Jupiter is known for its Great Red Spot, a feature discovered by Galileo over 400 years ago! Astronomers have tracked its size and shape for over a century, but the most accurate measurements come from the Hubble Space Telescope. Every time Earth and Jupiter are closest, Hubble takes a series of images and from these images it was determined that the spot wobbles from day to day. Not only does it change size, but it also changes length and width, baffling astronomers.
Jupiter is the largest planet in the solar system and, like the other outer planets, is a giant ball of gas. It's so big that it can fit all the other planets in the solar system, leaving plenty of room left over. Composed primarily of hydrogen and helium, it can be seen with amateur telescopes as a colorful disk with belts, storms and, of course, the Great Red Spot. The site was first discovered by Galileo around 1610, when he became the first person to point a telescope at the distant planet.
Side-by-side images show the opposite sides of Jupiter. The largest storm, the Great Red Spot, is the most noticeable feature in the lower left third of this view. Image credit: NASA, ESA, Amy Simon (NASA-GSFC).
The Great Red Spot is a storm that has raged for over 400 years. It's large enough that Earth could easily fit in more than once, and it's an anticyclonic system similar to those seen here on Earth. It rotates counterclockwise at speeds of over 400 mph. Over the years the overall size appears to have decreased, although not as quickly as expected.
“Great red spot from P7 Flyover”. Image credit: NASA / SwRI / MSSS / Jason Major © public domain
Images of the storm captured by Hubble were collected over a 90-day period between December 2023 and March 2024, when Jupiter was closest to Earth. Its high-resolution cameras showed that it wobbles like a bowl of jelly and is certainly not as stable as we once thought. Previous studies have shown that there is some movement along the long axis, but no evidence of size changing.
The team of astronomers, led by Amy Simon of NASA's Goddard Space Flight Center in Maryland, published their findings in the Planetary Science Journal. Simon's said: “This is really the first time we have the correct frame rate of the GRS. Because of Hubble's high resolution, we can say that the GRS is definitely moving in and out while moving faster and slower at the same time. This was very unexpected and currently there are no hydrodynamic explanations.”
The study was part of NASA's Outer Planet Atmospheres Legacy program (OPAL), whose goal is to obtain a long time series of observations of the outer planets to understand their evolution and atmospheres. However, these recent observations only served to explore and analyze the GRS. Projecting into the future, the team predicts that the GRS will continue to shrink before stabilizing into a less elongated shape than we see today. Currently it is particularly “wide” in width, but once it shrinks it will likely stabilize as the winds hold it in place.
The team hopes that understanding the GRS will lead to understanding the mechanisms of the solar system's largest storms, which would ultimately help us learn more about hurricane systems on Earth.
Source: NASA's Hubble observes Jupiter's Great Red Spot behaving like a stress ball
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