Astronomers using the NASA/ESA Hubble Space Telescope observed Saturn, the second largest planet in our Solar System, in 2018, 2019, and 2020, just after the northern hemisphere summer solstice. These observations are part of Hubble’s Outer Planets Atmospheres Legacy (OPAL) program.
Hubble images of Saturn taken in 2018, 2019, and 2020 as the planet’s northern hemisphere summer transitions to fall. Image credit: NASA / ESA / STScI / A. Simon / R. Roth.
Saturn is the sixth planet from our Sun and orbits at a distance of about 1.4 billion km (886 million miles) from the Sun.
It takes around 29 Earth years to orbit the Sun, making each season on Saturn more than seven Earth years long.
Earth is tilted with respect to the Sun, which alters the amount of sunlight each hemisphere receives as our planet moves in its orbit. This variation in solar energy is what drives our seasonal changes.
Saturn is tilted also, so as the seasons change on that distant world, the change in sunlight could be causing some of the observed atmospheric changes.
“These small year-to-year changes in Saturn’s color bands are fascinating,” said Dr. Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center.
“As Saturn moves towards fall in its northern hemisphere, we see the polar and equatorial regions changing, but we are also seeing that the atmosphere varies on much shorter timescales.”
“What we found was a slight change from year-to-year in color, possibly cloud height, and winds — not surprising that the changes aren’t huge, as we’re only looking at a small fraction of a Saturn year.”
“We expect big changes on a seasonal timescale, so this is showing the progression towards the next season.”
The new Hubble data show that from 2018 to 2020 the equator got 5-10% brighter, and the winds changed slightly.
In 2018, winds measured near the equator were about 1,600 kmh (1,000 mph), higher than those measured by NASA’s Cassini spacecraft during 2004-2009, when they were about 1,300 kmh (800 mph).
In 2019 and 2020, they decreased back to the Cassini speeds.
Saturn’s winds also vary with altitude, so the change in measured speeds could possibly mean the clouds in 2018 were around 60 km (37 miles) deeper than those measured during the Cassini mission.
The findings were published in the Planetary Science Journal.
_____
Amy A. Simon et al. 2021. Midsummer Atmospheric Changes in Saturn’s Northern Hemisphere from the Hubble OPAL Program. Planet. Sci. J 2, 47; doi: 10.3847/PSJ/abe40f
