SYDNEY: Observations of an unexpected behaviour in Venus’ magnetic field reveal that it may have more in common with Earth than previously thought, including its own spectacular aurora.
A phenomenon known as ‘magnetic reconnection’, normally only expected to be evident in planets containing a magnetic core, such as Earth, has been detected in the Venusian magnetic field. The discovery has important implications for our understanding of the physics of planetary atmospheres and thus the evolutionary history of the planets.
The researchers analysed data collected with the Venus Express spacecraft orbiting around Venus. By examining the movement of the plasma flow over time, they were able to determine that a plasmoid – a loop structure in the magnetic field that is found when magnetic reconnection occurs – had moved over the Venus Express spacecraft.
“Plasmoids are common features in the magnetospheres of planets such as Earth and Jupiter, but they were not expected in the magnetotail of an unmagnetised planet such as Venus,” said Tielong Zhang, planetary scientist at the Space Research Institute of the Austrian Academy of Science and lead author of the paper published in Science last week.
Tangled up in plasma
Much like Earth, Venus possesses an ionosphere containing a fluid plasma, which is made up of hot, charged gas particles. These particles generate magnetic fields that, due to the plasma’s turbulent nature, often get twisted up. “When magnetic field lines are twisted, they store energy like a coiled spring,” said John Morgan, a researcher and lecturer at the International Centre for Radio Astronomy Research at Curtin University in Perth, Western Australia, who commented on the paper. “In magnetic field reconnection, the magnetic field lines reconfigure and, in the process, transfer energy from the magnetic field to the plasma.”
Despite knowing of the Venus’ ionosphere, scientists previously didn’t think that magnetic reconnection could occur in a planet with a non-magnetic core. With the finding, researchers have another source of data against which to compare the behaviour of Earth’s atmosphere and add to the evolutionary history of the planets and their atmospheres.
The find may provide closure to the question of whether previously observed instances of ‘nightglow’ on Venus are auroras caused by charged particles entering the atmosphere. On Earth, auroras are caused by the collision of charged particles from the solar wind with atoms in the high atmosphere and are thought to be shaped by the Earth’s magnetic field.
“For many decades dim flashes of light have been observed at nightside of Venus by various means, and were interpreted as auroras,” said Zhang. Magnetic reconnection provides a pathway by which the particles in the ionosphere could enter Venus’ atmosphere to produce these flashes.
Having shown that the phenomenon occurs, Zhang said that his project will now focus on pinning down when, where, and how the magnetic reconnection happens. But there are limitations imposed by the scope of the Venus Express. “Since observations are limited by spacecraft trajectory, we would not know what happens beyond the spacecraft trajectory,” he said
Original paper in Science
An animation illustrating a magnetic reconnection event in Venus’ magnetosphere