The Messenger spacecraft achieved orbit around Mercury in March 2011. After 3 months of orbits, an update to the mission was reported by scientists. Link here to the June 16 highlights. The original diary about the mission is here.
On September 29, mission scientists held another press conference to explain their latest findings. Please join me for the details below. ⬇
The Hollows and High Reflectance |
Scientists were quoted in the
June 16 press conference expressing their puzzlement with these high reflectance hollowed out pits.
Among the fascinating features seen in flyby images of Mercury were bright, patchy deposits on some crater floors. Without high-resolution images to obtain a closer look, these features remained only a curiosity. New targeted MDIS observations at up to 10 meters per pixel reveal these patchy deposits to be clusters of rimless, irregular pits varying in size from hundreds of meters to several kilometers. These pits are often surrounded by diffuse halos of higher-reflectance material, and they are found associated with central peaks, peak rings, and rims of craters.
“The etched appearance of these landforms is unlike anything we’ve seen before on Mercury or the Moon,” says Brett Denevi, a staff scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and a member of the MESSENGER imaging team. “We are still debating their origin, but they appear to have a relatively young age and may suggest a more abundant than expected volatile component in Mercury’s crust.”
Follow-up detailed MDIS imaging merged into the following panorama reveals large networks of these hollows. Additional measurements in coming orbits may reveal their origins.
The multi-spectral MDIS has wide- and narrow-angle cameras similar to the CCDs found in digital cameras. It is used to map the surface features in monochrome, color, and stereo. The imager pivots to capture images without having to re-point the spacecraft. It is also able to follow the stars and other optical navigation guides.
The wide-angle camera has a 10.5° x 10.5° field of view. It can observe Mercury through 11 different filters from visible through near-infrared light. Multi-spectral imaging helps investigate rock types that form Mercury’s surface. The narrow-angle camera takes black-and-white images. It has a 1.5° x 1.5° field of view. The high resolution camera sees features as small as 10 meters across.
This patchwork image is a good illustration of the type of coverage given by this versatile camera system. The image below is linked to an interactive surface map of Mercury. Controls allow you to zoom into any region and view it with overlays of different types of measurements.
Plasma Ions in the Magnetosphere |
MESSENGER collected the first global observations of plasma ions in Mercury's magnetosphere. Over 65 days and 120 orbits, the team found that sodium is the most important ion contributed by the planet. Sodium was previously observed from ground observations. It was discovered that charged sodium particles are concentrated near Mercury's polar regions where they are likely liberated by solar wind ion sputtering knocking sodium atoms off Mercury's surface. The process is comparable to how auroras are generated in the Earth atmosphere near polar regions.
Sensors detected helium ions throughout Mercury's magnetosphere. Helium was delivered from the Sun by the solar wind, implanted on the surface of Mercury, and then fanned out in all directions. Mercury's weak magnetosphere provides the planet very little protection from the solar wind being so close to the Sun.
The image below is linked to a video showing a pass of Messenger through the region sensing these ions. If you have a slow connection, this video will take a long time to load.
Gamma Rays, Mercury's Surface and History |
MESSENGER's
Gamma-Ray Spectrometer (GRS) indicates cosmic rays interact with the surface of Mercury to a depth of tens of centimeters, where they produce high-energy neutrons. The neutrons further interact with surface material emitting gamma rays. Naturally occurring radioactive elements such as potassium (K), thorium (Th), and uranium (U) also emit gamma rays. The
chemical composition of the surface is determined by detection of these gamma rays and neutrons by GRS. Findings suggest Mercury was not formed from an impact.
The abundances of potassium, thorium, and uranium on the surface of Mercury measured by the MESSENGER Gamma-Ray Spectrometer rule out the giant impact, vaporization, and refractory condensation models. Formation from primitive material, similar to some forms of chondritic meteorites, is consistent with the GRS measurements.
The spacecraft is in a very eccentric 12 hour orbit. Orbit correction maneuvers modify it at certain times. It will continue to orbit for the next 6 months of the mission gathering specific targeted observation data. Details can be
found here.
MESSENGER's 12-month orbital mission phase covers two Mercury solar days; one Mercury solar day, from sunrise to sunrise, is equal to 176 Earth days. The first solar day is focused on obtaining global map products from the different instruments, and the second focuses on targeted science investigations.
As an educator myself, I would be remiss if I didn't promote the
Education and Public Outreach pages which are part of the MESSENGER Mission. As with so many of the NASA missions, there are teams of dedicated people who work hard to provide resources for students, teachers, and the general public. If you are an educator, you will find a lot of material here. There are tours, interactives, animations, podcasts, Q&A, and much more.
Future updates to the MESSENGER mission will be coming in the months ahead. Watch for them.