$8.7 million CU-Boulder Instrument to fly on MESSENGER Mercury Mission

A small, powerful University of Colorado at Boulder instrument will
fly on NASA’s MESSENGER mission, slated for launch Aug. 2 from Cape
Kennedy, Fla., to probe Mercury’s searing surface, oddball atmosphere
and bizarre magnetic field.

MESSENGER will be only the second mission to visit the tiny planet,
said Laboratory for Atmospheric and Space Physics Director Daniel
Baker. Baker and Senior Research Associate William McClintock are
co-investigators on the MESSENGER mission. McClintock led the
development of LASP’s $8.7 million Mercury Atmospheric and Surface
Composition Spectrometer, or MASCS, designed and built at CU-Boulder
and one of seven scientific instruments on the spacecraft.

“Studying Mercury’s surface, tenuous atmosphere and magnetic field
are a key to understanding the evolution of the inner solar system,
including Earth,” said Baker. “It is the least explored planet in
the inner solar system, so we are anxious to get back.”

The only other time Mercury was visited by spacecraft was during 1974
and 1975, when NASA’s Mariner 10 spacecraft made three flybys and
mapped roughly 45 percent of the planet’s rocky surface at the time.
“The Mariner 10 mission and subsequent ground-based observations have
raised additional questions that the MESSENGER team would like to
answer,” said Baker.

Some intriguing questions that MASCS will address involve the mineral
composition of Mercury’s surface, the distribution of gases in its
atmosphere and the workings of its comet-tailed sodium gas cloud.
Others include whether the 3,000-mile-in-diameter planet has a solid
or molten core and whether there have ever been volcanoes on its
surface, which reaches daytime temperatures of more than 800 degrees
Fahrenheit.

Managed by Johns Hopkins University’s Applied Physics Laboratory for
NASA, MESSENGER involves about 20 scientists. Sean Solomon of the
Carnegie Institution in Washington, D.C., is the chief MESSENGER
scientist.

More than three years in development at CU-Boulder, MASCS weighs
roughly 7 pounds, said LASP’s Mark Lankton, program manager for the
instrument. Although it is nearly three times as light as the highly
successful UVIS instrument package that LASP scientists used recently
to image the rings of Saturn on the Cassini mission, “the MASCS
instrument is comparable in power,” he said.

According to McClintock, geochemists, geophysicists, geologists and
atmospheric scientists involved with MESSENGER will be working
closely to link processes between the planet, its magnetic field,
atmosphere and solar wind. “One raging controversy is whether
Mercury ever had volcanoes,” he said.

In addition, ground-based observations since Mariner 10 have
determined that Mercury is enveloped in a huge, comet-like sodium
cloud. “There has to be a mechanism to replenish this cloud,” said
McClintock. “But we won’t know what it is until after the spacecraft
reaches orbit.”

Radar studies also show a high reflectivity near Mercury’s poles
hinting that some permanently shadowed craters may contain some form
of water ice. “Determining the nature of those deposits is a primary
science goal for MESSENGER,” said McClintock.

Baker, a space physicist, is particularly interested in the magnetic
field of Mercury and its interaction with the strong solar wind.
Scientists have believed the core of this rocky planet should have
solidified by now. “We are puzzled over Mercury’s relatively strong
magnetic field, which should require a liquid or molten core like
that on Earth,” said Baker.

There also is evidence for small solar “sub-storms” in Mercury’s
atmosphere, said Baker. “We are interested in how the planet gets
energy from the solar wind into the magnetosphere, and would like to
see if charged particles are crashing from the atmosphere onto the
planet’s surface and heating it.”

Lankton said the 13-day launch window for MESSENGER beginning Aug. 2
is only 11 seconds per day. In addition, the 1.2-ton spacecraft has
to fly past Earth once, Venus twice and Mercury three times to attain
Mercury orbit. “From a technical standpoint, it’s more difficult to
swing by Earth a year from now than to dock with the space station,”
said Lankton.

The circuitous route of the spacecraft to attain Mercury orbit — a
4.9 billion mile journey requiring more than seven years and 13 loops
around the sun — forced engineers to miniaturize instruments.

“All of the instruments on MESSENGER had to be extremely light, which
stretched our imaginations and creativity,” Lankton said. “We have
learned a lot, and wound up getting a lot of bang for our buck. I’ve
been involved in a number of missions over my career, and working on
MESSENGER is the most fun I have had.”

The spacecraft is equipped with a large sunshield and heat-resistant
ceramic fabric, since Mercury is about two-thirds of the way nearer
to the sun than Earth and is bombarded with 10 times the solar
radiation. “MESSENGER essentially will be on a huge rotisserie, with
the sun on one side and the hot planet on the other,” Baker said.

Unlike many planetary missions, MESSENGER is tailored so that
multiple instruments contribute complementary data to answer key
science questions, said Baker. “We are pushing the envelope, and
Mercury no doubt will surprise us in many ways.”

Boulder scientist Clark Chapman of the Southwest Research Institute
also is a co-investigator on the MASCS experiment. In addition,
Starsys Research of Boulder built the pivot motor for the Mercury
Dual Imaging System instrument package on the MESSENGER spacecraft.

Data from MESSENGER will be sent to NASA’s Deep Space Network
satellites, then to the Applied Physics Laboratory at Johns Hopkins
and finally to the LASP facility in CU’s Research Park. Baker
expects dozens of CU-Boulder undergraduate and graduate students to
be involved in data analysis in the coming years.