Biggest sun and moon secrets4/1/2023 As a result, its oceans evaporated within its first 600 million years, according to estimates. But due to many factors, including solar activity and the lack of an internally generated magnetic field, Venus lost its hydrogen - a critical component of water. Venus was once covered in water oceans and may have been habitable. “It could have been a much harsher environment,” Saxena noted.īut the Sun rotated at an ideal pace for Earth, which thrived under the early star. The Sun’s blasts would have decimated the atmosphere, reducing air pressure so much that Earth wouldn’t retain liquid water. Even Earth’s magnetic field wouldn’t have been enough to protect it. Had our Sun been a fast rotator, it would have erupted with superflares 10 times stronger than any in recorded history, at least 10 times a day. Airapetian worked with Saxena and Killen on the early Sun study. “We were lucky that Earth’s atmosphere survived the terrible times,” said Vladimir Airapetian, a senior Goddard heliophysicist and astrobiologist who studies how space weather affects the habitability of terrestrial planets. Earth also developed a magnetic field, which helped protect it from the Sun, allowing our atmosphere to transform into the oxygen- and nitrogen-rich air we breathe today. Over the next billion years, the earliest bacterial life consumed that carbon dioxide and, in exchange, released methane and oxygen into the atmosphere. Credit: Simone MarchiĪs Earth’s crust solidified, volcanoes gradually coughed up a new atmosphere, filling the air with carbon dioxide, water, and nitrogen. But outbursts from the young Sun stripped away that primordial haze within 200 million years.Īn artistic conception of the early Earth, showing a surface pummeled by large impact, resulting in extrusion of deep-seated magma onto the surface. When Earth formed 4.6 billion years ago, a thin envelope of hydrogen and helium clung to our molten planet. (Mercury, the closest rocky planet to the Sun, never had a chance.)Įarth’s atmosphere was once very different from the oxygen-dominated one we find today. But for Venus and Mars - both rocky planets similar to Earth - it may have precluded it. The rotation rate of the early Sun is partly responsible for life on Earth. “Space weather was probably one of the major influences for how all the planets of the solar system evolved,” Saxena said, “so any study of habitability of planets needs to consider it.” Life Under the Early Sun And they found that just one version - the slow-rotating star - was able to blast the right amount of charged particles into the Moon’s surface to knock enough sodium and potassium into space over time to leave the amounts we see in Moon rocks today. They determined this by simulating the evolution of our solar system under a slow, medium, and then a fast-rotating star. According to their estimates, within its first billion years, the Sun took at least 9 to 10 days to complete one rotation. Their computer simulations, which they described on May 3 in the The Astrophysical Journal Letters, show that the early Sun rotated slower than 50% of baby stars. Using sophisticated computer models, Saxena, Killen, and colleagues think they may have finally solved both mysteries. “As you learn about other stars and planets, especially stars like our Sun, you start to get a bigger picture of how the Sun evolved over time,” Saxena said. This insight was derived by scientists who studied the activity of thousands of stars discovered by NASA’s Kepler space telescope: The faster a star spins, they found, the more violent its ejections. Saxena incorporated the mathematical relationship between a star’s rotation rate and its flare activity. In 2012, she helped simulate the effect solar activity has on the amount of sodium and potassium that is either delivered to the Moon’s surface or knocked off by a stream of charged particles from the Sun, known as the solar wind, or by powerful eruptions known as coronal mass ejections. Killen’s earlier work laid the foundation for the team’s investigation. The two scientists suspected that one big question informed the other - that the history of the Sun is buried in the Moon’s crust. “The Earth and Moon would have formed with similar materials, so the question is, why was the Moon depleted in these elements?” said Rosemary Killen, a planetary scientist at NASA Goddard who researches the effect of space weather on planetary atmospheres and exospheres. 68815, a dislodged fragment from a parent boulder roughly four feet high and five feet long. A closeup view of Apollo 16 lunar sample no.
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