Captured by the Metis instrument on the Solar Orbiter, the Sun’s external atmosphere, or corona, is displayed as it extends into outer space. Metis is an advanced multi-wavelength device capable of operating in both visible and ultraviolet wavelengths. It serves as a coronagraph, effectively filtering the sun’s bright surface light and allowing only the dimmer light scattering off the particles in the corona to be visible. The image incorporates a fuzzy red disc symbolizing the coronagraph, while a white disc acts as a data compression mask to minimize redundant data transmission. Credit: ESA & NASA/Solar Orbiter/Metis team; D. Telloni et al (2023)
A fortuitous celestial alignment and some adept spacecraft maneuvers have led to a groundbreaking measurement that contributes to solving the longstanding enigma of why the Sun’s corona is unusually hot.
Known as the corona, the Sun’s atmospheric layer is made of electrically charged gas, or plasma, and has an average temperature of approximately one million degrees Celsius.
This temperature discrepancy has been a long-standing puzzle since the surface of the Sun has a temperature of merely around 6,000 degrees Celsius. The expectation is that the corona should be cooler than the surface as the Sun’s energy originates from its nuclear core, and temperatures usually decrease with distance from a heat source. However, the corona is over 150 times hotter than the surface.
What alternative mechanism for energy transfer to the plasma could possibly account for this?
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Theoretical Explorations and Investigative Constraints
For an extended period, it has been hypothesized that solar atmospheric turbulence might be responsible for significant heating of the plasma in the corona. However, investigating this hypothesis presents an empirical challenge: a single spacecraft is inadequate to collect all the required data.
Solar investigations can employ two methodologies: remote sensing and in-situ measurements. Remote sensing involves positioning a spacecraft at a certain distance to observe the Sun and its atmosphere through various wavelengths. In contrast, in-situ measurements entail navigating the spacecraft through the targeted area to capture data about particles and magnetic fields.
Each methodology has its merits. Remote sensing can capture large-scale outcomes but lacks the detail of the processes occurring in the plasma. In-situ measurements offer specific information about small-scale processes but are unable to portray their large-scale impact.
Dual Spacecraft Investigation Approach
Comprehensive understanding necessitates the deployment of two spacecraft, as is currently the case with ESA’s Solar Orbiter and NASA’s Parker Solar Probe. The Solar Orbiter is designed for both remote sensing and in-situ measurements, while Parker Solar Probe is primarily focused on in-situ observations.
To capitalize on their complementary capabilities, Parker Solar Probe must be within Solar Orbiter’s instrument field of view, thereby allowing the latter to document the large-scale effects of what the former is measuring directly.
Coordination in Astrophysics
Daniele Telloni, a researcher at the Italian National Institute for Astrophysics (INAF) at the Astrophysical Observatory of Torino, is part of the team responsible for Solar Orbiter’s Metis instrument. Telloni initiated the search for occasions when Parker Solar Probe would be properly aligned. He discovered that on June 1, 2022, the orbital configurations were nearly perfect, requiring only a 45-degree roll and slight repositioning of Solar Orbiter.
After obtaining approval for the unconventional maneuver, both spacecraft successfully completed simultaneous measurements, yielding the first-ever combined observational and in-situ estimate of coronal heating rates.
Breakthrough Observations and Interpretations
According to the collected data, the theory that turbulence serves as an energy transfer mechanism appears to be substantiated. The process resembles the transfer of energy in a stirred cup of coffee, where turbulence allows for energy conversion into heat at the smallest scales, thereby heating individual particles like protons.
Conclusive Remarks and Future Implications
While further research is essential for a definitive resolution of the solar heating conundrum, the initial measurements have paved the way for more focused inquiries.
Daniel Müller, Project Scientist, emphasized the scientific significance, stating, “This work represents a considerable advance in solving the coronal heating issue.”
The Solar Orbiter mission is an international collaborative endeavor between ESA and NASA, managed by ESA.
Frequently Asked Questions (FAQs) about Solar Orbiter
What is the main objective of the Solar Orbiter and Parker Solar Probe missions?
The main objective of these missions is to investigate the Sun’s atmosphere, specifically the long-standing mystery of why the corona, the Sun’s outer atmosphere, is much hotter than its surface.
What is the corona and why is its temperature puzzling?
The corona is the Sun’s external atmosphere composed of electrically charged gas, also known as plasma. The puzzling aspect is that while the Sun’s surface has a temperature of approximately 6,000 degrees Celsius, the corona’s temperature is around one million degrees Celsius, which contradicts expectations based on proximity to the Sun’s heat source.
What are the two main methodologies for investigating the Sun?
The two primary methods are remote sensing and in-situ measurements. Remote sensing involves observing the Sun from a distance through various wavelengths, while in-situ measurements involve flying the spacecraft through the targeted region to directly measure particles and magnetic fields.
How do the Solar Orbiter and Parker Solar Probe complement each other?
The Solar Orbiter is designed for both remote sensing and in-situ measurements, whereas the Parker Solar Probe mainly focuses on in-situ measurements. The complementary nature of these approaches allows for more comprehensive data collection, especially when the spacecraft are within each other’s field of view.
Who is Daniele Telloni and what role did he play?
Daniele Telloni is a researcher at the Italian National Institute for Astrophysics (INAF) at the Astrophysical Observatory of Torino. He is part of the team responsible for Solar Orbiter’s Metis instrument and played a crucial role in coordinating the alignment between the Solar Orbiter and Parker Solar Probe for simultaneous measurements.
What is the significance of the findings?
The collected data lends credence to longstanding theories that turbulence in the Sun’s atmosphere may be a key mechanism for the significant heating of the corona. This represents a significant step forward in solving the coronal heating problem.
Is the mystery of the Sun’s hot corona finally solved?
While the findings are groundbreaking and provide crucial insights, more research is needed for a definitive resolution of the solar heating enigma.
What is the next step in this research?
The next steps involve further analysis of the collected data and potentially additional coordinated observations by Solar Orbiter and Parker Solar Probe to refine the current findings and theories.
More about Solar Orbiter
- Solar Orbiter Mission Overview by ESA
- Parker Solar Probe Mission by NASA
- Introduction to Solar Corona by Encyclopedia Britannica
- Plasma Physics Explained by American Physical Society
- Solar Turbulence Theories by ResearchGate
- The Astrophysical Observatory of Torino
- Coordinated Space Missions in Astrophysics: A Review Article
- In-Situ Measurements in Space Research: A Journal Article
