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Distant Planets II

April 29, 2014

In 1988, astronomers at McDonald Observatory embarked on an ambitious new project. They used the Observatory’s 107-inch telescope to make frequent observations of more than two dozen stars. Their goal was to discover planets orbiting those stars by looking for a slight “wobble” in the stars’ light.

In the quarter-century since then, the project has expanded to cover hundreds of stars, using both the original telescope and the much larger Hobby-Eberly Telescope. It’s discovered several planets and confirmed many others, and it’s helping theorists understand how planetary systems form and evolve.

The search uses a technique known as radial velocity.

The concept is simple: An orbiting planet’s gravity tugs on its parent star, causing a tiny back-and-forth shift in the star’s spectrum — its individual wavelengths of light. Measuring that shift can not only reveal a planet’s presence, it can yield the planet’s mass and its distance from its star.

In practice, though, the technique is tough to implement — especially for planets that are a long way out from their stars. A distant planet’s gravitational tug is so gradual that the shift in the star’s light is quite small, so it takes a lot of observations to confirm it.

The McDonald search has looked at each of its target stars many times — from a few dozen to a couple of hundred. That’s yielded several planets that are far away from their stars — which we’ll talk about tomorrow.


Script by Damond Benningfield, Copyright 2014

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