The Juno probe has been delivering some epic science since it launched in 2011, and this time it’s delivered a glimpse into Jupiter’s mysterious depths – and its weird gravitational field.
Three studies, published today in the journal Nature, have probed Jupiter’s gravitational field to reveal exactly how dynamic Jupiter’s atmosphere is; how deep it extends; and what’s inside Jupiter when the atmosphere ends.
In the first paper, led by Luciano Iess of the Sapienza University of Rome in Italy, a team of researchers used the Doppler, or redshift, data of Juno as it orbits around Jupiter. This directly correlates to Juno’s velocity – which, in turn, is affected by Jupiter’s gravity.
The team’s analysis was assisted by a high precision transponder that measures Juno’s velocity down to 0.01mm/s accuracy, even while travelling at record speed orbits of 70 km/s.
As planetary scientist Jonathan Fortney of the University of California Santa Cruz put it in an accompanying editorial, this was “no mean feat,” since the team had to account for every tiny acceleration Juno underwent, including those not caused by Jupiter’s gravity.
We already knew that Jupiter’s gravitational field is asymmetrical for some reason. Iess’s team studied all components of the field, both symmetric and asymmetric.
Because Juno is in polar orbit, it can examine both poles separately, which is what the team did – and they found that part of Jupiter’s gravitational field does not have north-south symmetry.
Since the majority of the field is symmetrical, caused by the planet’s fast rotation, the team discovered that Jupiter’s internal flows were causing the asymmetry.
“Winds on Earth are caused by pressure gradients between areas of lows and highs. Lows and highs are associated to different atmospheric densities. The same mechanism is at play at Jupiter,” Iess told ScienceAlert.
“Winds are associated to density variations in the atmosphere. In turn, density variations have a gravitational signature. By measuring the magnitude of the gravity due to the winds, one has information about their depth.”
This link was explored further by a team led by Yohai Kaspi of the Weizmann Institute of Science in Israel, which studied the asymmetry of Jupiter’s magnetic field to determine the depth of its atmosphere.
They determined that the magnitude of the winds of Jupiter decayed with altitude, finally petering out at a depth of around 3,000 kilometres (1,864 miles) below cloud level.
In all, Jupiter’s atmosphere constitutes about 1 percent of the planet’s total mass – but the finding opens the door to learning a lot more about how Jupiter works.
“Galileo viewed the stripes on Jupiter more than 400 years ago. Until now we only had a superficial understanding of them, and have been able to relate these stripes to cloud features along Jupiter’s jets, Kaspi told ScienceAlert.
“Now, following the Juno gravity measurements, we know how deep these extend and what is their structure beneath the cloud-level. It’s like going from a 2D picture to a 3D one” he told ScienceAlert.
“In addition, the gravity signature of the jets is entangled with the gravity signal of [Jupiter’s] interior. Now that we know the gravity signature of the atmosphere, it will help us in better understanding the interior structure, core mass and eventually the origin of Jupiter.”
But what if we went even deeper than those 3,000 kilometres below cloud level? That’s where the team led by Tristan Guillot of the University of Côte d’Azur comes in.
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