Hubble observes mysterious storms on Uranus and Neptune

Uranus and Neptune have amazing atmospheres, just like Jupiter and Saturn. The Hubble telescope is used periodically to monitor the condition of these atmospheres and to help uncover their secrets.

Voyager 2 is the only human probe to have reached Uranus and Neptune, providing close-up images of these ice giants as well as their moons and rings. The late André Brahic, one of the discoverers of the rings of Neptune had also fallen under the spell of Triton, the satellite of Neptune with cryovolcanism.

On this occasion, in August 1989, Voyager 2 had revealed the existence of the Great Dark Spot (GDS) on Neptune, in its southern hemisphere, apparently similar to the Great Red Spot of Jupiter, that is, an anticyclonic storm. It is, however, much more unstable. While this phenomenon existed at least since the XIX the century on Jupiter, the GDS eventually dissipate or become invisible in 1994, the Hubble telescope that had detected its first light only in recent years. A new dark Great Spot has appeared in the northern hemisphere later, but to disappear from the gaze of telescopes a few years later, there too.
Astronomers continue to study the meteorology of Neptune, as well as that of Uranus, from the ground and, of course, again with Hubble. It is the only one with the necessary sensitivity to detect major storms in the band color blue in the visible and showed the existence of a Great Dark Spot on Neptune's northern hemisphere at the end of the year 2018. Although qu'éloignée the Sun and therefore less supplied power than the atmosphere of Earth, the Neptune is surprisingly turbulent and active. It is now estimated that a large dark spot would appear on average every six years but would only last about two years.

The Nasa has just made public the images of the latest observations of the activity of Neptune, as well as that of Uranus with the Hubble telescope. They take place in a long-term program of monitoring these planets to uncover their secrets just as it is necessary to monitor, with satellites, the state of the Earth's atmosphere in the long term to understand it and predict its evolution. The data collected for the giants are archived as part of the Outer Planet Atmospheres Legacy ( OPAL ).

Neptune and Uranus, laboratories to understand planetary atmospheres

In the photo below (right-hand thumbnail) showing the last appearance of a large dark spot, a procession of white, shiny clouds of methane crystals is again visible. They are thought to be formed by currents of hydrogen and helium (also containing this gas ) which are diverted to higher altitudes, in much the same way as on Earth, when a similar atmospheric current meets an isolated mountain. Steam then condenses as the pressure changes, gaining altitude and spreading cloud cover around the top of the mountain.

Like the one on Jupiter, the formation of Neptune's stain remains elusive, and many mysteries remain about it. Hubble, however, has shown that an increase in the formation of methane ice clouds in 2016 preceded the appearance of a new Dark Great Spot. This suggests that this giant anticyclonic storm is beginning to form deep within the atmospheric layer surrounding the vast mantle of ice, itself encircling the rock core of Neptune - which is not a gas giant like Jupiter and Saturn but well a giant ice cream - before going back to the surface.

As for Uranus, is observed a kind of large bright white cap, matching thunderclouds, centered on its north pole and occupying a significant portion of its hemisphere (see photograph Hubble above). It is thought that this amazing structure is related to the fact that the axis of rotation of the ice giant is particularly inclined to the perpendicular of the plane of its orbit to the point of being almost parallel. Thus, Uranus alternately presents to the Sun its north pole, then its south pole during each orbit which lasts 84 years. This surprising inclination is due to giant collisions between Uranus and celestial bodies in its past.

However, this particular configuration must be the source of seasonal phenomena that are just as much. We are currently in the midst of the summer season of Uranus and its polar cloud cap is growing. Here too, what happens in the atmosphere of Uranus remains, despite everything, a subject of interrogation.

In both cases, these planets allow us to explore our atmospheric models under different conditions and therefore, to reproduce the equivalent of experiments in physics where we can control the parameters governing them. This should allow to better understand our planet but also the exoplanets outside the Solar System.

WHAT YOU MUST REMEMBER

• Mankind has been trying to better understand Uranus and Neptune since their discovery about two centuries ago.
• However, their real faces are revealed only on the occasion of the mission Voyager 2 which has, in particular, shown that Neptune had a Great Dark Task similar to the Great Red Task of Jupiter.
• The Hubble telescope has been used for decades now to regularly monitor the atmospheres of Neptune and Uranus to unlock the secrets.

In brief: Hubble pays tribute to Neptune

By Jean-Baptiste Feldmann published on 15/07/2011

Neptune was discovered ... a year ago! At least in Neptunian time. The eighth planet of the Solar System has indeed completed its first complete orbit since its discovery in the 19 century. An anniversary that the Hubble Space Telescope had to celebrate.

On September 23, 1846, the German astronomer Johann Gottfried Galle found  Neptune in his telescope according to the calculations of position made by the French Urban Le Verrier. For the first time, a planet was discovered through mathematics.

Since 2006 and the decision of the International Astronomical Union to exclude Pluto from the solar system planets club, Neptune is the planet furthest away from the Sun. Orbiting about thirty astronomical units (which makes it invisible to the naked eye from the Earth with a magnitude of 8), Neptune puts 164.79 years to perform a complete revolution, the time that has elapsed since his discovery. In August 1989, the planet received a visit from the Voyager 2 spacecraft, which discovered 5 new satellites (13 of which are known today, the most famous of which is Triton ) and confirmed the presence of Trojan's rings and asteroids.

To celebrate Neptune's first complete orbit since its discovery, the Hubble telescope used its wide-field camera and photographed the different faces of the rotating planet on June 25 and 26. The thick atmosphere of Neptune (mainly consisting of hydrogen and helium) is the seat of tremendous storms where winds can reach 2,000 kilometers per hour.