Estimating orbital period of exoplanets in microlensing events

Our Milky Way galaxy contains a minimum of billion planets according to a detailed statistical study based on the detection of three extrasolar planets by an observational technique called microlensing. This means that there is likely to be a minimum of 1, planets within just 50 light-years of Earth. The telescope studied comets and asteroids, counted stars, scrutinized planets and galaxies, and discovered soccer-ball-shaped carbon spheres in space called buckyballs.

Spitzer Space Telescope. This artist concept depicts "multiple-transiting planet systems," which are stars with more than one planet. The planets eclipse, or transit, their host stars from the vantage point of the observer Star System Bonanza. This artist's concept illustrates the idea that rocky, terrestrial worlds like the inner planets in our Solar System may be plentiful, and diverse, in the Universe.

Rocky, Terrestrial Worlds. Today Keplerb is receiving 10 percent more energy from its parent star than the Earth is from the Sun. If Keplerb had the same mass as Earth it would be on the verge of experiencing the run A Window Into Time. Artist's representation of the "habitable zone," the range of orbits where liquid water is permitted on the surface of a planet.

Odds are on Oodles of Earths. Vulcan-like planet: Fact or fiction?

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This image from NASA's Kepler mission shows the telescope's full field of view -- an expansive star-rich patch of sky in the constellations Cygnus and Lyra. NASA's Kepler mission has discovered a world where two suns set over the horizon instead of just one.

Time Delay in Microlensing Event. Planet Janssen, or 55 Cancri e, orbits a star called Copernicus only 41 light years away. PSO J Wandering alone in the galaxy, they do not orbit a parent star. These rogue planets glow faintly from t Where the Nightlife Never Ends. How do coronagraphs find exoplanets? Find out in this animation narrated by Dr. This artist's concept shows the closest known planetary system to our own-Epsilon Eridani.

Double the Rubble. VLT image of the protoplanet around the young star HD The "super-Jupiter" Kappa Andromedae b, shown here in an artist's rendering, circles its star at nearly twice the distance that Neptune orbits the sun. With a mass about 13 times Jupiter's, the obj Artist's rendering of the "super-Jupiter" Kappa Andromedae b.

This artist's concept depicts giant planets circling between belts of dust.

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Hidden in a Dust Halo. Artistic rendering of a planet's transmission spectrum.

Exoplanet Detection Techniques: How to Find a Planet

A Planet's Transmission Spectrum. Weather here is deadly. Rains of Terror Poster. This artist's conception shows Keplerb orbiting its host star, which has been tidally d We now believe there is at least one planet for every star in our galaxy. This major finding from the Kepler mission, launMicrolensing is the only known method capable of discovering planets at truly great distances from Earth.

Whereas radial velocity searches look for planets in our immediate galactic neighborhood, up to light years from Earth, and transit photometry can potentially detect planets at a distance of hundreds of light years from Earth, microlensing can find planets orbiting stars near the center of the galaxy, thousands of light-years away.

Some methods almost sound like science fiction: Using gravity as a magnifying glass, watching stars wobble at turtle-like speeds, and searching for tiny dips in starlight. Microlensing is an astronomical effect predicted by Einstein's General Theory of Relativity. According to Einstein, when the light emanating from a star passes very close to another star on its way to an observer on Earth, the gravity of the intermediary star will slightly bend the light rays from the source star, causing the two stars to appear farther apart than they normally would.

This effect was used by Sir Arthur Eddington in to provide the first empirical evidence for General Relativity. Now, if the source star is positioned not just close to the intermediary star when seen from Earth, but precisely behind it, this effect is multiplied.

Light rays from the source star pass on all sides of the intermediary, or "lensing" star, creating what is known as an "Einstein ring.

The resulting effect is a sudden dramatic increase in the brightness of the lensing star, by as much as 1, times. This typically lasts for a few weeks or months before the source star moves out of alignment with the lensing star and the brightness subsides.

estimating orbital period of exoplanets in microlensing events

While this is the normal pattern of a microlensing event, things are substantially different when the lensing star has a smaller companion. If a planet is positioned close enough to the lensing star so that it crosses one of the two light streams emanating from the source star, the planet's own gravity bends the light stream and temporarily produces a third image of the source star.

When measured from Earth, this effect appears as a temporary spike of brightness, lasting several hours to several days, superimposed upon the regular pattern of the microlensing event. For planet hunters, such spikes are the telltale signs of the presence of a planet. Furthermore, the precise characteristics of the microlensing light-curve, its intensity and length, tell scientists a great deal about the planet itself.

Its total mass, its orbit, and its period can all be deduced with a high degree of accuracy and probablity from the microlensing event.

NASA's search for habitable planets and life - Gary H. Blackwood (SETI Talks 2017)

Microlensing is capable of finding the most distant and the smallest planets of any currently available method for detecting extrasolar planets. In January scientists announced the discovery through microlensing of a planet of only five Earth masses, orbiting a star near the center of our galaxy, 22, light-years away! It was the lowest mass planet detected up to that time, and also the farthest from Earth.

Exploring Exoplanets with Kepler

Microlensing, furthermore, is most sensitive to planets that orbit in moderate to large distances from their star. This makes it complementary to the radial velocity and transit detection methods, both of which are most effective at detecting planets orbiting very close to their stars.

In fact, microlensing events can reveal the presence of free-floating or rogue planets that don't orbit stars at all. Finally, like transit photometry, microlensing searches are massive, targeting tens of thousands of planets simultaneously. If a microlensing event takes place anywhere within the observed starfield, it will be detected. Because of its sensitivity to low-mass planets that orbit at relatively large distances from their stars, microlensing surveys can yield discoveries of Earth-sized and smaller worlds orbiting at Earth-like distances from Sun-like and larger stars.

Unlike planets detected by other methods, which are associated with particular stars and can be observed repeatedly, planets detected by microlensing will never be observed again. This is because microlensing events are unique and do not repeat themselves.

Thanks to a microlensing event we know, for example, that the planet known as OGLE—BLGLb is a cold, rocky world orbiting a small, cool star near the center of the galaxy.

After several years have passed and the background star has moved away, astronomers can sometimes observe the lensing star again and learn more about it. As for the alien world itself, we will probably never know anything more about it, since it will never be observed again. Another problem with microlensing is that the distance of the detected planet from the Earth is known only by rough approximation. When dealing with planets tens of thousands of light-years away, this could mean errors of thousands of light-years!Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect.

It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light stars or large objects that block background light clouds of gas and dust.

These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light. When a distant star or quasar gets sufficiently aligned with a massive compact foreground object, the bending of light due to its gravitational field, as discussed by Albert Einstein inleads to two distorted unresolved images resulting in an observable magnification. The time-scale of the transient brightening depends on the mass of the foreground object as well as on the relative proper motion between the background 'source' and the foreground 'lens' object.

It enables the study of the population of faint or dark objects such as brown dwarfsred dwarfsplanetswhite dwarfsneutron starsblack holesand massive compact halo objects. The lensing works upon all wavelengths, magnifying in brightness and with a wide range of possible warping distant source objects that emit any kind of electromagnetic radiation. Microlensing by an isolated object was first detected in Since then, microlensing has been used to constrain the nature of the dark matterdetect exoplanetsstudy limb darkening in distant stars, constrain the binary star population, and constrain the structure of the Milky Way's disk.

Microlensing has also been proposed as a means to find dark objects like brown dwarfs and black holes, study starspotsmeasure stellar rotation, and probe quasars [1] [2] including their accretion disks. Microlensing is based on the gravitational lens effect. A massive object the lens will bend the light of a bright background object the source.

This can generate multiple distorted, magnified, and brightened images of the background source. Microlensing is caused by the same physical effect as strong lensing and weak lensing, but it is studied using very different observational techniques. In strong and weak lensing, the mass of the lens is large enough mass of a galaxy or a galaxy cluster that the displacement of light by the lens can be resolved with a high resolution telescope such as the Hubble Space Telescope.

With microlensing, the lens mass is too low mass of a planet or a star for the displacement of light to be observed easily, but the apparent brightening of the source may still be detected.

In such a situation, the lens will pass by the source in a reasonable amount of time, seconds to years instead of millions of years. As the alignment changes, the source's apparent brightness changes, and this can be monitored to detect and study the event.This activity is related to a Teachable Moment from May 6, The Transit of Mercury.

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A transit happens when a planet crosses in front of a star. From our perspective on Earth, we only ever see two planets transit the sun: Mercury and Venus.

Both are pretty rare events. Transits of Mercury happen only about 13 times per century and the next transit of Venus won't happen until ! While rare, transits have been used for centuries to track the movements and properties of planets in our own solar system. This activity features real-world applications of math concepts related to transits and gives students practice calculating the movements of planets in our solar system and other star systems.

Worksheet - Download PDF. Answer key - Download PDF. Calculators optional. In the early s, Johannes Kepler discovered that both Mercury and Venus would transit the sun in Today, radar is used to measure the distance between Earth and the sun with greater precision than can be found using transit observations, but the transit of Mercury still provides scientists with opportunities for scientific investigation in two important areas: exospheres and exoplanets.

Some objects, like the moon and Mercury, were originally thought to have no atmosphere. But scientists have discovered that these bodies are actually surrounded in an ultra-thin atmosphere of gases called an exosphere. Exoplanet Discoveries.

Space-Warping Planets: The Microlensing Method

Scientists discovered they could use that phenomenon to search for planets orbiting distant stars, called exoplanets, that are otherwise obscured from view by the light of the star. When measuring the brightness of far-off stars, a slight recurring dip in the light curve a graph of light intensity could indicate an exoplanet orbiting and transiting its star.

estimating orbital period of exoplanets in microlensing events

Additionally, scientists have begun exploring the exospheres of exoplanets. Because the distance between Earth and the sun 1 AU iskm and one Earth year is days, the distance and orbital period of other planets can be calculated when only one variable is known.

Kepler Exoplanet Discoveries - Click on each planet referred to in the student worksheet to view an interactive of the exoplanet system, the light curve that led to its discovery, and a chart pinpointing its location in the sky.

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Stay Connected. Calculators are optional but can simplify the calculations.Curator: Penny D Sackett. Eugene M. A microlensing exoplanet is a planet orbiting a star other than our own Sun that is detectable due to the effects that the gravitational field of its planetary system has on the passing light of a distant background star.

The microlensing technique is particularly well-suited to finding low-mass planets and planets around distant or very dim stars. Astronomers have published findings on several different microlensing exoplanets, with masses ranging from more than Jupiter to only a few times more massive than our own Earth. In microlensing, the separation of order a milli-arcsecond between multiple images is generally too small to be resolved by modern telescopes. The combined light of all images is instead observed as a single image of the source, blended with any light that may be emanating from the lens itself.

The brightness of the combined image is a function of the projected separation of the source and lens on the observer's sky, and thus can change as the source, lens and observer move relative to one another. The time variability of the combined image namely an apparent change in source brightness as a function of time recorded as a microlensing lightcurve is the usual observational signature of microlensing.

If the lens is a single, isolated, compact object and relative motions are rectilinear, the lightcurve of the background source is simple, smooth and symmetric see Figure 1. The background star appears to brighten and then dim as the projected separation between the source and lens first decreases and then increases.

For sources and microlenses are in our own Galaxy, a typical timescale for the detectable rise and fall of the apparent brightness of the source star is on the order of weeks to months. The basic shape is the same see Fig. Beginning in the s and proceeding to this day, millions of stars have been monitored every night in search of the few that are microlensed by an observable amount at that time. These surveys were motivated by the desire to measure the contribution of dim stars, stellar remnants, black holesand brown dwarfs to the unseen dark matter in the Milky Way.

Soon thereafter, however, they became important to the search for exoplanets orbiting faint stars and brown dwarfs, which would be difficult to detect by any means other than microlensing. If the lens is multiple, as is the case when the lens is a binary star or a star with planets, the magnification pattern experienced by a background source is no longer circularly symmetric on the sky.

In this case, the shape and maximum amplitude of the lightcurve depends on relative path the background source takes through the lens magnification pattern. The resulting lightcurve can exhibit large changes in shape over rather short periods of time if the background star passes near what is known as a caustic in the lensing pattern Mao and Paczynski Because the planet has a gravitational mass that is much smaller than that of the lensing star, the percentage of the lensing pattern area influenced by the planet will be relatively small.

This means that the probability that the source trajectory will cross the planet-affected area is low, and thus the chance of detecting a planet by microlensing is also low, even if the planet is present. On the other hand, the combined gravitational field of the star and planet can create strong deviations in the lensing pattern caustics over this small area.

This means that the changes in the lightcurve of the background source can be quite dramatic if it does happen to cross the planet-affected area. This is true even for planets with masses as low as that of Earth, as long as the size of the background source star is not more than about 5 times larger that the area of anomalous lensing pattern created by the planet. Both denominators depend on the mass of the lensing star not the source starwhile the Einstein radius depends on the relative distance of the lensing star along the sight line of the observer.

In summary, the microlensing can be used to study the statistical abundance of exoplanets in our Galaxy with properties similar to the planets in our own Solar System. In sum, the microlensing technique requires intensive use of telescope time, and is unsuitable for continued detailed study of individual exoplanets. An up-to-date list of known microlensing exoplanets can be found in the microlensing section of the Extrasolar Planets Encyclopaedia.

ExoplanetsWeak gravitational lensing. Penny D SackettScholarpedia, 5 1 Fossil Hunters. Table 3. The microlensing discoveries are compared to other known exoplanets in Fig. The first planet discovered by microlensing is shown in Fig. The light curve is plotted in units of the source star flux, which is determined by the best microlensing model to the event, because the star field is too crowded to determine the unmagnified stellar flux directly. As a result, MOA was able to detect the second caustic crossing for this event, and arrange for the additional observations that caught the caustic crossing endpoint thanks to first author, Ian Bond, who was monitoring the photometry in real time.

The naming convention for planets discovered is that the name from the first team to find the microlensing event is used for the event, so in this case OGLE. The sensitivity of various exoplanet detection methods is plotted in the mass vs. Doppler radial velocity detections are shown in black, with 1-sided error bars for the m sin i uncertainty. Planets first detected by transits are shown in blue, and the microlensing planet discoveries are shown in red.

The light red and red curves show the sensitivity of current and future microlensing planet search programs, and the purple curve gives the sensitivity of the proposed Microlensing Planet Finder MPF mission. When referring to the lens system, we add a suffix "L", and when referring to the source, we add an "S". For a lens or source system that is multiple, we add an additional capital letter suffix for a stellar mass object or a lower case letter for a planetary mass companion.

This convention provides names for multiple components of the source star system. Instead, the planetary deviation was detected in the observations of one of the survey teams, and identified in time to obtain additional data to confirm the planetary nature of. The top-left panel presents the complete data set during main panel and the OGLE data inset. The bottom panel is the same as the top panel, but with the MOA data grouped in 1 day bins, except for the caustic crossing nights, and with the inset showing MOA photometry during The binary- and single-lens fits are indicated by the solid black and cyan dashed curves, respectively.

The right panel shows the light curve and models during caustic traverse. The insets show the second caustic crossing and a region of the declining part of the light curve where the best-fit nonplanetary binary-lens model fails to fit the data. We will return to this strategy later in the discussion of future microlensing projects given in Sect.

Another notable feature of this event is that the lens star has been identified in HST images Bennett et al. As indicated in Fig. This separation, plus the mass-distance relation, eq. These show the amplitude for the offset of the centroids of the blended lens plus source images in different color bands. The HST data indicate a marginal detection of this color-dependent centroid shift at a level consistent with the assumption that the excess flux is due to the lens. The dashed vertical lines indicate the medians, and the shading indicates the central With this marginal detection of the color-dependent centroid shift, we can't be absolutely sure that the lens star has been detected because it is possible that the excess flux could be due to a companion to the source star.

It is straight forward to deal with this uncertainty with a Bayesian analysis Bennett et al. The triple peak two large symmetric peaks surrounding a small peak indicates that the source passed three cusps of a caustic, the middle one being weak insets. From Udalski et al.

estimating orbital period of exoplanets in microlensing events

The top left inset shows the OGLE light curve extending over the previous 4 years, whereas the top right one shows a zoom of the planetary deviation, covering a time interval of 1. Fortunately, we are able to detect the lens star in a set of HST images, and the light curve yields weak detections of both a finite source size and the microlensing parallax effect.

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So, we expect to determine the host star and planet masses and to convert their separation into physical units, but this analysis is not yet complete Dong et alin preparation. This planet is currently tied with G1 c Udry et al. This event was detected through a planetary caustic deviation, and the amplitude of the deviation was significantly reduced by the finite angular size of the clump giant source star.Sam Brind holds a master's in physics with theoretical physics MPhys from the University of Manchester.

Exoplanets are a relatively new field of research within astronomy. The field is particularly exciting for its possible input into the search for extraterrestrial life. Detailed searches of habitable exoplanets could finally give an answer to the question of whether there is or was alien life on other planets. 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.

As of April 1,there have been exoplanets discovered. The definition of a solar system planet, set by the International Astronomical Union IAU inis a body that meets three criteria:.

Extrasolar Planet Detected by Gravitational Microlensing

There are multiple methods that are used to detect new exoplanets, lets look at the four main ones. Directly imaging exoplanets is extremely challenging because of two effects. There is a very small brightness contrast between the host star and the planet and there is only a small angular separation of the planet from the host.

In plain english, the star's light will drown out any light from the planet because of us observing them from a distance much larger than their separation. To enable direct imaging both of these effects need to be minimised. The low brightness contrast is usually addressed by using a coronagraph. A coronagraph is an instrument which attaches to the telescope to reduce the light from the star and hence increase the brightness contrast of nearby objects. Another device, called a starshade, is proposed which would be sent into space with the telescope and directly block the star light.

The small angular separation is addressed by using adaptive optics. Adaptive optics counteract the distortion of light due to the Earth's atmosphere atmospheric seeing.

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This correction is performed by using a mirror whose shape is modified in response to measurements from a bright guide star. Sending the telescope into space is an alternative solution but it is a more expensive solution. Even though these issues can be addressed and make direct imaging possible, direct imaging is still a rare form of detection. Planets orbit around a star because of the gravitational pull of the star.

However, the planet also exerts a gravitational pull on the star. This causes both the planet and the star to orbit around a common point, called the barycentre. For low mass planets, such as Earth, this correction is only small and the movement of the star is only a slight wobble due to the barycentre being within the star.

For larger mass stars, such as Jupiter, this effect is more noticeable.


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