MESSENGER is a scientific investigation of the planet Mercury, the least explored terrestrial planet. Understanding Mercury and how it was formed is essential to understanding the other terrestrial planets and their evolution. Mercury has been visited by only one other spacecraft, Mariner 10, so we know little more than its average density (the second greatest of all the planets), the composition of its atmosphere (thinnest of the terrestrial planets), the fact that it possesses a global magnetic field, and its extreme variations in temperature. Data from MESSENGER will serve to lift some of the uncertainty about this innermost planet of our solar system.
After making three flybys of the planet, the MESSENGER mission entered Mercury orbit in March 2011, and is using data collected during the flybys as an initial guide to perform a more focused scientific investigation of this mysterious world. MESSENGER is investigating six key scientific questions about Mercury’s characteristics and environment with a set of miniaturized space instruments.
The goals of the MESSENGER mission are to answer these questions:
- Why is Mercury so dense?
Mercury’s density implies that a metal-rich core occupies at least 60% of the planet’s mass, a figure twice as great as for Earth! MESSENGER is acquiring compositional and mineralogical information to distinguish among the current theories for why Mercury is so dense.
- What is the geologic history of Mercury?
Before the MESSENGER mission, only 45% of the surface of Mercury had been photographed by a spacecraft! Using its full suite of instruments, MESSENGER is investigating the geologic history of Mercury in great detail, including the portions of the planet never seen by Mariner 10.
- What is the nature of Mercury’s magnetic field?
Mercury has a global internal magnetic field, as does Earth, but Mars and Venus do not. By characterizing Mercury’s magnetic field, MESSENGER is helping to answer the question of why the inner planets differ in their magnetic histories.
- What is the structure of Mercury’s core?
Through a combination of measurements of Mercury’s gravity field and observations by the laser altimeter, MESSENGER is determining the size of Mercury’s core and verifying that Mercury’s outer core is molten.
- What are the unusual materials at Mercury’s poles?
At Mercury’s poles, some crater interiors have permanently shadowed areas that contain highly reflective material at radar wavelengths. Could this material be ice, even though Mercury is the closest planet to the Sun?
- What volatiles are important at Mercury?
MESSENGER measures the composition of Mercury’s thin exosphere, providing insights into the processes that are responsible for its existence.
- Mercury Atmospheric and Surface Composition Spectrometer (MASCS)
- MASCS Principal Investigator, William McClintock
LASP developed and built the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument onboard MESSENGER. MASCS is designed to detect minerals on Mercury’s surface, and determine the abundance and components of its thin atmosphere. Data from MASCS will help answer the questions: What is Mercury’s surface made out of? How is Mercury’s atmosphere generated? Does Mercury have ice at its poles?
Combining an ultraviolet spectrometer and infrared spectrograph, MASCS measures the abundance of atmospheric gases around Mercury and detects minerals in its surface materials.
The Ultraviolet and Visible Spectrometer (UVVS) determines the composition and structure of Mercury’s exosphere—the extremely low-density atmosphere—and studies its neutral gas emissions. It also searches for and measures ionized atmospheric species. Together these measurements are helping researchers understand the processes that generate and maintain the atmosphere, the connection between surface and atmospheric composition, the dynamics of volatile materials on and near Mercury, and the nature of the radar-reflective materials near the planet’s poles. The instrument has 25-kilometer altitude resolution at the planet’s limb.
Perched atop the ultraviolet spectrometer, the Visible and Infrared Spectrograph (VIRS) measures the reflected visible and near-infrared light at wavelengths diagnostic of iron and titanium-bearing silicate materials on the surface, such as pyroxene, olivine, and ilmenite. The sensor’s best resolution is 3 kilometers at Mercury’s surface.
For more information about the MESSENGER mission, see:
Launch date: August 3, 2004
Launch vehicle: Boeing Delta II
Mission target: Mercury orbit
Mission duration: 7 years to Mercury, 2 years in orbit (primary); Mission currently extended through March 2015
Other key dates:
- Mercury orbit insertion: March 17, 2011
- First one-year extended mission began on March 18, 2012
- Second mission extension to end in March 2015
Other organizations involved:
- Johns Hopkins University Applied Physics Laboratory (JHU/APL)
- Carnegie Institution for Science