Astronomical Union (IAU) only covers the Solar System and thus does not apply to exoplanets.[39][40] As of April 2011, the only definitional statement issued by the IAU that pertains to exoplanets is a working definition issued in 2001 and modified in 2003.[41] That definition contains the following criteria: Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our solar system. Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed or where they are located. Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate). Number of Stars with Planets Most of the discovered extrasolar planets lie within 300 light years of the Solar System. Planet-search programs have discovered planets orbiting a substantial fraction of the stars they have looked at. However the overall proportion of stars with planets is uncertain because not all planets can yet be detected. The radial-velocity method and the transit method (which between them are responsible for the vast majority of detections) are most sensitive to large planets in small orbits. Thus many known exoplanets are "hot Jupiters": planets of Jovian mass or larger in very small orbits with periods of only a few days. It is now estimated that 1% to 1.5% of sunlike stars possess such a planet, where "sunlike star" refers to any main-sequence star of spectral classes late-F, G, or early-K without a close stellar companion.[59] It is further estimated that 3% to 4.5% of sunlike stars possess a giant planet with an orbital period of 100 days or less, where "giant planet" means a planet of at least 30 Earth masses.[60] The proportion of stars with smaller or more distant planets is less certain. It is known that small planets (of roughly Earth-like mass or somewhat larger) are more common than giant planets. It also appears that there are more planets in large orbits than in small orbits. Based on this, it is estimated that perhaps 20% of sunlike stars have at least one giant planet while at least 40% may have planets of lower mass.[2][60][61][62] A 2012 study of gravitational microlensing data collected between 2002 and 2007 concludes the proportion of stars with planets is much higher and estimates an average of 1.6 planets orbiting between 0.5–10 AU per star in the Milky Way Galaxy, the authors of this study conclude "that stars are orbited by planets as a rule, rather than the exception."[4] Whatever the proportion of stars with planets, the total number of exoplanets must be very large. Since our own Milky Way Galaxy has at least 200 billion stars, it must also contain tens or hundreds of billions of planets. Characteristics of planet-hosting stars The Morgan-Keenan spectral classification. Most known exoplanets orbit stars roughly similar to the Sun, that is, main-sequence stars of spectral categories F, G, or K. One reason is that planet search programs have tended to concentrate on such stars. But in addition, statistical analysis indicates that lower-mass stars (red dwarfs, of spectral category M) are less likely to have planets massive enough to detect.[60][63] Stars of spectral category A typically rotate very quickly, which makes it very difficult to measure the small Doppler shifts induced by orbiting planets since the spectral lines are very broad. However, this type of massive star eventually evolves into a cooler red giant which rotates more slowly and thus can be measured using the radial velocity method. As of early 2011 about 30 Jupiter class planets have been found around K-giant stars including Pollux, Gamma Cephei and Iota Draconis. Doppler surveys around a wide variety of stars indicate about 1 in 6 stars having twice the mass of the Sun are orbited by one or more Jupiter-sized planets, vs. 1 in 16 for Sun-like stars and only 1 in 50 for class M red dwarfs. On the other hand, microlensing surveys indicate that long-period Neptune-mass planets are found around 1 in 3 M dwarfs. [64] Observations using the Spitzer Space Telescope indicate that extremely massive stars of spectral category O, which are much hotter than our Sun, produce a photo-evaporation effect that inhibits planetary formation.[65] Ordinary stars are composed mainly of the light elements hydrogen and helium. They also contain a small proportion of heavier elements, and this fraction is referred to as a star's metallicity (even if the elements are not metals in the traditional sense, such as iron). Stars of higher metallicity are much more likely to have planets, and the planets they have tend to be more massive than those of lower-metallicity stars.[59] The amount of planets for a star of given metallicity is directly proportional to that metallicity.[64] It has also been shown that stars with planets are more likely to be deficient in lithium.[66] Temperature and composition Comparison of sizes of planets with different compositionsOne can estimate the temperature of an exoplanet based on the intensity of the light it receives from its parent star. For example, the planet OGLE-2005-BLG-390Lb is estimated to have a surface temperature of roughly −220°C (50 K). However, such estimates may be substantially in error because they depend on the planet's usually unknown albedo, and because factors such as the greenhouse effect may introduce unknown complications. A few planets have had their temperature measured by observing the variation in infrared radiation as the planet moves around in its orbit and is eclipsed by its parent star. For example, the planet HD 189733b has been found to have an average temperature of 1205±9 K (932±9°C) on its dayside and 973±33 K (700±33°C) on its nightside.[76] If a planet is detectable by both the radial-velocity and the transit methods, then both its true mass and its radius can be found. The planet's density can then be calculated. Planets with low density are inferred to be composed mainly of hydrogen and helium, while planets of intermediate density are inferred to have water as a major constituent. A planet of high density is believed to be rocky, like Earth and the other terrestrial planets of the Solar System. Spectroscopic measurements can be used to study a transiting planet's atmospheric composition.[77] Water vapor, sodium vapor, methane, and carbon dioxide have been detected in the atmospheres of various exoplanets in this way. The technique might conceivably discover atmospheric characteristics that suggest the presence of life on an exoplanet, but no such discovery has yet been made. Another line of information about exoplanetary atmospheres comes from observations of orbital phase functions. Extrasolar planets have phases similar to the phases of the Moon. By observing the exact variation of brightness with phase, astronomers can calculate particle sizes in the atmospheres of planets. Stellar light is polarized by atmospheric molecules; this could be detected with a polarimeter. So far, one planet has been studied by polarimetry. en.wikipedia.org...
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Novi rezultati istraživanja Europske svemirske promatračnice (ESO) pokazali su da su stjenoviti planeti ne mnogo veći od Zemlje u nastanjivim zonama crvenih zvijezda vrlo uobičajeni te da bi ih mnogo moglo biti čak i u našem neposrednom susjedstvu Međunarodni tim znanstvenika procjenjuje da samo u Mliječnoj stazi postoje deseci milijardi takvih planeta te stotinjak njih na manje od 30 svjetlosnih godina od Zemlje. Ova studija predstavlja prvo izravno mjerenje učestalosti super-Zemalja u orbitama crvenih patuljaka čiji je udio u ukupnom broju zvijezda u našoj galaksiji oko 80 posto. Rezultati se temelje na podacima koje je prikupio spektrograf HARPS Europske svemirske promatračnice (ESO) u Čileu: 'Naša nova promatranja uz pomoć HARPS-a pokazuju da oko 40 posto svih crvenih patuljaka ima super-Zemlje u nastanjivoj zoni u kojoj na površini planeta može postojati tekuća voda', rekao je voditelj tima Xavier Bonfils i pojasnio: 'Budući da su crveni patuljci toliko česti – u Mliječnoj stazi ih ima oko 160 milijardi – možemo zaključiti da samo u našoj galaksiji ima na desetke milijardi nastanjivih planeta.' HARPS-ov je tim tijekom šest godina detaljno proučio 102 crvena patuljka na južnom dijelu neba. U istraživanju je otkriveno ukupno devet super-Zemalja (planeta mase od jedan do 10 puta veće od Zemljine), među kojima i dva u nastanjivim zonama - Gliese 581 i Gliese 667 C. Na temelju rezultata astronomi su utvrdili da je učestalost super-Zemalja u nastanjivim zonama negdje oko 41 posto. Istraživanje je istovremeno pokazalo da su golemi planeti poput Jupitera i Saturna u orbitama crvenih patuljaka rijetki – ima ih manje od 12 posto. Budući da su crveni patuljci prilično česti u našem susjedstvu, procjenjuje se da bi na udaljenosti manjoj od 30 svjetlosnih godina moglo biti stotinjak super-Zemalja. 'Sada kada znamo da u orbitama obližnjih crvenih patuljaka ima mnogo super-Zemalja, uz pomoć HARPS-a i drugih instrumenata trebali bismo ih otkriti više. Neki od njih na svojim će orbitama proći ispred svojih zvijezda, što će otvoriti mogućnost da istražimo njihove atmosfere i potražimo znakove života', rekao je član tima Xavier Delfosse. - Sviđa vam se članak? Preporučite ga prijateljima putem ovih servisa: Pošaljite mailom