RBradbury-SPST435-Week 1-Mercury

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Apr 3, 2024

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Mercury: Current State of Knowledge and Mission Timeline Reiley Bradbury American Military University SPST435: Planetary and Space Exploration Dr. Kunal Kothari February 9, 2024

Introduction Of all the planets in our Solar System, Mercury is of one the least explored and is rather difficult to do so. This is mainly due to two reasons. One is that it is the closest planet to our Sun, making it a challenge to observe in front of the sun’s brightness. The other reason being that the sun has such a large gravitational pull that probes, and other spacecraft have difficulties entering orbit without having to constantly hit the brakes and defy gravity (Three Reasons Why We Know so Little about Mercury, n.d.). While exploring Mercury may be challenging, it has not stopped scientists from wanting to learn more about it. Mercury’s Discovery Galileo Galilei was the first known person to discovery Mercury through a telescope in the 17 th century, but the belief among many scientists is that the earliest recorded observations were done by an Assyrian astronomer around the 14 th century on the Mul.Apin tablets. A telescope is not necessary to see it because it is visible to the naked eye, so there really is no way to know for sure who actually observed it for the very first time. Later in 1639, Mercury’s phases, similar to those of the Moon and Venus, were discovered by Giovanni Zupi. The planet gained its name from a Roman messenger god (a god of speed) due to its rapid orbit (the nine planets, 2019). What We Already Know Despite the challenges of exploration, successful past missions have given us a lot of insight into the characteristics of Mercury. We already know that it is the closest planet to the sun

at 57.91 or 0.4 AU, and it takes 3.2 minutes for sunlight to reach. It has a density of 5.43 g/cm 3 , a radius of 2.439 km and a diameter of 4.879 km, making it the densest and smallest planet, only about 1/3 the size of Earth. What is interesting is that though Mercury sits so close to the sun, it is not the hottest planet due to the lack of an atmosphere to protect it from extreme cold at night. Instead, Mercury has an exosphere composed of oxygen, sodium, hydrogen, helium and potassium. The exosphere is created by solar winds spitting atoms that collide with meteoroids. Mercury reaches temperatures of 430 degrees Celsius during the day, and dips to -180 degrees Celsius at night. Claiming the title of “fastest planet”, it takes Mercury just 88 Earth days to orbit the sun at a pace of 47 km/s. While it moves rapidly, it spins slowly on its axis, tilted at about 1/30 degrees, and in 59 Earth days it completes one rotation. The planet’s aphelion is 0.44 AU from the sun and perihelion is 0.30 AU, giving it the largest orbital eccentricity (the nine planets, 2019). Earth and Mercury are both structurally similar since they both possess a core, mantle and crust. The iron-rich core is about 2,074 km thick, accounting for roughly 85% of Mercury’s radius (Mercury: Facts – NASA Science, n.d.). Additionally, Mercury’s magnetic field, about 1.1% the size of Earth’s interacts with solar winds, sometimes resulting in a magnetic tornado directing hot plasma to the surface. The planet has no moons or rings and is also visually very similar to the moon with its grey, cratered surface, indicating that it has not experienced any geological activity in years (the nine planets, 2019). Mariner 10, MESSENGER and BepiColombo Space agencies like NASA and the ESA have been making efforts to explore our tiny neighboring planet since the 1970s. The Mariner series was the first mission to Mercury, followed by MESSENGER and now, most recently, BepiColombo. NASA’s Project Mercury,

however, was not a mission to Mercury despite the name. Rather, it was the mission to send the first astronauts into space (What Was Project Mercury? (Grades 5-8) – NASA, n.d.). The first spacecraft to not only reach Mercury as the seventh successful launch of the Mariner series, but also use the advantage of Venus’ gravitational pull to get there and visit two planets in one trip was none other than NASA’s Mariner 10. The mission was focused on measuring the environment, atmosphere, surface and body characteristics of both Mercury and Venus. Gaining experience with dual planet gravity assist, as well as running experiments in the interplanetary medium were among the other goals the team aspired to reach. Mariner 10 was launched out of Cape Canaveral on November 3, 1973, and placed in a parking orbit for about 25 minutes after launch. Following a retrograde heliocentric orbit, the spacecraft completed three Mercury flybys, capturing images and collecting data. It was during this mission that scientists made some major discoveries about Mercury, such as the confirmation that it does not have an atmosphere, the surface is very Moon-like, and that it contains a small magnetic field and iron- rich core. Before reaching Mercury, Mariner 10 completed a flyby of Venus to gather images and data, thus successfully utilizing gravity assist to travel from one planet to another (Venus to Mercury) for the first time (NASA – NSSDCA – Spacecraft – Details, 2019). Decades later in 2004, MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) had its turn to journey to Mercury. This was the seventh Discovery- class mission (part of NASA’s Discovery Program dedicated to planetary science) to reach Mercury and became the first spacecraft to enter orbit as well. The MESSENGER mission objectives were slightly different than those of previous mission as it aimed to study the geology (with focus on the core), magnetic field and chemical composition of Mercury. Like Mariner 10, MESSENGER was placed in parking orbit after launch on August 3, 2004, and completed not

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