Discovering Mercury With a Spacecraft
Mercury orbits the Sun once every 88 Earth days on an elliptical path which may bring it as close as 29 million miles or as far away as 43 million miles from our star.
Magnetic reconnection between the IMF and Mercury’s planet magnetosphere is the most efficient process for mixing plasma, allowing solar wind to enter its magnetosphere at dayside magnetopause.
Mercury’s orbit
Mercury, with its large iron core, is unusually slim and has very little obliquity (axial tilt) in its orbit, producing temperatures which vary between about 800 degrees Fahrenheit in direct sunlight to around minus 290degF at night.
Mercury’s greyish-brown surface is covered with craters and battered by solar winds, blowing fine dust particles around its globe. But the MESSENGER mission has revealed an unexpected brightness on some parts of Mercury dubbed “crater rays”. These bright streaks are made up of crushed fragments of rock formed when an asteroid or comet strikes Mercury; due to fine rocks being reflective, their reflection makes these “rays” far brighter than surrounding terrain.
Mercury orbits the Sun every 88 days, making it one of the innermost planets with the fastest orbit in our solar system. But due to its eccentric, egg-shaped orbit, Mercury can appear closer when at its “perihelion”, yet remain 1.5 times farther from it when at its “aphelion”.
Mercury’s surface
Mercury shares many features with the Moon’s surface, such as thousands of craters and large basins up to 1300 kilometers across. There is also an intricate network of scarps, some more than a kilometer high and hundreds of kilometers long.
MESSENGER’s instruments provided accurate measurements of Mercury’s surface composition and volcanic activity patterns. Their instruments discovered that its magnetic field is 100 times weaker than Earth’s and offers little protection from charged particles from the Sun.
Mariner 10 discovered a landscape marred by pitted and pitted terrain; by contrast, Mercury has large regions covered by plains. This may have occurred by raising temperature allowing rocks to settle and cover land surface; flowing lava which obliterated rough terrain as it moved past; or “wrinkling” of its crust as its shrinkage has occurred as cooling and contraction have taken effect. Furthermore, MESSENGER discovered streams of sodium particles similar to comet tails as the planet turned in its orbit – giving a real impression of what may happen as planet turns in its orbit!
Mercury’s magnetic field
The smallest planet in our Solar System boasts a relatively puny magnetic field compared to Earth, likely because its frigid temperatures make it impossible to create enough hot iron to power a dynamo dynamo dynamo generators.
The Mercury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission’s observations demonstrate that Mercury has a global magnetic field produced by convective motions within its liquid iron core through an ongoing dynamo process1.
MESSENGER observations reveal that Mercury’s magnetic poles have drifted slowly over time – something pilots and navigators need to account for when planning flights and plotting courses. This was unexpected given how quickly these shifts happened; scientists at TU Braunschweig and Max Planck Institute for Solar System Research propose an explanation: the outer layer of Mercury’s magnetosphere counteracts Mercury’s internal dynamo thus weakening its magnetic field; this new theory could be tested once bepiColombo launches its probe in 2020.
Mercury’s exosphere
Mercury lies so close to the Sun that its atmosphere consists primarily of an exosphere composed of hydrogen, oxygen, sodium, calcium and potassium vapor ejected into space by solar wind as a constant stream; leaving behind its signature comet tail behind it.
Planet Mercury’s thin and volatile atmosphere is produced through various means such as impact vaporization, thermal desorption by photons or thermal heating and outgassing from crustal outgassing. A weak magnetic field helps funnel gas from dayside to nightside of its planet but this cannot fully explain its spatial or temporal variability.
Mercury’s greyish-brown surface is peppered with bright streaks known as crater rays, created by collisions between asteroids and its surface that generate high energy impacts that send particles of crushed rock flying off and reflect sunlight back onto itself.