Jupiter's trademark Great Red Spot apparently isn't so great anymore.

The swirling anti-cyclonic storm, which is still much larger than the Earth, was recently measured by the National Aeronautics and Space Administration at its smallest size ever recorded.

Observations taken by NASA's Hubble Space Telescope confirm the Great Red Spot now is approximately 10,250 miles across, Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a news release.

In comparison, scientific analyses dating as far back as the late 1800s determined the storm was as large as 25,500 miles on its long axis, while NASA's Voyager 1 and Voyager 2 flybys of Jupiter in 1979 measured it to be approximately 14,500 miles across.

A Hubble image captured in 1995 showed the long axis of the spot stretching a smaller 13,020 miles across and then a 2009 image revealed the spot at only an estimated 11,130 miles across.

Then, starting two years ago, amateur observations detected an increase in the rate at which the spot is shrinking: by 580 miles per year and changing shape from an oval to a circle.

"In our new observations it is apparent very small eddies are feeding into the storm," said Simon. "We hypothesized these may be responsible for the accelerated change by altering the internal dynamics and energy of the Great Red Spot."

Simon said she and a team of fellow researchers plan to study the motions of the storm's small eddies and internal dynamics to determine whether those eddies are feeding or sapping the momentum of the vortex, and leading to the yet-to-be explained atmospheric downsizing.

Managed by the Goddard Flight Center, the Hubble Space Telescope is a cooperative project between NASA and the European Space Agency.

Operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C., the Space Telescope Science Institute in Baltimore conducts Hubble science operations.