By Dr. Gary L. Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
This is the first article in a seven-part series reviewing the extraterrestrial planets and other bodies of the solar system, as well as exploratory missions to study them.
Mercury is the smallest planet in our solar system at about 3,000 miles in diameter; it is also the closest planet to the Sun. Because of this, Mercury’s year is the shortest of all the planets, at just 88 Earth days. It takes 59 days to complete one rotation on its axis, so every Mercurian year is only about one and one-third Mercurian days. As Universe Today explains, “That means that if you could stand on the surface of Mercury, it would take a staggering 176 Earth days for the Sun to rise, set and rise again to the same place in the sky just once!”
Get started on your Space Studies Degree at American Military University.
Mercury orbits about 35 million miles from the Sun, a little more than one-third the distance of Earth from the Sun. The planet has an iron core and fleeting atmosphere of trace elements. Its magnetic field strength is only about 1 percent that of Earth’s. Several space missions have been sent to Mercury since the inception of space-flight, and more are currently being planned.
First Mercury Probe Was Launched in 1973
Mariner 10. The first mission to Mercury was NASA’s Mariner 10 space probe, launched in 1973. Mariner 10’s mission was to measure Mercury’s characteristics, including its surface and atmospheric dynamics. Mariner 10 was a pioneering mission for many reasons: It was the first mission to use a planetary gravitational assist (via Venus) to achieve its ultimate target orbit. It was also the first mission to use solar pressure on solar panels and on antenna arrays for flight attitude adjustment.
The space probe made three flyby orbits around Mercury, ranging in altitude from 48,000 km (29,825 miles) down to 327 km (203 miles), and was able to photograph about 45 percent of the planet’s surface. After its third flyby in 1975, Mariner 10’s fuel was spent and NASA shut down the probe; it is presumed that Mariner 10 is orbiting the Sun near Mercury’s orbit, although solar radiation would have long since damaged its electronics and prevented its operation.
Mariner 10 Revealed Mercury’s Topography is Moonlike
Mariner 10 made a number of important discoveries about Mercury. By photographing the surface, the space probe revealed that Mercury’s topography appears very Moon-like, with many impact craters. It was also able to measure Mercury’s weak magnetic field. Finally, Mariner 10 measured Mercury’s night side temperatures, which were as low as -180℃, (-292 F) and its dayside temperatures, which were as high as 427℃ (800.6 F).
MESSENGER. The second mission sent to Mercury was NASA’s MESSENGER probe, an acronym that stood for Mercury Surface, Space Environment, Geochemistry, and Ranging. This space probe was launched in 2004 and arrived at Mercury in 2011. it was the first probe to enter an orbit around Mercury. After launch, MESSENGER used gravity assists from Earth, then Venus, and then Mercury where it made three flybys until it was eventually maneuvered into a stable orbit.
MESSENGER’s original mission was scheduled to last only through 2012. But after it successfully completed its original objectives, its mission was extended until 2015. After eventually exhausting all of its fuel, it fell out of orbit and crashed into the Mercurian surface.
MESSENGER Discovered the Presence of Water Ice on the Surface
MESSENGER completed the photographic mapping of Mercury’s surface. In addition, the probe also discovered the presence of water ice on the surface, a phenomenon that surprised researchers, considering the extreme dayside temperatures on the surface of the planet. Researchers determined that this water ice exists at upper and lower latitudes of the planet, in the bottom of deep impact craters that remain in permanent shadow. MESSENGER also discovered the presence of organic compounds on the surface, as well as the fact that Mercury’s iron core is partially liquid.
BepiColombo. The next mission to Mercury is a space probe duo called BepiColombo. It’s a joint mission by the European Space Agency (ESA) and the Japanese Space Agency (JAXA) that was launched in 2018. BepiColombo is scheduled to arrive in orbit around Mercury in 2025, after gravity-assisted flybys from Earth and Venus.
The two satellites in the BepiColombo mission, the Mercury Magnetospheric Orbiter (Mio) and the Mercury Planetary Orbiter (MPO), are equipped with a variety of data collecting and scientific instruments, including tools to measure Mercury’s iron core, map gravitational and magnetic field dynamics, and verify the existence of water on the surface. BepiColombo will also measure the “exosphere” of Mercury, and how its very bleak atmosphere is constantly regenerated after being stripped away by the solar wind so close to our host star.
Mercury is a very interesting planet with many mysteries yet to be solved. Through the NASA Mariner 10 and NASA MESSENGER missions, we’ve learned a great deal about the closest planet to the Sun, but we still have much more to discover. Hopefully, BepiColombo will help fill in some of the blanks and piece together a more thorough working knowledge of the smallest planet in our solar system.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.