After 17 years, NASA’s STEREO-A spacecraft makes its first Earth flyby

On August 12, 2023, NASA’s STEREO-A spacecraft passes between the sun and Earth, marking the primary Earth flyby of the practically 17-year-old mission. The go to dwelling brings a particular likelihood for the spacecraft to collaborate with NASA missions close to Earth and reveal new insights into our closest star.

The dual STEREO (Photo voltaic TErrestrial RElations Observatory) spacecraft launched on Oct. 25, 2006, from the Cape Canaveral Air Drive Station in Florida. STEREO-A (for “Forward”) superior its lead on Earth as STEREO-B (for “Behind”) lagged behind, each charting Earth-like orbits across the sun.

Throughout the first years after launch, the dual-spacecraft mission achieved its landmark aim: offering the primary stereoscopic, or multiple-perspective, view of our closest star. On Feb. 6, 2011, the mission achieved one other landmark: STEREO-A and -B reached a 180-degree separation of their orbits. For the primary time, humanity noticed our sun as a whole sphere.

“Previous to that we had been ‘tethered’ to the sun-Earth line—we solely noticed one aspect of the sun at a time,” stated Lika Guhathakurta, STEREO program scientist at NASA Headquarters in Washington, D.C. “STEREO broke that tether and gave us a view of the sun as a three-dimensional object.”

The mission achieved many different scientific feats over time, and researchers studied each spacecraft views till 2014, when mission management misplaced contact with STEREO-B after a deliberate reset. Nonetheless, STEREO-A continues its journey, capturing solar views unavailable from Earth.

On Aug. 12, 2023, STEREO-A’s lead on Earth has grown to at least one full revolution because the spacecraft “laps” us in our orbit across the sun. Within the few weeks earlier than and after STEREO-A’s flyby, scientists are seizing the chance to ask questions usually past the mission’s attain.

A 3D view of the sun

Throughout the Earth flyby, STEREO-A will as soon as once more do one thing it used to do with its twin within the early years: mix views to realize stereoscopic imaginative and prescient.

Stereoscopic imaginative and prescient permits us to extract 3D data from two-dimensional, or flat, photographs. It is how two eyeballs, searching on the world from offset areas, create depth notion. Your mind compares the pictures from every eye, and the slight variations between these photographs reveal which objects are nearer or farther away.

STEREO-A will allow such 3D viewing by synthesizing its views with NASA’s and the European Area Company’s Photo voltaic and Heliospheric Observatory (SOHO) and NASA’s Photo voltaic Dynamics Observatory (SDO). Higher but, STEREO-A’s distance from Earth modifications all through the flyby, optimizing its stereo imaginative and prescient for various sized solar options at completely different instances. It is as if scientists had been adjusting the concentrate on a a number of million-mile-wide telescope.

STEREO scientists are utilizing the chance to make much-needed measurements. They’re figuring out lively areas, the magnetically advanced areas underlying sunspots, hoping to uncover 3D details about their construction normally misplaced in 2D photographs. They’re going to additionally check a brand new concept that coronal loops—big arches usually seen in close-up photographs of the sun—aren’t what they look like.

“There’s a current concept that coronal loops might just be optical illusions,” stated Terry Kucera, STEREO challenge scientist at NASA’s Goddard Area Flight Middle in Greenbelt, Maryland. Some scientists have prompt that our restricted viewing angles make them seem to have shapes they might not really have. “Should you have a look at them from a number of factors of view, that ought to turn out to be extra obvious,” Kucera added.

Inside a solar eruption

It is not simply what STEREO-A will see because it flies by Earth, but in addition what it’ll “really feel,” that would result in main discoveries.

When a plume of solar materials generally known as a coronal mass ejection, or CME, arrives at Earth, it could disrupt satellite and radio indicators, and even trigger surges in our energy grids. Or, it might have hardly any impact in any respect. All of it relies on the magnetic subject embedded inside it, which may change dramatically within the 93 million miles between the sun and Earth.

To grasp how a CME’s magnetic field evolves on the way in which to Earth, scientists construct laptop fashions of those solar eruptions, updating them with every new spacecraft statement. However a single spacecraft’s information can solely inform us a lot.

“It is just like the parable concerning the blind males and the elephant—the one who feels the legs says ‘it is like a tree trunk,” and the one who feels the tail says ‘it is like a snake,'” stated stated Toni Galvin, a professor on the College of New Hampshire and principal investigator for considered one of STEREO-A’s devices. “That is what we’re caught with proper now with CMEs, as a result of we usually solely have one or two spacecraft proper subsequent to one another measuring it.”

Throughout the months earlier than and after STEREO-A’s Earth flyby, any Earth-directed CMEs will go over STEREO-A and different near-Earth spacecraft, giving scientists much-needed multipoint measurements from inside a CME.

A basically completely different sun

STEREO-A was additionally near Earth in 2006, shortly after launch. That was throughout “solar minimal,” the low-point within the sun’s roughly 11-year cycle of excessive and low exercise.

As we method solar most predicted for 2025, the sun is not fairly so sleepy. “On this phase of the solar cycle, STEREO-A goes to expertise a basically completely different sun,” Guhathakurta stated. “There may be a lot information to be gained from that.”