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The first images of the Solar Orbiter mission built in Europe are the closest ever taken from the sun, and reveal never-before-seen mini-flares nicknamed “bonfires” that may offer clues to what makes the solar corona, or outer atmosphere , it is hotter than the surface of the sun. .
The Solar Orbiter mission led by the European Space Agency, built and launched in association with NASA, will become the first spacecraft to take pictures of the Sun’s polar regions. But Solar Orbiter is already setting records months after its February 9 launch from Cape Canaveral aboard a United Launch Alliance Atlas 5 rocket.
The first images from the Solar Orbiter spacecraft revealed new processes in operation on the sun. Scientists noted widespread miniature solar flares, which appear to be smaller versions of solar flares that are visible from Earth.
The scientific team dubbed the mini bonfires “bonfires,” one of several new terms coined by the Solar Orbiter team as researchers analyze the data sets now returned by the 10 spacecraft instruments.
“When you look at it in high resolution, it’s surprising, in the smallest details, the amount of things that are happening there,” said David Berghmans, principal investigator for the Solar Orbiter Extreme Ultraviolet Camera at the Royal University of Belgium.
“We couldn’t believe this when we first saw it, and we started giving it crazy names like bonfires and dark fibrils and ghosts and everything we saw,” Berghmans said at a press conference on Thursday. “So many new small phenomena are happening, on the smallest scales, that we are starting a new vocabulary to give it new names.”
Berghmans said the images from the Extreme Ultraviolet Imager, an instrument package in Solar Orbiter that contains three different telescopes, will improve in contrast and sharpness as scientists optimize image-processing software and the spacecraft gets closer to the sun.
The images released Thursday by the European Space Agency and NASA were taken when Solar Orbiter passed its first perihelion, the point on its closest elliptical orbit to the sun, at a distance of approximately 48 million miles (77 million km). That is about half the distance from Earth to the sun, and just outside of Mercury’s orbit.
No other solar telescope has observed the sun from such a close distance, but the images will improve as Solar Orbiter approaches the sun in the coming years.
“As far as we know, many of these spectacular features have not been seen before on this scale,” said Daniel Müller, ESA project scientist for the Solar Orbiter mission. “These are clearly just the test images, so it is too early to draw scientific conclusions, but our guess is that these campfires and ghosts are related to changes in the sun’s magnetic field, a process known as magnetic reconnection.” .
“These (magnetic fields) become tangled and stressed, and like rubber bands, they can eventually break and reconfigure into new configurations,” said Müller. “That tearing process can release energy in large quantities, and that can heat plasma locally to temperatures of over a million degrees, which is what we see in the EUI images.”
The Extreme Ultraviolet Imager instrument includes three telescopes, each tuned to view a different layer of the sun. Campfires appeared in images looking at the lower atmosphere of the sun, or corona, where temperatures exceed one million degrees Celsius, or 1.8 million degrees Fahrenheit.
Solar Orbiter carries six remote sensing instruments to take pictures of the sun, and four other instruments collect on-site data on the spacecraft environment.
“Campfires are small relatives of solar flares that we can observe from Earth, millions to billions of times smaller,” Berghmans said in a statement. “The sun may seem calm at first glance, but when we look closely, we can see those miniature flares everywhere.”
Berghmans said the smallest of the bonfires appears to be a few hundred kilometers in diameter, or “about the size of a European country.” Smaller bonfires can become visible later in the Solar Orbiter mission, when the spacecraft’s orbit approaches the sun.
The solar corona extends millions of miles into space, in a region where temperatures rise much higher than the sun’s surface, which averages around 10,000 degrees Fahrenheit (5,500 degrees Celsius).
“It is a bit contradictory because you would think that if you have a very hot body in the center and relatively cold on the surface, it would be even colder the farther you go,” Müller said. “But on the contrary, for the sun, we have a hot core and a relatively cold surface … surrounded by a super hot atmosphere of over a million degrees.”
Eugene Parker, a pioneering US solar physicist who theorized the solar wind before scientists confirmed its existence, predicted that the solar corona could be heated by numerous small flares invisible to solar telescopes around Earth.
“These bonfires are totally insignificant by themselves, but summing up their effect on the entire sun, they could be the dominant contribution to warming the solar corona,” says Frédéric Auchère of the Institut d’Astrophysique Spatiale in France, co-researcher at the Extreme Ultraviolet Imager.
Since launching in February, Solar Orbiter and its 10 instruments have been tested, calibrated, and confirmed ready for scientific operations. The post-launch commissioning of the $ 1.5 billion mission proceeded primarily on time despite significant disruptions to the coronavirus pandemic.
Solar Orbiter operations were halted for approximately 10 days in March after an employee at ESA’s mission operations center in Germany tested positive for COVID-19. Limited personnel were allowed to return to ESA’s control center, but instrument teams across Europe had to verify the performance of Solar Orbiter’s science load from home.
While ESA is leading the Solar Orbiter mission, NASA paid for the launch of the probe, and there is a United States-led instrument on the spacecraft.
With the launch of Solar Orbiter, scientists have two spacecraft that observe the sun from closer locations than any previous mission.
NASA’s Parker solar probe launched in August 2018 on a path that brings it closer to the Sun than the Solar Orbiter. But Solar Orbiter carries cameras and telescopes, while Parker flies so close to the sun that scorching temperatures could damage or destroy sensitive image sensors.
And Solar Orbiter will eventually circle the sun at a higher tilt than Parker, allowing views of the sun’s poles.
The 10 instruments in Solar Orbiter will allow scientists to connect what they see happening in the sun with the effects on the environment around the spacecraft.
“Most of the major big goals, the novel parts of the mission, are for us all to work together and be able to link the images of the dynamics of the sun with what is coming out of the spacecraft,” said Christopher Owen. Principal investigator of the Solar Orbiter’s Solar Wind Analyzer instrument at University College London.
Scientists are eager to try to link mini solar flares, or campfires, with magnetic field data to find out what causes the flares. Solar Orbiter could also collect data on the origin of the larger flares, which can trigger explosions in the solar wind that can affect space weather and cause geomagnetic storms on Earth, disturbances that can affect radio communications, satellite operations. and electrical networks.
The sun is currently in a relatively quiet period in its 11-year cycle. By the time the Solar Orbiter approaches the sun, our nearest star is forecast to be most active.
After a perfect launch into the target in February, Solar Orbiter is on its way for a rendezvous with Venus on December 26 to begin bringing the spacecraft closer to the sun. Solar Orbiter will have nine planetary flybys until 2030, eight with Venus and one with Earth, to steer the spacecraft into increasingly narrow orbits around the sun.
“In March 2022, we will have the first really close flyby, when we are 30 percent from the sun from Earth,” said Müller.
“We will gradually tilt our orbit to see the polar regions for the first time,” said Müller. “That will be the last change in perspective, and it is definitely worth the wait because we truly believe that this will give us a new insight into the sun’s cycle of activity. So what drives these 11-year periodic changes in the sun’s magnetic field activity?
The first good look at the poles of the sun will come in 2025, when Solar Orbiter reaches an angled path of 17 degrees from the ecliptic plane, the plane in which the planets of the solar system are located. Repeated flybys with Venus will gradually increase the probe’s tilt, or orbital tilt, thanks to the planet’s gravity.
By 2029, after the end of the Solar Orbiter’s main mission phase, the spacecraft should be in an orbit tilted more than 33 degrees toward the ecliptic plane, allowing for even better views of the Sun’s poles.
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