NASA probe to make historic arrival at Mercury

According to the US space agency, the Messenger probe, which has been making its way toward Mercury for more than six years, will fire its main thruster for 14 minutes to slow itself down enough to enter orbit around Mercury on Thursday.

If all goes well, Messenger is expected to spend the next year studying the solar system's innermost planet, mapping its surface and investigating its composition and magnetic environment, among other features, the Space.com reported.

Learning more about Mercury would help scientists better understand how the solar system -- and, in particular, the rocky planets Mercury, Mars, Venus and Earth -- formed and evolved, the researchers said.

Sean Solomon, of the Carnegie Institution of Washington, who is the chief investigator of the USD 446-million Messenger probe said "the cruise phase of the Messenger mission has reached the end game".

"Orbit insertion is the last hurdle to a new game level, operation of the first spacecraft in orbit about the solar system's innermost planet," Solomon said in a statement. The spacecraft was launched in August 2004. Over the past six and half years, the probe has taken a circuitous, 4.9 billion-mile, or 7.9 billion-km, route through the inner solar system, completing one flyby of Earth, two flybys of Venus and three flybys of Mercury in the process.

These Mercury close encounters have already produced some amazing photos, returning the first new spacecraft data from the planet since NASA's Mariner 10 mission more than 30 years ago. But Messenger hasn't even broken a sweat yet, mission managers said. The probe's real work begins late Thursday, when the probe drops into a highly elliptical orbit around desolate, scorched Mercury.

It is expected to circle the planet once every 12 hours, researchers said. At times, it will come as close as 124 miles (200 km) from the planet's surface; at others, it will drift off to more than 9,300 miles (15,000 km) away on its long, looping circuit.

According to the researchers, the spacecraft's science mission will last just two Mercury days, which is equivalent of a year on Earth. Mercury rotates on its axis just once every 176 Earth days.

During the mission, the scientists hope the probe will help them understand better about the planet's core structure, its geologic history, its atmosphere among others. "The Messenger team is ready and eager for orbital operations to begin," Solomon said.