|MadSci Network: Astronomy|
Planetary systems are a hot topic right now in astronomy! So you could keep reading my summary of planetary systems OR feel free to go to - www.exoplanets.org - for all the information you could possible want on the topic. It was only very recently in 1992 that a group of astronomers discovered a planet orbiting the neutron star, PSR 1257+12. Then the field began exploding with new discoveries of Jupiter-like planets around more normal stars like our own Sun. The total number of extrasolar planetary systems has risen to over 50!! Before these new discoveries, our only idea of what a planetary system might be like came from our own back yard - nine planets, some rocky, some gaseous, orbiting one, fairly average star. So classically, a planetary system consists of a group of terrestrial (Earth-like) and/or gas giant (Jupiter-like) planets orbiting around a star. While we have always assumed that if other planetary systems exist apart from our around the Sun they would have to be much like our own. This has proven to not be the case. There are a variety of different methods which can be used to identify extrasolar planetary systems - pulsar timing, radial Doppler shifts, direct imaging and transits - to name a few. Pulsar timing uses the outrageously accurate period of the radio pulses of a neutron star as it spins rapidly on its axis. The gravitational pull of an orbiting planet will disturb the pattern of the signals enough to be measured and then astronomers can use the physics of spinning bodies to determine the distance and mass of the otherwise invisible planet. This method was the first to detect any type of planet outside our own solar system and was a very significant result since it implied that our solar system is not unique. Even though pulsar timing was the first method to detect planets, it has not proven to be the most effective. That honor goes to a technique which uses the wobble of a normal star in the presence of a massive Jupiter-like planet. The light from the star undergoes a Doppler shift (like the change in the pitch of a car horn as it passed by you) as it wiggles toward and away from us due to gravitational pull of the massive planet. Most of the discoveries planetary systems using this method have been done by Geoff Marcy, Paul Butler, Michel Mayor and Didier Queloz. This type of planet search is good at finding massive planets near their parent stars since that results in a large enough wobble for us to detect at the Earth with present day large telescopes. The fact that so many gas giants exist so near their star (much closer than the Earth-Sun distance!) has surprised scientists since its so different than our solar system (Jupiter is 5 times further from the Sun than the Earth). Our ideas about how planetary systems are created and evolve has had to change to explain these observations. Another method of planet detection which is in its infancy involves seeing a planet block out the light from its parent star as it orbits around or "transits" the star. Since the planet does not produce that much light, the light from the star will dip as the planet orbits in front of it. This type of planet detection is tricky because it requires the orbit of the planet to be such that the planet travels between us and the star. Also, we need to be looking at the right star at the right time since the "event" might occur over a small percentage of the total orbit of the planet. Finally, we need to have telescopes which are sensitive enough to detect the ever so slight decrease in the star's light during the transit. This type of planet detection will become more common with bigger telescopes and more telescopes are being devoted to looking for such transit events. One simple method for finding planets is taking their picture or "direct imaging". This type of detection is not yet possible for even Jupiter-like planets due to the fact that a star is so much brighter than a gas planet that its light overwhelms any light from a planet close to the star. Even if the planet were far away from the star, our telescopes just don't presently have the light gathering power to see them. This will improve dramatically with bigger, more sensitive telescopes. There is a bright future for finding many more planetary systems as NASA is focusing a lot of resources on this endeavor through future space telescopes and present programs like the Doppler studies. One telescope, called the Terrestrial Planet Finder, has the goal of finding Earth-sized planets around neighboring stars using a special kind of telescope know as an interferometer. This is definitely a topic of astronomy to keep and eye on. I can guarantee you'll see many future stories of discovery on the news. Thanks for your question! I wish to pursue this type of research in the future so this was a great chance for me to review the topic. Angelle Tanner UCLA Astronomy
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