Scientists have discovered that Jupiter’s bowels are filled with the remnants of small planets that the gas giant devoured as it expanded to become the colossus we see today. The findings come from the first clear view of the chemistry beneath the planet’s murky outer atmosphere.
Despite being the largest planet in the solar system, Jupiter has disclosed very little about its internal workings. The telescopes have captured thousands of images of the swirling vortex clouds in the gas giant’s upper atmosphere, but these Van Gogh-like storms also act as a barrier blocking our view of what’s below.
“Jupiter was one of the first planets to form in ours solar system“In the first million years after the solar system took shape some 4.5 billion years ago, researcher Yamila Miguel, an astrophysicist at Leiden University in the Netherlands, told Live Science. However, we know next to nothing. certainly about how it formed, she added.
Related: “Little Jupiter” was discovered in the process of forming around a star 500 light years away
In the new study, the researchers were finally able to peer beyond Jupiter’s dark cloud cover using gravitational data collected by NASA’s Juno spacecraft. This data allowed the team to map the rocky material at the center of the giant planet, which revealed a surprisingly high abundance of heavy elements. The chemical composition suggests that Jupiter devoured small planets, or planetesimals, to fuel its expansive growth.
Raising a gas giant
Jupiter may be predominantly a swirling ball of gas today, but it began its life by accumulating rock material, just like every other planet in the solar system. Like that of the planet severity attracted more and more rocks, the rocky core became so dense that it began sucking in large quantities of gas from distant distances, mainly hydrogen and helium left over from the Sunbirth – to form its huge gas-filled atmosphere.
There are two conflicting theories as to how Jupiter managed to collect its initial rock material. One theory is that Jupiter has accumulated billions of smaller space rocks, which astronomers refer to as pebbles (although these rocks are likely closer in size to boulders than actual pebbles).
The opposite theory, which is supported by the results of the new study, is that Jupiter’s core formed from the absorption of many planetesimals – large space rocks that span several miles, which if left undisturbed could potentially act as seeds from which the smaller rocky planets like Land or Mars could develop.
However, until now it has not been possible to say for sure which of these theories is correct. “Since we can’t directly observe how Jupiter formed, we have to piece the pieces together with the information we have today,” said Miguel. “And this is not an easy task.”
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Probe the planet
To try to resolve the debate, the researchers needed to construct an image of Jupiter’s bowels. “Here on Earth, we use seismographs to study the interior of the planet using earthquakes,” said Miguel. But Jupiter has no surface to place such devices on, and Jupiter’s core is unlikely to have much tectonic activity anyway, he added.
Instead, the researchers built computer models of Jupiter’s bowels by combining data, mostly collected by Juno, and some data from her predecessor Galileo. The probes measured the planet’s gravitational field at various points in its orbit. The data showed that the rock material accumulated by Jupiter has a high concentration of heavy elements, which form dense solids and, therefore, have a stronger gravitational effect than the gaseous atmosphere. This data allowed the team to map slight variations in the planet’s gravity, which helped them see where the rocky material is within the planet.
“Juno provided very accurate gravity data that helped us limit the distribution of the material within Jupiter,” said Miguel. “These are truly unique data that we can only obtain with a spacecraft orbiting the planet.”
The researcher’s models revealed that there is an equivalent between 11 and 30 Earth masses of heavy elements inside Jupiter (3% to 9% of Jupiter’s mass), which is much more than expected.
Pebbles against planetesimals
The new models point to a planetesimal origin of Jupiter because the pebble accretion theory cannot explain such a high concentration of heavy elements, Miguel said. If Jupiter had initially formed from pebbles, any initiation of the gas accretion process, once the planet was large enough, would have immediately ended the rocky accretion phase. This is because the growing layer of gas would have created a pressure barrier that prevented the extraction of further pebbles within the planet, Miguel explained. This reduced phase of rock accretion would likely have given Jupiter a greatly reduced abundance of heavy metals, or metallicity, compared to what the researchers calculated.
However, the planetesimals may have concentrated on Jupiter’s core even after the start of the accretion phase of the gas; this is because the gravitational attraction on the rocks would have been greater than the pressure exerted by the gas. This simultaneous accretion of rock material and gas proposed by planetesimal theory is the only explanation for the high levels of heavy elements inside Jupiter, the researchers said.
The study also revealed another interesting finding: Jupiter’s interior doesn’t mix well with its upper atmosphere, which goes against what scientists previously expected. The new model of Jupiter’s interior shows that the heavy elements the planet absorbed remained largely close to its core and lower atmosphere. The researchers speculated that convection mixed Jupiter’s atmosphere, so that the hottest gas near the planet’s core would rise into the outer atmosphere before cooling down and falling back; if so, the heavy elements would be mixed more evenly throughout the atmosphere.
However, it’s possible that some regions of Jupiter may have a small convection effect, and more research is needed to determine exactly what’s going on inside the gas giant’s atmosphere, Miguel said.
The researchers’ findings could also change the origin histories of other planets in the solar system. “Jupiter was the most influential planet in the formation of the solar system,” said Miguel. Its gravitational pull helped shape the size and orbits of its cosmic neighbors, and thus determining how it became has major knock-on effects for other planets, he added. The findings also suggest a potential planetary origin for the other gas giants in the solar system: Saturn, Uranus And Neptune.
Other gas worlds in other star systems may also have formed by devouring planetesimals rather than pebbles, meaning they may also have a higher metallicity than their appearance would suggest. It is, therefore, important that when we find these new worlds, that they are searched for using those of NASA James Webb telescopewe don’t judge them by their cloud cover, the researchers said.
The study was published online June 8 in the journal Astronomy and Astrophysics (opens in a new tab).
Originally published in Live Science.