Scientists discover the story of the sun buried in the crust of the moon

The sun is the reason we are here. This is also why Martians and Venusians are not.

When the Sun was just a baby, four billion years ago, it suffered intense bursts of intense radiation, burning clouds, high-energy clouds, and particles throughout the system. solar. These growing pains favored life on the primitive Earth by triggering chemical reactions that kept the Earth warm and moist. However, these sunbursts have also been able to prevent life from emerging on other worlds by robbing them of their atmospheres and zapping nutrient chemicals.

How much these primordial explosions were destructive to the other worlds would have depended on the speed with which the baby sun rotated on its axis. The faster the sun turned, the faster it would have destroyed the conditions of habitability.

But Prabal Saxena, an astrophysicist at NASA's Goddard Space Flight Center in the Greenbelt of Maryland, said the critical element in the Sun's history has discouraged scientists. Saxena studies the interactions between space weather, variations in solar activity and other radiation conditions in the space and surfaces of planets and moons.

Now, he and other scientists are finding that the Moon, where NASA will send astronauts by 2024, contains clues to the ancient mysteries of the Sun, which are essential to understanding the development of life.

"We did not know what the Sun looked like during its first billion years, and that's very important because it probably changed the way the atmosphere of Venus evolved and the how quickly it lost water, it probably also changed the speed with which Mars lost its atmosphere, changed the atmospheric chemistry of the Earth, "said Saxena.

ConnectionSaxena stumbled upon the mystery of the Sun's rotation at the beginning of his career, while considering a seemingly unrelated problem: Why, when the Moon and Earth are essentially made of the same material, is there much less sodium and potassium in lunar regolith or moon soil than in the earth's soil?

This question, also revealed by analyzes of lunar and lunar meteorites from the Earth's Apollo period, has intrigued scientists for decades – and challenges the main theory of Moon formation.

According to the theory, our natural satellite took shape when an object the size of Mars crashed on Earth about 4.5 billion years ago. The force of this crash sent materials into orbit, where they merged into the moon.

"The Earth and the Moon would have formed with similar materials, so the question is, why has the moon been reduced to these elements?" said NASA Goddard's planetary science scientist Rosemary Killen, who studies the effects of space weather on planetary atmospheres and exospheres.

Both scientists suspected a great question to inform the other – that the story of the Sun was buried in the crust of the Moon.

Earlier work by Killen laid the foundation for the team's investigation. In 2012, she helped simulate the effect of solar activity on the amount of sodium and potassium delivered to the Moon's surface or released by a stream of charged particles from the Sun, known as solar wind, or by powerful known eruptions. as coronal mass ejections.

Saxena has incorporated the mathematical relationship between the speed of rotation of a star and its illuminating activity. This idea was developed by scientists who studied the activity of thousands of stars discovered by NASA's Kepler Space Telescope: the faster a star turned, the more violent ejections they found. "By learning about other stars and planets, especially stars like our Sun, you begin to have a more complete picture of how the Sun has evolved over time," Saxena said.

Using sophisticated computer models, Saxena, Killen, and his colleagues believe they have finally solved these two mysteries. Their computer simulations, described on May 3 in The Astrophysical Journal Letters, show that the primitive Sun rotated more slowly than 50% of baby stars. According to their estimates, in the first billion years, the Sun took at least 9 to 10 days to rotate.

They determined this by simulating the evolution of our solar system under a slow, medium and then fast spinning star. And they discovered that only one version – the slow-spinning star – was able to blow the right amount of charged particles onto the surface of the moon in order to pump enough sodium and potassium into the atmosphere. space over time to let the quantities that we see today in the rocks of the Moon.

"The space weather has probably been one of the major influences of the evolution of all planets in the solar system," Saxena said. "Any study on the habitability of the planets must therefore take this into account."

Life under the rising sun The speed of rotation of the rising sun is partly responsible for life on Earth. But for Venus and Mars, two rocky planets similar to the Earth, that may have prevented it. (Mercury, the closest rocky planet to the Sun, has never had a chance.)

The Earth 's atmosphere was once very different from the oxygen one we find today. When the Earth formed 4.6 billion years ago, a thin envelope of hydrogen and helium hung on our molten planet. But the sunsets of the young Sun have removed this primordial haze in 200 million years.

As the earth's crust solidified, the volcanoes gradually spewed out a new atmosphere, filling the air with carbon dioxide, water, and nitrogen. Over the billions of years that followed, the oldest bacteria consumed this carbon dioxide and, in return, released methane and oxygen into the atmosphere. The Earth has also developed a magnetic field that has protected it from the sun, allowing our atmosphere to turn into a rich air of oxygen and nitrogen that we breathe today.

"We were lucky that the Earth's atmosphere survived this terrible time," said Vladimir Airapetian, Goddard's senior heliophysiologist and astrobiologist, who is studying the impact of space weather on the planet's climate. 39, habitability of terrestrial planets. Airapetian worked with Saxena and Killen on Sun's first study.

If our Sun had been a fast rotator, it would have burst with super flares 10 times stronger than any other in history, at least 10 times a day. Even the Earth's magnetic field would not have been enough to protect it. Explosions from the Sun would have decimated the atmosphere, reducing as much the atmospheric pressure as the Earth would not retain the liquid water. "It could have been a much harder environment," Saxena said.

But the Sun was turning at an ideal pace for the Earth, which was thriving under the early star. Venus and Mars have not been so lucky. Venus was once covered with water and could be habitable. But due to many factors, including solar activity and the lack of an internally generated magnetic field, Venus has lost its hydrogen, an essential component of water. As a result, it is estimated that its oceans have evaporated over its 600 million years. The atmosphere of the planet has become thick with carbon dioxide, a heavy molecule that is harder to dispel. These forces led to an uncontrollable greenhouse effect that allows Venus to stay at 462 degrees Celsius (864 degrees Fahrenheit), far too hot for life.

Mars, farther from the Sun than the Earth, would seem to be more secure against stellar explosions. Yet he had less protection than the Earth. Partly because of the weak magnetic field of the red planet and its low gravity, the rising sun could gradually evacuate its air and water. About 3.7 billion years ago, the Martian atmosphere had become so thin that liquid water immediately evaporated into space. (The water still exists on the planet, frozen in the polar ice caps and in the ground.)

After having influenced the course of his life (or lack thereof) on the inner planets, the aging sun has gradually slowed down and continues to do so. Today, it runs once every 27 days, three times slower than it was in its infancy. The slower rotation makes it much less active, although the sun still has violent explosions from time to time.

Exploring the Moon, Witnessing the Evolution of the Solar System To learn more about the Early Sun, Saxena explained that you did not need to look any further than the Moon, one of the the best preserved artifacts of the young solar system.

"The reason the moon ends up being a really useful calibrator and a window to the past is that it does not have an annoying atmosphere or tectonic plates resurfacing the crust," he said. declared. "As a result, you can say:" Hey, if solar particles or anything else hits it, the moon's ground should show the evidence. "

Apollo samples and lunar meteorites are an excellent starting point for probing the early solar system, but they are just small pieces of a mysterious puzzle. The samples come from a small region near the lunar equator, and scientists can not say with certainty where meteorites originate on the moon, which complicates their setting in geological context.

Since the South Pole houses the permanently shaded craters where we expect to find the best preserved material on the moon, including frozen water, NASA plans to send a human expedition to the region by 2024 .

If astronauts can get lunar soil samples from the southernmost region of the moon, this could provide more physical evidence of the Sun's rotational speed, said Airapetian, who suspects that solar particles have been diverted by the magnetic field of the Moon, there are 4 billion years. deposited at the poles: "You would expect – though we have never examined this before – that the chemistry of this part of the Moon, that exposed to the young Sun, would be much more altered than the equatorial regions. to do there. "

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