What? The earth is leaking air?

Review expert: Gan Qiang, lecturer at Beijing Institute of Technology, PhD in Applied Chemistry

Previously, there was a report saying: "Scientists have discovered that a type of helium-3 gas formed after the Big Bang is constantly leaking from the Earth's core to the outside." This report surprised many people. The Earth's core is divided into an inner and outer core. The outer core is liquid, and the inner core is presumed to be solid, mainly composed of high-temperature, high-density solid matter composed of iron and nickel elements, with a temperature of 4000~6800℃. So, where does the helium-3 gas in the Earth's core come from , and why are scientists so concerned about this?

Schematic diagram of the earth's structure Source: Baidu Encyclopedia

What is Helium-3?

Friends who have studied chemistry know that helium is a colorless, odorless, and very low-density monatomic gas. Its chemical properties are stable and it is not easy to react chemically with other substances . The helium element ranks second in the entire periodic table. According to the number of neutrons in the helium nucleus, it is further divided into a variety of isotopes. On Earth, the vast majority of helium nuclei are composed of two protons and two neutrons, that is, helium-4, which accounts for 99.99986% of all helium elements on Earth. In addition, another stable structure of the helium nucleus consists of only two protons and one neutron, called helium-3, and its content accounts for only 0.000137%.

Nuclear structure of helium-4 and helium-3 Source: Baidu Encyclopedia

What is the relationship between helium-3 in the Earth's core and the origin of the Earth?

There are many ways to generate helium-3. For example, we can use the radioactive decay of tritium to obtain it. However, the half-life of tritium is relatively long, as long as twelve years, and the efficiency of producing helium-3 in this way is very low. In fact, most of the helium-3 in the universe comes from the Big Bang 13.8 billion years ago . What is its connection with the origin of the earth?

Nebulae in the universe are composed of gas and dust, most of which are hydrogen, followed by helium, and other metal and non-metal elements. The predecessor of the solar system is a huge, rotating nebula.

Solar Nebula Source: Baidu Encyclopedia

It is generally believed in the academic community that the Earth was born during the transformation of the solar nebula into the solar system. It continuously aggregated the rocks and dust floating in the nebula and then squeezed them into shape. During this development process, the gravity generated by the Earth attracted the gas in the nebula to the Earth , and the helium-3 floating in the solar system was naturally brought into the Earth's core.
The detection of helium-3 leaking out from the core of the Earth is strong evidence for this theory of the origin of the Earth.

Helium-3 - the perfect fuel for nuclear fusion

Scientists are so concerned about helium-3 gas not only because it is extremely rare, but more importantly, helium-3 itself is an energy source with huge development potential .

At present, human research on nuclear fusion is based on deuterium and tritium as nuclear fuels. Although the reaction conditions of these two nuclear fuels are harsh, they have considerable reserves on the earth and release large amounts of energy, which has attracted the favor of scientists.

The origin of the nuclear fusion reaction of deuterium and tritium丨Baidu Encyclopedia

The only drawback is that the fusion process of deuterium and tritium will release a large number of neutrons, which have no charge and cannot be bound by the magnetic field. These neutrons carry extremely high energy and will directly bombard the inner wall material, causing a large number of defects on the surface of the material, causing damage to the inner wall, affecting the mechanical properties of the material, and posing a serious safety hazard. Therefore, scientists hope to find a safer nuclear fuel to promote the development and production of nuclear energy.

Helium-3 is just such a nearly perfect nuclear fuel . Its fusion reaction process does not release neutrons, but only releases positively charged protons. Protons can be effectively confined in a magnetic field, so the safety of fusion reactions is greatly improved and no excessive nuclear waste is produced. Unfortunately, the amount of helium-3 on Earth is too small. The proven reserves available for human exploitation are only about 500 kilograms, which is impossible to put into large-scale production. Is mankind destined to miss this ideal nuclear fuel?

Nuclear fusion reaction of helium atoms Source: Baidu Encyclopedia

The answer is on the moon

The Moon, a natural satellite that has accompanied the Earth for 4.5 billion years, has been detected to have at least 1 million tons of helium-3 reserves . Based on the current level of resource consumption, these reserves are enough for human use for 10,000 years!

The moon has always been a huge attraction for humans. Since the last century, countries led by the United States and the Soviet Union have been scrambling to launch exploration satellites to the moon. In particular, the United States has brought back soil samples from the moon for research many times, greatly improving human understanding of the moon.

In 2020, the Chang'e 5 probe was successfully launched and completed the first automatic sampling and return work on the moon, bringing back 1,731 grams of lunar soil. Through the study of these soils, we have more ideas on how to extract the rich helium-3 resources in the lunar soil.

Chang'e 5 probe source: Baidu Encyclopedia

However, humans have only just begun to uncover the moon, and developing its resources is extremely difficult. The method of collecting helium-3 from the moon is only a conjecture in the science fiction novel The Distance to the Sun.

I believe that with the development of nuclear industry technology and aerospace industry, the development of lunar helium-3 and other resources will be realized. Perhaps in the near future, spacecrafts traveling back and forth between the moon and the earth will deliver abundant helium-3 resources to humans. By then, human exploration and understanding of the universe will surely enter a new stage.