The Great Red Spot on Jupiter is a little less great than it used to be.
New images of the spot taken in April by the Hubble Space Telescope indicate that it’s about 10,250 miles across, according to Amy Simon, an expert on Jupiter’s atmosphere at NASA’s Goddard Space Flight Center in Greenbelt, Md. That’s the smallest it’s been since astronomers began keeping track of it more than 100 years ago.
The Great Red Spot is actually a giant anticyclonic storm that’s bigger than Earth. Inside the storm, winds can reach speeds of several hundred kilometers per hour, according to the European Space Agency’s Hubble team.
Hubble’s latest observations show that “very small eddies are feeding into the storm,” Simon said in a statement from NASA. The eddies “may be responsible for the accelerated change by altering the internal dynamics and energy of the Great Red Spot,” she said.
In the late 1800s, astronomers estimated that the storm was 25,500 miles wide – big enough to fit three Earths side by side. By the time Voyager 1 and Voyager 2 flew by in 1979, the spot was only 14,500 miles across.
Hubble, which launched in 1990, took a picture of the Great Red Spot in 1995 that showed the storm was slightly more than 13,020 miles wide. Another photo from 2009 pegged it at only 11,130 miles wide, according to NASA.
The shrinking accelerated in 2012, with the storm losing about 580 miles each year. In the process, the once-oval spot has become more circular, NASA says.
Simon says she plans to investigate whether the eddies Hubble witnessed are changing the storm’s momentum. In the meantime, the source of the spot’s shrinking remains a mystery.