STEREO-A, NASA's Solar Terrestrial Relations Observatory-A spacecraft, recently completed a significant milestone by passing between the sun and Earth for the first time since its launch in 2006. The spacecraft, which was initially planned to operate for two years, has been drifting through space for nearly 17 years, conducting groundbreaking research on the sun. Its companion spacecraft, STEREO-B, also lost contact with NASA in 2015 and was subsequently abandoned.
The STEREO spacecraft provided scientists with a unique perspective on the sun, allowing them to observe it from two different angles and capture a complete 360-degree view. This was a major advancement compared to instruments on Earth, which can only observe a single slice of the sun facing Earth at any given time. The spacecraft's observations helped scientists gain a better understanding of the sun's turbulent surface and the potential dangers it poses, such as coronal mass ejections (CMEs) that can impact Earth's power grid and satellites.
As STEREO-A continues to pass by Earth, it will be utilized for new research on the sun, aided by newer NASA satellites that have been developed since its launch. The spacecraft's recent flyby between the sun and Earth offers it an opportunity to demonstrate its relevance and contribute to ongoing scientific discoveries.
However, STEREO-A emerged unharmed from the opposite side of the sun and began its long journey back towards Earth. According to NASA, earlier this month, the spacecraft passed between Earth and the sun, reaching a distance of approximately 5 million miles from Earth.
The return of the spacecraft near Earth is opportune, as stated by Guhathakurta. When STEREO-A was launched 17 years ago, it observed the sun during a period of low solar activity known as solar minimum. This limited the spacecraft's initial observations of coronal mass ejections and other phenomena. This year, STEREO-A's return coincides with a period of intense solar activity.
This flyby allows STEREO-A to resume the work it previously conducted with its lost counterpart. NASA mentioned that a capable fleet of satellites and probes near Earth will assist STEREO-A in recreating the 3D imaging of the sun that it once achieved with STEREO-B.
STEREO-A will continue its research on the fringes of solar physics. Scientists aim to utilize the new data collected during the spacecraft's flyby to investigate a recent hypothesis suggesting that coronal loops, which are large arcs of solar material that intersect the sun's surface when viewed in ultraviolet light, might be optical illusions.
For Guhathakurta, who has been involved in the STEREO mission since 1998, STEREO-A's perseverance after such a lengthy journey is inspiring. She compared it to watching one's children grow up and accomplish extraordinary things. Guhathakurta also mentioned that STEREO-A's mission may not be over, depending on NASA's budget decisions. Regardless, STEREO-A will continue its orbit around the sun.
"They don't stay home," Guhathakurta added, chuckling. "They quickly drift away."
