Messenger spacecraft has been orbiting Mercury for 3 months. The instrument payload is providing a wealth of information.
“MESSENGER has passed a number of milestones just this week,” offers MESSENGER principal investigator Sean Solomon of the Carnegie Institution of Washington. “We completed our first perihelion passage from orbit on Sunday, our first Mercury year in orbit on Monday, our first superior solar conjunction from orbit on Tuesday, and our first orbit-correction maneuver on Wednesday. Those milestones provide important context to the continuing feast of new observations that MESSENGER has been sending home on nearly a daily basis.”
Some excerpts from the June 16 press conference are at the end of the original diary written May 15.
Original Diary
On March 17, 2011, at 9:10 p.m. EDT, engineers in the MESSENGER Mission Operations Center at Johns Hopkins University received signals confirming successful insertion of the MESSENGER probe into orbit around the planet Mercury. It is the first spacecraft to orbit that planet.
On May 6th, MESSENGER started its 100th orbit around Mercury. Since its insertion into orbit about the innermost planet on March 17, the spacecraft has executed nearly 2 million commands.
The data gathered so far include more than 70 million magnetic field measurements, 300,000 visible and infrared spectra of the surface, 16,000 images, and 12,000 X-ray and 9,000 gamma-ray spectra probing the elemental composition of Mercury’s uppermost crust.
“As the primary orbital phase of the MESSENGER mission unfolds, we are building up the first comprehensive view of the innermost planet,” states MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “The surface is unraveling before our eyes in great detail, and the planet’s topography and gravity and magnetic fields are being steadily filled in. As the Sun becomes increasingly active, Mercury’s extraordinarily dynamic exosphere and magnetosphere continue to display novel phenomena.”
The spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. More mission details and images ⤵
How Do You Get to Mercury?
This animation illustrates how MESSENGER followed a path through the inner solar system, including one flyby of Earth, two flybys of Venus, and three flybys of Mercury. The fullscreen button makes it easier to watch. Several repeat viewings helps, too. Keep your eye on the spacecraft.
Each time the craft made a flyby of a planet, its speed and direction were altered by what is known as the slingshot effect. The speed of Messenger changed due to the gravitational pull as it was passed by the planet. With the new speed and direction, the craft was set on a new orbit around the Sun that intersected the orbit of the next planet. As it fell inward toward the Sun in these stages, it gradually settled into a final orbit that intersected the orbit of Mercury. On March 17, the on-board engine was able to slow the craft into a final eccentric orbit of Mercury. It will remain in this configuration for the coming year gathering 75,000 images and a wealth of data.
Why Go To Mercury?
The planet has been visited before. We already have images of it. It's too hot and dangerous for habitation. The first craft to visit was Mariner 10 in 1974-1975.
It was also the first spacecraft to reach one planet by using the gravity of another planet (in this case, Venus) to alter its speed and trajectory. This has become an extremely important technique.
During three flybys of Mercury, Mariner 10 photographed half the planet's moonlike surface and transmitted data indicating a surprising magnetic field, a metallic core comprising about 80 percent of the planet's mass, and temperatures ranging from 187°C on the dayside to -183°C on the nightside.
Six Important Questions
It is hoped the Messenger mission can
help answer several questions.
1. Why is it so dense? A metal-rich core occupies at least 60% of the planet's mass, a figure twice as great as for Earth.
2. What is its geologic history? The suite of 7 instruments will map the surface history of the entire surface in fine detail adding to the 45% done by Mariner 10.
3. What is the nature of the magnetic field? Earth and Mercury have global magnetic fields. Venus and Mars do not. Why the differences?
4. What is the nature of its core? Measurements of Mercury's gravity field and observations by the laser altimeter will determine the size of Mercury's core and verify that the outer core is molten.
5. What are the highly reflective materials at the poles? Radar reflections of the interior of some permanently shadowed craters suggest there may be ice in them.
6. What volatile gases are important in its exosphere? Seven elements are known to exist in Mercury's very thin exosphere: hydrogen, helium, oxygen, sodium, potassium, calcium, and magnesium.
What Instruments Are Being Used?
The process of selecting the scientific instrumentation for a mission is typically a balance between answering as many science questions as possible and fitting within the available mission resources for mass, power, mechanical accommodation, schedule, and cost. In the case of MESSENGER, the mass and mechanical accommodation issues were very significant constraints. Payload mass was limited to 50 kilograms (110 pounds) because of the propellant mass needed for orbit insertion. The instrument mechanical accommodation was difficult because of the unique thermal constraints faced during the mission; instruments had to be mounted where Mercury would be in view but the Sun would not, and they had to be maintained within an acceptable temperature range in a very harsh environment.
Gallery Highlights
The Gallery contains a wide variety of
images, photos, animations, and movies about all aspects of the mission. New materials are added regularly as the mission progresses.
Four Easy Steps to Explore Mercury in Google Earth
Watch Movies compiled by the Messenger team
View Animations of Highlights of Messenger's Flight
Photo Album of Featured Releases with recent examples below.
End of Original Diary
Update based on June 16 press conference
A Surface Revealed in Unprecedented Detail
The Mercury Dual Imaging System (MDIS) is getting global monochrome and stereo base maps with an average resolution of 250 meters per pixel and a color base map at an average of 1.2 kilometer per pixel. These base maps are providing the first global look at the planet under optimal viewing conditions.
Images reveal broad expanses of smooth plains near Mercury’s north pole. The plains are likely among the largest expanses of volcanic deposits on Mercury and confirm that volcanism shaped much of Mercury’s crust and continued through much of Mercury’s history.
MDIS observations at up to 10 meters per pixel reveal light patchy deposits to be clusters of rimless, irregular pits varying in size from hundreds of meters to several kilometers 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). “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.”
Mercury’s Surface Composition
The X-Ray Spectrometer (XRS) revealed the magnesium/silicon, aluminum/silicon, and calcium/silicon ratios averaged over large areas of the planet’s surface show that Mercury’s surface is not dominated by feldspar-rich rocks. XRS observations have also revealed substantial amounts of sulfur at Mercury’s surface.
The Gamma-Ray and Neutron Spectrometer has detected the decay of radioactive isotopes of potassium and thorium.
“The abundance of potassium rules out some prior theories for Mercury’s composition and origin,” says Larry Nittler, a staff scientist at the Carnegie Institution of Washington. “Moreover, the inferred ratio of potassium to thorium is similar to that of other terrestrial planets, suggesting that Mercury is not highly depleted in volatiles, contrary to some prior ideas about its origin.”
Mapping of Mercury’s Topography and Magnetic Field
The Mercury Laser Altimeter has been systematically mapping Mercury’s northern hemisphere. More than two million observations are revealing the shape and profiles of geological high detail. The north polar region of Mercury, for instance, is a broad area of low elevations.
Tests for polar ice deposits preserved on the cold, permanently shadowed floors of high-latitude impact craters are being done. To date, the depths of craters hosting polar deposits show they are in permanent shadow.
Mercury has an asymmetrical magnetic field. The geometry of magnetic field lines is different in Mercury’s north and south polar regions. The magnetic “polar cap” is much larger near the south pole and exposes that region to more charged particles heated and accelerated by solar wind–magnetosphere interactions.
The impact of those charged particles onto Mercury’s surface contributes both to the generation of the planet’s tenuous atmosphere and to the “space weathering” of surface materials.
Energetic Particle Events at Mercury
Mariner 10, during the first of its three flybys of Mercury in 1974, showed bursts of energetic particles in Mercury’s Earth-like magnetosphere. With MESSENGER now in near-polar orbit about Mercury, energetic events are being seen almost like clockwork, says MESSENGER Project Scientist Ralph McNutt, of APL.
“While varying in strength and distribution, bursts of energetic electrons — with energies from 10 kiloelectron volts (keV) to more than 200 keV — have been seen in most orbits since orbit insertion,” McNutt says. “The Energetic Particle Spectrometer has shown these events to be electrons rather than energetic ions, and to occur at moderate latitudes. The latitudinal location is entirely consistent with the events seen by Mariner 10.” The mechanisms of the acceleration of energetic electrons will be the subject of study over the coming months.
“One mystery has been answered, only to be replaced by another, but that is how science works,” McNutt says. “In the coming months as MESSENGER’s orbit swings around the planet, we will be able to observe the overall geometry of these events, providing yet more clues to their production and interaction with the planet.”
“We are assembling a global overview of the nature and workings of Mercury for the first time,” adds Solomon, “and many of our earlier ideas are being cast aside as new observations lead to new insights. Our primary mission has another three more Mercury years to run, and we can expect further surprises as our solar system’s innermost planet reveals its long-held secrets.”
If you are interested,
further details about these findings and others are provided by 4 presenters at the news conference.