WASHINGTON - Jupiter's Great Red Spot seems to be on a cosmic diet, shrinking rapidly before our eyes.

Astronomers using the Hubble Space Telescope calculate that the spot, a giant long-lasting storm, is narrowing by about 580 miles a year, much faster than before.

In the late 1800s the red spot was an oval 25,500 miles wide. Now it's a circle that's 10,250 miles across.

Michael Wong, a scientist at the University of California, Berkeley, said astronomers don't know why it's red or shrinking, or what will happen next. If this pace continues, in 17 years the spot could be gone.

Wong said one theory is the spot eats smaller storms, and it is consuming fewer of them.