Solar Orbiter returns the first data, takes the closest images of the Sun

The first images of the ESA / NASA Solar Orbiter are now available to the public, including the closest images ever taken of the Sun.

Solar Orbiter is an international collaboration between the European Space Agency, or ESA, and NASA, to study our closest star, the Sun. Launched on February 9, 2020 (EST), the spacecraft completed its first close pass of the Sun in mid-June.

“These unprecedented images of the Sun are the closest we’ve ever obtained,” said Holly Gilbert, a NASA project scientist for the mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “These amazing images will help scientists reconstruct the Sun’s atmospheric layers, which is important for understanding how it drives space weather near Earth and throughout the solar system.”

“We did not expect such good results so early,” said Daniel Müller, a scientist at ESA’s Solar Orbiter project. “These images show that Solar Orbiter is off to an excellent start.”

Getting to this point was not a simple feat. The new coronavirus forced mission control at the European Space Operations Center, or ESOC, in Darmstadt, Germany, to shut down entirely for more than a week. During commissioning, the period when each instrument is thoroughly tested, ESOC staff were reduced to a team of skeletons. Everything but the essential staff worked from home.

“The pandemic forced us to perform critical operations remotely, the first time we did it,” said Russell Howard, principal investigator for one of the Solar Orbiter images.

But the team adapted, even preparing for an unexpected encounter with the comet and ATLAS ion and dust tails on June 1 and 6, respectively. The spacecraft completed commissioning just in time for its first nearby solar pass on June 15. As it flew 48 million miles from the Sun, all 10 instruments went on and Solar Orbiter took the closest images of the Sun to date. (Other spacecraft have been closer, but none have carried images of the Sun.)

Solar Orbiter carries six imaging instruments, each of which studies a different aspect of the Sun. Normally, the first images from a spacecraft confirm that the instruments are working; Scientists do not expect new discoveries from them. But the Extreme Ultraviolet Imager, or EUI, at Solar Orbiter returned data hinting at solar features never observed in such detail.

Lead researcher David Berghmans, an astrophysicist at the Royal Belgian Observatory in Brussels, points to what he calls “bonfires” that dot the Sun in EUI images.

“The campfires we are talking about here are the little nephews of solar flares, at least a million, perhaps a billion times smaller,” Berghmans said. “Looking at the new high-resolution EUI images, they are literally everywhere.”

It is still unclear what these bonfires are or how they correspond to the solar flare observed by other spacecraft. But they may be mini-explosions known as nanoflares – small but ubiquitous sparks theorized to help heat the Sun’s outer atmosphere, or corona, to its temperature 300 times hotter than the solar surface.

To be sure, scientists need a more accurate measurement of the temperature of the campfires. Fortunately, the spectral image of the coronal environment, or the SPICE instrument, also in Solar Orbiter, does exactly that.

“So we look forward to our next data set,” said Frédéric Auchère, principal investigator for SPICE operations at the Institute for Space Astrophysics in Orsay, France. “The hope is to safely detect nanoflares and quantify their role in coronal heating.”

Other images of the spacecraft show additional promise for later in the mission, when Solar Orbiter is closer to the Sun.

The solar and heliospheric imager, or SoloHI, led by Russell Howard of the Naval Research Laboratory in Washington, DC, revealed the so-called zodiacal light, the light of the Sun reflecting off interplanetary dust, a light so faint that the face Bright from the sun usually obscures it. To see it, SoloHI had to reduce sunlight to one billionth of its original brightness.

“The images produced such a perfect, clean zodiac light pattern,” said Howard. “That gives us a lot of confidence that we will be able to see solar wind structures when we get closer to the Sun.”

Images from the Polar and Helioseismic Imager, or PHI, showed that it is also ready for later observations. PHI maps the Sun’s magnetic field, with a special focus on its poles. It will have its peak later in the mission, as Solar Orbiter gradually tilts its orbit 24 degrees above the plane of the planets, giving it an unprecedented view of the Sun’s poles.

“The magnetic structures we see on the visible surface show that PHI is receiving high-quality data,” said Sami Solanki, principal investigator for PHI at the Max Planck Institute for Solar System Research in Göttingen, Germany. “We are prepared for great science as more poles of the Sun appear.”

Today’s launch highlights images of Solar Orbiter, but the mission’s four on-site instruments also revealed initial results. On-site instruments measure the space environment immediately surrounding the spacecraft. The solar wind analyzer, or SWA instrument, shared the first dedicated measurements of heavy ions (carbon, oxygen, silicon, iron, and others) in the solar wind from the internal heliosphere.

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