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Deadly solar outburst detected by spacecraft around the solar system

The Sun unleashed a widespread and massive solar outburst, called a coronal mass ejection (CME), that simultaneously reached Mars, the Earth, and the Moon.

Never before has this type of cosmic event been documented in this manner. Despite being on opposite sides of the Sun and separated by about 250 million kilometers, both planets were bombarded with an intense surge of energetic particles.

This extraordinary solar eruption was reported in a recent Geographical Research Letters paper. An international ensemble of spacecraft, including ESA’s ExoMars Trace Gas Orbiter (TGO), NASA’s Curiosity Mars rover, the CNSA’s Chang’e-4 Moon lander, NASA’s Lunar Reconnaissance Orbiter (LRO), and DLR’s Eu:CROPIS Earth orbiter, detected the solar outburst.

The event presented an unprecedented opportunity to observe and measure solar eruption event’s effects on the surfaces of the Earth, Moon, and Mars simultaneously.

The interplanetary data captured from the event is crucial to advancing our understanding of solar outbursts, their impact, and the role a planet’s magnetic field and atmosphere play in providing protection against these occurrences.

Comparing solar outbursts on different worlds

Notably, this solar event on October 28, 2021, was a rare type of outburst known as a ‘ground level enhancement.’ During such occurrences, particles from the Sun carry enough energy to penetrate Earth’s magnetic shield.

Ordinarily, our planet’s magnetic shield safeguards us from less energetic solar outbursts. This marked only the 73rd recorded instance of a ground level enhancement since records commenced in the 1940s. Scientists haven’t observed another one since.

Solar particles can easily reach the surfaces of the Moon and Mars. This is because neither celestial body generates its own magnetic field. The particles can even interact with the soil on these surfaces, giving rise to secondary radiation. Although Mars boasts a thin atmosphere that hinders most lower-energy solar particles and decelerates the highly energetic ones, it doesn’t offer complete protection.

Radiation levels from this coronal mass ejection

Understanding the potential effects of these solar eruption events is of utmost importance for future human exploration of the Moon and Mars. This is especially important considering the risk of radiation sickness astronauts face.

A radiation dose above 700 milligray may cause radiation sickness. This dosage can lead to the destruction of bone marrow, infections, and internal bleeding. If an astronaut receives more than 10 gray of radiation, they are highly unlikely to survive beyond two weeks.

For instance, a solar outburst in August 1972 would have proved lethal for any astronaut on the lunar surface. Fortunately, it occurred between the Apollo 16 and 17 missions.

For perspective, the dose of radiation in lunar orbit during the October 28, 2021, event, as measured by NASA’s Lunar Reconnaissance Orbiter, was only 31 milligray.

Scientist Jingnan Guo, who studied this particular event, stated, “Our calculations of the past ground level enhancement events show that on average one event every 5.5 years may have exceeded the safe dose level on the Moon if no radiation protection had been provided. Understanding these events is crucial for future crewed missions to the surface of the Moon.”

How Mars and other solar system missions compared

Comparative measurements made by ExoMars TGO and the Curiosity rover shed light on the protective value of Mars’s atmosphere. The TGO registered 9 milligray — 30 times more than the 0.3 milligray detected on the surface.

ESA’s inner Solar System missions — the Solar Orbiter, SOHO, and BepiColombo — were also caught in the outburst’s path. This provided scientists with further perspectives to study this massive solar event.

As Marco Pinto, an ESA research fellow working on radiation detectors, expressed, “Currently, we live in a golden age of Solar System physics. Radiation detectors aboard planetary missions such as BepiColombo, on its way to Mercury, and Juice, cruising to Jupiter, add much-needed coverage to study the acceleration and propagation of solar energetic particles.”

Protecting astronauts from CME’s during space missions

Ensuring astronaut safety as we explore further into space is paramount. To this end, understanding and predicting intense radiation events is a critical part of the mission for space agencies like ESA.

Dedicated instruments measure the radiation environment in space. These instruments help to safeguard critical spaceborne and ground-based infrastructure, as well as astronauts. Given a timely warning, astronauts can take preventative measures like seeking shelter or donning protective gear.

Lunar Gateway

The Artemis program, which aims to send astronauts back to the Moon, includes a space station in lunar orbit, named the Gateway.

Here, three suites of instruments — ESA’s European Radiation Sensors Array (ERSA), NASA’s Heliophysics Environmental and Radiation Measurement Experiment Suite (HERMES), and the ESA/JAXA Internal Dosimeter Array (IDA) — will monitor the radiation environment around the Moon.

The data gathered will help us better understand the radiation environment that astronauts will encounter in interplanetary space.

Luna Twins

As part of this preparation, space agencies are also exploring protective attire to minimize the impact of space radiation on astronauts’ bodies. Two mannequins, Helga and Zohar, created by the German Aerospace Center (DLR), were equipped with radiation sensors and sent on the Artemis I test flight.

Helga and Zohar passed by the Moon in late 2022. Helga flew unprotected, while a newly developed radiation protection vest outfitted Zohar. DLR researchers are presently comparing the datasets measured by Helga and Zohar.

ExoMars TGO project scientist Colin Wilson concluded, “Space radiation can create a real danger to our exploration throughout the Solar System. Measurements of high-level radiation events by robotic missions is critical to prepare for long-duration crewed missions. Thanks to data from missions like ExoMars TGO, we can prepare for how best to protect our human explorers.”

More about coronal mass ejections (CMEs)

Coronal mass ejections (CMEs) are large-scale expulsions of plasma and magnetic field from the Sun’s corona, its outermost layer. As the most energetic events in the Solar System, CMEs occur when magnetic field lines in the Sun’s corona become twisted and realign. This solar shift releases energy and matter into space.


CMEs vary in size and speed, with some reaching speeds of up to 3200 kilometers per second. The mass of the plasma ejected during a CME can exceed ten billion tons.

When directed towards Earth, CMEs can cause significant disturbances in the Earth’s magnetosphere. Earth’s magnetic field dominates this region of space.

Impact on Earth

On Earth, CMEs can produce geomagnetic storms that disrupt power grids, satellite communications, and navigation systems. They can also generate harmful radiation, which can cause a phenomenon known as a solar radiation storm. This can pose a danger to astronauts in space, as well as to high-altitude aircraft flying near the poles.

Geomagnetic storms can also lead to increased auroral activity. This means that areas far from the poles may witness the spectacular light displays of the aurora borealis (northern lights) and aurora australis (southern lights).

Impact on humans

CMEs pose a potential risk to human health, particularly to those in space. The high-energy particles from the Sun, if not shielded by Earth’s magnetic field or the walls of a spacecraft, can harm the human body.

For example, a high radiation dose can lead to radiation sickness, damaging bone marrow and causing infections or internal bleeding. A dose above 10 gray is potentially lethal.

Protection from solar outbursts

Understanding and predicting CMEs and associated radiation events are key to protecting humans in space. Dedicated instruments measure the radiation environment in space, aiding in the protection of astronauts and infrastructure. Timely warnings can enable astronauts to seek protection in designated areas or don radiation-protective bodywear.

On Earth, scientists monitor the Sun’s activity to predict CME events. This helps to mitigate their impact on power grids and communication systems. For instance, power grid operators can take preventive measures, like adjusting voltages and loads, to avoid blackouts during solar storms.

Coronal mass ejections and future space exploration

As we venture further into space, understanding the effects of CMEs is critical. Future crewed missions to the Moon, Mars, and beyond will need to consider the potential impact of CMEs. For instance, during the Artemis program, which aims to send humans back to the Moon, radiation sensors will monitor the lunar radiation environment to ensure astronaut safety.

Space agencies are also researching protective attire to shield astronauts from space radiation. The Artemis I test flight, as mentioned above, sent mannequins equipped with radiation sensors to the Moon.

One of the mannequins wore a newly developed radiation protection vest. Researchers are comparing the radiation levels experienced by both mannequins to assess the effectiveness of the vest.

Coronal mass ejections, as formidable demonstrations of solar energy, have far-reaching effects on our planet. They also pose significant challenges for human space travel. Continued research and technological advancements will be crucial in mitigating these impacts and ensuring the safety of future space explorers.

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