Earth’s “sister star”
Earth has two close “sisters”, one is Venus and the other is Mars, which are distributed on both sides of the Earth’s orbit, orbiting the sun with the Earth. However, the “temperaments” of the two “sisters” are diametrically opposed, Venus is “hot as fire” and Mars is “cold as frost”. Only Earth is mild, neither too cold nor too hot, and thus a thriving home for humans and other terrestrial life.
At one time, people were more interested in Venus than Mars, because Venus is so bright and attractive. Venus is always present at dawn and dusk and is the brightest object in the sky other than the sun and moon. When it appears at dawn, people call it “Enlightenment”. And when it appears at dusk, people call it “Chang Geng”. “Book of Songs” has a cloud: “East has Qiming, west has Chang Geng.” In fact, it refers to Venus. In Western civilization, the splendid Venus is regarded as “the goddess of love and beauty”, the ancient Greeks called it “Aphrodite”, and the ancient Romans called it “Venus”.
However, human research on Venus is full of twists and turns, because for a long time, Mars, another “sister” of the earth, has attracted most of the attention of human beings, while Venus is obviously “cold”. But now, things are starting to turn around and scientists are turning their attention back to Venus. In June 2021, two space exploration missions to Venus-“Da Vinci+” and “Truth” were officially confirmed. The two space missions to study Venus were selected from four NASA candidates. Two other missions, including a trip to Jupiter’s moon Io and a trip to Neptune’s largest moon, Triton, were not approved, and people ended up devoting limited resources to Venus.
In fact, in history, Venus has also attracted great attention from astronomers. In 1761, Russian scientist Lomonosov determined that there is an atmosphere on Venus after observing the transit of Venus. The atmosphere is an important indicator of a planet’s activity, which means that the planet may be very similar to Earth. As a result, it has been speculated that Venus is another planet with a warm climate, with hot and humid forests similar to Earth’s, and oceans that cover the world with a lot of life.
In the 1960s and 1980s, the Soviet Union launched a series of probes to Venus, which for the first time lifted a corner of the mystery of Venus. These probes probed the environment on the surface of Venus, obtained some data about the atmosphere and temperature, and showed people the real face of Venus. The misty sky, orange-yellow clouds and strong air currents suggest that Venus beneath the thick clouds is a “purgatory” that is simply not suitable for life. The air pressure there is extremely high, 100 times that of the earth; it is as hot as fire, and the surface temperature reaches 475 ° C, which is the highest temperature among the planets and moons in the solar system, where sulfur, lead, and tin will melt. Such an environment is too different from what people imagined in advance, so astronomers turn their attention to Mars more, which is also an important reason why people’s research on Mars is far better than Venus. Although Mars is a cold planet, the hope for the existence of water and life is far greater than that of Venus.
Despite this, human exploration of Venus has not completely stopped. In 1989, the space shuttle Atlantis launched a Venus probe called Magellan into space.
The important achievement of “Magellan” is to map the topography of Venus. The detection shows that 80% of the surface of Venus is covered by plains, and the material that constitutes this plain is cooled volcanic lava, which is the product of a series of volcanic activities, indicating that there have been violent volcanoes in the history of Venus eruption period. There are also some huge volcanic terrains on Venus. Since the volcanic outflows are mainly low-viscosity basalt magma, the slopes are very gentle and have a wide top surface.
In 2005, another Venus probe developed by the European Space Agency, the Venus Express, embarked on a journey to Venus on a Russian Soyuz rocket. For the first time, the Venus Express has given scientists the opportunity to closely observe and study the mysterious clouds on Venus. Previous observations have confirmed that the clouds, which contain a lot of dust and sulfuric acid, move very fast, but scientists still know very little about other clouds.
In addition, the “Venus Express” also captured lightning on Venus. Scientists believe this is an extraordinary discovery that proves that Venus’ atmosphere is capable of producing its own lightning, possibly more frequently than on Earth. Often, lightning is of extraordinary significance to a planet, affecting the chemistry of the planet’s atmosphere, and the electrical energy released may have the function of enabling life in the primordial ooze. Previously, people have found that in the solar system, in addition to the earth, other planets such as Jupiter and Titan also have lightning. But lightning on Venus is different from them all, it happens in a “sulfuric acid cloud”.
The “sulfuric acid cloud” is a unique sight on Venus. “Venus Express” found that “sulfuric acid clouds” mostly exist in places 50 to 100 kilometers away from the surface of Venus. Above them is a thin atmosphere, ranging from 100 kilometers above the surface to 500 kilometers above the surface. Under the action of the solar wind and cosmic rays, this layer is ionized to form the ionosphere. Below the “sulfuric acid cloud” is mostly carbon dioxide and water vapor. Little is known about the rest of the cloud.
The detection of Venus by probes such as “Venus Express” has helped people to further understand Venus. In fact, Venus and Earth are very similar in many ways. The radius of Venus is 6073 kilometers, which is only 300 kilometers smaller than the radius of the earth. Its volume is 88% of the earth’s, its mass is 80% of the earth’s, and its average density is only slightly less than that of the earth. In addition, its position in the solar system is close to the earth. , was also born at the same time as the earth, so it is very appropriate to call it the “sister planet” of the earth. But why is it so different from Earth?
This is a mystery that scientists have not been able to answer so far. However, based on the above-mentioned human detection results of Venus, some views that are close to speculation came into being. At present, scientists believe that the early Venus was likely to be a habitable planet like Earth, with water, suitable temperature and atmosphere, but over billions of years, this good environment was gradually destroyed by carbon dioxide.
Venus’ atmosphere is surprisingly high in carbon dioxide. In the atmosphere of modern Venus, carbon dioxide accounts for 96% of the total amount of matter, while the carbon dioxide in Earth’s atmosphere only accounts for 0.033%. The reason for this may be that, on Earth, water dissolves carbon dioxide in the air, turning it into carbonate and depositing it in rock layers. Although Venus may have had a lot of water in its early days, it all escaped into space. This is because Venus’s slow rotation makes it difficult for it to generate a strong magnetic field that can protect itself from the solar wind. Therefore, the solar wind directly hits the upper atmosphere of Venus and decomposes the water vapor in the upper atmosphere of Venus into hydrogen and oxygen. Due to its low mass, the hydrogen atoms escaped into space, while the oxygen combined with material in the Venusian crust, causing a lack of oxygen in the Venusian atmosphere and eventually causing the water on the surface to disappear
In this way, on Venus, all the carbon dioxide has entered the atmosphere. After billions of years of accumulation, the proportion of greenhouse gases is getting higher and higher, and the greenhouse effect continues to affect Venus. As a result, Venus seemed to be wrapped in a quilt, and the temperature continued to rise, eventually evolving into what it is today.
The greenhouse effect on Venus has sounded the alarm for people on earth, because the earth is also experiencing a process of greenhouse effect, and the direct consequence of it is the continuous warming of the global climate. Is Earth repeating the mistakes of Venus? Will Venus’s yesterday be the same as today’s vibrant earth, and whether the earth’s tomorrow will fall into a fiery “purgatory” like Venus?
Venus’ atmosphere is very dense and hot. Scientists hope to reveal the evolution of Venus’ environment by studying the evolutionary history of Venus’ atmosphere. That would require a probe deep into Venus’ hot atmosphere to collect data. “Da Vinci+” is the probe that performs this mission. It is a sphere about one meter in diameter that will spend an hour traversing the atmosphere of Venus to measure changes in the content of matter in the atmosphere from top to bottom. At the same time, during its fall, it will also take some high-resolution photos of the Venusian surface. These detections help scientists figure out how Venus lost its water, how large its volcanic activity was, and whether it still has volcanic activity.
Unlike “Da Vinci+”, “Truth” is an orbiter around Venus that focuses on the surface environment of Venus, trying to answer questions about Venus’ history and why it is so different from Earth. In addition, “Truth” will use radar to map Venus and three-dimensional topographical maps, and find out whether there is plate tectonics on Venus and whether there are still remnants of its volcanic activity. The answers to these questions will provide clues to understanding the evolutionary history of Venus, and will also provide data for future exploration missions to land on Venus.
According to the plan, “Da Vinci+” and “Truth” will travel to Venus sometime between 2028 and 2030. At the same time, the European Space Agency also plans to send an orbiter called Envision to Venus. “Vision” will conduct detailed observations of the surface environment of Venus to understand the evolution of Venus, and it will pay particular attention to the link between changes in Venus’ atmosphere and the evolution of Venus’ geology.
If Venus really had a habitable period like the earth today, then in history, Venus must have encountered an important event that caused it to undergo dramatic changes, and this event directly caused Venus to fall into “purgatory” . If something like this happened on Venus, would it happen on Earth as well? This is a very disturbing question. People are desperate for answers. Especially now that the earth is also suffering from the greenhouse effect, this problem has become more concerned. This is also an important reason why scientists are eagerly looking forward to “returning to Venus”.