4 July:Volcanoes and not external impacts were involved in shaping Mercury’s surface and its magnetic field is actively produced by the planet’s molten core that contracted over time leading to its shrinking at an unexpected rate.
Researchers announced after studying new data from a flyby space craft.
The US space agency NASA’s Messenger spacecraft also gave the scientists a first look at the chemical composition of the surface of the sunbaked planet, 77 million kilometres away from the Earth.
The tiny craft probed the composition of Mercury’s thin atmosphere, sampled charged particles or ions near the planet, and demonstrated new links between both sets of observations and materials on its surface.
The controversy over the origin of Mercury’s smooth plains began with the 1972 Apollo 16 moon mission, which suggested that some lunar plains came from material that was ejected by large impacts and then formed smooth "ponds."
When Mariner 10 imaged similar formations on Mercury, the smallest planet of our solar system, in 1975, some scientists believed that the same processes were at work.
Others thought Mercury’s plains material came from erupted lavas, but the absence of volcanic vents or other volcanic features in images from that mission prevented a consensus.
But now researchers have found evidence of volcanic events along the margins of the Caloris basin, one of the solar system’s youngest impact basins.
They also found that Caloris has a much more complicated geologic history than previously believed.The first altitude measurements at Mercury also found that craters on the planet are about a factor of two shallower than those on Earth’s moon. The measurements also show a complex geologic history for Mercury.
Mercury’s core makes up at least 60 per cent of its mass, a figure twice as large as any other known terrestrial planet.The flyby revealed that the magnetic field, originating in the outer core and powered by core cooling, drives very dynamic and complex interactions among the planet’s interior, surface, exosphere and magnetosphere.
The flyby also made the first-ever observations of the ionized particles in Mercury’s unique exosphere. The exosphere is an ultrathin atmosphere in which the molecules are so far apart they are more likely to collide with the surface than with each other.
The planet’s highly elliptical orbit, its slow rotation and particle interactions with the magnetosphere, interplanetary medium and solar wind result in strong seasonal and day-night differences in the way particles behave.Courtsey :DD NEWS