Key takeaways

  • Jupiter’s metals show it consumed many rocky planetesimals in its early years.
  • NASA’s Juno spacecraft has been collecting detailed data about Jupiter since 2016.
  • The Gravity Science instrument on Juno helps scientists understand Jupiter’s inner composition.
  • Jupiter likely formed by accumulating large planetesimals rather than just small pebbles.
  • Metals are concentrated more at Jupiter’s core, indicating less mixing than previously thought.

Jupiter is made up almost completely of hydrogen and helium. The amounts of each roughly match the theoretical quantities in the initial solar nebula. It does, however, include heavier elements known as metals. Even though metals are a minor component of Jupiter, their presence and distribution provide scientists with valuable information.

According to a recent research, Jupiter’s metal content and distribution indicate that the planet consumed a large number of rocky planetesimals in its childhood.

Since July 2016, NASA’s Juno probe has been gathering extensive data about Jupiter, altering our knowledge of the planet’s genesis and evolution. One of the mission’s highlights is the Gravity Science equipment. It transmits radio communications between Juno and the Deep Space Network on Earth. The procedure monitors Jupiter’s gravitational field and provides researchers with further information about the planet’s composition.

NASA’s Juno spacecraft captured this view of Jupiter during the mission’s 40th close pass by the giant planet on Feb. 25, 2022. The large, dark shadow on the left side of the image was cast by Jupiter’s moon Ganymede. Image data: NASA/JPL-Caltech/SwRI/MSSS Image processing by Thomas Thomopoulos

Jupiter developed by accreting rocky debris. Following then, there was a period of fast gas accretion from the solar nebula, and Jupiter eventually evolved into the monster it is today. However, there is a substantial dispute over the early time of rocky accumulation. Did it accumulate greater masses of rocks, such as planetesimals? Or did it accumulate pebble-sized material? Jupiter developed at various times, depending on the response.

A recent study aimed to answer that question. The article, titled “Jupiter’s inhomogeneous envelope,” is published in the journal Astronomy and Astrophysics. The primary author is Yamila Miguel, an Assistant Professor of Astrophysics at the Leiden Observatory and the Netherlands Institute for Space Research.

We’ve become accustomed to stunning views of Jupiter courtesy to the Juno spacecraft’s JunoCam. However, what we see is simply skin deep. All of those breathtaking views of clouds and storms come from the planet’s outermost 50 km (31 miles) layer of atmosphere. The secret to Jupiter’s genesis and evolution lies hidden deep in its tens of thousands of kilometers thick atmosphere.

The Juno mission is helping us piece together a better understanding of Jupiter’s mysterious interior. Image: By Kelvinsong – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31764016

Jupiter is usually considered as the oldest planet in the Solar System. However, scientists want to know how long it took to create. The authors of the research wished to investigate the metals in the planet’s atmosphere using Juno’s Gravity Science instrument. The presence and distribution of pebbles in Jupiter’s atmosphere are critical to understanding its creation, and the Gravity Science experiment examined their dispersion across the atmosphere. Prior to Juno and the Gravity Science mission, there was no exact data on Jupiter’s gravity harmonics.

The researchers discovered that Jupiter’s atmosphere is not as homogeneous as previously believed. There are more metals at the planet’s center than in the other layers. Overall, the metals weigh between 11 and 30 Earth masses.

With the data in hand, the researchers created models of Jupiter’s interior processes. “In this paper, we assemble the most comprehensive and diverse collection of Jupiter interior models to date and use it to study the distribution of heavy elements in the planet’s envelope,” according to the researchers.

The team developed two sets of models. The first collection includes 3-layer models, while the second has dilute core models.

The researchers created two contrasting types of models of Jupiter. The 3-layer models contain more distinct regions, with an inner core of metals, a mid-region dominated by metallic hydrogen, and an outer layer dominated by molecular hydrogen (H2.) In the dilute core models, the inner core’s metals are mixed into the middle region, resulting in a dilute core.

“There are two mechanisms for a gas giant like Jupiter to acquire metals during its formation: through the accretion of small pebbles or larger planetesimals,” said Miguel, the study’s lead author. “We know that once a young planet reaches a certain size, it begins to emit stones. The abundance of metals within Jupiter that we observe today was impossible to produce before then. As a result, we can rule out the possibility that Jupiter formed entirely of pebbles. Planetesimals are too large to be blocked, thus they must have had an impact.”

The amount of metals in Jupiter’s core diminishes with distance from its center. That indicates a lack of convection in the planet’s deep atmosphere, which scientists assumed existed. “Earlier, we thought that Jupiter has convection, like boiling water, making it completely mixed,” Miguel recalled. “But our finding shows differently.”

“We robustly demonstrate that the heavy element abundance is not homogeneous in Jupiter’s envelope,” the scientists write in the research. “Our results imply that Jupiter continued to accrete heavy elements in large amounts while its hydrogen-helium envelope was growing, contrary to predictions based on the pebble-isolation mass in its simplest incarnation, favouring instead planetesimal-based or more complex hybrid models.”

Artistic rendition of a protoplanet forming within the accretion disk of a protostar Credit: ESO/L. Calçada http://www.eso.org/public/images/eso1310a/

The authors also conclude that Jupiter did not mix by convection after its formation, even while it was still young and heated.

The team’s findings also apply to the study of gaseous exoplanets and efforts to identify their metal content. “Our result … provides a base example for exoplanets: a non-homogeneous envelope implies that the metallicity observed is a lower limit to the planet bulk metallicity.”

There was no way to determine Jupiter’s metallicity from a distance. Only after Juno landed could scientists assess metallicity indirectly. “Therefore, metallicities inferred from remote atmospheric observations in exoplanets might not represent the bulk metallicity of the planet.”

When the James Webb Space Telescope begins science operations, one of its duties will be to measure and characterize the composition of exoplanet atmospheres. As this study demonstrates, Webb’s data may not capture what is happening in the deepest layers of large gas planets.

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