When a solar storm strikes Earth, it can disrupt technology that’s vital for our daily lives. Solar storms occur when magnetic fields and electrically charged particles collide with the Earth’s magnetic field. This type of event falls into the category known as “space weather”.
The Earth is currently experiencing one of the most intense solar storms of the past two decades, reminding us of the need for ways to understand these events.
An international team of researchers (including us) is working on a spacecraft mission that would enable researchers to study the conditions that create solar storms, leading to improved forecasts of space weather.
The proposed mission, known as Mesom (Moon-enabled Sun Occultation Mission), aims to create total solar eclipses in space. This would allow researchers to view the Sun’s atmosphere in more detail than ever before.
The need for a better understanding of solar storms is evident from looking at past disruptions. In 1989, for example, the Canadian province of Quebec was forced into a nine-hour electricity blackout by a coronal mass ejection (CME) – a huge burst of hot plasma and magnetic field thrown off from the Sun’s atmosphere towards space.
The event, which affected both Canada and the US, is estimated to have cost tens of millions of US and Canadian dollars – both in lost business productivity and the need to replace damaged power equipment.
In May 2024, a succession of similar solar eruptions caused thousands of satellites in low-Earth orbit to abruptly drop in altitude. GPS outages cost US farmers alone an estimated US$500 million (£370 million).
But these storms were significantly weaker than one in 1859, also the result of a CME, which is known as the Carrington Event. Electrical currents flowing through telegraph wires caused a range of effects in telegraph offices across North America and Europe. Operators received electric shocks – with one in Washington DC receiving a serious injury – and sparks triggered small fires in some telegraph offices.
Today, a Carrington-like event would have far more dramatic consequences on our technology-dependent world, as has been recognised by different UK governments since 2012.
Yet, our view of the Sun’s outer atmosphere, the solar corona – from which CMEs and other adverse space weather events originate – remains dazzled by the bright light emanated from the Sun itself. A new UK-led spacecraft mission aims to change that by recreating total solar eclipse conditions in space.
Better forecasting
During total solar eclipses, the incredibly high-intensity radiation emanating from the visible surface of the Sun is occulted (covered) by the Moon, leaving behind a faint glow of light that comes directly from the outer layers of the Sun’s atmosphere, the corona.
Observing the physical processes in the corona at different timescales and wavelengths is key to enabling better forecasting of space weather – a crucial part of protecting Earth against Carrington-like events – as well as solving longstanding mysteries of our star. These include how the hot plasma of its volatile atmosphere is confined and released by the evolving magnetic fields that thread through it.
Unfortunately, total solar eclipses are predictable yet rare events that only last for a few minutes. All total eclipses predicted in the 21st century will last less than seven minutes each, and will occur only once every 18 months, on average.
Total solar eclipse measurements from the ground are also subject to weather conditions and suffer from distortions and loss of detail, caused by the interaction of the faint coronal light with the Earth’s atmosphere.
For decades, scientists and engineers have observed the corona by artificially covering the Sun using clever optics and instrument design inspired by the pioneering work of Bernard Lyot, a French astronomer who first come up with the idea of a “coronagraph”.
Coronagraphs are telescopes equipped with an occulting disk to block out the overwhelming radiation emanated from the visible surface of the Sun, along with optical stops and filters that are positioned to suppress the light diffracted (scattered) by the disk itself.
In a coronagraph, the faint coronal light can finally reach the instrument’s focal plane, where it is converted into digital signals using photoelectric sensors. This is the working principle of the Large Angle and Spectrometric Coronagraph (Lasco 3) onboard the Solar and Heliospheric Observatory (Soho 4) spacecraft, which has returned stunning images of the Sun’s corona since its launch in 1995.
However, even ground-based and space-based coronagraphs cannot capture images of the deepest layers of the Sun’s atmosphere, due to artifacts – artificial effects such as streaks of light that appear in images – and instrument limitations that significantly degrade the quality of the measurements closer to the Sun’s surface.
Neither is the recently launched Proba-3 able to image the solar atmosphere’s deepest layers. Proba-3 is a European Space Agency-led technology demonstration mission that relies on a pair of satellites flying in a close formation (up to 150m apart during observations) to recreate total solar eclipse conditions in space.
Celestial neighbour
An alternative approach, first proposed by UK Airbus engineers Steve Eckersley and Stephen Kemble, advocates the use of celestial bodies as natural occulters (covers).
The idea is to fly a spacecraft mission in the shadow cast by a celestial object to enable prolonged and high-quality measurements of the corona down to the Sun’s chromosphere – the layer of the Sun’s atmosphere located just below the corona. This would effectively recreate the same total solar eclipse conditions we experience occasionally on Earth, but without the degradations caused by the atmosphere of our planet.
Our celestial neighbour, the Moon, is a more perfect sphere (its polar radius is only 2km shorter than the equatorial one) and does not have a thick atmosphere, which makes it among the best natural occulting disks found in the solar system.
A pool of engineers at the Surrey Space Centre has investigated the possibility of using the Moon as a natural occulting disk for studying the solar corona, and came up with the Mesom concept.
Mesom is a mini-satellite mission that capitalises on the chaotic dynamics of the Sun-Earth-Moon system to collect high-quality measurements of the inner Sun corona once a month, for observation windows as long as 48 minutes – much longer than the sporadic total solar eclipse on Earth.
Funded by the UK Space Agency, the feasibility study of Mesom has grown into a wider international consortium led by UCL’s Mullard Space Science Laboratory and including the Universities of Surrey and Aberystwyth, plus partners from Spain, the US and Australia.
The project has recently been submitted to the European Space Agency for consideration as a future mission. The current mission design proposes a launch in the 2030s, returning at least 400 minutes of high-resolution, low-altitude coronal observations during its two-year nominal science operations.
To collect the same amount of data on Earth, eclipse hunters would have to wait for more than 80 years. This makes Mesom a once-in-a-lifetime opportunity to unravel some of the secrets of the Sun’s atmosphere.
- is a Lecturer in Orbital Mechanics, Surrey Space Centre, University of Surrey
- is a Reader in Physical Sciences, Aberystwyth University
- is a Professor of Physics, UCL
- This article first appeared in The Conversation
