Posts Tagged ‘doppler effect’

Old Method Finally Yields Results

Monday, June 1st, 2009 by Bellatrix

Modern develops in hunting for planets outside of our own solar system have yielded the discovery of well over a hundred different planets now. These newer methods include very new telescopes with the resolving power of being able to actually see an exoplanet, with which only 1 so far has been confirmed photographed, and other methods include using radial stellar velocity, or the Doppler effect, and the transit method. Now for the first time since its inception 50 years ago the method of astrometry has found an exoplanet.

The method of astrometry was first thought of 50 years ago to search for planets outside our solar system, called exoplanets. It involves measuring the precise motions of a star on the sky as an unseen planet tugs the star back and forth. But the method requires very precise measurements over long periods of time, and until now, has failed to turn up any exoplanets. This method is different from the more commonly used method of using the Doppler Effect or radial velocity of a star. Most exoplanets have been detected by watching for a wobble of a star, a gravitational tug from an orbiting planet due to the Doppler Effect. Astrometry also looks for a wobble but it is different  it measures the displacement the planets cause in their parent star’s apparent position on the sky, due to their mutual orbit around the center of mass of the system.

Two astronomers from NASA’s jet propulsion laboratory in California have been collecting data for the past 12 years from an instrument mounted on a telescope at the Palomar Observatory near San Diego. After looking at data from 30 different stars they have finally found what they were looking for: a planet surrounding the star VB 10. The planet itself is about 6 times the mass of Jupiter and an orbit a bit farther out making a cold Jupiter.  The star itself is quite small, a dwarf, at only 1/12 the mass of the sun. For a long time VB 10 was known as one of the smallest stars and now is the smallest star with a planet around it.  Because the star is so small, its planetary system would be a miniature, scaled-down version of our own. For example, VB 10b is located about as far from its star as Mercury is from the Sun. Any rocky Earth-sized planets that might happen to be in the neighborhood would lie even closer in.

The finding confirms that astrometry could be a powerful planet-hunting technique for both ground- and space-based telescopes. For example, a similar technique would be used by SIM Lite, a NASA concept for a space-based mission that is currently being explored. This is an exciting discovery because it shows that planets can be found around extremely lightweight stars. It seems that nature likes to form planets, even around stars quite different from our Sun. Now that it’s proven that this technique actually works and yields results it seems likely others might take it up, and more exoplanets will be found. One more tool in the planet hunter’s arsenal; one step possibly closer to finding a planet like our own.

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Extrasolar Planet Finding

Monday, September 15th, 2008 by Bellatrix

As of September 2008 a total of 309 extrasolar planets have been discovered. So far only massive gas giants, like Jupiter, have been detected, although some as small as Neptune. No terrestrial, or earth like planets, have been discovered yet. This is because of the current limitations on the technology, or the method, used to detect planets. However, this will hopefully be changing soon.

Currently it is difficult to locate earth-sized planets because they are very small, and do not give off much reflected light from their stars. So far no planet has been bright enough on its own to be detected by our telescopes. We can only detect planets by the small gravitational effects these planets have on their host stars. Planets do not have much mass compared to stars but the little mass they have exerts a pull on their stars; it makes them wobble slightly. We can use the Doppler effect to measure this wobble. The Doppler effect makes it so that the light from the star is bluer when moving toward us, and redder when moving away from us. So when watching a star with a planet around it, the pull from the planet as it orbits the star causes this shift in the observed light from the star, thus we know the planet is there. However, the mass of earth-sized planets is too small to create any noticeable wobble.

However, progress is definitely being made. The Subaru Telescope, located atop mount Mauna Kea in Hawaii, has an 8.2-meter mirror and has recently started scanning nearby stars looking for planets. There are eight innovative cameras and spectrographs at Subaru optimized for various astronomical investigations in optical and near-infrared wavelengths. One of these cameras is called HiCIAO, or High Contrast Instrument for the Subaru Next Generation Adaptive Optics. It is designed to block out the harsh direct light from a star, so that nearby faint objects such as planets can be viewed. The new adaptive optics system uses 188 actuators behind a deformable mirror to remove the atmospheric distortion from its view, allowing Subaru Telescope to observe close to its theoretical performance limits. The Subaru Telescope hopes to be the first to directly observe a planet outside our solar system.

Now even though Subaru hopes to be the first to direct image a planet, it still cannot detect an earth-sized planet. NASA was planning on launching a space telescope for this purpose called the terrestrial planet finder. This would consist of two observatories planned to not only detect these types of planets but also even study their characteristics such as size, distance from star, and even atmospheric components. However, due to budget cuts at NASA the project has been postponed indefinitely. I think until this project, or a similar one is funded and launched, we will continue to be limited by our current earth-based telescopes, and earth-like planets will remain outside our view.

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