ESA and NASA team up to study solar wind

Teaming up to study the solar wind 

In the run-up to the 8 April 2024 total solar eclipse, the ESA-led Solar Orbiter and NASA-led Parker Solar Probe are both at their closest approach to the Sun. They are taking the opportunity to join hands in studying the driving rain of plasma that streams from the Sun, fills the Solar System, and causes dazzlement and destruction on Earth.

Both Solar Orbiter and Parker Solar Probe have very eccentric orbits, meaning that they fly in close to the Sun to get a close-up look and then fly far out to give their onboard tech a chance to recover from the intense heat and radiation. For the first time ever, during the next week, the two spacecraft will both be at their closest approach to the Sun—what we call the ‘perihelion’—at the same time.

What’s more, this closest approach coincides with the Solar Orbiter and Parker Solar Probe being at right angles to each other as they look towards the Sun.

Daniel Müller, ESA Solar Orbiter Project Scientist, explains why this positioning is special. “On this day, we have a unique spacecraft configuration, where Solar Orbiter will have its full suite of instruments pointed towards the region on the Sun where the solar wind is produced that will hit Parker Solar Probe a few hours later.”

Scientists will compare data collected by both missions to better understand the properties of the solar wind. Because the Solar Orbiter is closest to the Sun, its telescopes will observe with the highest resolution. The simultaneous close approach by Parker Solar Probe means that only a few hours after the solar wind source regions have been imaged by Solar Orbiter, the plasma of this nearly pristine solar wind is sampled in space by Parker Solar Probe. This will allow scientists to better understand the link between the Sun and its heliosphere, the huge plasma bubble it blows into space.

But wait… at its closest approach, Solar Orbiter is 45 million km from the Sun, while Parker Solar Probe is just 7.3 million km away. So how does Solar Orbiter observe something that later hits Parker Solar Probe?

To answer this question, we need to distinguish between remote sensing and in situ instruments. Both missions carry both instrument types on board, but Solar Orbiter carries more remote sensing instruments, while Parker Solar Probe carries mostly in situ instruments (no current camera technology could look at the Sun from so close a distance and survive).

Solar Orbiter Instruments

Remote sensing instruments work like a camera or our eyes; they detect light waves from the Sun at different wavelengths. As light travels at 300,000 km/s, it takes 2.5 minutes to reach the Solar Orbiter’s instruments at the closest approach.

Meanwhile, Parker Solar Probe’s in situ instruments work more like our noses or tastebuds. They directly ‘taste’ the particles and fields near the spacecraft. In this case, Parker Solar Probe will measure solar wind particles that travel away from the Sun at more than a million kilometers per hour. Though this seems very fast, it is more than 500 times slower than the speed of light.

“Solar Orbiter alone can use both methods,” points out Andrei Zhukov from the Royal Observatory of Belgium, who is working on the joint observations. However, Parker Solar Probe comes much closer to the Sun, so it can directly measure the properties of the solar wind—like its density and temperature—closer to its birthplace before these properties change on its journey away from the Sun.”

“We will really hit the jackpot if Solar Orbiter observes a coronal mass ejection (CME) heading towards Parker Solar Probe,” adds Andrei. “We will then be able to see the restructuring of the Sun’s outer atmosphere during the CME in great detail, and compare these observations to the structure seen in situ by Parker Solar Probe.”

Teamwork makes the dream work.

This is just one example of how Solar Orbiter and Parker Solar Probe work together throughout their missions. Parker Solar Probe’s instruments are designed to sample the Sun’s corona (its outer atmosphere), targeting the region of space where the coronal plasma detaches to become the solar wind. This gives scientists direct evidence of the plasma conditions in that region and helps pinpoint how it is accelerated outwards towards the planets.

Beyond accomplishing its own science goals, Solar Orbiter will provide contextual information to improve the understanding of Parker Solar Probe’s in situ measurements. By working together in this way, the two spacecraft will collect complementary data sets, allowing more science to be distilled from the two missions than either could manage.

Credits: ESA