Planets of the Solar System: Mercury and Venus

There are a total of eight planets in our Solar System. In this blog we will be discussing the first two of the four inner, terrestrial planets of our Solar System: Mercury and Venus. The word "Terrestrial" is used for a planet that has a solid surface (terra being the root word for Earth). Although the terrestrial planets all share common traits, such as a rocky composure and solid surfaces, they are also distinctly different. Furthermore, in order to understand information given about planets in this blog, it is important to understand the difference between a rotation and a revolution, as well as what an AU (astronomical unit) is. A rotation refers to the time that a planet takes to turn on its axis once, and a revolution refers to the time it takes for a planet to orbit the Sun once. For example, the Earth takes about 24 hours to complete one rotation, and about 365 days to complete a revolution. Finally, an AU, or astronomical unit, is a unit used to measure distance in space, just as a meter is used to measure distance on Earth. One AU is equivalent to the distance between the Sun and the Earth. Therefore, because the planet Venus's distance from the Sun is 0.7 AU, it is 0.7th of the distance between the Sun and the Earth.

Mercury

Named after the swiftest of the Roman gods, Mercury is the closest planet to the Sun, with a distance of 58 million kilometers (36 million miles), or 0.4 AU, and is also the smallest planet in our solar system. In fact, it is only slightly larger than the Earth's moon! Because of its close proximity to the Sun, the Sun appears to be three times as large on Mercury's surface as it does on the Earth's surface. Taking a total of 88 Earth days to revolve around the Sun, with an elliptical orbit, Mercury has the fastest and shortest orbit, with a speed of 29 miles per second. Its rotation is so slow that it takes about 59 Earth days to make one rotation. Its atmosphere, consisting of oxygen, sodium, helium, and potassium, is very thin due to atoms located within being blasted off into space by solar wind caused by the Sun. Because of its thin atmosphere, meteoroids and comets are easily able to penetrate through it, creating a multitude of craters on its surface. Temperatures here can range from about -180º Celsius (-290º Fahrenheit), during the night, to about 430º Celsius (800º Fahrenheit), during the day. It has no moons orbiting it and its width consists of 2,440 kilometers, or 1516 miles, which is only one third of the width of the Earth. The first mission to Mercury was called Mariner 10, the first ever flyby of Mercury, and the first ever mission to orbit it was Messenger, both by NASA. BepiColombo is a current mission of a probe being conducted by ESA, the European Space Agency, with a mission to "help us understand [Mercury][...] more fully, building on the data collected by NASA's Messenger mission" (ESA, n.d.). Life here is unlikely to exist, or have even existed in its past, due to its extreme temperatures and solar radiation.

Venus

Named after the Roman goddess of love and beauty, Venus is often called Earth's twin due to its similar size and density. It is the second planet from the Sun in our Solar System and it has a thick atmosphere filled with carbon dioxide and clouds made up of sulfuric acid. Because of the carbon dioxide, the Sun's heat often gets trapped in the atmosphere, causing a greenhouse effect, and making Venus the hottest planet in our Solar System. Temperatures here can rise up to about 475 degrees Celsius, which is about 900 degrees Fahrenheit. The surface of Venus consists of "intensely crushed mountains and thousands of volcanoes" that may still be active today (NASA, 2021). One rotation of Venus takes about 243 Earth days, and one revolution around the Sun is about 225 Earth days. A unique feature of Venus is that it rotates in the opposite direction of most planets; here the Sun rises in the West and sets in the East. It is also the brightest object in the night sky of Earth, after the Moon. Life is also unlikely to exist on its surface due to its extreme temperatures, but scientists theorize that it may exist high in the clouds. Furthermore, theories suggest that life may have existed on Venus in the past, when it may have had a habitable ocean. The first mission to ever flyby Venus was NASA's Mariner 2. There have also been further missions sent to Venus in the past, such as NASA Magellan, NASA Pioneer Venus Mulitprobe. More recent missions include ESA's Venus Express and NASA's Parker Solar Probe. In fact, NASA's Parker Solar Probe took the first ever visible light images of Venus in July 2020, but they were announced on February 9, 2022. NASA has announced plans to send two new missions to Venus that are expected to be launched somewhere between 2028 to 2030, and ESA has announced its mission called EnVision.

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Thank you for taking time out of your day to read our blog- we hope you learned something new! To find out more about planets in general check out our previous blog by clicking the link below! Stay tuned for our next blog about Earth and Mars to continue learning about the planets in our Solar System! Make sure to like, comment, and share with your friends, as well as subscribe for our blog to receive updates on new posts! If you’re on Instagram, follow us by clicking the Instagram icon on the top right, or go to @midnight___eclipse. As always, keep gazing skywards!

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Bibliography

NASA. (2021, July 14). Planets. NASA. Retrieved February 12, 2022, from

https://solarsystem.nasa.gov/planets/overview/

BepiColombo's first views of Mercury. ESA. (n.d.). Retrieved February 12, 2022, from

https://www.esa.int/Science_Exploration/Space_Science/BepiColombo/BepiColombo_s_first_views_of_Mercury