If you had clear skies this week, you probably noticed the big, bright moon next to the big, bright planet Jupiter. Jupiter drew closest to the Earth on April 8 and now appears brighter in the night sky than at any other time in the year. Not only are beginners and amateurs alike pointing telescopes at this brilliant dot to enjoy views of its shifting cloud belts and dancing moons, professional astronomers are, too.
On Monday, April 3, the Hubble Space Telescope took advantage of this happy alignment and turned its sharp eye towards Jupiter to snap fresh photos in ultraviolet, visible and infrared light. The final image shown above reveals a wealth of features in its dense atmosphere as small as 80 miles (130 km) across.
The surface — or really the atmosphere, since Jupiter offers no hard surface to see like Mars or the moon — is divided into a half dozen or more distinct, colorful bands or cloud belts running parallel to the equator and separated by brighter “zones.” The bright zones have higher, thicker clouds with a greater concentration of ammonia ice crystals compared to the ruddy-gray belts that lie deeper in the atmosphere and are overlaid with a thick, smoggy haze. Wind speeds up to 400 mph (650 km/hour) stretch Jupiter’s clouds out into bands and zones; they also keep the differing concentrations of ammonia separate.
The Great Red Spot (GRS) is Jupiter’s most recognizable feature. It’s a hurricane-like storm 1.3 times the size of the Earth, and like a cherry on a sundae, it really does sit atop the lower cloud deck. This latest Hubble photo confirms that this whirlpool of ruddy clouds which has raged on the planet since the 1600s continues to shrink. Astronomers still aren’t sure why. Riding the sea of ammonia clouds well to the west of the GRS is a similar but smaller storm fittingly nicknamed “Red Spot Junior.
These recent observations of Jupiter form part of the Outer Planet Atmospheres Legacy (OPAL) program, where astronomers use the Hubble each year to observe the outer planets to help us better understand not only their atmospheres but also our own and those of the many exoplanets discovered around other stars. The program began in 2014 with Uranus, and has been studying Jupiter and Neptune since 2015. In 2018, it will begin viewing Saturn.
The moon slides further from Jupiter tonight, moving about a fist a day to the east in its orbit. But the planet will make a great nighttime companion for months to come. Take a look at your next opportunity for bright, pale yellow “star” in the southeastern sky after about 9 p.m.