Washington, September 29 (ANI): The Neutron Spectrometer flying aboard NASA’s MESSENGER spacecraft is all set to take a closer look at Mercury to understand the planet’s crust, as the spacecraft make its third and final pass around Mercury today.

The current flyby is designed to slow the spacecraft and to prepare its trajectory for orbital insertion.

William C. Feldman, a senior scientist at the Tucson-based Planetary Science Institute, is excited about taking a close look at the side of Mercury that MESSENGER flew by on its second encounter with the planet in October 2008 and about seeing another five percent of the planet’s surface that is being imaged for the first time.

During the second flyby, the Neutron Spectrometer was not favorably positioned and the spacecraft was flying faster than it will be on the third pass.

The slower encounter speed on the this third flyby will allow the spacecraft to remain close to the planet for a longer time and will yield better Neutron Spectrometer data than the instrument recorded on the first two encounters, according to Feldman.

Feldman is excited both by what scientists expect to measure and by what will turn up serendipitously.

MESSENGER’s Gamma-Ray and Neutron Spectrometer detected iron and/or titanium during the spacecraft’s first flyby.

But Feldman expects to get an even better assessment of the iron and titanium on the planet’s surface this time around because the Neutron Spectrometer will be pointed in the direction the spacecraft is flying, and it will be going about twice as fast as the neutrons travel.

This will allow it to scoop up many more neutrons than if it were looking straight down at the planet’s surface.

Examining the spectrometer data will then help scientists answer two important questions: What form does iron take on Mercury and how much is there?

“The planet’s surface is much darker than the Moon’s, indicating that there should be a high iron and/or titanium content,” Feldman said.

“This could be in the form of ilmenite, an iron-titanium oxide, or it might be nanophase iron, which gets distributed on the surface because of space weathering,” he added.

For the Neutron Spectrometer, iron and titanium are the known attractions on this part of MESSENGER’s road trip.

“We will sample a composition on this side of the planet that could be very different from what we saw on the other side of the planet during the first flyby,” said Feldman. “It would be very surprising if we found the exact same composition that we saw on that first flyby,” he added. (ANI)