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Solar Orbiter Reveals Magnetic Push Behind Solar Wind
Context:
- ESA’s Solar Orbiter spacecraft, in collaboration with NASA’s Parker Solar Probe, has made a groundbreaking discovery about the origin of the energy that heats and accelerates the solar wind.
- This discovery answers a long-standing question in solar physics and provides new insights into how the sun’s magnetic field influences the solar wind.
Solar Wind
- The solar wind is a steady flow of charged particles emitted from the sun’s outer atmosphere, called the corona.
- This wind interacts with Earth’s atmosphere to create stunning auroras in polar regions.
- While the solar wind moves at incredibly high speeds—over 500 km/s, or 1.8 million km/h—it exits the sun’s corona at much lower speeds.
- As the solar wind expands, it cools and becomes less dense, akin to the cooling air as one ascends a mountain on Earth. However, it cools more slowly than anticipated, suggesting that additional energy is involved in its acceleration and heating.
Key Highlights:
- Recent research has confirmed that Alfvén waves, large-scale oscillations in the sun’s magnetic field, are the source of the sun’s extra energy.
- In a typical gas like Earth’s atmosphere, energy is expressed through density, temperature, and velocity. However, in a plasma—like the sun’s corona—energy is also stored in the magnetic field.
- Alfvén waves, which are waves travelling along the magnetic field lines, store and transfer this energy through the plasma.
- In February 2022, Parker Solar Probe (13.3 solar radii from the sun) and Solar Orbiter (128 solar radii from the sun) aligned to measure the same solar wind stream at different points.
- At Parker, 10% of the total energy was in the magnetic field, but this dropped to 1% at Solar Orbiter, suggesting that the lost magnetic energy was being used to accelerate the solar wind and slow its cooling.
- The study emphasised the importance of switchbacks—significant deflections in the sun’s magnetic field lines and a type of Alfvén wave.
Implications:
- The findings not only enhance our understanding of solar wind dynamics but also offer insights into other stars with similar magnetic environments.
- The team is extending their research to slower solar wind forms to explore the role of magnetic field energy further.
- Understanding the mechanisms behind the solar wind is crucial for predicting space weather, which can impact satellite operations, communication systems, and power grids on Earth.
Alfvén waves
- Alfvén waves involve oscillations perpendicular to the magnetic field, with their restoring force coming from the magnetic field’s resistance to deformation, unlike sound waves that rely on gas compression.
- These waves, crucial in stars with strong magnetic fields, can accelerate stellar winds through the dissipation of energy and momentum, and are generated by motions in the photosphere that shift the magnetic field lines.
