NASA announced that its STEREO-A spacecraft is currently passing between the sun and Earth on Saturday.
This marks the first Earth flyby for the mission that has been ongoing for nearly 17 years.
The twin Solar Terrestrial Relations Observatory spacecraft were launched on October 25, 2006, from the Cape Canaveral Air Force Station in Florida. STEREO-A was launched first, followed by STEREO-B, and both have been orbiting the sun ever since.
This dual spacecraft mission enabled researchers to obtain three-dimensional information from 2D images, providing the first stereoscopic view of the sun. In 2011, when both spacecraft reached a separation of 180 degrees in their orbits, the sun was seen as a complete sphere for the first time.
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Technicians at Astrotech Space Operations wait to maneuver NASA’s Solar Terrestrial Relations Observatory (STEREO) during a media opportunity August 11, 2006, in Titusville, Florida. ((Photo by Matt Stroshane/Getty Images))
Although mission control lost contact with STEREO-B after a planned reset in 2014, STEREO-A has continued its journey.
As the spacecraft completes its laps around the sun, its lead over Earth has grown to one full revolution.
NASA stated that this flyby presents an opportunity for collaboration with other NASA missions near Earth, allowing for new insights into the sun.
By combining views with NASA and the European Space Agency’s Solar and Heliospheric Observatory, as well as NASA’s Solar Dynamics Observatory, the STEREO-A spacecraft will once again achieve stereoscopic vision, extracting three-dimensional information about the sun’s features at different times.
Throughout the flyby, Earth’s conditions are changing, so NASA is “optimizing its stereo vision for different sized solar features at different times.”
A Boeing Delta 2 rocket lifts off from launch pad 17B at Cape Canaveral Air Force Station carrying NASA’s STEREO spacecraft at Cape Canaveral, Florida, October 26, 2006. ((Photo by Matt Stroshane/Getty Images))
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Scientists are taking advantage of this opportunity to test a new theory that coronal loops may not be what they seem, and they are identifying active regions in order to reveal their true 3D structure, which is normally lost in 2D images.
“There is a recent idea that coronal loops might just be optical illusions,” said Terry Kucera, the STEREO project scientist.
Additionally, the spacecraft’s flyby of Earth could lead to significant discoveries.
Images from NASA’s Solar Dynamics Observatory show the sun at solar minimum in October 2019 (left) and the last solar maximum in April 2014 (right). Dark coronal holes cover the sun during solar minimum, while bright active regions — indicating more solar activity — cover it during solar maximum. (Credits: NASA’s Solar Dynamics Observatory/Joy Ng)
During and after STEREO-A’s Earth flyby, any Earth-directed coronal mass ejections – plumes of solar material – that occur will travel across STEREO-A and other near-Earth spacecraft, allowing scientists to obtain multipoint measurements from inside the ejection.
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Notably, in 2006, when STEREO-A was close to Earth, it was during a low point in the sun’s cycle of high and low activity. This time around, NASA reports that things will be different.
“In this phase of the solar cycle, STEREO-A is going to experience a fundamentally different sun,” said Lika Guhathakurta, the STEREO program scientist. “There is so much knowledge to be gained from that.”
