A closer look at Jupiter’s origin story

Jupiter, as seen by the Juno spacecraft. Credit: NASA/JPL

One of the most important open questions in planetary formation theory is the story of Jupiter’s origin. Using sophisticated computer modeling, researchers of the University of Zurich (UZH) and the National Centre of Competence in Research (NCCR) PlanetS now shed new light on Jupiter’s formation history. Their results were published in The Astrophysical Journal Letters.

A curious enrichment of heavy elements

When the Galileo spacecraft released a probe that parachuted into Jupiter’s atmosphere in 1995, it showed among other things that (elements heavier than helium) are enriched there. At the same time, recent structure models of Jupiter that are based on gravity field measurements by the Juno spacecraft suggest that Jupiter’s interior is not uniform but has a complex structure.

“Since we now know that the interior of Jupiter is not fully mixed, we would expect heavy elements to be in a giant gas planet’s deep interior as heavy elements are mostly accreted during the early stages of the planetary formation,” study co-author, Professor at the University of Zurich and member of the NCCR PlanetS, Ravit Helled begins to explain. “Only in later stages, when the growing planet is sufficiently massive, can it effectively attract large amounts of light element gases like hydrogen and helium. Finding a formation scenario of Jupiter which is consistent with the predicted interior structure as well as with the measured atmospheric enrichment is therefore challenging yet critical for our understanding of giant planets,” Helled says. Of the many theories that have so far been proposed, none could provide a satisfying answer.

A long migration

“Our idea was that Jupiter had collected these heavy elements in the late stages of its formation by migrating. In doing so, it would have moved through regions filled with so-called planetesimals—small planetary building blocks that are composed of heavy element materials—and accumulated them in its atmosphere,” study lead-author Sho Shibata, who is a postdoctoral researcher at the University of Zurich and a member of the NCCR PlanetS, explains.

Yet, migration by itself is no guarantee for accreting the necessary material. “Because of complex dynamical interactions, the migrating planet does not necessarily accrete the planetesimals in its path. In many cases, the planet actually scatters them instead—not unlike a shepherding dog scattering sheep,” Shibata points out. The team therefore had to run countless simulations to determine if any migration pathways resulted in sufficient material accretion.

“What we found was that a sufficient number of planetesimals could be captured if Jupiter formed in the outer regions of the solar system—about four times further away from the Sun than where it is located now—and then migrated to its current position. In this scenario, it moved through a region where the conditions favored material accretion—an accretion sweet spot, as we call it,” Sho reports.

A new era in planetary science

Combining the constraints introduced by the Galileo probe and Juno data, the researchers have finally come up with a satisfying explanation. “This shows how complex giant gas planets are and how difficult it is to realistically reproduce their characteristics” Ravit Helled points out.

“It took us a long time in to get to a stage where we can finally explore these details with updated and numerical simulations. This helps us close gaps in our understanding not only of Jupiter and our solar system, but also of the many observed giant orbiting far away stars,” Helled concludes.

More information:
Sho Shibata et al, Enrichment of Jupiter’s Atmosphere by Late Planetesimal Bombardment, The Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac54b1

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NCCR PlanetS

A closer look at Jupiter’s origin story (2022, April 4)
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Hexbyte Glen Cove A closer look at how immune cells attack and heal thumbnail

Hexbyte Glen Cove A closer look at how immune cells attack and heal

Hexbyte Glen Cove

Credit: CC0 Public Domain

Macrophages—immune cells that both fight infections and fix the damage they cause—are often placed into two categories: those that increase inflammation (known as “M1”) to attack, and those that decrease inflammation to begin the healing process (“M2”).

Researchers in the lab of Kathryn Miller-Jensen, associate professor of and molecular, cellular & , used single-cell RNA sequencing to get a closer read on how individual macrophages react to different stimuli. They found that, while these cells tend to be multitaskers, some are more inclined toward responding to certain cues than others. The results are published in Nature Communications.

The M1–M2 paradigm has helped scientists understand the innate immune response. Researchers, though, have long suspected that there’s more flexibility among macrophages in vivo than this two-category system suggests—that is, a cell can be both an attacker or healer depending on the circumstances. But what do individual macrophages do when confronted with M1 and M2 cues at the same time in a , such as a tissue culture dish?

“No one had looked at that, and we decided to try it with single-cell sequencing,” Miller-Jensen said. By doing so, the Miller-Jensen lab was able to get a much more detailed picture of macrophages’ responses when stimulated with both inflammatory and resolving stimuli. They found a great deal of variability, including a subset of cells that seem to respond to only one cue or the other for certain key functions like secretion.

“The stimuli are the environmental cues, but we’re thinking that there might be some variability in the regulatory network inside the cells that allow some of them to respond more strongly to one cue versus another at any given time,” Miller-Jensen said.

It’s an important step toward a better understanding of the different types of macrophages.

“It could help us identify how macrophages exist in these different states in a tumor, or non-healing wounds, and other disease environments,” she said. “If we had a more sophisticated understanding of what subsets exist, we might better figure out how to target them or regulate them.”

The researchers note that the diverse responses to opposing cues may allow macrophages to more readily adapt to changing environments, as well as to quickly transition from attack mode to focusing on tissue repair.

“They might need to respond to a lot of cues at the same time, so a few of the macrophages might be primed to respond and be the attackers,” she said. “So when they see both of those cues at the same time, it’s important to have at least some of those cells to secrete what needs to be secreted—but maybe not all of those , because some may need to do something else.”

Miller-Jensen also noted that the single-cell RNA sequencing technology, and the single-cell secretion device—invented by Prof. Rong Fan, also in biomedical engineering—played a critical part in making the groundbreaking observations.

More information:
Andrés R. Muñoz-Rojas et al. Co-stimulation with opposing macrophage polarization cues leads to orthogonal secretion programs in individual cells, Nature Communications (2021). DOI: 10.1038/s41467-020-20540-2

A closer look at how immune cells attack and heal (2021, January 21)
retrieved 22 January 2021
from https://phys.org/news/2021-01-closer-immune-cells.html

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