Mercury


With a diameter of 4,879 kilometers and an average orbital distance of only 57,909,100 kilometers, Mercury, named after the Roman god of trade and travellers, [1] is both the smallest and the closest to the Sun of all the planets [2] (Ceres newly promoted to dwarf planet, Pluto newly demoted to dwarf planet and Haumea, Makemake and Eris all dwarf planets and all newly discovered are smaller). [3]


Any life on Mercury would have to be hardy indeed. In 1974 and 1975 three flybys by the Mariner 10 spacecraft (the first probe to reach Mercury) revealed a world even more inhospitable than the Moon, Earth's satellite, heavily cratered in some areas smooth in others a barren rock pitilessly blasted by the Sun's radiation with a mean surface temperature of 179 °Celsius.

NASA's spacecraft Messenger (the second probe to reach Mercury and the first in orbit) performed flybys on January 14, 2008, October 6, 2008, and September 29, 2009, before final orbit insertion on March 18, 2011. The fresh, more detailed, and somewhat surprising information it transmitted home is being added to what till now has been a rather skimpy knowledge base (e.g., water ice and frozen organic compounds found inside permanently shadowed polar craters, water vapor in the exosphere and signs of intense past volcanic activity on the surface).

All things come to an end, however, and
after surpassing expectations, Messenger, out of fuel and out of time, its mission extended twice, crashed into the Solar System's innermost planet on April 30, 2015, at 19:26 GMT. A final tweet "It is time to say goodbye." An exceptional finish to an exceptional mission.

BepiColombo a joint venture between ESA and JAXA is the next Mercury mission on the horizon. It's presently scheduled for launch in April 2018 (there's been a lot of rescheduling) and following two Venus and five Mercury flybys will arrive in orbit around Mercury in 2024. It consists of the Mercury Planetary Orbiter which will examine the surface and internal structure of our system's innermost planet and the Mercury Magnetospheric Orbiter which will probe its magnetosphere. The spacecraft will use a combination of gravity assists and solar-electric propulsion to reach its destination.



[1] Later to be equated with Hermes, the Greek messenger of the gods.


[2] A "planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round shape) and (c) has cleared the neighborhood around its orbit.

[3] A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round shape), (c) has not cleared the neighborhood around its orbit and (d) is not a satellite.




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