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Magnetosphere monitoring: a corner piece in the space weather puzzle
Our understanding of space weather – the environmental conditions in space caused by the Sun’s activity – depends on understanding many different factors: the behaviour of the Sun, how the solar wind travels through space, and how Earth’s magnetosphere responds.
With Cluster, ESA took on the challenge of uncovering how Earth’s magnetosphere responds to the solar wind. Other ESA missions have studied different parts of the process, with Solar Orbiter, SOHO, Proba-2 and Ulysses keeping watching on the Sun itself, and Swarm and Double Star also studying Earth’s magnetic environment. Double Star focused on the ‘magnetotail’ that stretches away from planet Earth, and Swarm continues to analyse Earth’s magnetic field itself.
Cluster’s scientific torch will be passed on to the ESA/Chinese Academy of Sciences Solar wind Magnetosphere Ionosphere Link Explorer (Smile) mission, set to launch in late 2025.
A few years later, ESA’s Vigil mission will head into space to put the different puzzle pieces together, aiming to provide continuous, near real-time data on potentially hazardous solar activity. Ultimately this will help us ensure safe satellite communications and space and air travel.
What made Cluster so special?
While most missions exploring Earth’s magnetic phenomena focus on the equator, the Cluster quartet circled over the poles, where there is a lot of magnetic activity. Solar wind in this area can dive deeper into Earth’s upper atmosphere, giving rise to the spectacular auroras.
Cluster’s ability to observe higher latitudes than other missions meant that it revealed parts of the magnetosphere that we’ve never been able to ‘see’ before with multiple spacecraft at the same time.
Through its mapping of Earth’s magnetic field, and comparison of this to Mars’s lacklustre present-day magnetism, Cluster has reaffirmed the importance of our magnetosphere in shielding us from the solar wind.
The mission also helped us understand weaknesses in the magnetosphere, including how solar wind particles can break through the shield. It even discovered the origin of ‘killer electrons’, energetic particles in the outer belt of radiation surrounding Earth, that can cause havoc for satellites.
By continually monitoring and recording the dynamics and properties of Earth’s magnetosphere over two decades, Cluster has amassed an unprecedented wealth of data, allowing scientists to make truly ground-breaking findings, including on longer-term trends.
After an incredibly successful 24 years in space, ESA took the decision to deorbit the four Cluster satellites throughout 2024–2026. Planning the reentries at this time made it possible for the Cluster spacecraft to contribute to reentry science as a final farewell.