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Cassini's legacy throws more light on the special thriller of the Nordic polar hexagon of Saturn.
Cassini has seen Saturn's hex since 2012. NASA / JPL-Caltech / Region Science Institute.
And without a doubt, one of the most bizarre elements of the solar arrangement is the hexagon that adorns the critical situation of Saturn. First spotted by the Voyager 1 spacecraft in its historical survey of 1980, this lens is abnormal among the many planets in the solar array.
Now, an original watch of the mark printed in Nature: Communications suggests that the hexagon – an example in the Saturn troposphere – could likely have an impact on a similar construction in the stratosphere, more than 300 kilometers away.
The polar hexagon of Saturn circulates. NASA / JPL-Caltech / Institute of Regional Sciences / University of Hampton
The results were achieved by NASA's Cassini spacecraft, which arrived in Saturn's spherical orbit in July 2004 and completing its mission with atmospheric entry and elimination planned for one year on September 15, 2017. Scientists have implementation of key measures Spectrometer (CIRS) from 2014
"While we were doing a quiz to score a vortex of some form at Saturn's North Pole as it warmed up, its shape is really horrible," says Leigh Fletcher (University of Leicester, UK) in a new communicated. "Either a hexagon appeared spontaneously and identically at two different altitudes, or the hexagon is actually an imposing construction covering a vertical range of hundreds of kilometers.
Seasons on Saturn
Saturn revolves around the Sun once every 29.5 years, so its "seasons" last for seven years. Winter weather in the northern hemisphere ended in 2009, the year that marked the vernal equinox and the initiation of Cassini's two-year equinox mission.
But the CIRS instrument of Cassini wanted (reasonably) higher temperatures to create stratospheric observations on the north hex; at the closing of the ice, temperatures have oscillated at -158 ° C, 20 ° below what CIRS wants to create observations. The initiation of the summer season of the north of Saturn offered a last chance to the closed observations at the end of Cassini's mission.
Brightness / temperature maps of the northern polar hexagon of Saturn from 2013 to 2017, showing the emerging stratospheric component. NASA / JPL-Caltech / University of Leicester / GSFC / L.N. Fletcher et al. 2018
A contemporary system emerges
In 2014, as the northern hemisphere entered the summer season, Cassini began surveying the pole's stratosphere. The researchers quickly realized that they were seeing the obsolete ridges of a stratospheric hex, reflecting the now familiar sample located below in the troposphere. This unexpected discovery is in contradiction with what the researchers expected to obtain: on Earth or on Saturn, the wind speed is a critical substitute for the environment, making it impossible for the presence of cloud structures Extended life. A cloudy construction that the north of the polar hex needs to smooth itself remains trapped in the lower troposphere.
So, how does the outline of the hexagon persist? One of the most likely mechanisms recommended by researchers is a phenomenon called evanescence, in which a decaying wave presents adequate vitality to persist in the upper environment.
"We are able to use background atmospheric instances (especially temperature and wind gradients) to determine whether a wave is trapped or not, or whether it is free to propagate vertically." says Fletcher. "As long as the two regions where the hexagon can spread do not seem to be too far apart, it would probably be enough to work from the troposphere to really reach the stratosphere, which is why we recognize the hexagon at all. Heights. "
If the polar hexagon evolves from the troposphere to the stratosphere, this construction crosses several kilometers in height. However, it is not easy to know whether or not this is really the case: "The hexagon is potentially continuous, from the troposphere to the stratosphere, but there is a part of the environment between hexagon", explains Linda Spilker (NASA-JPL). "Future atmospheric modeling will be invaluable to give practical advice on what is observed."
There was no hex on the South Pole, both at the top and above, when it was observed at the beginning of Cassini's mission throughout the summer season in the south. The circulation of the north jets on Saturn (at seventy-eight degrees north latitude) seems to be more unstable than its southern counterpart, probably contributing to its abnormal hexagonal aspect.
Watch North hexagon
And without doubt, it is rather frustrating that Cassini ended her exploration of Saturn, as things drew more toward the north. But even with Cassini's past, future observations of this phenomenon are likely to be optimal with Hubble and his forthcoming infrared successor, the James Webb region telescope.
Saturn of 2017, pictured from the observatory of the Pic du Midi, with the polar hexagon clearly visible. Damian Peach
The north polar hex appears even the day of the Earth, based primarily on astrophotos. Indeed, it is interesting to know that no Saturn sighting has ever seen the hexagon before its discovery in the 1970s, although such a statement was most likely made by narrow-eyed observers. Saturn's rings – and the planet itself – skew at a maximum of 27 ° from our design line, alternating every hemisphere every 14 to 15 years. The rings have been inclined to their biggest final year in 2017, the northern hemisphere being visible, and they are also headed towards 2025.
One component is obvious: it will be a moment before we return to Saturn, by chance when / if the mission of the Titan helicopter explorer is taking place. But for the moment, we can be shocked by Cassini's smooth production of a treasure trove of intelligent scientific discoveries.
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