Physics
Exoplanet Detection
Exoplanet detection is the process of identifying planets outside our solar system. This is done through various methods such as radial velocity, transit photometry, and direct imaging. The discovery of exoplanets has greatly expanded our understanding of the universe and the potential for life beyond Earth.
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10 Key excerpts on "Exoplanet Detection"
eBook - PDFExtra-Solar Planets
The Detection, Formation, Evolution and Dynamics of Planetary Systems
- Bonnie Steves, Martin Hendry, Andrew C. Cameron(Authors)
- 2010(Publication Date)
- CRC Press(Publisher)
Part I Detection of Extra-Solar Planets: Methods and Observations 1 3 Detection of extra-solar planets in wide-field transit surveys Andrew Collier Cameron SUPA, School of Physics and Astronomy, University of St Andrews, Scotland In this lecture I describe the observational and transit-detection strategies adopted by current wide-field surveys aimed at discovering bright transiting gas-giant planets using arrays of small cameras with apertures of order 11 cm. The advantage of using such small instruments is that their wide sky coverage permits discovery of relatively bright systems amenable to detailed follow-up studies. I present algorithms commonly used to identify and remove sources of sys-tematic error from the data, and to detect the presence of periodic transit signals. I shall then discuss methods for identifying and eliminating astro-physical false positives using the photometric discovery data combined with publicly-available photometric and astrometric catalogue information. 1 Introduction Among more than 300 extra-solar planets that have been discovered since 1995, the 35 that transit their parent stars offer the greatest physical insights into their structure and evolution. The geometry of a transit, combined with radial-velocity measurements of the star’s reflex orbit, yields direct measure-ments of the stellar density and the planetary surface gravity (Southworth et al 2007). Other parameters of interest, including the planetary density, can be determined once the stellar mass is known. The planetary density is an important diagnostic of the mass of a planet’s rock/ice core (Fortney et al 2007, Seager et al 2008), and hence of its formation history.
eBook - ePub- Arnold Hanslmeier(Author)
- 2018(Publication Date)
- WSPC(Publisher)
Chapter 3Exoplanets
In this chapter we give an introduction to the rapidly growing field of exoplanets, and we will start with the discussion how exoplanets can be detected. The main problem in finding exoplanets comes from: •Planets are smaller than stars. •Planets only reflect light from a star. •Seen from a large distance, they appear very close to their parent star. •Planets mainly radiate in the IR.The main methods are through observations of transits, radial velocity measurements, astrometric measurements, direct imaging and microlensing. Relevant satellite missions such as Kepler, COROT and GAIA will be mentioned. It is even possible to detect exoplanetary atmospheres. We will review the different types of detected exoplanets and, finally, we discuss aspects of the orbits of exoplanets and their stability.3.1Methods to detect exoplanets
3.1.1Transits
If the orbital plane of an exoplanet lies in the same/similar plane as the one from an observer on Earth, we can see the planet passing in front of its host star (transiting exoplanet). This causes a periodic dimming of the stellar lightcurve and can be revealed by precise photometry. Figure 3.1 shows the lightcurve variations due to a transiting planet.Fig. 3.1The transit of a planet can be observed as a dip in the lightcurve of the star. Credit: Wikipedia Commons, CC BY-SA 3.0. Table 3.1.Transit properties of solar system planets. For a circular orbit, the duration of a transit can be estimated froma is the semi-major axis of the planet’s orbit, M* the mass of the star and d* the stellar diameter in solar units. The duration alone does not give any information about the physical nature of the planet. The size of a planet follows from the transit depth because the fractional change in brightness is equal to the ratio of the planet’s area to the star’s area. As an example we give the transit properties of solar system objects in Table 3.1 (from http://kepler.nasa.gov/sci/basis/character.html ). P is the orbital period in years, a the semi-major axis in AU, T the transit duration in hours, D
eBook - PDFLife beyond Earth
The Search for Habitable Worlds in the Universe
- Athena Coustenis, Thérèse Encrenaz(Authors)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
5.1.4 How to detect exoplanets from planetary transits Four years after the detection of 51 Peg b, a major new result was achieved: the first detection of an exoplanet around a solar-type star, by David Charbonneau and his colleagues (2000), using the transit method and ground-based stellar photometry. What is this all about? The transit method is another indirect way of detecting exoplanets. It consists in measuring the light of the star when, by chance, a planet crosses the field of view in front of the star. At that point, the stellar flux is slightly decreased because of the planetary occultation. If the Sun were observed from outside the Solar System, its occultation by Jupiter (a tenth the diameter of the Sun) would induce a decrease of the solar flux by 1 per cent; occultation by the Earth (about 100th the diameter of the Sun) would induce a decrease by 0.01 per cent. By measuring the stellar light very precisely, before, during and after a planetary transit, and by repeating the observation over a large number of transits, it is possible to detect the presence of the planet and, if we know the stellar diameter, to derive the planetary diameter (Box 5.2). Of course, this technique requires a special geometry: the Earth must be located in the plane of the planet’s orbit or close to it. This probability is higher if the exoplanet is big and close to its star. Fortunately, this is exactly the case for the first exoplanets discovered 5.1 from dream to reality 199 box 5.2 The method of planetary transits Transits of terrestrial planets in front of the Sun have been known for centuries. Transits of Venus across the face of the Sun have been used since the eighteenth century to determine the distance of Venus, and hence the Sun–Earth distance and all distances in the Solar System. The same method has been successfully used to detect exoplanets around nearby stars. The only condition to be respected is that the Earth must be close to the orbital plane of the exoplanet.
eBook - PDF- Ludmilla Kolokolova, James Hough, Anny-Chantal Levasseur-Regourd(Authors)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
All but a few percent of the currently known exoplan- ets have been detected using indirect methods: here, the influence of the planet on the star is detected and not radi- ation from the planet itself. The most successful planet detection methods are the so-called “radial velocity” or “Doppler” method, in which the line-of-sight velocity of the star due to the gravitational pull of an orbiting planet is measured; and the so-called “transit” method, in which stellar fluxes are monitored for temporary, periodic, percent-level decreases that can be attributed to orbiting planets traversing the stellar disk and blocking a fraction of the star’s total flux. In particular, NASA’s dedicated Kepler mission (Borucki et al. 2003, 2010) has identified thousands of exoplanets and exoplanet candidates. Indirect detection methods have proved their worth in finding exoplanets. In addition, combinations of these methods provide planet parameters such as a plan- et’s orbital period, its radius, and its minimum mass. Information about the atmospheric composition, tem- perature, and dynamics have also been derived for some exoplanets, for example from the spectrum of starlight filtered through the upper layers of the atmosphere of a planet during the planet’s transit (Charbonneau et al. 2002) or from careful monitoring of the temporal changes in the combined flux spectrum of a star and an orbiting and transiting planet (Queloz et al. 2000). Not surprisingly, indirect detection methods are most sensitive to large, massive planets in relatively close-in orbits. The amplitude of planet-induced radial velocity of a star increases both for increasing planet mass and for decreasing orbital separation. The probability of a planet- ary transit also increases for decreasing orbital separation, and transit depth increases with increasing planet radius.
eBook - PDFSolar Planetary Systems
Stardust to Terrestrial and Extraterrestrial Planetary Sciences
- Asit B. Bhattacharya, Jeffrey M. Lichtman(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
• Polarimetry : With the polarimetry method, a polarized light reflected off the planet can be separated from unpolarized light emitted from the star. No new planets have been found with this method, although a few discovered planets have been detected by applying the technique [35,36]. • Circumstellar disks : Disks of space dust surround many stars that are believed to originate from collisions among asteroids and comets or other interstellar objects. The dust can be detected, as it absorbs starlight and reemits it as infrared radia-tion. Features in the disks may suggest the presence of planets, although this is not considered a definitive detection method. • Relativistic beaming : Relativistic beaming determines the observed flux from the star owing to its motion. The brightness of the star varies as the planet moves closer or further away from its host star [37]. • Ellipsoidal variations : Massive planets close to their host stars can slightly deform in shape due to of the host stars tugging motion, thus varying the brightness [38]. 7.5 Exoplanet Discoveries and Their Sizes Figure 7.13 shows a histogram of exoplanet discoveries. In the figure, the gray bar displays new planets verified by multiplicity . The exoplanets reported are up to February 26, 2014. Since 1998, over 1800 extrasolar planets have been discovered [39] either through radial velocity, direct imaging, transit, microlensing, and timing methods. The histogram shown in Figure 7.14 presents exoplanets by size. In the figure, the deep gray bars represent Kepler’s latest newly verified exoplanets. The data used are up to February 26, 2014. The majority of planetary detections so far have been obtained by using the radial velocity method from ground-based telescopes. The method needs the light from a star to be passed through a prism and split into a spectrum, rather like water droplets in the atmosphere splitting sunlight into a rainbow. Figure 7.15 illustrates radial velocity data from 51 Pegasi.
- Ivan Padron(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
9 Interferometry to Detect Planets Outside Our Solar System Marija Strojnik and Gonzalo Paez Centro de Investigaciones en Optica Mexico 1. Introduction Humanity has been interested in exploring its environment since earliest historical times. After traveling across oceans using star navigation (Scholl, 1993), we turned our attention to getting to know the planets inside our Solar system (Arnold et al., 2010). After they were visited at least once with robotic vehicles (Scholl & Eberlein, 1993) or with an orbiting satellite, we asked ourselves whether conditions existed on any other planet for some form of life. It has been reported that nearly 500 planets were discovered with indirect methods: (a) passage of a dark planet in front of the bright solar disc (Brown et al., 2001); (b) movement of the center of gravity of a two-body system and Doppler shift (Butler et al., 2001); (c) Gravitational bending of rays passing a solar system larger than due to only star (Udalski et al, 2005); (d) using spectroscopy (Richardson, 2007); and (e) astrometry, to list a few. Initial research findings include dust clouds and double stars with different sizes (Moutou et al, 2011; Wright et al., 2001). We rely principally on the visual system to receive the information about our environment. Such information is carried by the electromagnetic radiation. For a standard observer the visual spectral width covers only from about 0.38 m to about 0.78 m (1 m =10 -6 m, according to the MKS units employed in this paper) (Strojnik & Paez, 2001). Scientists have developed detectors to cover the electromagnetic spectrum from neutrinos and x-rays to radio waves. We use the word optical to cover visible and infrared (IR). Long-wave IR smoothly transitions into the sub-millimeter range. Many scientists differentiate between them upon incorporation of distinct detecting schemes.
eBook - PDFAstrobiology
An Evolutionary Approach
- Vera M. Kolb(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
The planet and star both orbit the system’s common center of mass. This means that the star’s spectral lines are shifted through the Doppler effect. This can then be used to determine the line-of-sight (or radial) velocity of the star and hence determine the properties of the orbiting planet. (Courtesy of European Southern Observatory [ESO], Garching, Germany.) 34 ◾ Astrobiology The radial velocity method is the most successful planet-hunting method to date, with more than 500 Exoplanet Detections. This ranges from planets with masses half that of the Earth, but with orbital periods of less than a day, to planets with masses more than 10 times that of Jupiter orbiting 6 times further from their star than the Earth is from the Sun. 2.5.1.2 Transit Method Another indirect method for detecting exoplanets works by looking for dips in the bright-ness of a star that might indicate that a body has passed between us and the host star, blocking some of the starlight. This is known as the transit method and is illustrated in Figure 2.8, which also shows actual data from the Wide Angle Search for Planets (WASP)-22 system (Johnson et al. 2009). If a transit repeats, then you can be reasonably confident that it is an orbiting body, rather than some transient event. The orbital period can then be used to determine orbital distance. The fraction of the starlight blocked can also be used to estimate the radius of the orbiting body and, hence, whether or not it might be a planet. The transit method alone, however, cannot typically be used to establish if the dip is due to an orbiting planet. It could be a brown dwarf star, which is a very-low-mass star with a radius similar to that of Jupiter-like planets. It could be an unresolved, distant binary star system that makes the brightness of the nearby star appears to dip periodically (in this case, even the periodicity would not imply a companion to the nearby star). It could be a grazing eclipse of a stellar companion.
eBook - ePub- Ian Morison(Author)
- 2013(Publication Date)
- Wiley(Publisher)
Chapter 4Extra-solar Planets
This is one of the most exciting areas of research being undertaken at the moment with the discovery of new planets being announced on a monthly basis. This chapter will describe the techniques that are being used to discover them and then discuss their properties. Perhaps a word of warning might be in order. An obvious quest is to find planetary systems like our own which could, perhaps, contain planets that might harbour life. So far, to many astronomers’ surprise, the vast majority of solar systems found have been very unlike our own which might lead one to the conclusion that solar systems like ours are very rare. The author has even heard this point of view put forward by an eminent astro-biologist. At this time, one should not draw this conclusion. For reasons which shortly become apparent, the techniques largely used to date would have found it very difficult to detect the planets of our own Solar System so it should not be surprising that we have so far failed to find many other similar solar systems. As new techniques are used, this situation will improve, but it will be many years before we have any real idea how often solar systems like our own have arisen in the galaxy. The story of the discovery of the first planet to orbit a sun-like star is very interesting in its own right, but, in order to appreciate its nuances, we need first to understand how this, along with the great majority of planets so far detected, has been discovered.4.1 The radial velocity (Doppler wobble) method of planetary detection
Our own Solar System gives us a good insight into this method and its strengths and weaknesses. Astronomers often use, as in this book, the phrase ‘the planets orbit the Sun’. This is not quite true. Imagine a scale model of the Solar System with Sun and planets having appropriate masses and positions in their orbits from the Sun. All the objects are mounted on a flat, weightless, sheet of supporting material. By trial and error, one could find a point where the model could be balanced on just one pin. This point is the centre of gravity of the Solar System model. The centre of gravity of the Solar System is called its barycentre, and both the Sun and planets rotate about this position in space (Figure 4.1
eBook - PDF- David A. Rothery, Iain Gilmour, Mark A. Sephton(Authors)
- 2018(Publication Date)
- Cambridge University Press(Publisher)
Another project likely to contribute greatly to the study of exoplanets is the European Extremely Large Telescope, which is scheduled to begin operations at Cerro Armazones, Chile, in 2024 (Figure 6.10). This will have a 39 m segmented mirror array and will use adaptive optics to achieve exceptional image quality. Figure 6.10 Artist’s impresson of the European Extremely Large Telescope (ESO/L. Calçada) AN INTRODUCTION TO ASTROBIOLOGY 222 6.4 Absorbed or occulted radiation In astronomy, the term ‘absorption’ refers to radiation having its energy absorbed by some matter. Strong absorption at certain wavelengths allows astronomers to detect the presence of gases in interstellar space, or in atmospheres of stars and planets. As mentioned in Section 6.3, once a planet has been discovered, these absorption lines can give us important information on what gases are present. However, this does not offer an effective means of planet hunting because exposure times of several days may be required to observe absorption lines of a star’s atmosphere. Occultation, as used in astronomy, refers to a situation in which one object blocks out some light from another object. A solar eclipse is an example of an occultation, as are planetary transits in front of the Sun (Figure 6.11). The passage of one object across another of larger apparent diameter, e.g. Mercury or Venus in front of the Sun, is known as a transit. Figure 6.11 (a) A solar eclipse, where the Moon covers the bright solar disc. (b) A transit of Venus in front of the Sun, seen at 171 nm (ultraviolet) ((a) NASA; (b) NASA/SDO) (a) (b) 6.4.1 The transit photometry method Let us now consider the drop in solar radiation incident on Earth that occurs when Venus passes directly between the Earth and the Sun. We will work this out mathematically and insert values only at the end. This will allow us to reapply the theory to planets around other stars.
eBook - PDF- Andrew Fraknoi, David Morrison, Sidney C. Wolff(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
as Saturn’s shepherd moons affect the orbits of the material in its rings. Protoplanets that grow to be 10 times the mass of Earth or bigger while there is still considerable gas in their disk can then capture more of that gas and become giant planets like Jupiter in the solar system. 21.4 Planets beyond the Solar System: Search and Discovery Several observational techniques have successfully detected planets orbiting other stars. These techniques fall into two general categories—direct and indirect detection. The Doppler and transit techniques are our most powerful indirect tools for finding exoplanets. Some planets are also being found by direct imaging. 21.5 Exoplanets Everywhere: What We Are Learning Although the Kepler mission is finding thousands of new exoplanets, these are limited to orbital periods of less than 400 days and sizes larger than Mars. Still, we can use the Kepler discoveries to extrapolate the distribution of planets in our Galaxy. The data so far imply that planets like Earth are the most common type of planet, and that there may be 100 billion Earth-size planets around Sun-like stars in the Galaxy. About 2600 planetary systems have been discovered around other stars. In many of them, planets are arranged differently than in our solar system. 21.6 New Perspectives on Planet Formation The ensemble of exoplanets is incredibly diverse and has led to a revision in our understanding of planet formation that includes the possibility of vigorous, chaotic interactions, with planet migration and scattering. It is possible that the solar system is unusual (and not representative) in how its planets are arranged. Many systems seem to have rocky planets farther inward than we do, for example, and some even have “hot Jupiters” very close to their star. Ambitious space experiments should make it possible to image earthlike planets outside the solar system and even to obtain information about their habitability as we search for life elsewhere.
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