Feb 16, 2017. Key to the radial velocity method is how it takes advantage of Newton's third law: While a planet is influenced by the gravity of its parent star, it also exerts a proportionate and reciprocal pull on the star, causing it to “wobble” just a tiny little bit. Modern telescopes and sophisticated software can detect the tiny. An exoplanet is a planet that orbits a star other than our Sun (there are also free-floating planets that aren't orbiting a host star). This is a relatively new field of research in astronomy and is particularly exciting for its input to the search for extraterrestrial life. As of April 1, 2017, there have been 3607.

Any is an extremely faint light source compared to its parent. For example, a star like the is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons, very few of the reported as of April 2014 have been observed directly, with even fewer being resolved from their host star. Instead, have generally had to resort to indirect methods to detect extrasolar planets.

As of 2016, several different indirect methods have yielded success. A simulated of (and 3 of its moons) transiting our Sun, as seen from another star system While the radial velocity method provides information about a planet's mass, the method can determine the planet's radius. If a planet crosses () in front of its parent star's disk, then the observed visual brightness of the star drops by a small amount; depending on the relative sizes of the star and the planet.

For example, in the case of, the star dims by 1.7%. However, most transit signals are considerably smaller; for example, an Earth-size planet transiting a Sun-like star produces a dimming of only 80 parts per million (0.008 percent). This method has two major disadvantages. First, planetary transits are observable only when the planet's orbit happens to be perfectly aligned from the astronomers' vantage point. The probability of a planetary orbital plane being directly on the line-of-sight to a star is the ratio of the diameter of the star to the diameter of the orbit (in small stars, the radius of the planet is also an important factor). About 10% of planets with small orbits have such an alignment, and the fraction decreases for planets with larger orbits.

For a planet orbiting a Sun-sized star at 1, the probability of a random alignment producing a transit is 0.47%. Therefore, the method cannot guarantee that any particular star is not a host to planets. However, by scanning large areas of the sky containing thousands or even hundreds of thousands of stars at once, transit surveys can find more extrasolar planets than the radial-velocity method.

Several surveys have taken that approach, such as the ground-based,,, and and the space-based and missions. The transit method has also the advantage of detecting planets around stars that are located a few thousand light years away. The most distant planets detected by are located near the galactic center.

However, reliable follow-up observations of these stars are nearly impossible with current technology. The second disadvantage of this method is a high rate of false detections. A 2012 study found that the rate of false positives for transits observed by the could be as high as 40% in single-planet systems. For this reason, a star with a single transit detection requires additional confirmation, typically from the radial-velocity method or orbital brightness modulation method. Radial velocity method is especially necessary for Jupiter-sized or larger planets as objects of that size encompass not only planets, but also brown dwarfs and even small stars. As false positive rate is very low in stars with two or more planet candidates, they often can be validated without extensive follow-up observations.

Some can also be confirmed through the transit timing variation method. Branch stars have another issue for detecting planets around them: while planets around these stars are much more likely to transit due to the larger size, these transit signals are hard to separate from the main star's brightness light curve as red giants have frequent pulsations in brightness with a period of few hours to days. This is especially notable with.

In addition, these stars are much more luminous and transiting planets block much smaller percentage of light coming from these stars. In the contrary, planets can completely occult a neutron star or a white dwarf which would be easily detectable from Earth.

However, due to their small sizes, chance of a planet aligning such a stellar remnant is extremely small. Properties (mass and radius) of planets discovered using the transit method, compared with the distribution, n (light gray bar chart), of minimum masses of transiting and non-transiting exoplanets. The main advantage of the transit method is that the size of the planet can be determined from the lightcurve. When combined with the radial-velocity method (which determines the planet's mass) one can determine the density of the planet, and hence learn something about the planet's physical structure.

The planets that have been studied by both methods are by far the best-characterized of all known exoplanets. The transit method also makes it possible to study the atmosphere of the transiting planet. When the planet transits the star, light from the star passes through the upper atmosphere of the planet. By studying the high-resolution stellar spectrum carefully, one can detect elements present in the planet's atmosphere.

A planetary atmosphere (and planet for that matter) could also be detected by measuring the polarisation of the starlight as it passed through or is reflected off the planet's atmosphere. Additionally, the secondary eclipse (when the planet is blocked by its star) allows direct measurement of the planet's radiation and helps to constrain the planet's eccentricity without the presence of other planets. If the star's intensity during the secondary eclipse is subtracted from its intensity before or after, only the signal caused by the planet remains. It is then possible to measure the planet's temperature and even to detect possible signs of cloud formations on it. In March 2005, two groups of scientists carried out measurements using this technique with the. The two teams, from the, led by, and the, led by L. Deming, studied the planets and respectively.

The measurements revealed the planets' temperatures: 1,060 (790°) for TrES-1 and about 1,130 K (860 °C) for HD 209458b. In addition the hot Neptune enters secondary eclipse. However some transiting planets orbit such that they do not enter secondary eclipse relative to Earth; is over 90% likely to be one of the latter. A mission,, began in 2006, to search for planetary transits from orbit, where the absence of atmospheric allows improved accuracy. This mission was designed to be able to detect planets 'a few times to several times larger than Earth' and performed 'better than expected', with two exoplanet discoveries (both 'hot jupiter' type) as of early 2008.

In June 2013, CoRoT's exoplanet count was 32 with several still to be confirmed. The satellite unexpectedly stopped transmitting data in November 2012, (after its mission had twice been extended) and is currently being decommissioned with final shut-off scheduled for spring 2014. In March 2009, mission was launched to scan a large number of stars in the constellation with a measurement precision expected to detect and characterize Earth-sized planets. The NASA uses the transit method to scan a hundred thousand stars in the constellation Cygnus for planets. It was hoped that by the end of its mission of 3.5 years, the satellite would have collected enough data to reveal planets even smaller than Earth.

By scanning a hundred thousand stars simultaneously, it was not only able to detect Earth-sized planets, it was able to collect statistics on the numbers of such planets around Sun-like stars. On 2 February 2011, the Kepler team released a list of 1,235 extrasolar planet candidates, including 54 that may be in the. On 5 December 2011, the Kepler team announced that they had discovered 2,326 planetary candidates, of which 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. Compared to the February 2011 figures, the number of Earth-size and super-Earth-size planets increased by 200% and 140% respectively. Moreover, 48 planet candidates were found in the habitable zones of surveyed stars, marking a decrease from the February figure; this was due to the more stringent criteria in use in the December data. By the June 2013, the number of planet candidates was increased to 3,278 and some confirmed planets were smaller than Earth, some even Mars-sized (such as ) and one even smaller than Mercury ().

Reflection/Emission modulations [ ] Short-period planets in close orbits around their stars will undergo reflected light variations because, like the, they will go through from full to new and back again. In addition, as these planets receive a lot of starlight, it heats them, making thermal emissions potentially detectable. Since telescopes cannot resolve the planet from the star, they see only the combined light, and the brightness of the host star seems to change over each orbit in a periodic manner. Although the effect is small — the photometric precision required is about the same as to detect an Earth-sized planet in transit across a solar-type star – such Jupiter-sized planets with an orbital period of a few days are detectable by space telescopes such as the. Like with the transit method, it is easier to detect large planets orbiting close to their parent star than other planets as these planets catch more light from their parent star. When a planet has a high albedo and is situated around a relatively luminous star, its light variations are easier to detect in visible light while darker planets or planets around low-temperature stars are more easily detectable with infrared light with this method.

In the long run, this method may find the most planets that will be discovered by that mission because the reflected light variation with orbital phase is largely independent of orbital inclination and does not require the planet to pass in front of the disk of the star. It still cannot detect planets with circular face-on orbits from Earth's viewpoint as the amount of reflected light does not change during its orbit.

The phase function of the giant planet is also a function of its thermal properties and atmosphere, if any. Therefore, the phase curve may constrain other planet properties, such as the size distribution of atmospheric particles. When a planet is found transiting and its size is known, the phase variations curve helps calculate or constrain the planet's. It is more difficult with very hot planets as the glow of the planet can interfere when trying to calculate albedo.

In theory, albedo can also be found in non-transiting planets when observing the light variations with multiple wavelengths. This allows scientists to find the size of the planet even if the planet is not transiting the star.

The first-ever direct detection of the spectrum of visible light reflected from an exoplanet was made in 2015 by an international team of astronomers. The astronomers studied light from – the first exoplanet discovered orbiting a star (a ), using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the European Southern Observatory's La Silla Observatory in Chile.

Both Corot and Kepler have measured the reflected light from planets. However, these planets were already known since they transit their host star. The first planets discovered by this method are and, found by Kepler. Relativistic beaming [ ] A separate novel method to detect exoplanets from light variations uses relativistic beaming of the observed flux from the star due to its motion. It is also known as Doppler beaming or Doppler boosting.

The method was first proposed by and Scott Gaudi in 2003. As the planet tugs the star with its gravitation, the density of photons and therefore the apparent brightness of the star changes from observer's viewpoint. Like the radial velocity method, it can be used to determine the orbital eccentricity and the minimum mass of the planet. With this method, it is easier to detect massive planets close to their stars as these factors increase the star's motion.

Unlike the radial velocity method, it does not require an accurate spectrum of a star, and therefore can be used more easily to find planets around fast-rotating stars and more distant stars. One of the biggest disadvantages of this method is that the light variation effect is very small. A Jovian-mass planet orbiting 0.025 AU away from a Sun-like star is barely detectable even when the orbit is edge-on. This is not an ideal method for discovering new planets, as the amount of emitted and reflected starlight from the planet is usually much larger than light variations due to relativistic beaming. This method is still useful, however, as it allows for measurement of the planet's mass without the need for follow-up data collection from radial velocity observations. The first discovery of a planet using this method () was announced in 2013. Ellipsoidal variations [ ] Massive planets can cause slight tidal distortions to their host stars.

When a star has a slightly ellipsoidal shape, its apparent brightness varies, depending if the oblate part of the star is facing the observer's viewpoint. Like with the relativistic beaming method, it helps to determine the minimum mass of the planet, and its sensitivity depends on the planet's orbital inclination. The extent of the effect on a star's apparent brightness can be much larger than with the relativistic beaming method, but the brightness changing cycle is twice as fast. In addition, the planet distorts the shape of the star more if it has a low semi-major axis to stellar radius ratio and the density of the star is low. This makes this method suitable for finding planets around stars that have left the main sequence. Pulsar timing [ ].

Artist's impression of the pulsar 's planetary system A is a neutron star: the small, ultradense remnant of a star that has exploded as a. Pulsars emit radio waves extremely regularly as they rotate. Because the intrinsic rotation of a pulsar is so regular, slight anomalies in the timing of its observed radio pulses can be used to track the pulsar's motion. Like an ordinary star, a pulsar will move in its own small orbit if it has a planet. Calculations based on pulse-timing observations can then reveal the parameters of that orbit.

This method was not originally designed for the detection of planets, but is so sensitive that it is capable of detecting planets far smaller than any other method can, down to less than a tenth the mass of Earth. It is also capable of detecting mutual gravitational perturbations between the various members of a planetary system, thereby revealing further information about those planets and their orbital parameters. In addition, it can easily detect planets which are relatively far away from the pulsar. There are two main drawbacks to the pulsar timing method: pulsars are relatively rare, and special circumstances are required for a planet to form around a pulsar. Therefore, it is unlikely that a large number of planets will be found this way.

Also, life as we know it could not survive on planets orbiting pulsars due to the intensity of high-energy radiation there. In 1992, and used this method to discover planets around the pulsar. Their discovery was quickly confirmed, making it the first confirmation of planets outside our.

[ ] Variable star timing [ ] Like pulsars, some other types of are regular enough that could be determined purely from the of the pulsation frequency, without needing. This method is not as sensitive as the pulsar timing variation method, due to the periodic activity being longer and less regular. The ease of detecting planets around a variable star depends on the pulsation period of the star, the regularity of pulsations, the mass of the planet, and its distance from the host star. The first success with this method came in 2007, when was discovered around a pulsating subdwarf star. Transit timing [ ]. The, A NASA mission which is able to detect extrasolar planets The transit timing variation method considers whether transits occur with strict periodicity, or if there is a variation. When multiple transiting planets are detected, they can often be confirmed with the transit timing variation method.

This is useful in planetary systems far from the Sun, where radial velocity methods cannot detect them due to the low signal-to-noise ratio. If a planet has been detected by the transit method, then variations in the timing of the transit provide an extremely sensitive method of detecting additional non-transiting planets in the system with masses comparable to Earth's. It is easier to detect transit-timing variations if planets have relatively close orbits, and when at least one of the planets is more massive, causing the orbital period of a less massive planet to be more perturbed. The main drawback of the transit timing method is that usually not much can be learned about the planet itself. Transit timing variation can help to determine the maximum mass of a planet. In most cases, it can confirm if an object has a planetary mass, but it does not put narrow constraints on its mass.

There are exceptions though, as planets in the and systems orbit close enough to accurately determine their masses. The first significant detection of a non-transiting planet using TTV was carried out with NASA's spacecraft. The transiting planet shows TTV with an amplitude of five minutes and a period of about 300 days, indicating the presence of a second planet,, which has a period which is a near-rational multiple of the period of the transiting planet. In, variations of transit timing are mainly caused by the orbital motion of the stars, instead of gravitational perturbations by other planets. These variations make it harder to detect these planets through automated methods. However, it makes these planets easy to confirm once they are detected.

[ ] Transit duration variation [ ] 'Duration variation' refers to changes in how long the transit takes. Duration variations may be caused by an, for eccentric planets due to another planet in the same system,. When a circumbinary planet is found through the transit method, it can be easily confirmed with the transit duration variation method. In close binary systems, the stars significantly alter the motion of the companion, meaning that any transiting planet has significant variation in transit duration.

The first such confirmation came from. Eclipsing binary minima timing [ ] When a system is aligned such that – from the Earth's point of view – the stars pass in front of each other in their orbits, the system is called an 'eclipsing binary' star system. The time of minimum light, when the star with the brighter surface is at least partially obscured by the disc of the other star, is called the primary, and approximately half an orbit later, the secondary eclipse occurs when the brighter surface area star obscures some portion of the other star. These times of minimum light, or central eclipses, constitute a time stamp on the system, much like the pulses from a (except that rather than a flash, they are a dip in brightness). If there is a planet in circumbinary orbit around the binary stars, the stars will be offset around a binary-planet.

As the stars in the binary are displaced back and forth by the planet, the times of the eclipse minima will vary. The periodicity of this offset may be the most reliable way to detect extrasolar planets around close binary systems. With this method, planets are more easily detectable if they are more massive, orbit relatively closely around the system, and if the stars have low masses. The eclipsing timing method allows the detection of planets further away from the host star than the transit method.

However, signals around stars hinting for planets tend to match with unstable orbits. [ ] In 2011, Kepler-16b became the first planet to be definitely characterized via eclipsing binary timing variations. Gravitational microlensing [ ].

Image of a planet near Beta Pictoris Planets are extremely faint light sources compared to stars, and what little light comes from them tends to be lost in the glare from their parent star. So in general, it is very difficult to detect and resolve them directly from their host star. Planets orbiting far enough from stars to be resolved reflect very little starlight, so planets are detected through their thermal emission instead. It is easier to obtain images when the star system is relatively near to the Sun, and when the planet is especially large (considerably larger than ), widely separated from its parent star, and hot so that it emits intense infrared radiation; images have then been made in the infrared, where the planet is brighter than it is at visible wavelengths.

Are used to block light from the star, while leaving the planet visible. Direct imaging of an Earth-like exoplanet requires extreme.

During the accretion phase of planetary formation, the star-planet contrast may be even better in than it is in infrared – an H alpha survey is currently underway. Direct imaging can give only loose constraints of the planet's mass, which is derived from the age of the star and the temperature of the planet. Mass can vary considerably, as planets can form several million years after the star has formed.

The cooler the planet is, the less the planet's mass needs to be. In some cases it is possible to give reasonable constraints to the radius of a planet based on planet's temperature, its apparent brightness, and its distance from Earth. The spectra emitted from planets do not have to be separated from the star, which eases determining the chemical composition of planets.

Sometimes observations at multiple wavelengths are needed to rule out the planet being a. Direct imaging can be used to accurately measure the planet's orbit around the star. Unlike the majority of other methods, direct imaging works better with planets with rather than edge-on orbits, as a planet in a face-on orbit is observable during the entirety of the planet's orbit, while planets with edge-on orbits are most easily observable during their period of largest apparent separation from the parent star. The planets detected through direct imaging currently fall into two categories. First, planets are found around stars more massive than the Sun which are young enough to have protoplanetary disks. The second category consists of possible sub-brown dwarfs found around very dim stars, or brown dwarfs which are at least 100 AU away from their parent stars.

Planetary-mass objects are found through direct imaging as well. Early discoveries [ ]. Image of exoplanet c using astrometry data from ’s NACO and SINFONI instruments. In 2004, a group of astronomers used the 's array in Chile to produce an image of, a companion to the 2M1207. In the following year, the planetary status of the companion was confirmed.

The planet is estimated to be several times more massive than, and to have an orbital radius greater than 40 AU. In September 2008, an object was imaged at a separation of 330 AU from the star, but it was not until 2010, that it was confirmed to be a companion planet to the star and not just a chance alignment. The first multiplanet system, announced on 13 November 2008, was imaged in 2007, using telescopes at both the and.

Three planets were directly observed orbiting, whose masses are approximately ten, ten, and seven. On the same day, 13 November 2008, it was announced that the Hubble Space Telescope directly observed orbiting, with a mass no more than 3 M J. Both systems are surrounded by disks not unlike the. In 2009, it was announced that analysis of images dating back to 2003, revealed a planet orbiting. [ ] In 2012, it was announced that a ' planet with a mass about 12.8 M J orbiting was directly imaged using the in Hawaii. It orbits its parent star at a distance of about 55 AU, or nearly twice the distance of from the sun. An additional system,, was imaged in November 2009, by a team using the instrument of the, but it was a brown dwarf.

Other possible exoplanets to have been directly imaged include,, and. As of March 2006, none have been confirmed as planets; instead, they might themselves be small. Imaging instruments [ ]. VLT image of exoplanet Some projects to equip telescopes with planet-imaging-capable instruments include the ground-based telescopes,,,, and the space telescope. The proposes a large occulter in space designed to block the light of nearby stars in order to observe their orbiting planets. This could be used with existing, already planned or new, purpose-built, telescopes. In 2010, a team from demonstrated that a could enable small scopes to directly image planets.

They did this by imaging the previously imaged planets, using just a 1.5 meter-wide portion of the. Another promising approach is. It has also been proposed that space-telescopes that focus light using instead of mirrors would provide higher-contrast imaging, and be cheaper to launch into space due to being able to fold up the lightweight foil zone plate.

Main article: Light given off by a star is un-polarized, i.e. The direction of oscillation of the light wave is random. However, when the light is reflected off the atmosphere of a planet, the light waves interact with the molecules in the atmosphere and become polarized. By analyzing the polarization in the combined light of the planet and star (about one part in a million), these measurements can in principle be made with very high sensitivity, as polarimetry is not limited by the stability of the Earth's atmosphere.

Another main advantage is that polarimetry allows for determination of the composition of the planet's atmosphere. The main disadvantage is that it will not be able to detect planets without atmospheres.

Larger planets and planets with higher albedo are easier to detect through polarimetry, as they reflect more light. Astronomical devices used for polarimetry, called polarimeters, are capable of detecting polarized light and rejecting unpolarized beams. Groups such as and are currently using polarimeters to search for extrasolar planets. The first successful detection of an extrasolar planet using this method came in 2008, when, a planet discovered three years earlier, was detected using polarimetry.

However, no new planets have yet been discovered using this method. Astrometry [ ]. In this diagram a planet (smaller object) orbits a star, which itself moves in a small orbit. The system's center of mass is shown with a red plus sign. (In this case, it always lies within the star.) This method consists of precisely measuring a star's position in the sky, and observing how that position changes over time. Originally, this was done visually, with hand-written records.

By the end of the 19th century, this method used photographic plates, greatly improving the accuracy of the measurements as well as creating a data archive. If a star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit. Effectively, star and planet each orbit around their mutual centre of mass (), as explained by solutions to the.

Since the star is much more massive, its orbit will be much smaller. Frequently, the mutual centre of mass will lie within the radius of the larger body. Consequently, it is easier to find planets around low-mass stars, especially brown dwarfs.

Motion of the center of mass (barycenter) of solar system relative to the Sun Astrometry is the oldest search method for, and was originally popular because of its success in characterizing systems. It dates back at least to statements made by in the late 18th century. He claimed that an unseen companion was affecting the position of the star he cataloged as. The first known formal astrometric calculation for an extrasolar planet was made by in 1855 for this star. Similar calculations were repeated by others for another half-century until finally refuted in the early 20th century.

For two centuries claims circulated of the discovery of unseen companions in orbit around nearby star systems that all were reportedly found using this method, culminating in the prominent 1996 announcement, of multiple planets orbiting the nearby star. None of these claims survived scrutiny by other astronomers, and the technique fell into disrepute. Unfortunately, changes in stellar position are so small—and atmospheric and systematic distortions so large—that even the best ground-based telescopes cannot produce precise enough measurements. All claims of a planetary companion of less than 0.1 solar mass, as the mass of the planet, made before 1996 using this method are likely spurious.

In 2002, the did succeed in using astrometry to characterize a previously discovered planet around the star. The space-based observatory, launched in 2013, is expected to find thousands of planets via astrometry, but prior to the launch of Gaia, no planet detected by astrometry had been confirmed. Was a US project (cancelled in 2010) that would have had similar exoplanet finding capabilities to. One potential advantage of the astrometric method is that it is most sensitive to planets with large orbits. This makes it complementary to other methods that are most sensitive to planets with small orbits. However, very long observation times will be required — years, and possibly decades, as planets far enough from their star to allow detection via astrometry also take a long time to complete an orbit.

Planets orbiting around one of the stars in binary systems are more easily detectable, as they cause perturbations in the orbits of stars themselves. However, with this method, follow-up observations are needed to determine which star the planet orbits around. In 2009, the discovery of by astrometry was announced. This planetary object, orbiting the low mass star, was reported to have a mass seven times that of. If confirmed, this would be the first exoplanet discovered by astrometry, of the many that have been claimed through the years. However recent independent studies rule out the existence of the claimed planet.

In 2010, six binary stars were astrometrically measured. One of the star systems, called, was found with 'high confidence' to have a planet. Other possible methods [ ] Transit imaging [ ] An optical/infrared array doesn't collect as much light as a single telescope of equivalent size, but has the resolution of a single telescope the size of the array. For bright stars, this resolving power could be used to image a star's surface during a transit event and see the shadow of the planet transiting. This could provide a direct measurement of the planet's angular radius and, via, its actual radius.

This is more accurate than radius estimates based on, which are dependent on stellar radius estimates which depend on models of star characteristics. Imaging also provides more accurate determination of the inclination than photometry does. Magnetospheric radio emissions [ ] Radio emissions from magnetospheres could be detected with future radio telescopes. This could enable determination of the rotation rate of a planet, which is difficult to detect otherwise.

Auroral radio emissions [ ] emissions from giant planets with sources, such as 's volcanic moon, could be detected with radio telescopes such as. Modified interferometry [ ] By looking at the wiggles of an interferogram using a Fourier-Transform-Spectrometer, enhanced sensitivity could be obtained in order to detect faint signals from Earth-like planets. Detection of extrasolar asteroids and debris disks [ ] Circumstellar disks [ ]. An artist's conception of two -sized dwarf planets in a collision around Disks of space dust () surround many stars. The dust can be detected because it absorbs ordinary starlight and re-emits it as radiation. Even if the dust particles have a total mass well less than that of Earth, they can still have a large enough total surface area that they outshine their parent star in infrared wavelengths.

The is capable of observing dust disks with its NICMOS (Near Infrared Camera and Multi-Object Spectrometer) instrument. Even better images have now been taken by its sister instrument, the, and by the 's, which can see far deeper into wavelengths than the Hubble can. Dust disks have now been found around more than 15% of nearby sunlike stars. The dust is thought to be generated by collisions among comets and asteroids.

From the star will push the dust particles away into interstellar space over a relatively short timescale. Therefore, the detection of dust indicates continual replenishment by new collisions, and provides strong indirect evidence of the presence of small bodies like comets and that orbit the parent star.

For example, the dust disk around the star indicates that that star has a population of objects analogous to our own Solar System's, but at least ten times thicker. More speculatively, features in dust disks sometimes suggest the presence of full-sized planets. Some disks have a central cavity, meaning that they are really ring-shaped. The central cavity may be caused by a planet 'clearing out' the dust inside its orbit. Other disks contain clumps that may be caused by the gravitational influence of a planet. Both these kinds of features are present in the dust disk around, hinting at the presence of a planet with an orbital radius of around 40 (in addition to the inner planet detected through the radial-velocity method).

These kinds of planet-disk interactions can be modeled numerically using techniques. Contamination of stellar atmospheres [ ] Spectral analysis of ' often finds contamination of heavier elements like and.

These elements cannot originate from the stars' core, and it is probable that the contamination comes from that got too close (within the ) to these stars by gravitational interaction with larger planets and were torn apart by star's tidal forces. Up to 50% of young white dwarfs may be contaminated in this manner. Additionally, the dust responsible for the atmospheric pollution may be detected by infrared radiation if it exists in sufficient quantity, similar to the detection of debris discs around main sequence stars. Data from the suggests that 1-3% of white dwarfs possess detectable circumstellar dust. In 2015, minor planets were discovered transiting the white dwarf. This material orbits with a period of around 4.5 hours, and the shapes of the transit light curves suggest that the larger bodies are disintegrating, contributing to the contamination in the white dwarf's atmosphere. Space telescopes [ ] Most confirmed extrasolar planets have been found using space-based telescopes (as of 01/2015).

Many of the detection methods can work more effectively with space-based telescopes that avoid atmospheric haze and turbulence. (2007-2012) and were space missions dedicated to searching for extrasolar planets using transits. COROT discovered about 30 new exoplanets. Kepler (2009-2013) and K2 (2013- ) have discovered over 2000 verified exoplanets.

And have also found or confirmed a few planets. The infrared has been used to detect transits of extrasolar planets, as well as s of the planets by their host star and. The, launched in December 2013, will use astrometry to determine the true masses of 1000 nearby exoplanets. And, to be launched in 2017, and in 2024 will use the transit method.

Primary and secondary detection [ ] Method Primary Secondary Transit Primary eclipse. Planet passes in front of star. Secondary eclipse. Star passes in front of planet. Radial velocity Radial velocity of star Radial velocity of planet. This has been done for. Astrometry Astrometry of star.

Position of star moves more for large planets with large orbits. Astrometry of planet. Color-differential astrometry. Position of planet moves quicker for planets with small orbits. Theoretical method—has been proposed for use for the. Verification and falsification methods [ ] • Verification by multiplicity • Transit color signature • • Dynamical stability testing • Distinguishing between planets and stellar activity • Transit offset Characterization methods [ ] • • Emission spectroscopy, phase-resolved • / to detect companion stars that the planets could be orbiting instead of the primary star, which would alter planet parameters that are derived from stellar parameters.

• Photoeccentric Effect • See also [ ] • • References [ ].

Photo: David Schneider Star Track: The rotation of the Earth causes stars to continuously shift position in the sky. Detecting the subtle signs of the existence of an orbiting exoplanet requires compensating for this shift.

To do that, I built my own hinged “barn door” tracker. Since 1995, when astronomers announced orbiting the star 51 Pegasi, exoplanets—which orbit stars other than the sun—have been a hot topic. I knew that dedicated amateurs could detect some of these exoplanets, but I thought it required expensive telescopes. Then I stumbled on the website of the project at Ohio State University, in Columbus. The project’s astronomers find exoplanets not with a giant telescope but by combining a charge-coupled-device (CCD) detector with a Mamiya-Sekor lens originally designed for high-end cameras.

That got me wondering: Might I be able to detect an exoplanet without a telescope or a research-grade CCD detector? I discovered that one amateur astronomer had already about how he had detected a known exoplanet using a digital single-lens reflex (DSLR) camera outfitted with a telephoto lens. Drivers Licence Testing Centres Mpumalanga there. He was able to discern the dip in the brightness of a star as an orbiting planet passed in front of it—a technique known as transit detection. The was a gas giant that belongs to a binary star system variously named HD 189733, HIP 98505, or V452 Vulpeculae, depending on the star catalog.

It was the obvious choice because its parent star is relatively bright (although still invisible to the naked eye), and the star drops in apparent brightness during a transit by 2.6 percent, which is a lot as these things go. (Astronomers, who use a logarithmic scale to describe the magnitude of a star’s brightness, would call that a 28-millimagnitude difference.) So I decided to follow this lead and went shopping for a telephoto lens for my Canon EOS Rebel XS DSLR. With old manual-focus lenses now useless to most photographers, I was able to acquire a 300-millimeter Nikon telephoto lens on eBay for a song (US $92, shipped), along with a ($17 from Amazon). Video: David Schneider The next task was to figure out how to make the camera track a star during long exposures. I could have bought a commercial star tracker, but that would have put me back several hundred dollars. Instead I built a “—essentially two pieces of plywood hinged together. Aligning the hinge to your hemisphere’s celestial pole allows you to track a star as the plywood “doors” separate at a constant rate.

Photos: David Schneider (4) The Long Shot: Sixty-three light-years away, HD 189733 is too dim to be seen with the naked eye. Finding it required the use of such waypoints as the Dumbbell Nebula [top]. Once the star system is targeted, the Earth’s rotation causes the sky’s image to blur [second from top] during long exposures. An Arduino-controlled star tracker [bottom] compensated for this motion [third from top]. To drive the tracker, I pulled some gears out of a defunct inkjet printer, attaching one gear to a stepper motor and the other to a nut screwed onto a gently curved length of threaded rod. Rotating the nut pushes the doors of the tracker apart.

The stepper motor is controlled, via a, by an Arduino microprocessor that lets me set the rate at which the doors separate. Initially, I mounted my tracker on a camera tripod. But I soon abandoned that as being too precarious and built a sturdy wooden platform. The final component of the tracker is ($18 on Amazon) bolted to the top, which allows me to orient the camera in any direction. The trickiest step in the operation is getting the camera pointed at the target star.

I aim my camera by first eyeballing things and then walking the field of view from star to star. A right-angle viewfinder attachment ($20, used) makes that easier, but it’s still a challenge. Some nights it has taken me 15 minutes or more to get the target star framed. To take images, I used software that came with my Canon camera. It allows you to adjust the camera settings, take shots, record images directly to your computer, and program a sequence of timed exposures. I also purchased a $14 so that I could run my camera for hours without its battery giving out.

I took test sequences of images of HD 189733 for a few nights, settling on a routine of taking one 50-second exposure per minute. I figured that duration would minimize variations in brightness that come from scintillation—twinkling—and that it would also average over small periodic errors in tracking. Billy Squier The Tale Of The Tape Rar Extractor. With such long-duration exposures, I used a low ISO setting to avoid saturating the camera’s CMOS imaging sensor. The hardest part of the whole project proved to be waiting for an opportunity to observe the transit of HD 189733’s exoplanet, which takes place once every 2.2 days. That sounds frequent, but transits that occur during daytime or are too close to the horizon are impossible to observe.

(The Czech Astronomical Society provides a for determining opportunities to observe this and other exoplanet transits.) And of course, I needed clear skies. Finally, after weeks of waiting, an opportunity came in mid-October. I recorded images for almost 3 hours, beginning about a half-hour before the start of the 108-minute transit. That, I figured, would capture the transition from normal brightness to ever-so-slightly dimmed and back to normal again. Of course, you can’t just look at the images to see the subtle effects of a transit: There are too many confounding influences, such as changes in the transparency of the atmosphere.

And the response of a camera’s imaging sensor is seldom uniform: If the position of the target shifts in the field of view (which is hard to avoid over the course of an evening), the amount of light registered will also change, even if there is no actual change in brightness. To compensate, I used free software called, which allowed me to perform the corrections needed to calculate the brightness of HD 189733, as well as four reference stars. I loaded the results from Iris into Microsoft Excel to make differential-photometry calculations—that is, comparing HD 189733 with one of the four reference stars to compensate for changes in atmospheric conditions. The scatter in the final results was about the same size as the signal I was attempting to measure, but the general dip in brightness was easy enough to discern nevertheless. The average magnitude of the target star diminished and recovered just as the exoplanet’s transit began and ended. And the shift in magnitude was very close to, if not precisely, the 28 mmag expected.

So it seems my home-brew observatory did detect an exoplanet—using little more than run-of-the-mill DSLR and a $92 eBay camera lens!