Jupiter is smaller and more squashed than we thought
The impression of an artist of the Juno spaceship on the southern pole of Jupiter
NASA / JPL-CALTECH
Jupiter is not as tall as astronomers thought, according to the first measures of its radius taken in more than 40 years.
Jupiter is a gas giant and has no solid external surface like Earth. But astronomers can always assess its shape by measuring how the height of its gas, for a certain level of pressure, fluctuates around the planet, similar to the measurement where sea level is located.
Our best measures of this gas pressure level were taken by the spatial travel and pioneer of NASA over 40 years ago. The probes sent radio waves through the atmosphere of Jupiter to the earth, where the data were then measured and the properties of the radio waves used to calculate the gas pressure at a given height, a technique called radio-occultation.
Now, Eli Galanti at the Weizmann Institute of Science in Israel and his colleagues have measured the department of Jupiter by using Radio Radio of Occultation of NASA Juno Spacecraft, which has been in orbit around the gas giant since 2016.
“Based on the occultations of the Juno radio, we note that the size of Jupiter is smaller, more oblat, because at the equator, the change is about four kilometers smaller,” Galanti at the Europlanet Science Congress (EPSC) told Helsinki, Finland, September 11.
Galanti and his team took 13 different radio blackouts with Juno, compared to the six for traveling and combined pioneer, then used known measures of Jupiter’s wind speeds to calculate its diameter. For gas at 1 bar, which is the pressure of the terrestrial atmosphere at sea level, the planet measured 142,976 kilometers with its poles and 133,684 kilometers with its equator.
“It is not a question of knowing exactly where the radius is, but it is really a question of understanding its internal functioning,” explains Oded Aharonson at the Weizmann Institute of Science, which was not involved in the analysis. “The interior of the planet is mysterious and otherwise difficult to probe, so having these new constraints could help us create more precise interior models.”
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