MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) was a scientific investigation of the planet Mercury that launched in August 2004 and entered Mercury orbit in March 2011, after making three flybys of Mercury and one each of Earth and Venus over six and a half years. Scientists used data collected during the flybys as an initial guide to perform a more focused scientific investigation of this mysterious world. MESSENGER investigated six key scientific questions about Mercury’s characteristics and environment with a set of miniaturized space instruments.
The goal of the prime mission was to understand Mercury and how it was formed in order to better understand the other terrestrial planets and their evolution. Prior to MESSENGER, Mercury had been visited by only one other spacecraft, Mariner 10, and we knew little more than Mercury’s 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 has lifted some of the uncertainty about this innermost planet of our solar system.
After more than four years in orbit, the MESSENGER spacecraft impacted the surface of the planet at 1:26 p.m. MDT on April 30, 2015. MESSENGER scientists will continue to analyze data from the mission, including that from the final, very low-altitude “hover campaign” that spanned the final months of investigations.
The goals of the MESSENGER mission were 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 acquired 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 investigated 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 helped 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 sought to determine the size of Mercury’s core and verify 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 measured the composition of Mercury’s thin exosphere, providing insights into the processes that are responsible for its existence.
Some of the key findings from the MESSENGER mission were:
- Support for the hypothesis that Mercury harbors abundant frozen water and other volatile materials in its permanently shadowed polar craters, or “hollows.”
- Data indicated the ice in Mercury’s polar regions, if spread over an area the size of Washington, would be more than two miles thick.
- For the first time, scientists began seeing clearly a chapter in the story of how the inner planets, including Earth, acquired water and some of the chemical building blocks for life.
- A dark layer covering most of the water ice deposits supports the theory that organic compounds, as well as water, were delivered from the outer solar system to the inner planets and may have led to prebiotic chemical synthesis and life on Earth.
- Confirmed that Mercury has a lopsided magnetic field and an immense iron core.
- Detected, for the first time, magnesium in Mercury’s exosphere and showed that magnesium, sodium, and calcium exhibit distinctive spatial patterns that repeat every Mercury year, suggesting a seasonality not unlike Earth’s.
In addition to science discoveries, the mission provided many technological firsts, including the development of a vital heat-resistant and highly reflective ceramic cloth sunshade that isolated the spacecraft’s instruments and electronics from direct solar radiation—vital to mission success given Mercury’s proximity to the sun. The technology will help inform future designs for planetary missions within our solar system.
- 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 was designed to detect minerals on Mercury’s surface, and determine the abundance and components of its thin atmosphere. Data from MASCS is helping scientists 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 measured the abundance of atmospheric gases around Mercury and detects minerals in its surface materials.
The Ultraviolet and Visible Spectrometer (UVVS) was designed to measure the composition and structure of Mercury’s exosphere—the extremely low-density atmosphere—and study its neutral gas emissions. It also searched for and measured 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 had 25-kilometer altitude resolution at the planet’s limb.
Perched atop the ultraviolet spectrometer, the Visible and Infrared Spectrograph (VIRS) measured 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 was 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: Seven years to reach Mercury orbit and over four years of scientific investigations
Other key dates:
- Mercury orbit insertion: March 17, 2011
- First one-year extended mission began on March 18, 2012
- Spacecraft impacted the surface of Mercury on April 30, 2015
Other organizations involved:
- Johns Hopkins University Applied Physics Laboratory (JHU/APL)
- Carnegie Institution for Science