But continues to play in stereo. And its orbital trajectory around the Sun meant that it had a chance to do what few NASA spacecraft could: finally return home.
That turned out to be the case earlier this month, when STEREO-A passed between the Sun and Earth for the first time since its launch in 2006, NASA announcement. The flyby marked a milestone for the spacecraft and the team that monitored its progress — and a chance to prove STEREO-A’s relevance nearly two decades later. As it passes by Earth, STEREO-A will be used to perform new studies of the Sun, aided by new NASA satellites developed since its launch.
“This is a point in time for this mission to shine again,” Lika Guthakurta, STEREO’s program scientist, told The Washington Post.
The two STEREO spacecraft launched in October 2006 with an ambitious mission: to create a 360-degree view of the Sun by observing the star from two vantage points as they orbit it in opposite directions from Earth. STEREO-A is driven into an orbit around the Sun in front of Earth, and STEREO-B begins orbiting the Sun in the opposite direction behind Earth.
The difference in perspective was groundbreaking, Guthakurta said. Earthbound instruments can observe only one Earth-facing Sun fragment at a time, while the rest of the rapidly changing solar surface remains obscured. The twin stereo spacecraft, from their offset positions, allowed scientists to capture A 360-degree view of the Sun for the first time, a feat that still amazes cavemen.
“Seeing the sun from the front and from a distance at the same time – amazing,” he said. “We’re on planet Earth, people, and we’re getting it.”
The stereo craft allowed scientists to better study the sun’s rolling surface and the hazards it poses. The two craft, working in the same way as the two eyes create depth perception, provide a three-dimensional view of the sun Coronal mass ejections — An event in which plumes of plasma and magnetic fields are ejected from the Sun’s outer atmosphere at hundreds or thousands of miles per second, potentially threatening Earth’s power grid and satellites, as well as other planets and NASA spacecraft. Those images allow scientists to track the shape, density and velocity of coronal mass ejections as they spread across the solar system.
Stereo-A and Stereo-B continue in their orbits nearby 2014 Sun’s Distant Distance. It was a testament to how far they had traveled, but it was also a huge risk — going directly behind the Sun would cut off communication between the spacecraft and NASA for months.
The two wayward spacecraft, past their expiration dates, were not designed to operate without communication from NASA for that long. While conducting tests in preparation for the downtime, the agency lost contact with STEREO-B. NASA briefly restored contact with the spacecraft in 2016 but prescribed A faulty component sent it into an uncontrolled spin, leaving it unable to properly orient its antennas or solar panels, and the company abandoned recovery efforts.
In stereo, however, the Sun emerged intact from the far side—and began its long journey back toward Earth. Earlier this month, the spacecraft passed between Earth and the Sun, coming within about 5 million miles of Earth. According to to NASA
The spacecraft returned to Earth in good time, Guthakurta said. When STEREO-A launched 17 years ago, it observed the Sun at solar minimum, a low point in the Sun’s 11-year cycle of high and low solar activity. This limited the number of coronal mass ejections and other events initially observed by the spacecraft. This year, STEREO-A’s return coincided with a period of intense solar activity.
And its flyby means it may eventually return to the task it once performed with its lost sibling. A capable fleet of near-Earth satellites and probes will help STEREO-A recreate 3D imaging of the Sun once captured by STEREO-B, the agency said.
STEREO-A will continue to work at the cutting edge of solar physics. Scientists hope to use the new data collected during the spacecraft’s flyby to conduct a recent experiment theory That coronal loops—giant arcs of solar material that cross the Sun’s surface when seen in ultraviolet light—can be optical illusions.
For Guthakurta, who started working on the STEREO mission in 1998, STEREO-A’s persistence after such a long journey is gratifying.
“It’s like watching your children grow up and do amazing things,” Guthakurta said. He added that depending on NASA’s budget decisions, STEREO-A’s mission may not be completed. Either way, STEREO-A will continue on its course for another orbit around the Sun.
“They don’t stay at home,” Guthakurta adds with a laugh. “They go away very quickly.”