The US space probe MESSENGER made its second successful fly-by of the year of the planet Mercury on October 6, revealing like never before 30 percent of the solar system's smallest planet, scientists said Thursday.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) soared past the innermost planet's equator at an altitude of 201 kilometers (125 miles) at a speed of 23,818 kilometers per hour (14,800 miles per hour).

"When combined with data from our first flyby and from Mariner 10 (three passes in 1974 and 1975), our latest coverage means that we have now seen about 95 percent of the planet," said Sean Solomon, principal investigator and director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington.

"The region of Mercury's surface that we viewed at close range for the first time this month is bigger than the land area of South America," he said.

The image-capturing instruments aboard MESSENGER functioned normally throughout the pass, scientists said, as cameras took more than 1,200 images of the surface and the probe's laser altimeter surveyed the ground.

Correlating the data with the craft's previous fly-bys, scientists were able to observe Mercury's mysterious magnetic field, and piece together a never-before-seen map of the planet.

"These topographic measurements now improve considerably the ability to interpret surface geology," said Maria Zuber, co-investigator and head of the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology.

"The previous flybys by MESSENGER and Mariner 10 provided data only about Mercury's eastern hemisphere," said Brian Anderson of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

"The most recent flyby gave us our first measurements on Mercury's western hemisphere, and with them we discovered that the planet's magnetic field is highly symmetric," he said.

Scientists said that MESSENGER's cameras have captured how unlike Mercury's surface is to that of the moon or Mars, as previously suspected.

"Mercury's surface is more homogeneously ancient and heavily cratered, with large extents of younger volcanic plains lying within and between giant impact basins," said co-investigator Mark Robinson of Arizona State University in Tempe.

Mercury is the closest of all the planets to the Sun, and because of the high-risks of its proximity -- the Sun's enormous gravitational pull, and massively high levels of radiation -- it is one of the most mysterious bodies in the solar system, even though it is relatively close to Earth.

Scientists and observers hoped MESSENGER would yield answers to the physical processes that govern Mercury's atmosphere, along with more information about the charged particles located around the planet's dynamic magnetic field.

The January visit this year showed scientists that volcanic eruptions produced many of Mercury's expansive plains, littered with meteor craters, and that its magnetic field appears to be actively generated in a molten iron core.

For more information visit http://messenger.jhuapl.edu/mer_flyby2.html.