"20 years late" discovery: the moon is in the Earth's atmosphere

Ping Jinsong is a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences

Can you think of it? Maybe the moon has always been in the "arms" of the earth.

In one study, the researchers analyzed diffuse data from the Earth's atmosphere collected three times at the first Lagrange point between 1996 and 1998, confirming the observation that the Earth's atmosphere extends to an altitude of about 630,000 kilometers, equivalent to 100 Earth radii. This means that the Moon is also wrapped in the Earth's atmosphere.

This conclusion subverts previous understanding of the scope of the coronal range: scientists have estimated that the coronal layer is about 9-10 earth radii high, and the moon is 32-34 million kilometers away from the outermost layer of the earth's atmosphere.

Since 2020, in response to a new peak solar activity year, the research team has also continuously monitored the solar wind and its impact on the earth's corona.

"The discovery of a wide range of coronas has further expanded human understanding of the composition and existence of planetary atmospheres, as well as the interaction of central stars with the atmospheres of planets (such as the sun and earth)." Ping Jinsong, a researcher at the National Astronomical Observatories of the Chinese Academy of Sciences, told the Science and Technology Daily reporter.

The height of the coronal is unimaginable at 100 Earth's radii

The atmosphere surrounding the Earth's surface is called the atmosphere, and from the inside to the outside are the troposphere, stratosphere, mesosphere, warm layer, and dispersal layer. As part of the dispersal layer, the corona is located in the outermost layer of The Earth's atmosphere, extending all the way to interplanetary space.

"The team's recent space observations have found that the height of the coronal layer can extend as far as 100 Earth's radii, and even the moon cannot be placed outside." Ping Jinsong pointed out that the key basis for this research conclusion is that the Solar and Heliospheric Observatory SOHO, jointly developed by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA), carries a solar wind anisotropy detector SWAN payload that records the interaction between the solar wind and the earth's hydrogen gas, and found that at an altitude of 630,000 kilometers from the surface, there is still an interaction between the solar wind and the Earth's plasma.

He introduced that the coronal layer mainly scatters far-ultraviolet rays from the sun, and itself emits faint ultraviolet light, but compared with solar radiation, the radiation emitted by the coronal layer is minimal. The shape of the coronal layer looks a bit like the tail of a comet flying near the sun.

In terms of composition, the coronal layer is very different from the rest of the Earth's atmosphere. For example, the coronal layer is a low-density gas halo composed mainly of hydrogen, helium atoms and ions, while the Earth's atmosphere at an altitude of 1000 kilometers is mainly composed of molecules such as nitrogen, oxygen, carbon dioxide and water, as well as ions. In addition, between the Earth's lower atmosphere and the coronal layer, there is a plasma layer transition zone.

"Enveloping the Earth's corona in a wide area, blocking the solar wind blowing toward the Earth, preventing far-ultraviolet radiation from reaching the ground directly, and protecting the hydrographic and biosphere of the blue planet earth." In other words, the crown of such a magnetically magnetic earth-like planet provides support for the protection of the living environment and life itself that may exist on the surface of the planet. Ping Jinsong said.

It is worth mentioning that the discovery of a large-scale coronal is of great significance, and new research content has been added to planetary science. "This discovery raises entirely new questions for scientists to explore. For example, when did the corona emerge and how did it stabilize in the process of planets that collapsed from asteroids to planets and evolve? For another example, what are the similarities and differences in the composition and evolution of the crowns of terrestrial planets and the crowns of gas planets? Ping Jinsong said.

Very different from the coronal corona of stars The coronal "lifespan" is only a few dozen days

Not only does Earth have a coronal layer, but Venus, Mars, Mercury, and Jupiter in the solar system all have their own planetary coronas. The Sun, as a star, also has its own corona, known as the corona.

Planetary coronas are very different from stellar coronas. Ping Jinsong explained that stars, especially young stars like the Sun, have a relatively thick, thin, and extremely low density of atmospheric layers in their outermost layers, which is the star corona. The thickness of the star corona can reach millions of kilometers or more, and the temperature can reach millions of degrees Celsius or higher, which can completely ionize the hydrogen and helium atoms in them and form plasma. The corona of stars consists mainly of protons, highly ionized ions, and high-velocity free electrons. These charged particles move so fast that they are constantly being charged particles that break free of the gravitational constraints of the central star and shoot out to the periphery, forming a stellar wind. The gas in the corona of stars continues to grow in the photosphere at the bottom, maintaining the existence of the corona itself.

"The ions in the planetary corona exchange charges with the stellar wind protons, resulting in a 'lifetime' of only a few tens of days, which also limits the size of the planetary coronal." Ping Jinsong stressed.

Because of the above differences, planetary coronas are more difficult to observe from an astronomical point of view, and stellar coronas are easier to observe. Ping Jinsong said that the star corona not only has radiation in the optical band, but also has burst radiation in the radio band, so it can be observed by humans in multiple electromagnetic wave bands. However, the planetary crown is not mysterious enough to be seen by the world, and scientists have also used a variety of detectors to see the "aroma" of the planetary crown.

"Shielding" the ultraviolet band The corona makes astronomical observations more difficult

The corona absorbs ultraviolet radiation from cosmic objects, blocking the opportunity for scientists to observe the stars of the universe from the ground or from the planetary space using electromagnetic waves in ultraviolet, especially the medium and far ultraviolet bands.

So scientists took a different approach. "In these bands, scientists can only use ultraviolet telescopes flying in or beyond the mid-to-high coronal, such as lagrange flat points set in the solar-Earth system, to circumvent the absorption interference of the corona on the ultraviolet band and make astronomical observations." Ping Jinsong said.

In the process of human exploration of extraterrestrial life, an important task is to find a "second Earth".

Usually in the optical band, astronomers search for habitable objects by shielding exoplanets from changes in the luminosity of stars larger than them. Ping Jinsong introduced: "Because of the existence of the corona, scientists will monitor the absorption of ultraviolet electromagnetic wave radiation at a specific wavelength closely related to hydrogen and helium atoms in the ultraviolet band when the exoplanet blocks the central star, to determine the existence and size of the corona, and then presume the condition of the exoplanet being protected and the probability of life on it." ”

In addition to the ultraviolet and optical bands, using the characteristics of radio electromagnetic bursts that can radiate wavelengths of thousands to tens of meters by using the corona and the terrestrial planetary coronronation, scientists can use very sensitive terrestrial radio devices to search for and monitor the electromagnetic radiation of exoplanets in this band to find more exoplanet candidate objects.

Although the existence of a corona has caused some obstacles to astronomical observations, fortunately, the corona has left a window for humans to observe themselves.

"They absorb the electromagnetic radiation of hydrogen and helium in the sun's far ultraviolet band, and the hydrogen, helium atoms and ions excited by radiation emit weak ultraviolet radiation that can be seen by detectors far away from Earth." Ping Jinsong said.

The coronal data for this study comes from the solar wind anisotropy detector SWAN carried by SOHO, which was launched in 1995. The probe orbits the sun and studies the sun. In addition, it measures light from the earth's corona. Surprisingly, this data was acquired by SOHO between 1996 and 1998. As a result, the latest findings have been jokingly called "twenty years late."

After China's Chang'e-3 lunar probe was launched at the end of 2013 and successfully landed on the front of the moon, it also "saw" the corona and confirmed the existence of the Earth's "plasma layer" between the ionosphere and the magnetosphere. Chang'e-3 carried ultraviolet telescopes to observe the plasma layer of the Earth's outer atmosphere and monitored the "shadow" of the earth's corona changing over time.

Source: Science and Technology Daily