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May 6th 2020

Solar Orbiter Mission Takes Aim at Sun’s Polar Zone

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Last February, an Atlas booster rocket lifted off from Cape Canaveral. Less than an hour after launch, the Centaur top stage released its payload on an orbit that will take it to the planet Venus.

But as Space News reports, the spacecraft is not intended to explore Venus. Instead, it will use the planet as a gravitational slingshot on its way to its real objective, a pair of destinations that no human has ever yet seen: the north and south polar regions of the sun.

The Solar Orbiter, a joint project of NASA and the European Space Agency (ESA), is only the second mission ever launched to explore the sun’s upper latitudes and polar zone. But according to Space News, the only previous mission, the ESA/NASA Ulysses probe of the ’90s, didn’t carry a camera. Thus, the Solar Orbiter mission will provide us with our first actual images of the solar polar zone.

Exploring the Sun’s Turbulent Poles

At first blush, the very idea of the sun having north and south poles sounds odd, almost contradictory. After all we think of Earth’s polar zone as cold, something the sun emphatically is not. But every rotating object has an axis of rotation, accompanied by north and south poles, and the sun is no exception.

Because the sun produces its own heat, its poles are as hot as the rest of the solar surface, around 10,000 degrees F. But the sun’s polar zones are interesting to scientists for other reasons, says Discover magazine. The sun’s rotation produces a powerful magnetic field, aligned with the solar poles. And the sun’s magnetic field is the driving force of solar eruptions, visible from Earth as sunspots, that can both endanger space travelers and disrupt radio communications here on Earth.

All of which means that direct observation of the sun’s polar zones will not only be interesting and kind of awesome (though at 10,000 degrees, it won’t exactly be cool), but could also provide insights into some of the most disruptive solar phenomena.

A Long Climb to the Good Seats

So if the Solar Orbiter mission is intended to study the sun, why is it heading for Venus? It’s all about location, and good locations for looking down at the solar poles aren’t easy to reach. Earth, along with Venus and most everything else in the solar system, orbits in nearly the same plane as the sun’s equator.

Reaching good look-down positions “above” the sun’s polar zone thus requires enormous energy — much more than any booster rocket can deliver. But NASA has gotten very good at devising bank-shot orbits that make the most of the gravitational slingshot effect.

According to Discover, the Solar Orbiter will make multiple passes by Venus over the next two years to pump itself into a high-inclination orbit, giving a good view of the solar poles. In addition, says Discover, its orbit will sometimes get closer to the sun than Mercury. The spacecraft thus carries a heat shield to protect itself from 1,000-degree temperatures during its closest approaches.

“Touching” the Sun

But the Solar Orbiter mission is only half of a spacecraft team that is gearing up for what one scientist quoted by Space News described as a “kind of a golden age for solar physics.”

The other half of the team, NASA‘s Parker Solar Probe mission, launched in 2018, will carry a heavily shielded suite of instruments within 4 million miles of the solar surface, at a hurtling velocity of about 125 miles per second.

The Parker Solar Probe does not carry a camera, perhaps because direct sunlight at that distance would incinerate it before it could snap any pictures. But other instruments, protected behind a heat shield, will be able to measure conditions so close to the sun as to be inside the solar corona that we see during a solar eclipse.

With high angle shots and close-ups alike, the sun is sitting for its scientific portrait like never before.

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