NASA’s STEREO-A flies by Earth after a 17-year journey across the solar


For almost 17 years, NASA’s Photo voltaic Terrestrial Relations Observatory-A spacecraft drifted by way of area on a lonely mission. It traveled across the solar far forward of Earth, conducting groundbreaking analysis on the photo voltaic system’s star.

Like many NASA spacecraft, STEREO-A outlived its mission life span of two years. As an alternative, it traveled additional and additional away from Earth on a journey that turned fraught with uncertainty because it handed behind the solar in 2015, briefly severing contact with NASA. The identical yr, the company misplaced contact with STEREO-A’s sibling vessel, STEREO-B, which was touring an identical path.

However STEREO-A stored going. And its orbital trajectory across the solar meant that it had an opportunity to do what only a few different NASA spacecraft might: ultimately make its approach again towards house.

That got here to fruition earlier this month, when STEREO-A handed between the solar and the Earth for the primary time since its launch in 2006, NASA introduced. The flyby marked a milestone for the spacecraft and the group that has monitored its progress — and an opportunity for STEREO-A to show its relevance nearly twenty years later. Because it continues to move by Earth, STEREO-A will likely be used to carry out new analysis on the solar, aided by newer NASA satellites which have been developed since its launch.

“This can be a time limit for this mission to shine once more,” Lika Guhathakurta, STEREO’s program scientist, advised The Washington Publish.

The 2 STEREO spacecraft launched in October 2006 with an formidable mission: to generate a 360-degree view of the solar by observing the star from two vantage factors as they circled it on orbits that diverged from the Earth in reverse instructions. STEREO-A maneuvered into an orbit across the solar forward of Earth, and STEREO-B started circling the solar in the wrong way behind the Earth.

The distinction in perspective was groundbreaking, Guhathakurta stated. Earthbound devices can solely ever observe one Earth-facing slice of the solar at a time, whereas the remainder of the quickly altering photo voltaic floor stays obscured. The dual STEREO spacecraft, from their offset positions, allowed scientists to seize a 360-degree view of the solar for the primary time, a feat that also awes Guhathakurta.

“Seeing the solar from the entrance and from the far aspect on the similar time — extraordinary,” she stated. “We’re on planet Earth, human beings, and we’re reaching that.”

The STEREO craft additionally allowed scientists to raised examine the solar’s roiling floor and the hazards that erupt from it. The 2 craft, working the identical approach two eyes create depth notion, offered a three-dimensional view of the solar and of coronal mass ejections — a phenomenon wherein plumes of plasma and magnetic subject shoot outward from the solar’s outer environment at lots of or hundreds of miles per second, probably threatening Earth’s energy grid and satellites, in addition to different planets and NASA spacecraft. That imagery allowed scientists to trace the form, density and velocity of coronal mass ejections as they rippled throughout the photo voltaic system.

As STEREO-A and STEREO-B continued on their orbits, they neared the far aspect of the solar in 2014. It was a testomony to how far they’d traveled, but in addition an enormous threat — transferring straight behind the solar would sever communication between the spacecraft and NASA for a interval of a number of months.

The 2 wayward spacecraft, years previous their expiration dates, had not been designed to function with out communication from NASA for that lengthy. Whereas conducting exams in preparation for the downtime, the company misplaced contact with STEREO-B. NASA briefly regained contact with the spacecraft in 2016 however decided {that a} malfunctioning element had despatched it into an uncontrollable spin, leaving it unable to orient its antenna or photo voltaic panels correctly, and the company gave up on restoration efforts.

STEREO-A, nonetheless, emerged from the far aspect of the solar unscathed — and started the lengthy journey again towards Earth. Earlier this month, the spacecraft handed between Earth and the solar, coming inside round 5 million miles of Earth, in accordance to NASA.

The spacecraft arrived again close to Earth at an opportune time, Guhathakurta stated. When STEREO-A was launched 17 years in the past, it seen the solar throughout a photo voltaic minimal, a low level within the solar’s 11-year cycle of excessive and low photo voltaic exercise. That restricted the variety of coronal mass ejections and different phenomena that the spacecraft initially noticed. This yr, STEREO-A’s return has coincided with a interval of intense photo voltaic exercise.

And its flyby means it may possibly lastly return to the work it as soon as carried out with its misplaced sibling. A succesful fleet of satellites and probes close to Earth will assist STEREO-A re-create the 3D imaging of the solar it as soon as captured with STEREO-B, the company stated.

STEREO-A will proceed to work on the sting of photo voltaic physics. Scientists hope to make use of the brand new knowledge gathered through the spacecraft’s flyby to look at a current concept that coronal loops — big arcs of photo voltaic materials that crisscross the solar’s floor when seen in ultraviolet gentle — could also be optical illusions.

For Guhathakurta, who started engaged on the STEREO mission in 1998, STEREO-A’s perseverance after such a protracted journey is heartening.

“It’s like seeing your youngsters develop up and do extraordinary issues,” Guhathakurta stated. She added that STEREO-A’s mission might not be completed, relying on NASA’s budgeting selections. Both approach, STEREO-A will proceed on its course for one more orbit across the solar.

“They don’t keep house,” Guhathakurta added, laughing. “They drift away in a short time.”

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