Is Jupiter's Red Spot on its way out?

by Isheeta Sumra - Cosmos Online

New high-resolution maps of Jupiter have provided the best evidence yet that the planet's Great Red Spot - the biggest storm in the Solar System - is shrinking.

Scientists led by Xylar Asay-Davis at the University of California, Berkeley, collected both new and historical data from instruments mounted on space probes such as Galileo and Cassini and used it to create detailed maps of wind speeds in the planet's atmosphere.

"We have shown much more definitively [than before] that the Great Red Spot has been shrinking over the past decade," said Davis, based at the university's Computational Fluid Dynamics Laboratory.

365 km smaller each year

From 1996 to 2006, the spot's diameter has shrunk at an average rate of 365 km a year, he said. The research will be published later this year in the journal Icarus.

The Red Spot is twice as large as the Earth. The colossal weather system has lasted at least 300 years (when observations began), but may be much older. It has sparked the interest of numerous experts as it offers clues about the climate of Jupiter, a gas giant with no visible solid surface.

The storm is made up of gases such as hydrogen, helium, ammonia, methane and water vapour; the same gases and particles that constitute the Jovian atmosphere. What gives it the distinctive red colour has yet to be confirmed, but scientists believe it may result from material drawn up from deeper in Jupiter's atmosphere, below the ammonia clouds.

Previously, changes in the size of the spot were estimated by looking at cloud patterns created by the storm. To get a more accurate measure Asay-Davis' team has developed new software - using methods for studying fluid dynamics - that can precisely follow the movement of cloud patterns over long periods of time.

Cloud patterns

The shrinking of the spot tells us about the energy balance in the surrounding atmosphere, said Asay-Davis. The amount of energy leaving the Red Spot is not being balanced by the energy the storm is gaining, he said.

What has brought this about, though, is not yet known. "My suspicion is that the spot may undergo periods where it grows, and periods where it shrinks, but this is not well understood and we have never seen the Great Red Spot growing," said Davis.

Warrick Couch, President of the Astronomical Society of Australia and an astrophysicist at Swinburne University of Technology, in Melbourne, said the research was significant.

"The fact that we see gross changes in Jupiter's weather over time is of much interest, given the prominence of the current debate over climate change on Earth," he said.

"Advanced instrument technologies and the use of clever measurement techniques are allowing astronomers to get the first glimpses of weather on planets orbiting stars other than our Sun," added Couch.

Great Red Spot

Shrinking spot: Image shows a series of images of the storm taken by the Hubble telescope. Researchers now say that the amount of energy leaving the Red Spot is not being balanced by the energy the storm is gaining.

Credit: Amy Simon et al. & the Hubble Heritage Team (AURA/ STScI/ NASA)