Finally, a look at enduring mysteries of Mercury - Space
http://www.msnbc.msn.com/id/42113293/ns/technology_and_science-space/
updated 10:34 AM ET, Wed., Mar 16, 2011
Space
Finally, a look at enduring mysteries of Mercury
NASA's Messenger probe set to begin orbit and start long-awaited
research
NASA / JHUAPL / CIW
Color differences on Mercury are subtle, but they reveal important
information about the nature of the planet's surface material. A number
of bright spots with a bluish tinge are visible in this image taken by
Messenger on Jan. 14, 2008, which is a mosaic from three different
images.
By Charles Q. Choi
Space.com
NASA's Messenger spacecraft will make history Thursday when it becomes
the first probe to orbit the planet Mercury. But it also promises to
help solve a host of mysteries about the solar system's innermost
planet.
The seven instruments aboard Messenger, fortified to withstand the
blistering environs near the sun, will help researchers investigate the
many enigmas of Mercury â€" such as its its unexpected magnetic
field, and whether the planet
has water ice at its poles.
As the solar system's innermost planet, Mercury is relatively unexplored
considering its proximity to Earth. Discovering more about this searing
hot, rocky sibling of Earth could shed light on how our solar system
formed, and how alien planets coalesced around faraway stars,
researchers said.
"Many exoplanets discovered to date are as close or closer than Mercury
is to our host star," said Messenger principal investigator Sean Solomon
of the Carnegie Institution of Washington. He and his colleagues
discussed Messenger at a press conference Tuesday.
Arriving at Mercury
Since it launched in August 2004, the $446 million Messenger (short for
Mercury Surface, Space Environment, Geochemistry and Ranging) orbiter
has made nearly 15 laps around the sun, flying by Earth, Venus and
Mercury to slingshot itself into position for orbital entry.
During its orbital insertion maneuver Thursday at about 8:45 p.m., the
spacecraft will fire its main thruster for about 15 minutes. The burn
â€" which will slow the probe down enough for Mercury's gravity to
capture it â€" will consume nearly a third of the propellant that
the spacecraft carried at launch, researchers said.
"It will be the largest rocket burn of the mission," said Messenger
propulsion subsystem lead Carl Engelbrecht of Johns Hopkins University's
Applied Physics Laboratory (APL).
By 2:47 a.m. EDT on Friday, the spacecraft is expected to begin its
first full orbit around Mercury.
"For the first two weeks of orbit, we’ll be focused on ensuring
that the spacecraft systems are all working well in Mercury’s
harsh thermal environment," Messenger mission systems engineer Eric
Finnegan, of APL, said in a statement.
After that, "we'll get the first global observations of the surface, of
aspects of the interior, of the tenuous atmosphere Mercury has, of the
magnetosphere â€" the envelope of space as a result of the planet's
internal magnetic field â€" and the environment that Mercury passes
through, which is quite unique as a consequence of it being the closest
planet to the sun," Solomon explained.
Investigating Mercury's secrets
During Messenger's 6 1/2-year journey to Mercury, the probe's seven
scientific instruments have not remained idle. Researchers have been
calibrating them and enhancing their software over the years to optimize
their performance, said Messenger mission operations manager Andy
Calloway, also of APL.
But that work was just a dress rehearsal for what's coming up.
"On April 4, we begin prime science," Calloway said.
Among the first gear scheduled to start operating is Messenger's
gamma-ray spectrometer, part of the probe's Gamma-Ray and Neutron
Spectrometer instrument.
The gamma-ray device needs to cool down starting March 22 to function
â€" a special challenge so close to the sun. It will measure
gamma-ray emissions from Mercury's surface to determine the abundance of
elements in the crust, including reflective materials at the planet's
poles that might be water ice.
On March 23, most of the other instruments should turn on, researchers
said. Messenger's magnetometer will measure the unexpected magnetic
field around Mercury in detail to determine its strength, while the
Mercury Atmospheric and Surface Composition Spectrometer will study the
planet's tenuous atmosphere by measuring ultraviolet light emissions.
The atmospheric and magnetic processes the equipment should observe
"happen at extremely dynamic time scales, and we benefit tremendously
from being on site as opposed to trying to monitor them from Earth,"
Solomon said.
Mercury probe, activate!
Also on March 23, the Mercury Laser Altimeter will activate. This
instrument will scan the planet's surface with an infrared laser to map
its topography. By analyzing the depth of the floors and the height of
the rims of craters at Mercury's poles, scientists should be able to
tell if these pits could spawn the permanent shadows needed for ice to
survive, Solomon said.
In addition, the Energetic Particle and Plasma Spectrometer will analyze
the charged particles in the magnetosphere around Mercury and those
coming from its surface, and the spacecraft's X-Ray Spectrometer will
help map surface mineral composition.
The probe's neutron spectrometer will analyze Mercury's surface
composition, which could help shed light on how the surprisingly dense
planet formed and evolved, researchers said.
Perhaps lighter elements on Mercury's surface got seared away by the
sun, for example, or perhaps a giant planet-sized object smashed into
Mercury and ripped off its less-dense surface shell.
"These are all rather simple theories, and I and the science team will
wager that the true story is more complicated, and maybe involves a
combination of processes," Solomon said. "We hope to reject one or more
of these theories, and it would not surprise any of us if we have to
come up with new theories to explain Mercury."
On March 29, the Mercury Dual Imaging
System will power on. This camera system will provide a complete map of
the surface of Mercury with resolutions as fine as 250 meters per pixel.
By orbiting Mercury, "we'll be able to control viewing direction, the
lighting direction, to a much greater degree than during flybys, for
much better pictures," Solomon said.
An Earth year at Mercury
Arranging which of Messenger's many instruments should be aimed at
Mercury at any given time is an elaborate dance. Many factors must be
taken into consideration, researchers said â€" such as the need to
keep Mercury's sunshade between it and the sun to keep the probe from
frying.
Messenger's highly elliptical orbit also poses challenges, as does its
varying distance from Earth, which limits how much data the probe can
relay back home.
"We developed an automated science planning software package to come up
with a year-long sequence of science observations to accomplish all the
mission objectives yet satisfy these constraints," Solomon said.
The plan is for Messenger to observe Mercury for a year, "which should
be sufficient to answer the basic questions that framed the mission we
set out to answer," Solomon said.
Messenger might be able to keep flying and observing Mercury beyond that
timeframe, Solomon added, but a decision about whether or not to extend
the probe's mission will come at a later date.
Follow Space.com for the latest in space science and exploration news on
Twitter@Spacedotcomand on Facebook.
Video: Messenger's Mercury Orbit Arrival
New Views of Mercury From NASA's Messenger Probe
Most Enduring Mysteries of Mercury
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