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The brightest star in the night sky stands due south at nightfall. The "dog star" Sirius is the leading light of Canis Major, the big dog. It represents the dog's head.

Down near the dog's tail is a cluster of dozens of young stars. Known as NGC 2362, it's easily visible through binoculars. And if you have especially clear, dark skies, you can even see it with your eyes alone.

Because all of its stars were born at the same time, from the same giant cloud of gas and dust, the cluster is a good laboratory for studying the processes that give birth to stars and planets. In fact, a recent study of the cluster suggests that giant planets form in a hurry.

Astronomers used Spitzer Space Telescope to detect the infrared glow of gas and dust around the cluster's stars. The gas is the key ingredient for forming giant planets like Jupiter, the giant of our own solar system. The planet forms a dense core as chunks of rock and ice merge into a single body. Then its gravity sweeps up enormous amounts of gas, so the planet grows to giant proportions.

In NGC 2362, there's no gas left around stars as massive as the Sun or bigger, and almost none around smaller stars. The gas has already been scooped up, or blown away by the star. So there's nothing left to give birth to giant planets.

Since the cluster is only about five million years old, that means that if giant planets are going to form at all, they have to do so within five million years.

Script by Damond Benningfield, Copyright 2009

For more skywatching tips, astronomy news, and much more, read StarDate magazine.