The Sun is the closest star to us and yet there are still many unknowns. Some of these mysteries include the complex processes within the star itself, while others are almost banal in comparison but equally important. For example, humanity has never seen what the poles of the Sun look like.
The answer to that and many more questions will soon be closer to reality thanks to the European Space Agency’s Solar Orbiter in collaboration with NASA. The mission is launching this week from NASA's Kennedy Space Center in Cape Canaveral. The Solar Orbiter will study the internal structure of the Sun and the inner heliosphere, the bubble created by the electrically charged particles that make up the solar wind. By combining the data with models, solar scientists hope to have a better idea of the type of elements present in our star.
“I think the most exciting thing is that we're going to see the poles of the Sun and that's never been seen before,” Dr David Williams, one of the three instrument operations scientists for Solar Orbiter, told IFLScience. “On a slightly more scientific level, the most exciting thing for me is that we will be able to track the composition and origin of the stuff in the solar wind.”
“We always had some idea ‘maybe it comes from there, maybe not from there' but with Solar Orbiter we’ll know. We've got chemical fingerprinting technology onboard that can detect the balance of different chemical elements. So how much carbon, oxygen, helium, and so on. And we've got a telescope that can see what the chemical composition of every bit of the Sun is. We've got what we need to find out what the solar wind “smells” like!”
The mission is slotted to launch on Sunday, February 9, 23:03 EST (04:03 GMT Monday, February 10). Once the spacecraft is safely separated from the Atlas V 411 rocket supplied by NASA, it will begin a 22-minute activation sequence that will deploy the solar arrays and critical instrumentation.
The science mission, featuring its suite of 10 instruments, won’t start straight away but towards the end of 2021. As the craft heads towards the Sun, it will perform two gravity-assist maneuvers around Venus and one around Earth. This will put Solar Orbiter on an elliptical trajectory the gets as close as 42 million kilometers (26 million miles) from the star.
To eventually image the poles, the spacecraft needs to be “lifted” above the ecliptic, the plane where the planetary orbits lie. This is possible using the gravity of Venus again. The craft’s orbit is in resonance with Venus, so every few orbits it is close to the planet. As the spacecraft passes near Venus, it can use the planet's gravity to shift its orbit by doing a fuel burn. This will be used to raise Solar Orbiter on a more tilted orbit, up to potentially 33 degrees with respect to the ecliptic. While this is exciting, it also requires a lot of long-term planning to make sure the probe is always at the right place at the right time.
“It's really like a planetary-encounter mission. But this time, the 'planet' is the biggest object in the solar system, the Sun,” Dr Williams explained.
The Solar Orbiter mission will be enhanced with a collaboration with NASA’s Parker Solar Probe, and vice versa. The two missions have been a long time in the making; Dr Williams likes to think of them as siblings, even though their focus and distance from the Sun will be different. Parker will be less than 6.9 million kilometers (4.3 million miles) away.
“Because [Parker] is so close to the Sun, it whizzes around it quite rapidly. That means there are a number of times every year where the two spacecraft sort of lie on the same stream of plasma that comes off the Sun. Parker can measure upstream solar wind and we can measure downstream to find out if the solar wind is smooth flowing further upstream or more turbulent like cosmic rapids,” Dr Williams explained about the future work.
“When you launch your mission, you discover all sorts of stuff that you just didn't think existed in nature. And cracking those mysteries is going to be really fun, especially with a sibling mission exploring the same idea but from further into the solar system.”
Astronomers can hardly wait for Solar Orbiter's new detailed observations of the turbulent solar surface, the inexplicably hot corona, and how the solar wind changes. It has a nominal mission of seven years, and the team hopes that it will be extended for a further three.