Earth’s Northern Hemisphere is not the only one in the midst of summer. The northern region of Saturn is also in summer, and now the Hubble Space Telescope has captured a crisp image of its cloud layers and glistening rings.
"It's amazing that even over a few years, we're seeing seasonal changes on Saturn," lead investigator Amy Simon, of NASA's Goddard Space Flight Center, said in a statement.
This image is particularly striking when compared to the previous Hubble portrait of Saturn from last year and the Cassini spacecraft's observations from a few years back. The spacecraft witnessed first-hand the seasonal changes of Saturn over 13 years, but Hubble has conducted observations for over twice as long. The changes in color are particularly striking.
The change in color is believed to be due to a red haze that spreads across the planet's hemisphere during spring and summer. The timing of the haze suggests it is linked to the increased sunlight that part of the planet receives during this time of year. However, the exact mechanism is uncertain. One possible solution is that the spring and summer months are reducing the amount of ice in the atmosphere, letting aerosols out. Another possibility is that the increase in sunlight produces chemical reactions in the hydrocarbons in the atmosphere, which creates a photochemical haze that envelopes half of the planet.
In this photo, a more intense blue is detected from the southern hemisphere, where the reddish haze is probably lacking. This is similar to the color of Saturn’s peculiar hexagonal polar vortex during the Northern winter and early spring.
As the planet goes around the Sun, different areas of the planet experience varying amounts of illumination. Saturn has a tilt relative to its orbit of 27 degrees, similar to Earth’s own of 23 degrees. A full orbit takes about 30 years, so each Saturnian season is roughly 7.5 years instead of 4 months.
Hubble has been active for three decades, observing Saturn for most of this time, including the southern spring and summer, as well as the Northern spring and the beginning of summer. The northern hemisphere of Saturn had its summer solstice in May 2017, so in a few more months the planet will reach mid-summer.