MESSENGER Results Returned En Route

MESSENGER launched August 3rd, 2004 as it settled into a definitive orbit about Mercury in March 2011 only. Meanwhile he had performed three flybys of the planet in January and October 2008, and September 2009. Data were returned during that journey

(notices by chronological order)

First Findings 2007 Radar Study Second Passage at Mercury (October 2008) Mercury's Magnetosphere and Atmosphere

Last Passage at Mercury (September 2009) Most Recent Data (July 2010) Studies Based on Data Collected During the 1st and 2nd Flybys (August 2010)

First Findings

Recentest data returned by NASA's MESSENGER mission during its first steps towards Mercury are the following: Caloris basin, one of the largest impact basins in the solar system had its interior filled with lava according to a process similar to what occurred at the Moon; the magnetic field of Mercury likely is due to a core magneto; it's the cooling of the oversized core which triggered a remarkable contraction of the planet, with scarps and faults, with the contraction of Mercury one third greater than previously thought; the magnetosphere of Mercury is filled with many charged particles forming a 'plasma nebula' akin to Io plasma torus; the thin Mercury atmosphere -its 'exosphere' is replenished with particles from the surface processes and provides for a long tail of atoms flowing behind the planet. Variability in the planet's magnetic field is likely linked too to the radiation coming from the nearby Sun

2007 Radar Study

A radar study in 2007 might have that Mercury really has a molten core due to that the radar echoes showed tiny twists in Mercury's orbit around the Sun, hinting to such a molten core, or, at least, an outer molten core. Such a molten state might well be the explanation to the current, slight magnetic field observed at Mercury. To maintain such a molten core, Mercury would have had to contain a lighter element, such as sulfur in its center. At last, to get sulfur in its composition, Mercury would have had to combine elements from close to the Sun and from farther away -an idea known under 'radial mixing'

Second Passage at Mercury (October 2008)

click to the hemisphere of Mercury unveiled by the MESSENGER's flyby in October 2008. picture NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

During the second of its three scheduled passages at Mercury, in October 2008, NASA's MESSENGER helped unveiled a whole hemisphere of Mercury which was unknown until now! The only striking discovery, on the other hand, consisted of the view that the hemisphere is completely striated by longitudinal rays which emanate from a northern crater! Messenger revealed too that there was more volcanism at Mercury than thought, having more of influence on shaping the planet. Some craters have been seen filled with more than 1-mile deep lava about 3.8 to 4 billion years ago. Mercury thus, might have a different geological history than the Moon -to which it had been compared until now. The whole planet, on the other hand, is covered with a light blue material which might be partly iron. That material might have been brought to surface by volcanoes from Mercury's core. The Mercury's crust might have been mostly yielded by volcanoes spreading lava, which dried. Such observations tend to show that Mercury be more like Mars than like our Moon. Multiple stages of volcanism or tectonic activity occurred over time. The Heavy Bombardment period, further, which occurred 4 billion years ago when the leftovers of the formation of the solar system heavily impacted the newly born planets, might well have stripped Mercury from its original surface. Hence the surface we see nowaday likely not is the original, differentiation-processed crust of Mercury. New chemicals have been found in Mercury's tenuous atmosphere, like some magnesium. Magnesium is an important constituent of Mercury's surface. check that view from the thumbnail!

Mercury's Magnetosphere and Atmosphere

The solar wind might cross into the magnetosphere of Mercury, and blast atoms off the surface, replenishing the planet's thin atmosphere. Like at Earth, some connections may establish between the solar wind and the protective magnetosphere of Mercury, allowing the solar wind to reach down to the surface. At Mercury that takes the form of joined magnetic fileds turning into vortex-like tubes, through which the solar wind is entering. This action unto the surface of Mercury is further allowed as Mercury has about no atmosphere. The proximity of Mercury to the Sun strenghten too the reconnection events occurring between the interplanetary, and planetary magnetic fields. MESSENGER's first flyby on January 14, 2008, confirmed that the planet has a global magnetic field, as first discovered by the Mariner 10 spacecraft during its flybys of the planet in 1974 and 1975

Last Passage at Mercury (September 2009)

MESSENGER performed its last flyby at Mercury on Sept. 29. The craft just flew at a mere 142 miles above Mercury as the flyby served like the last gravity-assisted flyby before the definitive arrival at Mercury, in 2011. MESSENGER's speed was reduced from 12,000 to 6,000 mph (19000 to 10000 km/h). A data glitch unluckily affected the craft and half of the scheduled measures only could be performed. 98 percent of the planet now has been imaged however. MESSENGER could perform observations in three domains, with the atmosphere of Mercury found to endure 'seasonal' changes due to the change of the solar pressure along the planet's orbit, as varied chemicals are knocked out from the surface, or by high-speed miniature meteoroids called micrometeoroids, to form that 'exosphere'. Sodium, calcium and magnesium vary in quantities, with sodium, for example, found in smaller amounts than during last flyby. Calcium and magnesium showed less variation. Those variations are showing that the surface of Mercury too might have changed over time, likely leading to the atmosphere being the result of billions of years of such processes! MESSENGER then performed its first measurements of the chemical on the surface of the planet and unexpectedly found that Mercury possesses much more iron and titanium, those heavy metals than thought. The numbers of the metals are similar to what is seen at the Moon's maria, inside the basalts there, providing thus a important step into what was known of Mercury until now. The planet's core is estimated to represent 60 percent of the mass total, making Mercury the densest planet in the solar system. MESSENGER at last continued to discover some features at the surface of Mercury, like some kind of a volcanic vent, or a 180-mile (290-km) wide double-ringed impact basin dating back to 1 billion years only, as such basins usually are 4 billion-year old! The flyby also revealed seasonal changes under the form of varying chemical compositions in Mercury's thin atmosphere

Most Recent Data (July 2010)

Most recent data are showing that Mercury’s exosphere varies around the planet in terms of the distribution of individual chemical elements, with considerable variability for sodium, calcium, and magnesium. Ionized calcium in Mercury's exosphere is concentrated over a relatively small portion of the exosphere, with most of the emission occurring close to the equatorial plane. Mercury's early history was marked by pervasive volcanism which endured several episodes. That suggest the planet spanned a much greater duration volcanism than previously thought, perhaps extending well into the second half of solar system history. At last, for the first time, the spacecraft revealed substorm-like build-up, or loading, of magnetic energy in Mercury's magnetic tail. The increases in energy measured in Mercury's magnetic tail were very large. They occurred quickly, lasting only two to three minutes from beginning to end. These increases in tail magnetic energy at Mercury are about 10 times greater than at Earth, and the substorm-like events run their course about 50 times more rapidly as that strength might be due to the extreme tail loading and unloading

Studies Based on Data Collected During the 1st and 2nd Flybys (August 2010)

Studies as published from the data collected by MESSENGER during the first and second flybys at Mercury have been released. Because both the particles forming the planet's exosphere and Mercury's surface materials respond to sunlight, the solar wind, Mercury's own magnetic sheath (the magnetosphere) and other dynamic forces, the exosphere may not look the same from one observation to the next. The position of Mercury on its orbit too is a factor too. The greatest amount of sodium for example in the exosphere is when Mercury is at a middle distance from the Sun. The main factor releasing sodium atoms into the exosphere seems to be photons releasing sodium in a process called photon-stimulated desorption (PSD), which may be enhanced in regions impacted by ions. Once a soil grain depleted of its sodium, for example, the material then has to make a longer journey out from inside. Much of the sodium is observed at the North and South poles of Mercury, but a lopsided distribution was found during the first MESSENGER flyby, with four times more solar protons are hitting Mercury near the north pole than near the south pole because the magnetic field coming from the Sun was tilted during the Mercury flyby. After protons from the solar wind bombard Mercury's surface and free species from the soil, intense sunlight can strike those liberated materials and convert them into positive ions (the process of photoionization). A 'drift belt' might thence exist around Mercury maybe yiedling a magnetic depression in this region. A mystery is lingering about a strong concentration of magnesium over the north pole during the third flyby which then suddenly dropped as the temperature of the region reached tens of thousands of degrees Kelvin, which is far above the surface temperature, a whole process which still remains unexplained