Searching for Planets - Essay Example

Topic 11: Searching for Planets Your name: Course Name:  Professors’ Name: Name of University: City, State: Date: Introduction The search for exo-planets is an interesting field in astronomy and will one day give humans answers to many questions of whether humans are alone in the universe (Gribbin, 2005). Although searching for other form of living in the universe dates back to thousands and thousands of years, the techniques or methods that have been used to search exo-planets have only recently been developed with the first exo-planet being discovered in early 1990’s (Schneider, 2011). Exo-planets are very hard to be discovered because most of them don’t emit light of their own are completely masked by other bright stars. Currently there are approximately 250 extra-solar planets that have been discovered since 1992 (Schneider, 2011), but this number is continuously changing every month partly due to the fact that current methods that are used to detect extra-solar planets are being improved every now and then (Gribbin, 2005). This paper will discuss the common methods or techniques that have been used in the past to detect exo-planets will include: Direct observation; Astrometry; Doppler Shift; Pulsar Timing; Brightness Variations; Gravitational microlensing (Schneider, 2011). Exo-planets Detection Methods a. Direct Observation This is the most obvious method-seeing the exo-planets themselves. Following the discovery of extra-solar planets or exo-planets by the radial velocity technique in the mid-90s an international effort have seen been used to try and detect these extra-solar planets directly (Dvořák, 2008). The radial velocity technique pioneered by Marcy & Butler and Mayor & Queloz has provided a lot of information about planetary orbits, such information include the fact that many exo-planets revolve very close to the parent star (Dvořák, 2008). Limitation: with our modern techniques sometimes it is difficult to directly detect exo-planets because most of these planets are swamped by the light from other stars or parent stars (Hidas et al 2005). Sometimes, trying to detect light from an exo-planet can be compared to trying to pick out the light from a firefly flying next to searchlight in New York on a foggy night using a telescope in San Francisco. Another limitation for direct observations is that this technique doesn’t give the mass of the exo-planets and their orbital inclination (Hidas et al 2005). Direct observation method also does not give information about the composition of the exo-planet composition. b. Astrometry Method This technique for detecting exo-planets focuses on precise measurements of the movements and positions of stars and other extra celestial bodies (Walter, 2000). Until recently telescopes that were used to observe movements of stars did not have enough resolution that was needed to detect this type of movement. Most people always think a planet is the one which orbit a star, but what is actually happening is that both the planet and the star have a shared center of mass (Walter, 2000). The planet is not massive when you compare it with the star, so the center of mass of the planet will be closer to the star, and thus the planet’s orbit is much more pronounced while star’s orbit is very small or tiny (Kovalevsky and Seidelman, 2004). Therefore, any small change in the star’s position due to the tug of the planet will be detectable through a close study of the star’s position for a period of time. This technique has benefits over other methods that are used to detect exo-planets because it can be used to located exo-planets that orbit far out from the star. Limitation: this method is that due to the difficulties of measurements, it is difficult to detect exo-planets using this method (Walter, 2000). c. Pulsar Timing A pulsar is a rapidly rotating neuron exo-planet that has a strong magnet field. The radiation that is being produced by the neutron exo-planet is focused into two oppositely-directed beams by a magnetic field (Holman, 2004). As the exo-planet rotates, its beam will be swept across the sky; if the exo-planet beams are intercepted on the earth, then regular pulses of radiation will be seen just like a lighthouse (Holman, 2004). When the planet is introduced to the process, the gravitational pull between the pulsar and the planet means they will orbit about their common center of mass (Miralda, 2001). This is because two large masses which have equal weight, their center will be approximately halfway between the two objects. But in other situations, the center of mass for the two between the two objects may lie close to the more massive object (Miralda, 2001). In the case of a planet and a pulsar, the center of mass will be seen to be closer to the pulsar, since it is heavier as compared to the other planet (Holman, 2004). Therefore, during the revolution the pulsar will move at a small distance than the exo-planet. Although the pulsar distance moved will be small, it will have an effect on the timing of the pulses that will be emitted by the pulsar (Holman, 2004). During the movement away from the earth-planet, the pulsar time between each pulse will be longer (Miralda, 2001). Conversely, when the pulsar moves towards the planet-earth, the time between the pulses is recorded to be slightly shorter (Miralda, 2001). When these periodic changes in pulse timing are measured, it is possible not only to estimate the semi-major axis of the exo-planet, but also to deduce the existence of a exo-planet orbiting around the pulsar. In 1994, an exo-planet was detected using this technique by Wolszczan. Limitation: the main limitation for this technique is that pulsars are relatively rare, so it is impossible to detect large number of exo-planet using this technique. d. Doppler Shift This method is used to detect the periodic velocity of the stellar spectrum that has been caused by orbiting of a giant exo-planet (Townsend, 2003). This method also relies on the fact that the star and planet are orbiting a shared center of mass. If the orbit is edge-on, the exo-planet will move towards the planet and then away from the planet in its small orbit (Townsend, 2003). When the exo-planet is moving away from us, the light that will be detected will be red-shifted having long wavelengths than normal. When the exo-planet is moving towards us, the light that will be detected will be blue-shifted (Townsend, 2003). The Doppler shift for light emitted by exo-planet is similar to the Doppler shift for sound. Therefore, the changes in the exo-planet’s spectrum due to the Doppler shift can be detected (Townsend, 2003). In 1995, the first exo-planet was detected using this method, the star 51 Pegasi which was detected by Meyor & Queloz. This technique has been the most successful so far in detecting extra-solar planets (Wright et al 2008). Limitation: One major drawback for this technique is that it can only measure movement along the line-of-sight. “This means is the orbital plane of the exo-planet is tilted away from the line of sight, then the true effect of the planet on the motion of the star will be greater than the measured variation in the star's radial velocity” (Wright et al 2008). e. Gravitational Microlensing Techniques This technique uses a complex mathematics equation from Einstein's theory of general relativity (Santerne et el 2012). The basis of this principle is the fact that object which have heavy mass curve the space around them so that when light travel near the object, the light is magnified (Santerne et el 2012). Astronomers that have used this kind of technique to detect exo-solar planets look at a star that might have a exo-planet as the star passes in front of a distant background star (Santerne et el 2012).. The light will then be magnified in a special way by the exo-planet of the foreground star. Limitation: practically, microlensing events are very infrequent and this makes it difficult to find extra-solar planets. Detected Exo-planets and Lesson Learnt Exo-planets or extra-solar planets are planets that can be found outside of the solar system. Since 1992, astronomers have been able to locate approximately 837 such planets in 660 planetary systems around the Milky Way galaxy (Hidas et al 2005). Some of the well known exo-planets or extra-solar planets include: Europa, Ganymede, Callisto, Europa, Titan, Gliese 581 d, Kepler-22b, Alpha Centauri etc. Until recently, planet mars has always been seen to be the only planet other than earth that can support life. The most recent discovery of exo-planet Europa, a moon of the planet Jupiter. Most of the evidence points to a mobile surface provided by liquid water (Miralda, 2001). Water, scientists believe, could exist below the surface of this exo-planet because of internal tidal heating from gravitational interactions with planet Jupiter and the other Galilean moons (Kovalevsky and Seidelman, 2004). Another exo-planet that has been discovered and has connections with life in the solar system is Titan; this is the largest of the moons of planet Saturn (Miralda, 2001). Just like the planet earth, Titan’s atmosphere has been discovered to be largely composed of nitrogen, and with less than 1 per cent of methane. While the surface pressure of this exo-planet atmosphere is higher than that of planet earth, but the temperature is very cold. A rich element of organic molecules has also been found in Titan’s atmosphere, as products of the methane and ammonia chemistry (Wright et al 2008). This mixture includes hydrogen cyanide which is a compound in the process to the synthesis of amino acids. This discovery has led to scientist speculating that they might be some primitive life form in the exo-planet Titan. Reference List Agol, S and Steffen, C 2004, "On detecting terrestrial planets with timing of giant planet transits". Monthly Notices of the Royal Astronomical Society 359 (2): 567–579. Deming, D and Harrington, J 2005, "Infrared radiation from an extrasolar planet" (PDF). Nature 434 (7034): 740–743. Dvořák, R 2008, Extrasolar Planets: Formation, Detection and Dynamics, Wiley Publisher, London. Gribbin, J 2005, Companion to the Cosmos, Weidenfed & Nicolson, London. Hidas, M. G et al 2005, "The University of New South Wales Extrasolar Planet Search: methods and first results from a field centred on NGC 6633". Monthly Notices of the Royal Astronomical Society 360 (2): 703–717 Holman, M 2004, "The Use of Transit Timing to Detect Extrasolar Planets with Masses as Small as Earth". Science, 307 (1291). Kovalevsky, J and Seidelman, P. K 2004, Fundamentals of Astrometry, Cambridge University Press, London. Miralda, E 2001, "Orbital perturbations on transiting planets: A possible method to measure stellar quadrupoles and to detect Earth-mass planets". The Astrophysical Journal 564 (2): 1019. Santerne, A., et el 2012, "SOPHIE velocimetry of Kepler transit candidates", Astronomy & Astrophysics 545: A76. Schneider, J 2011, "Interactive Extra-solar Planets Catalog", The Extrasolar Planet Encyclopedia, 11 (30). Townsend, R 2003, The Search for Extrasolar Planets (Lecture). Department of Physics & Astronomy, Astrophysics Group, University College, London. Walter, H.G 2000, Astrometry of fundamental catalogues: the evolution from optical to radio reference frames, Springer, New York. Wright , J.T. et al 2008, "Ten New and Updated Multi-planet Systems, and a Survey of Exoplanetary Systems". The Astrophysical Journal 693 (2): 1084–1099. Read More

Most people always think a planet is the one which orbit a star, but what is actually happening is that both the planet and the star have a shared center of mass (Walter, 2000). The planet is not massive when you compare it with the star, so the center of mass of the planet will be closer to the star, and thus the planet’s orbit is much more pronounced while star’s orbit is very small or tiny (Kovalevsky and Seidelman, 2004). Therefore, any small change in the star’s position due to the tug of the planet will be detectable through a close study of the star’s position for a period of time.

This technique has benefits over other methods that are used to detect exo-planets because it can be used to located exo-planets that orbit far out from the star. Limitation: this method is that due to the difficulties of measurements, it is difficult to detect exo-planets using this method (Walter, 2000). c. Pulsar Timing A pulsar is a rapidly rotating neuron exo-planet that has a strong magnet field. The radiation that is being produced by the neutron exo-planet is focused into two oppositely-directed beams by a magnetic field (Holman, 2004).

As the exo-planet rotates, its beam will be swept across the sky; if the exo-planet beams are intercepted on the earth, then regular pulses of radiation will be seen just like a lighthouse (Holman, 2004). When the planet is introduced to the process, the gravitational pull between the pulsar and the planet means they will orbit about their common center of mass (Miralda, 2001). This is because two large masses which have equal weight, their center will be approximately halfway between the two objects.

But in other situations, the center of mass for the two between the two objects may lie close to the more massive object (Miralda, 2001). In the case of a planet and a pulsar, the center of mass will be seen to be closer to the pulsar, since it is heavier as compared to the other planet (Holman, 2004). Therefore, during the revolution the pulsar will move at a small distance than the exo-planet. Although the pulsar distance moved will be small, it will have an effect on the timing of the pulses that will be emitted by the pulsar (Holman, 2004).

During the movement away from the earth-planet, the pulsar time between each pulse will be longer (Miralda, 2001). Conversely, when the pulsar moves towards the planet-earth, the time between the pulses is recorded to be slightly shorter (Miralda, 2001). When these periodic changes in pulse timing are measured, it is possible not only to estimate the semi-major axis of the exo-planet, but also to deduce the existence of a exo-planet orbiting around the pulsar. In 1994, an exo-planet was detected using this technique by Wolszczan.

Limitation: the main limitation for this technique is that pulsars are relatively rare, so it is impossible to detect large number of exo-planet using this technique. d. Doppler Shift This method is used to detect the periodic velocity of the stellar spectrum that has been caused by orbiting of a giant exo-planet (Townsend, 2003). This method also relies on the fact that the star and planet are orbiting a shared center of mass. If the orbit is edge-on, the exo-planet will move towards the planet and then away from the planet in its small orbit (Townsend, 2003).

When the exo-planet is moving away from us, the light that will be detected will be red-shifted having long wavelengths than normal. When the exo-planet is moving towards us, the light that will be detected will be blue-shifted (Townsend, 2003). The Doppler shift for light emitted by exo-planet is similar to the Doppler shift for sound. Therefore, the changes in the exo-planet’s spectrum due to the Doppler shift can be detected (Townsend, 2003). In 1995, the first exo-planet was detected using this method, the star 51 Pegasi which was detected by Meyor & Queloz.

This technique has been the most successful so far in detecting extra-solar planets (Wright et al 2008). Limitation: One major drawback for this technique is that it can only measure movement along the line-of-sight.

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