From NASA Goddard Space Flight Center (US) : “Total Solar Eclipses Shine a Light on the Solar Wind with Help from NASA’s ACE Mission”

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From NASA Goddard Space Flight Center (US)

Jun 15, 2021

Mara Johnson-Groh
mjohnson-groh@sesda.com
NASA’s Goddard Space Flight Center in Greenbelt, Md.

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Special filters enable scientists to measure different temperatures in the corona during total solar eclipses, such as this one seen in Mitchell, Oregon, on August 21, 2017. The red light is emitted by charged iron particles at 1.8 million degrees Fahrenheit and the green are those at 3.6 million degrees Fahrenheit.
Credits: Image produced by M. Druckmuller and published in Habbal et al. 2021.

More Than Just Pretty Pictures

Scientists have used total solar eclipses for over a century to learn more about our universe, including deciphering the Sun’s structure and explosive events, finding evidence for the theory of general relativity, and even discovering a new element – helium. While instruments called coronagraphs are able to mimic eclipses, they’re not good enough to access the full extent of the corona that is revealed during a total solar eclipse. Instead, astronomers must travel to far-flung regions of the Earth to observe the corona during eclipses, which occur about every 12 to 18 months and only last a few minutes.

Through travels to Australia, Libya, Mongolia, Oregon, and beyond, the team gathered 14 years of high-resolution total solar eclipse images from around the world. They captured the eclipses using cameras equipped with specialized filters to help them measure the temperatures of the particles from the innermost part of the corona, the sources of the solar wind.

The researchers used light emitted by two common types of charged iron particles in the corona to determine the temperature of the material there. The results unexpectedly showed that the amount of the cooler particles – which were more abundant and found to contribute most of the solar wind material – were surprisingly consistent at different times during the solar cycle. The sparse hotter material varied much more with the solar cycle while the solar wind speed varied from 185 to 435 miles per second.

“That means that whatever is heating the majority of the corona and solar wind is not very dependent on the Sun’s activity cycle,” said Benjamin Boe, a solar researcher at the University of Hawai’i (US) involved in the new research.

The finding is surprising as it suggests that while the majority of solar wind is originating from sources that have a roughly constant temperature, it may have wildly different speeds. “So now the question is, what processes keep the temperature of the sources of the solar wind at a constant value?” Habbal said.

The Dynamic Sun

The team also compared the eclipse data with measurements taken from NASA’s Advanced Composition Explorer, or ACE, spacecraft, which sits in space 1 million miles away from Earth in the direction of the Sun and was also essential in revealing the properties of the dynamic component of the solar wind.

The variable speeds of the dynamic wind were distinguished by the variability of the iron charge states associated with them. The spacecraft data showed that the speeds of the particles seen in the variable solar wind changed in relationship to the iron charge states associated with them. The high temperature sheaths around events called prominences, discovered from eclipse observations, were found to be responsible for the dynamic wind and the occasional coronal mass ejection – a large cloud of solar plasma and embedded magnetic fields released into space after a solar eruption.

While the team doesn’t know why the sources of the solar wind are at the same temperature, they think the speeds vary depending on the density of the region they originated from, which itself is determined by the underlying magnetic field. Fast-flying particles come from low-density regions, and slower ones from high-density regions. This is likely because the energy is distributed between all the particles in a region. So in areas where there are fewer particles, there’s more energy for each individual particle. This is similar to splitting a birthday cake – if there are fewer people, there’s more cake for each person.

The new findings provide new insights into the properties of the solar wind, which is a key component of space weather that can impact space-based communication satellites and astronomical observing platforms. The team plans to continue traveling the globe to observe total solar eclipses. They hope their efforts may eventually shed a new light on the longstanding solar mystery: how the corona reaches a temperature of a million degrees, far hotter than the solar surface.

Science paper:
The Astrophysical Journal Letters

See the full article here.


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NASA/Goddard Campus

NASA’s Goddard Space Flight Center, Greenbelt, MD (US) is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

GSFC also operates two spaceflight tracking and data acquisition networks (the NASA Deep Space Network(US) and the Near Earth Network); develops and maintains advanced space and Earth science data information systems, and develops satellite systems for the National Oceanic and Atmospheric Administration(US) .

GSFC manages operations for many NASA and international missions including the NASA/ESA Hubble Space Telescope; the Explorers Program; the Discovery Program; the Earth Observing System; INTEGRAL; MAVEN; OSIRIS-REx; the Solar and Heliospheric Observatory ; the Solar Dynamics Observatory; Tracking and Data Relay Satellite System ; Fermi; and Swift. Past missions managed by GSFC include the Rossi X-ray Timing Explorer (RXTE), Compton Gamma Ray Observatory, SMM, COBE, IUE, and ROSAT. Typically, unmanned Earth observation missions and observatories in Earth orbit are managed by GSFC, while unmanned planetary missions are managed by the Jet Propulsion Laboratory (JPL) in Pasadena, California(US).

Goddard is one of four centers built by NASA since its founding on July 29, 1958. It is NASA’s first, and oldest, space center. Its original charter was to perform five major functions on behalf of NASA: technology development and fabrication; planning; scientific research; technical operations; and project management. The center is organized into several directorates, each charged with one of these key functions.

Until May 1, 1959, NASA’s presence in Greenbelt, MD was known as the Beltsville Space Center. It was then renamed the Goddard Space Flight Center (GSFC), after Robert H. Goddard. Its first 157 employees transferred from the United States Navy’s Project Vanguard missile program, but continued their work at the Naval Research Laboratory in Washington, D.C., while the center was under construction.

Goddard Space Flight Center contributed to Project Mercury, America’s first manned space flight program. The Center assumed a lead role for the project in its early days and managed the first 250 employees involved in the effort, who were stationed at Langley Research Center in Hampton, Virginia. However, the size and scope of Project Mercury soon prompted NASA to build a new Manned Spacecraft Center, now the Johnson Space Center, in Houston, Texas. Project Mercury’s personnel and activities were transferred there in 1961.

The Goddard network tracked many early manned and unmanned spacecraft.

Goddard Space Flight Center remained involved in the manned space flight program, providing computer support and radar tracking of flights through a worldwide network of ground stations called the Spacecraft Tracking and Data Acquisition Network (STDN). However, the Center focused primarily on designing unmanned satellites and spacecraft for scientific research missions. Goddard pioneered several fields of spacecraft development, including modular spacecraft design, which reduced costs and made it possible to repair satellites in orbit. Goddard’s Solar Max satellite, launched in 1980, was repaired by astronauts on the Space Shuttle Challenger in 1984. The Hubble Space Telescope, launched in 1990, remains in service and continues to grow in capability thanks to its modular design and multiple servicing missions by the Space Shuttle.

Today, the center remains involved in each of NASA’s key programs. Goddard has developed more instruments for planetary exploration than any other organization, among them scientific instruments sent to every planet in the Solar System. The center’s contribution to the Earth Science Enterprise includes several spacecraft in the Earth Observing System fleet as well as EOSDIS, a science data collection, processing, and distribution system. For the manned space flight program, Goddard develops tools for use by astronauts during extra-vehicular activity, and operates the Lunar Reconnaissance Orbiter, a spacecraft designed to study the Moon in preparation for future manned exploration.