Jupiter's Great Red Spot

Located nearly 500 million miles away, the giant planet Jupiter’s atmosphere is a roiling cauldron of activity. It includes lightning, oppositely moving cloud belts, and hundreds of rotating storms that appear as large red, white, or brown ovals. The largest of these storms is the legendary anticyclone called the Great Red Spot (GRS). In fact, the GRS is the largest known storm in the solar system.

Located in Jupiter’s southern hemisphere, the GRS is larger than Earth, with winds inside it raging at 500 miles per hour. While its longitude drifts relative to surrounding atmospheric bands, the storm’s latitude has been stable for as long as records of it have been kept. The GRS may have been seen as early as 1632 by Leander Bandtius, Abbot of Dunisburgh. In 1664, the philosopher, architect, and polymath Robert Hooke reported observing a spot that moved from east to west on the planet. The next year, astronomer, mathematician, and engineer Giovanni Cassini was the first to note a “permanent spot.”

The Voyager spacecraft in 1979 measured the long axis of the GRS to be 14,500 miles across; historic observations as far back as the late 1800s gauged the GRS to be 25,500 miles across. Hubble’s long life has allowed astronomers to follow Jupiter’s atmospheric activity over a period spanning nearly two decades. In a study led by Amy Simon of NASA’s Goddard Space Flight Center, Hubble observations show that the GRS is now approximately 8,000 miles from top to bottom and 10,250 miles across: the GRS has now shrunk to the smallest size ever measured, having lost half its size over the past hundred years.

The Hubble observations indicate that the GRS is getting smaller by 580 miles per year along its major axis and its shape is changing from an oval to a circle. At the current rate, the storm is expected to become circular in four years. The vortex could completely disappear or grow larger, since the fate of such storms (even storms on Earth) is difficult to model and predict precisely due to their complexity.

In the new Hubble observations, it is apparent that very small eddies are feeding into the storm. Simon and her team hypothesize that these eddies may be responsible for the sudden change by altering the internal dynamics and energy of the GRS. They plan to study the future motions of the small eddies, along with the internal motions of the GRS, to determine whether such eddies can feed or sap momentum entering the upwelling vortex and contribute to changes in the size and shape of the Great Red Spot.

Distance: 5th planet from the Sun; average distance from the Sun is 778 million km (484 million miles) or 5.2 astronomical units (AU)

Instrument: WFC3/UVIS

Image Filters: 395nm, 502nm, 631nm