Sunlight, starlight, moonlight (which is actually reflected sunlight) are known to all of us. Indeed, light is the type of space radiation we are most familiar with. Light can be described as being made of waves or as being made of particles, called photons.
What we call light is in fact the part of the broader electromagnetic spectrum that has wavelengths between about 400 and 700 nanometers (nm, equal to 1 millionth of a millimetre). Radiation with shorter wavelengths (from 100 to 400 nm) is called ultraviolet (UV) and at even shorter wavelength (0.01 nm down to 0.000001 nm) we have gamma rays. UV and gamma rays are increasingly energetic and damaging to life and infrastructure.
The shorter the wavelength, the more energetic or powerful the photons. UV photons have high energy and can damage DNA and accelerate skin ageing, causing cancer. Gamma ray photons are even more energetic and penetrate deeper into our bodies. They are extremely dangerous as they can remove electrons from atoms and molecules and cause damage to cells and DNA.
But there are other types of space radiation besides photons. These are typically high-energy charged particles accelerated by astronomical events such as solar flares, supernova explosions, and cosmic rays from distant sources. Some of the primary types of radiation particles from space include protons, electrons, alpha particles, neutrons and heavy ions.
- High-energy protons are one of the primary components of solar and cosmic radiation. Solar flares and coronal mass ejections (CMEs) from the Sun can release a large number of high-energy protons, known as solar energetic particles (SEPs), which can pose risks to astronauts and satellites.
- High-energy electrons are also present in solar and cosmic radiation. They are accelerated by various astrophysical processes and can affect spacecraft and electronic systems.
- Alpha particles (the nuclei of helium atoms) are composed of two protons and two neutrons and are commonly found in cosmic radiation. They have a significant ionising potential and can pose health risks to astronauts and electronic components in space.
- Neutrons are uncharged particles that can be produced in various nuclear reactions and interactions. They are challenging to shield against due to their ability to penetrate materials.
- Cosmic rays consist of highly energetic atomic nuclei (mostly protons) that originate from outside the solar system. They travel through space at nearly the speed of light and can interact with atmospheres, producing secondary particles like muons, pions, and neutrons. Cosmic rays can also include heavier atomic nuclei, such as helium nuclei (alpha particles) and heavier elements. These heavy ions are less common than protons in cosmic radiation but can be more damaging due to their larger mass and charge.
As discussed in other posts, planets with large magnetic fields can “grab” this radiation and create intense radiation environments. The JUICE mission will be embedded in such an extreme radiation environment when exploring the powerful magnetosphere of the Jupiter system.
The Earth’s atmosphere provides some degree of protection against these space radiation particles. Planetary magnetic field and atmospheres act as a shielding mechanisms, absorbing and deflecting many of the harmful particles before they reach the surface. However, astronauts in space or missions beyond Earth‘s protective magnetosphere may still be exposed to increased levels of radiation, requiring careful planning and shielding for their safety. In places with no atmosphere (Moon) or very thin atmospheres (Mars) there is virtually no protection.
Space radiation is not only a problem for humans. Its destructive effects affect nearly all life forms. The exceptions are called extremophiles, usually bacteria (an example is Deinococcus radiodurans) and certain archaea and fungi. These extremophiles can repair their DNA very quickly, and so resist the destructive effects of radiation. Maybe we can learn how these wonders of nature do their trick and teach our bodies to do the same. Until then, we need protection from radiation.