#planet core

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Space stimboard

Event: @stimming-puppet Boardtober Day 12

Themes: Space

Song:

"The well-known banded structure of the gas giant Jupiter varies considerably on the multi-year time scale of 3 to 10 years. There are noticeable colour changes, brightening events, and stormy outbreaks visible at the cloud tops, capturing the imaginations of amateur and professional observers alike.  These bursts of activity are sometimes called ‘global upheavals’ and demonstrate quasi-predictable patterns. They have been witnessed for over 100 years by ground-based telescopes, but their underlying causes remain a long-standing mystery."

(Two images of Jupiter at 5μm wavelength (adopted from Antuñano et al. Astron. J 2019). Captured by NASA’s Infrared Telescope Facility (IRTF): (a) on 31 December 2011 and (b) on 2 May 2001. Those images reveal thermal emission from Jupiter’s lower atmosphere, the troposphere. The dashed lines indicate latitudes of 21 degrees and 7 degrees in the northern hemisphere.)

"We are proposing that torsional oscillations due to Jupiter’s magnetic field are responsible for the periodicity. The longitude-independent oscillations are a special type of magnetic waves, the Alfvén waves, that are provided by a tension of the magnetic field line: see figure 2 for an explanation of what these torsional oscillations are. The disturbances can propagate as waves, both towards or away from the rotation axis (see figures 2b-c), which means they move in latitude at the surface. Torsional oscillations have been detected in the Earth’s liquid iron core, with a 6-year oscillation period that is detected in the geomagnetic field record, and also through small variations in the length of day. They can also be seen in geodynamo models, which encouraged us to look for them in our models of Jupiter’s dynamo.  Our simulations did show torsional oscillations driven by the turbulent convection that transports heat outwards through the planet."

A planetary smashup billions of years ago may be to blame for Jupiter’s weirdly puffy core.

Recent measurements of Jupiter’s gravitational field indicate that, rather than a dense pit of rock and ice, Jupiter’s core is a haze of heavy elements possibly spanning half the planet’s radius (SN: 6/24/17, p. 14). That observation, made by NASA’s Juno spacecraft that started orbiting Jupiter in 2016, flies in the face of current planet formation models (SN: 6/25/16, p. 16). Those models suggest that Jupiter would have formed from a dense kernel that accumulated a thick envelope of gas.

New computer simulations now show that a collision between Jupiter and another large planetary body could have shattered Jupiter’s original compact core into the scattered collection of heavy elements seen today. Understanding the origins of Jupiter’s internal structure may give insight into the processes that shape other gas giants in our solar system and around other stars, researchers report in the Aug. 15 Nature.

“This impact may have happened when the solar system was very, very young, and in a chaotic phase when there were lots of objects roaming around,” says Andrea Isella, an astronomer at Rice University in Houston. As the biggest planetary body in its neighborhood, Jupiter was liable to gravitationally attract other objects wandering the solar system, he says.

Heavy hitter

Billions of years ago, Jupiter may have collided with a rogue planetary body equal to about 10 Earth masses (impact and its aftermath seen from left to right in this computer simulation). That impact could have fractured the gas giant’s original compact core and mixed the heavy elements there into its gaseous envelope to create the bloated, fuzzy core seen today.

Simulation of how a planetary collision would affect Jupiter’s core

CREDIT: S. LIU ET AL/NATURE 2019

In the simulations, Isella and colleagues found that a planetary body of about 10 Earth masses could have broken apart and merged with Jupiter’s dense core, causing that jumble of material to mix into the planet’s inner gaseous envelope. Within hours, the merger would have transformed Jupiter’s original core, around only 15 percent the planet’s radius, into a dilute core that extended to nearly half of Jupiter’s radius. Further simulations confirmed that this diffuse core could have persisted for over 4 billion years to the present day.