SUMMARY: one extrasolar planet, or exoplanet, is a planet outside of our solar system that orbits a star other than our Sun.

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Sections:Detection MethodsGeneral nature of known ExoplanetsComparing Exoplanets come Planets in our Solar SystemKepler MissionRelated LinksRelated Lessons:Space travel Guide

Swiss astronomers Michael Mayor and also Didier Queloz discovered the an initial exoplanet in 1995. Due to the fact that then, the number of verified exoplanets has surpassed 200. There space a few different approaches scientists use once trying to detect extrasolar planets.

Detection Methods:Direct Evidence:Images of the planetSpectra that the planetIndirect Evidence:Doppler techniqueTransits

Direct proof of exoplanets is very an overwhelming to obtain. Think about the pictures we have of Pluto as taken indigenous Earth. The finest pictures we have present Pluto together a an extremely small, round blob. It"s hard to take it a good quality picture of something that is so much away. Pluto orbits, ~ above average, about 40 times farther indigenous the sunlight than Earth. That"s nice far. Now think around a world that is 4 million times farther from our sunlight than us are. You can imagine how hard it is for united state to gain a photo of miscellaneous that much away. Not just are they really much away, yet planets room really dim compared to their parent stars for this reason they"re really tough to see. Indirect monitorings (such as the Doppler technique, transits, and eclipses) are much an ext commonly offered when searching for exoplanets.


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The Doppler effect on a star(click come enlarge)

The Doppler technique is a good method for finding out exoplanets. It provides the Doppler impact to analysis the motion and also properties that the star and planet. Both the planet and also the star room orbiting a common facility of mass. This method that the star and the earth gravitationally tempt one another, leading to them to orbit about a point of mass central to both bodies. It is favor trying to perfect balance a large child and a small child on a teeter-totter. If the teeter-totter is rely in the center, the bigger child will certainly be on the ground, however if you move the larger child very close come the center, both children will it is in in perfect balance. If we could rotate the children about each other, both the big child and also the tiny child orbit a common center of mass.

SHOW ME THE MATH:THE DOPPLER EFFECT

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In our solar system, every bodies orbit a common facility of mass, including the Sun, but the sunlight is so big in comparison come the planets, the center of mass actually lies inside the Sun! This renders the sunlight seem come wiggle back and forth, and the spectrum of the sunlight shifts back and forth as well. We find for this spectral transition in other stars to identify if there room one or an ext planets orbiting the star. When the star moves towards us, the light emitted has a much shorter wavelength, so we say that spectrum is blue shifted. Once it is moving away from us, the light has a much longer wavelength, so us say its spectrum is red shifted. When the Doppler technique is most widely offered for detecting extrasolar planets, that is best suited to look for very massive planets orbiting close come their parent star. This is because the parent star will certainly wiggle much more with a big planet nearby, thereby creating a bigger and more easily detectable spectral shift. Most planets discovered about other stars have been very massive and also orbit very close come their parental star.

Another indirect observational tool is referred to as a transit. This is as soon as a earth crosses in former of its parent star, temporarily decreasing the star"s brightness by a small amount. This technique allows scientists to calculate the density and size of the earth with respect come the dimension of the star.

Although these methods give us one idea that size, distance, and also orbital period of the planets, castle can"t really give us any concrete information about the planet. Straight observation is a much better tool 보다 indirect, but since these planets room so much away and essentially hidden from view as result of how little and dim castle are contrasted to their parent stars, direct observation is often impossible.


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Certain qualities are usual in most well-known exoplanets, as well as the stars they are orbiting. Many of the stars that hold planets are main-sequence stars similar in spectral class to our very own Sun. Most known exoplanets are fairly massive. This doesn"t median that Earth-sized exoplanets don"t exist—remember, our detection techniques favor finding huge planets orbiting close to stars. Some also orbit an ext closely 보다 Mercury orbits the Sun. Unequal the virtually circular orbits that the planets in ours solar system, most exoplanets exhibit mostly eccentric orbits. Many of the known exoplanets space gaseous, similar to the huge planets in our solar system, although some of the smaller exoplanets discovered show signs of rockier, terrestrial compositions.

SHOW ME THE MATH:FINDING MASSES OFEXTRASOLAR PLANETS
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Scientists have discovered that most recognized exoplanets share numerous similarities v the jovian planets in our solar system, such together size, density, and also composition. Exoplanets are probably made of hydrogen and also helium gas. Because these planets orbit nearby to your stars, their temperatures are probably much greater than temperature on the jovian planets. If Jupiter orbited as carefully as some of these exoplanets, theoretically it need to actually be larger in radius since Jupiter"s gas would heat up and also expand. Confirming this, we have observed a planet around star HD209458 that looks similar to a puffed up Jupiter. Researchers have called these close-orbiting gaseous planets "hot Jupiters". Warm Jupiters probably have cloud layers, but such high temperatures would average that different facets could condense. It would certainly be far too hot for ammonia, methane and water come condense, choose they execute in Jupiter"s atmosphere. This high temperatures can even enable for clouds do from products we would usually think of as solids on earth (for example, some metals).


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Comparison in between Jupiter and a "hot Jupiter"(click come enlarge)

With the landslide of exoplanet discoveries in the critical decade, scientists have begun to concern the theories us have around the formation of our own solar system. Exactly how is it the the planets in our solar system have such different qualities than the extrasolar planets we have actually found? The nebular theory says that the within planets room rocky due to the fact that rocks and also metals condensation at high temperatures, when the outer planets are mainly gaseous because hydrogen compounds condensation at lower temperatures, therefore farther from the Sun. Hot Jupiters, prefer so numerous of the recognized exoplanets, need to not exist so close to your stars according to our version of formation, so exactly how did castle form? Although it is not well-known for sure, one opportunity is that these hot Jupiters formed farther native their parental star and also migrated inward to a smaller, an ext eccentric orbit.

The expertise of other planetary systems absolutely puts a glitch in our concept of formation, yet it doesn"t necessarily average it"s wrong. Our concept works because that us, however it is simply that: a theory. It is very specific to what us have found through centuries of research, and the century of research study to come will certainly surely readjust the way we perceive our world and also the universe.


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Image the the Milky means in the Cygnus region(click come enlarge)

The majority of extrasolar planets detected thus far are gas giants, prefer the outer planets in ours solar system. Researchers are details that life, together we know it, might not exist on the outer planets in our solar system. The an obstacle now is to find terrestrial exoplanets that might be qualified of maintain life. Scheduled for beginning in 2009, the Kepler Mission is design to search our an ar of the Milky means for smaller, Earth-sized exoplanets in or close to the habitable zone the their parent star. Kepler will stare at a single portion of the sky in the Cygnus region along the Orion arm for its entire mission with hopes of detecting hundreds much more exoplanets.

There are particular conditions crucial to do a planet habitable, and there room a couple of key determinants that influence these conditions. The size and also temperature that the star, as well as the orbit the the planet, largely recognize the condition of having liquid water on the surface. Planets as well close come a star space so hot that any kind of water on the surface ar would cook away, when planets too much from a star room so cold that any type of liquid water freezes. The size and also mass that the planet recognize whether or no it deserve to sustain one atmosphere. Smaller sized planets might not be substantial enough to have the surface ar gravity important to maintain an atmosphere. Various other factors, such as the ingredient of the atmosphere, will influence the temperature the the planet and also the type of security from various forms of harmful radiation.


In bespeak to uncover planets, Kepler will usage the detection an approach known as a transit. A transit is an occasion in i m sorry a world passes in front of a star as checked out from Earth. Contrasted to a bigger planet, transits through terrestrial-sized planets produce a tiny change in the brightness that the star. This adjust in brightness lasts only a few hours, depending upon the distance in between the planet and the star. We know a planet is bring about the adjust in brightness if the change is periodic, which means that it wake up again and also again top top the exact same time period.

The main Kepler instrument is a telescope dubbed a photometer, or irradiate meter, through a very huge field the view. It will certainly stare in ~ the exact same star field for the entire mission and continuously and simultaneously monitor the brightness of much more than 100,000 stars. If Earth-size planets are common, Kepler should detect numerous them.

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Want come know much more about the Kepler mission? You have the right to learn more about the Kepler mission from the official home page.


RELATED LINKSLinks come lists of well-known extrasolar planets:Astrobiology WebCalifornia & Carnegie world SearchJohnston"s Archive: Extrasolar Planets and Brown Dwarfs