Math in the Physical Sciences

Astronomy and Math

How was math used to discover extrasolar planets?

Astronomers have always dreamed about detecting other planets outside our solar system—extrasolar planets. In 1994, Polish astronomer Alekzander Wolszczan (1946-) announced the discovery of the first extrasolar planet—actually, two planets with masses 3.4 and 2.8 times that of Earth’s mass—orbiting the pulsar PSR B1257+12. A pulsar star sends out a periodic pulse of light detected from Earth; Wolszczan found the planets by measuring the periodic variation in the pulse arrival time.

There are several major methods used to search for extrasolar planets, and all entail using mathematics. For example, the Doppler shift method measures the change in wavelength (color) of light coming from a star over the course of days, months, and years. The change in wavelength—or the Doppler shift of the light—is caused by the star orbiting a common center of mass with a companion planet. An example in our own solar system is the gas giant Jupiter. Its massive gravitational pull causes the Sun to wobble around a circle with a velocity of 39.4 feet (12 meters) per second.

Another detection method is called astrometry, which measures the periodic wobble that a planet causes in the position of its parent star. In this case, the minimum detectable planet mass gets smaller in inverse proportion to the planet’s distance from the star.

These methods work, and as of 2011 more than 700 such planets have been discovered. If you want to see an updated list of the extrasolar planets, try maintained by astronomers at the Paris Observatory in France.


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