Could gamma rays destroy the earth

Influence of cosmic rays on humans

The atmosphere works like a giant protective shield, but the further we move away from the earth's surface, the more energetic particles from space hit our bodies and can cause serious damage there. This becomes a problem, especially for astronauts.

On earth as well as in space we are exposed to cosmic rays at all times. High-energy particles with energies from a few megaelectron volts up to 10 hit the earth20 Electron volts. For comparison: The largest particle accelerator to date, the Large Hadron Collider at the CERN research center near Geneva, accelerates the particles to just a few 1012 Electron volts. This energy roughly corresponds to the kinetic energy of a flying mosquito - but concentrated on the size of a proton - while the energy of one of the most energetic particles of cosmic radiation already corresponds to the energy of a tennis ball falling to the ground from a height of ten meters. However, only very few of such highest-energy particles hit the earth: around one particle per square kilometer and century.

Energy spectrum of cosmic rays

The particles in cosmic rays are mainly protons, helium nuclei and electrons. However, especially with the highest energies, there are also many iron cores. In addition to our sun, star explosions in the Milky Way and active galaxy nuclei outside the Milky Way are traded as possible sources. The origin of the high-energy particles in particular has not yet been clearly clarified. While the number of high-energy particles from distant sources remains almost constant for years, the amount of low-energy particles from the sun can sometimes fluctuate very strongly. This is mostly caused by eruptions on the sun's surface.

Today cloudy with a shower of particles

The primary cosmic radiation hits the earth's atmosphere from all directions in space and is slowed down there by oxygen and nitrogen atoms. Sometimes complex physical processes result in various secondary particles, especially neutrons, protons and pions. Because of these reactions, the highest radiation intensity is at a height of around twenty kilometers above the earth's surface, below which it decreases again. The radiation exposure also depends on the geographical latitude, since the cosmic radiation is not evenly distributed across the earth's atmosphere: the intensity is greater at the geomagnetic poles than at the equator. Responsible for this is the earth's magnetic field, which deflects the electrically charged particles from their original path. In the earth's orbit there is also the Van Allen radiation belt - a ring of high-energy charged particles that are, so to speak, trapped by the earth's magnetic field. The radiation belt extends over an area of ​​around 700 to 6000 kilometers above the earth's surface and must be taken into account because of the high radiation exposure for astronauts, for example when positioning space stations.

On the earth's surface, the natural background radiation through the rock predominates, as cosmic radiation is shielded from the atmosphere. However, people are now increasingly exposed to it through space travel and air traffic. In general, the further you move away from the earth's surface, the stronger the influence of cosmic rays becomes. Their effect can sometimes differ significantly from natural radioactivity. On the one hand, this is due to the fact that cosmic rays are much more energetic. On the other hand, cosmic radiation is not absorbed through food or the air you breathe.

Particle shower

Radiation causes damage by ionizing atoms and molecules in our bodies: The energy introduced, for example, allows an electron to leave the atomic or molecular group and a positively charged ion remains. Processes of this kind can trigger chemical or biochemical reactions in the affected cells and in this way - especially in the genetic material - lead to damage. Because of their depth of penetration, the different types of radiation have different target organs. Alpha particles (helium nuclei) are quickly decelerated in matter. The penetration depth into the human body is a few micrometers, so the skin is primarily affected by damage. The penetration depth of beta particles (electrons) depends on the energy and is about 0.5 centimeters per megaelectron volt. Gamma rays, on the other hand, penetrate all of the body's organ systems and can cause damage here. The effective dose is a measure of human radiation exposure. It takes into account both the different biological effectiveness of the various types of radiation and the sensitivity of the various organs and tissues to ionizing radiation. The unit for the biologically weighted radiation dose is the Sievert (see blue box).

In a space station in space, the effective radiation dose is around 200 millisieverts per year, while the radiation exposure from cosmic rays on earth is only around 0.3 millisieverts per year (at sea level). Compared to the total effective dose from natural radiation sources, which in Germany adds up to one to six millisieverts per year depending on where you are, cosmic radiation is only a fraction. During a space walk, astronauts learned the annual radiation dose on earth after just one day. When planning long-term missions, radiation-related damage to health is a factor to be taken into account. A particular problem for space travel is solar eruptions, which so far cannot be predicted with certainty. During these events, the radiation dose can increase many times over, causing short-term and long-term health problems.

Effect on the genetic make-up

Cosmic radiation means a chronic burden on the organism. If the high-energy particles or high-energy electromagnetic radiation hit the body and penetrate it, the absorption of the energy there can set a chain of reactions in motion. If, for example, the energetic state of a molecule changes, in particular the DNA as the carrier of genetic information, this may lead to the death of a cell or cell mutations. But ionizing particles or secondary electrons can also cause great damage indirectly: if, for example, they hit a water molecule in the body and destroy it, so-called radicals may form - atoms or molecules that are particularly reactive. Radicals can also damage cells and cause diseases, including cancer. The biological effects of ionizing radiation show a considerable time span between the primary, direct physical interactions (immediately) and tumors that appear late (several years) up to genetic changes in subsequent generations (many years).

Radiation damage to the DNA

If you look at the molecules within a cell, the damage to the enzymes, proteins, RNA molecules or the biomembranes caused by ionizing radiation is less important than radiation damage to the DNA, which can be of various types. These include, for example, single or double strand breaks, base damage or loss, and faulty crosslinking of the base pairs. Chromosome damage is also possible: If a DNA strand is interrupted, this can lead to the loss of a chromosome fragment and thus to a loss of genetic information. In addition, cross-linking of the base pairs caused by ionized radiation can lead to incorrect connections within a chromosome or to the connection of two chromosomes.

Every living organism has the ability to repair or compensate for radiation damage to a certain extent. At the molecular level, single-strand breaks or individual base damage can be repaired better than double-strand breaks or multiple damage. However, incorrect repairs can also occur, which may activate genes that were previously inactive. In the best case this leads to cell death, in the worst case the cell changes genetically and a tumor cell with uncontrolled cell division is formed.

Tissues and cells that divide quickly are particularly sensitive to radiation, while those with a low division rate are less sensitive to radiation. But the phase of the cell cycle and external factors such as temperature and oxygen partial pressure also play an essential role in the radiation sensitivity of a cell. The blood-forming stem cells of the bone marrow are one of the most sensitive tissues to radiation due to their high division rates. If these cells are damaged, the production of blood cells can be disturbed, making the body more prone to infections or bleeding. The active tissues also include the digestive tract and the skin. Whether a tumor ultimately develops, however, depends on many factors - such as the growth rate of the cells in this tissue, the type of cell and which gene is affected. For example, tumors in slowly growing tissues, for example in the prostate, are sometimes not of clinical relevance.

DNA damage to sperm or egg cells can also lead to genetic changes in future generations. In the testes, the stem cells that produce sperm are particularly sensitive, and the sperm themselves are quite resistant. In women, all egg cells are already present at birth. Damage to it accumulates over time. A fertilized egg cell can also be damaged in the womb by ionizing radiation. The less advanced the development, the greater the consequential damage. Damage in the first two weeks often leads to the death of the embryo.

Radiation doses in spacecraft and aircraft

The higher the radiation dose, the greater the likelihood that ionizing radiation will damage cells in the body. This increases the likelihood of developing cancer, especially on long-term flights. In astronauts, increased mutation rates of cells have actually been detected, but the data situation for flight personnel is controversial. Other risks are also discussed, such as an increased likelihood of cataracts, clouding of the lens of the eye, and an increased risk of arteriosclerosis (changes in the artery wall). Due to the low number of astronauts, an accurate assessment of the risks is currently only possible to a limited extent.

Occasional flights in airplanes certainly do not have to be done without because of the cosmic radiation, because the effective dose calculated over the year is still very low and with a few microsieverts is below the critical range. A short-haul flight increases the average annual effective dose from natural radiation exposure by less than one percent, a long-haul flight by around five percent. The radiation exposure fluctuates depending on the flight route, duration and altitude as well as the current solar activity. According to current knowledge, the health risk of flying is assessed as low even for pregnant women. However, there are no clear figures on this. However, it is better to postpone a space flight until after pregnancy.

The matroshka experiment

In order to better estimate the radiation risk in space, researchers measure the radiation doses there with the help of the Matroshka experiment, for example. A special dummy equipped with sensors weighing seventy kilograms records the radiation exposure inside and outside the international space station ISS. As part of the project, the scientists are also investigating how humans can best be shielded from cosmic rays. This question plays a crucial role, especially in longer space missions, such as flights to Mars, and must be taken into account in the future when building spaceships and especially when realizing visionary ideas such as “generation ships”. Here, however, the radiation is only one of various risk factors that have been difficult to control up to now, which are caused, among other things, by the lack of gravity or the narrowness and monotony on board. These include problems such as massive bone and muscle breakdown, mental illness, difficulties in social interaction and with nutritional issues, to name a few.