In the 1660s, Italian astronomer Gian Domenico Cassini made a significant discovery while observing Jupiter – a massive spot that is now known as Jupiter’s signature feature, the Great Red Spot or Permanent Spot. This planetary feature is believed to be evidence of a massive Jovian storm. However, recent research suggests that the storm we see today is not the same one that Cassini observed nearly four centuries ago.
What appears as a red spot is actually a huge anticyclone vortex that is twice the size of Earth. Modern observations indicate that the storm is characterized by winds blowing at speeds of up to 400 miles per hour, with its distinct color possibly resulting from interactions between elements in Jupiter’s atmosphere and radiation. Despite the spot being known for centuries, it continues to hold many mysteries for scientists.
Cassini, a pioneer of telescopic astronomy, first observed the spot in 1665 as a dark oval and noted that it was a permanent feature that consistently appeared in the same location with the same size and shape. Although spot sightings were recorded until 1713, observations ceased, only to be revived by other scientists in 1831. Through historical observations, modern researchers were able to track the size and movement of the spot over the years, comparing older observations with current ones, and simulating various scenarios for its origin.
The analysis conducted by the researchers revealed that the spot we see today is more akin to the one observed in the 1800s rather than the one Cassini spotted. The spot has undergone changes over time, contracting and becoming more circular, likely as a result of increased rotation. The researchers believe that the spot may have formed due to unstable winds that initially created a visible proto-storm that disappeared before reemerging. Agustín Sánchez-Lavega, a professor of applied physics at the University of the Basque Country in Bilbao, Spain, who spearheaded the research, expressed his inspiration from exploring Cassini’s notes and drawings, stating that they have now quantified the results of others who had previously examined these observations.