Mercury, the smallest and innermost planet
The image, acquired by NASA’s MESSENGER spacecraft, shows the planet Mercury, whose rugged cratered surface resembles that of the Moon great escarpments.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 

On 18 March 2011, after voyaging in interplanetary space for more than 6 years, NASA’s MESSENGER spacecraft successfully entered orbit around Mercury, the innermost planet. This is the first mission to orbit Mercury. Its objects are to study Mercury’s surface, geochemistry and space environment, for a year. The acronym MESSENGER stands for MErcury, Surface, Space ENvironment, Geochemistry and Ranging.

Mercury (4,880 km across) is a bizarre small world. It is a terrestrial (Earth-like) planet, like Venus and Mars, but its atmosphere is extremely tenuous. Mercury’s rugged heavily cratered surface bears close resemblance to that of the Moon (3.476 km across), and features magnificent escarpments. Mercury orbits the Sun in a significantly elongated elliptical orbit, and its distance from the Sun ranges between 46 million km and 70 million km. Due to its proximity to the Sun, the temperature on the day side of Mercury reaches about 430 C, but it drops to about -170 C, on the planet’s night side. This is the most drastic temperature variation among the planets. Studying Mercury is crucial for a better understanding of the formation and evolution of the Solar System.
 

The terrestrial planets
The picture shows relative sizes the four terrestrial (rocky) planets.
Credit: NASA
 
 

MESSENGER is the second Mercury-bound mission. Its predecessor was the Mariner 10 spacecraft, which flew by Mercury three times, the last of which occurred in 1975. The images of Mariner 10 allowed only 45% of Mercury’s surface to be mapped.

MESSENGER was launched into space on 3 August 2004, from Cape Canaveral Air Force Station in Florida, aboard a powerful Delta II rocket. Before reaching Mercury, MESSENGER was orbiting the Sun, and completed 15 revolutions. During its journey to Mercury, it approached Earth on 2 August 2005, and encountered Venus twice, on 24 October 2006, and 5 June 2007, respectively, and flew by Mercury three times, on 14 January 2008, 6 October 2008 and 29 September 2009, respectively. Interestingly, MESSENGER utilized the gravity of Venus to adjust its trajectory.

MESSENGER will study Mercury from a highly elongated elliptical orbit, allowing to approach the planet’s surface closely, and observe the space near Mercury. In the coming weeks, MESSENGER’s engineers will focus on verifying the spacecraft’s systems are performing well in Mercury’s hot space environment. Starting on 23 March, the instruments will be turned on and examined, and on 4 April, MESSENGER’s science mission will begin.

References

www.nasa.gov/
Wikipedia

Further Reading

MESSENGER Website
http://messenger.jhuapl.edu/index.php


Aymen Mohamed Ibrahem
Senior Astronomy Specialist