How many planets surround other star systems?
How many planets surround other star systems?
Standing under a dark night sky, looking out at the Milky Way, it's hard to imagine countless planets don't exist elsewhere in the universe. After all, some 200 to 400 billion
stars inhabit our galaxy, and astronomers estimate at least 125 billion other galaxies exist. That's one heck of a number of stars in the universe — at least 25,000 billion billion. Looking at the nebular hypothesis, which describes how the solar system formed (see "How did the
In 2002, astronomers measured the mass of Gliese 876b, an exoplanet orbiting a red dwarf star 15 light-years away in the constellation Aquarius. They found the little planet, depicted here in artwork, has only half Jupiter's mass.
solar system form?" p. 77), it seems clear most stars would form planets as their pro- togenitor clouds collapsed. Yet, due to the immense distances, seeing other planetary
systems remained a supreme challenge for astronomers until the past decade.
The first suspected detections of extrasolar planets, or exoplanets, as they are called, occurred in 1989. That year, astronomers reported variations in the radial velocities of two stars — HD 114762 in Coma Berenices and Alrai (Gamma Cephei) — and attributed those observations to the pull of exoplanets.
LONG-RANGE WEATHER. In 2001, astronomers measured an atmosphere around an exoplanet. In this artwork, the planet appears as a Jupiter-like world only 4 million miles from its star.
However, follow-up data showed the cause was unknown, and it took another 10 years to confirm exopianets orbit these stars. Meanwhile, in 1992, another astronomer claimed to detect an exoplanet orbiting the pulsar PSR 1257+12. Astronomers eventually confirmed this "pulsar planet," as it came to be known.
During the mid-1990s, exoplanet detection boomed. Astronomers honed their techniques and created improved instruments, and, by 1995, they observed the first exoplanet around a Sun-like star. The first discovery of an exoplanet was around the star 51 Pegasi. By November 2006, astronomers had discovered 210 planets in 180 separate Sun-like systems. Additionally, four exoplanets are known to orbit two pulsars.
Detecting exoplanets is tricky because the feeble light from the planets appears next to the bright glare of the host stars. At present, astronomers use six techniques to find exoplanets. The first is pulsar timing, the method used to find the planet orbiting PSR 1257+12. This technique measures anomalies in the regularity of the pulsar's pulses.
Second, astronomers have employed astrometry, precise positional measurements, to attempt exoplanet detection since 1943. However, it has failed to uncover an extrasoiar planet.
Third is the radial velocity method, which measures the speed at which an object (in this case, a star) moves toward or away from Earth. An exoplanet's gravitational tug creates
anomalies in the star's speed.This is by far the most successful method astronomers now use in the exoplanet hunt, resulting in most of the finds thus far.
The fourth technique is called gravitational microlensing, in which the gravitational field of a star and its exoplanet bend the light from a distant background object.
A lone star bends light differently than one with a planet orbiting it. The number of background stars seen with this technique is maximized when astronomers look at stars between Earth and the galactic center.
Fifth is the transit method.Through this technique, astronomers detect exoplanets
as they pass in front of their host star, causing a drop in light intensity.
The final method, direct observation, first worked in 2005, when astronomers used the Spitzer Space Telescope to image infrared radiation from two exoplanets.
With the number of exoplanets growing week by week, researchers plan new and ambitious projects to expand the number of discoveries dramatically.The exoplanets found thus far are nearly all large "hot Jupi- ters." Future missions such as COROT, Darwin, and Kepler will attempt to find smaller, rocky, earthlike planets that must inhabit the galaxy in vast numbers.hs
EVAPORATING PLANET. In ‘ 2003, astronomers discovered the planet designated HD 209458b. It lies so close to its parent star> it's scorched like a moth that flies too close to a flame.
Standing under a dark night sky, looking out at the Milky Way, it's hard to imagine countless planets don't exist elsewhere in the universe. After all, some 200 to 400 billion
stars inhabit our galaxy, and astronomers estimate at least 125 billion other galaxies exist. That's one heck of a number of stars in the universe — at least 25,000 billion billion. Looking at the nebular hypothesis, which describes how the solar system formed (see "How did the
In 2002, astronomers measured the mass of Gliese 876b, an exoplanet orbiting a red dwarf star 15 light-years away in the constellation Aquarius. They found the little planet, depicted here in artwork, has only half Jupiter's mass.
solar system form?" p. 77), it seems clear most stars would form planets as their pro- togenitor clouds collapsed. Yet, due to the immense distances, seeing other planetary
systems remained a supreme challenge for astronomers until the past decade.
The first suspected detections of extrasolar planets, or exoplanets, as they are called, occurred in 1989. That year, astronomers reported variations in the radial velocities of two stars — HD 114762 in Coma Berenices and Alrai (Gamma Cephei) — and attributed those observations to the pull of exoplanets.
LONG-RANGE WEATHER. In 2001, astronomers measured an atmosphere around an exoplanet. In this artwork, the planet appears as a Jupiter-like world only 4 million miles from its star.
However, follow-up data showed the cause was unknown, and it took another 10 years to confirm exopianets orbit these stars. Meanwhile, in 1992, another astronomer claimed to detect an exoplanet orbiting the pulsar PSR 1257+12. Astronomers eventually confirmed this "pulsar planet," as it came to be known.
During the mid-1990s, exoplanet detection boomed. Astronomers honed their techniques and created improved instruments, and, by 1995, they observed the first exoplanet around a Sun-like star. The first discovery of an exoplanet was around the star 51 Pegasi. By November 2006, astronomers had discovered 210 planets in 180 separate Sun-like systems. Additionally, four exoplanets are known to orbit two pulsars.
Detecting exoplanets is tricky because the feeble light from the planets appears next to the bright glare of the host stars. At present, astronomers use six techniques to find exoplanets. The first is pulsar timing, the method used to find the planet orbiting PSR 1257+12. This technique measures anomalies in the regularity of the pulsar's pulses.
Second, astronomers have employed astrometry, precise positional measurements, to attempt exoplanet detection since 1943. However, it has failed to uncover an extrasoiar planet.
Third is the radial velocity method, which measures the speed at which an object (in this case, a star) moves toward or away from Earth. An exoplanet's gravitational tug creates
anomalies in the star's speed.This is by far the most successful method astronomers now use in the exoplanet hunt, resulting in most of the finds thus far.
The fourth technique is called gravitational microlensing, in which the gravitational field of a star and its exoplanet bend the light from a distant background object.
A lone star bends light differently than one with a planet orbiting it. The number of background stars seen with this technique is maximized when astronomers look at stars between Earth and the galactic center.
Fifth is the transit method.Through this technique, astronomers detect exoplanets
as they pass in front of their host star, causing a drop in light intensity.
The final method, direct observation, first worked in 2005, when astronomers used the Spitzer Space Telescope to image infrared radiation from two exoplanets.
With the number of exoplanets growing week by week, researchers plan new and ambitious projects to expand the number of discoveries dramatically.The exoplanets found thus far are nearly all large "hot Jupi- ters." Future missions such as COROT, Darwin, and Kepler will attempt to find smaller, rocky, earthlike planets that must inhabit the galaxy in vast numbers.hs
EVAPORATING PLANET. In ‘ 2003, astronomers discovered the planet designated HD 209458b. It lies so close to its parent star> it's scorched like a moth that flies too close to a flame.
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