Hubble: a decade of revelations about the giant planets of the Solar System

It is thanks to the OPAL program (for Outer Planet Atmosphere Legacy) that the Hubble space telescope, sometimes considered the ancestor of James-Webb, delivers magnificent images of our gas giant planets. In the case of Uranus and Neptune, they are even precious images, because we ultimately only have very few of them. Indeed, the only flyby of these planets at the edge of the Solar System was carried out by Voyager 225 years ago now!

We know that the atmosphere of the planets evolves over the course of their orbit and their possible seasons, those of Saturn and Uranus being good examples. Indeed, a planet has seasons as long as its orbit is inclined relative to the plane of the ecliptic — the Earth east at 23°.

The gas giant Jupiter has almost no seasons, but its atmosphere nevertheless varies enormously. Its Great Red Spot can thus increase or decrease in volume, its cloud bands become tinged with yellow, its hurricanes become particularly active, etc.

A Jovian year seen by Hubble

The atmosphere of Jupiter, the largest and most massive planet in the Solar System, is also the most tormented. Its large white cyclones on the south side are called “the string of pearls”, its atmospheric bands (including the rotation is differential), modify very regularly, changing color, sometimes pale, then yellowish, then rosaceous. Jupiter also experiences permanent storms and its atmosphere thousands of kilometers deep is covered in ammonia ice crystals… Brrrrrr!

Here are two views of Jupiter which are reminiscent of those captured by James-Webb, yet it is indeed Hubble's infrared cameras which took the image on the right.

As a bonus, here is a photo taken by the NASA Juno probewhere we see a strange cloud in the shape of a dolphin.

When Saturn plays magician and makes his rings disappear!

In 2025, that is to say in a few weeks, the rings of beautiful Saturn will play hide and seek with the terrestrial observer. The planet's 27° inclination means that during the 29 years of its orbit, for a few months – every 14 or 15 years – we see its rings really edge-on, giving the impression that they are disappearing. !

Distant Uranus and Neptune offer visible changes

At 97° to the ecliptic plane, Uranus has the greatest inclination of all the planets in the Solar System. It can be seen as “rolling” in its 84-year orbit around the Sun. It thus shows us the same pole for 42 years, then the next for 42 years. Yes, it's been many days and nights for 42 years, it's better not to put off urgent matters until tomorrow… But a gigantic cloud of photochemical mist appears on the North Pole of Uranus and will become more and more brilliant until at the summer solstice in 2028.

4.5 billion kilometers away, Neptune also has significant atmospheric activity, particularly dark cyclones that appear and disappear toward its North Pole. Its winds are strangely the most powerful in the entire Solar System: they can reach 2100 km/h!