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Solar Orbiter returns to Earth before starting its main science mission

on 25 November 2021

Solar Orbiter is returning to Earth for a flyby before starting its main science mission to explore the Sun and its connection to ‘space weather’. During the flyby Solar Orbiter must pass through the clouds of space debris that surround our planet, making this manoeuvre the riskiest flyby yet for a science mission.

Solar Orbiter’s Earth flyby takes place on 27 November. At 04:30 GMT (05:30 CET, 06:30 Romania Time) on that day, the spacecraft will be at its closest approach, just 460 km above North Africa and the Canary Islands. This is almost as close as the orbit of the International Space Station.

The manoeuvre is essential to decrease the energy of the spacecraft and line it up for its next close pass of the Sun but it comes with a risk. The spacecraft must pass through two orbital regions, each of which is populated with space debris.

The first is the geostationary ring of satellites at 36 000 km, and the second is the collection of low Earth orbits at around 400 km. As a result, there is a small risk of a collision. Solar Orbiter’s operations team are monitoring the situation very closely and will alter the spacecraft’s trajectory if it appears to be in any danger.

On the plus side, the flyby offers a unique opportunity to study the Earth’s magnetic field. This is a subject of intense interest because the magnetic field is our atmosphere’s interface with the solar wind, the constant ‘wind’ of particles given off by the Sun. Not only can particles from the solar wind penetrate the magnetic field and spark the aurora in our skies, but atoms from our atmosphere can also be lost into space.

The details of these interactions are being studied by two ESA missions: Cluster’s four satellites at 60 000 km in altitude and Swarm’s three spacecraft at 400 km. Multiple spacecraft are needed to break the so-called space-time ambiguity. This is the name given to the uncertainty over whether a change has taken place because a spacecraft has flown into a different region with different conditions (a change in space) or is flying through a region that changes its conditions (a change in time).

Solar Orbiter’s flyby offers a unique opportunity to take even more data. It will sweep into the Earth’s magnetic field from out beyond Clusters orbit, approach Swarm’s orbit at closest approach and then fly back out again. This will provide even more data points from which to reconstruct the condition and behaviour of Earth’s magnetic field during the flyby.

More details here.

Image credit: ESA