Mercury Flyby Mercury as Never Seen Before
When Mariner 10 flew past Mercury three times in 1974 and 1975, the probe imaged less than half the planet. In January, 2008, during MESSENGER's first flyby, its cameras returned images of about 20 percent of the planet's surface missed by Mariner 10. On Monday, Oct. 6, 2008, at 4:40 a.m. EDT, MESSENGER successfully completed its second flyby of Mercury, and its cameras captured more than 1,200 high-resolution and color images of the planet - unveiling another 30 percent of Mercury's surface that had never before been seen by spacecraft.

"The MESSENGER team is extremely pleased by the superb performance of the spacecraft and the payload," said MESSENGER principal investigator Sean Solomon of the Carnegie Institution of Washington.  "We are now on the correct trajectory for eventual insertion into orbit around Mercury, and all of our instruments returned data as planned from the side of the planet opposite to the one we viewed during our first flyby. When these data have been digested and compared, we will have a global perspective of Mercury for the first time."

On Tuesday, Oct. 7, at about 1:50 a.m. EDT, MESENGER turned to Earth and began transmitting data gathered during its second Mercury encounter. The spectacular image above -- one of the first to be returned - was snapped by the Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS) instrument, about 90 minutes after MESSENGER's closest approach to Mercury, when the spacecraft was at a distance of about 27,000 kilometers (about 17,000 miles).

The bright crater just south of the center of the image is Kuiper, identified on images from the Mariner 10 mission in the 1970s. For most of the terrain east of Kuiper, toward the edge of the planet, the departing images are the first spacecraft views of that portion of Mercury's surface. A striking characteristic of this newly imaged area is the large pattern of rays that extend from the northern region of Mercury to regions south of Kuiper.

WAC imageThe WAC image at left is one in a sequence of 55: a five-frame mosaic with each frame in the mosaic acquired in all 11 of the WAC filters. This portion of Mercury's surface was previously imaged under different lighting conditions by Mariner 10, but this new MESSENGER image mosaic is the highest-resolution color imaging ever acquired of any portion of Mercury's surface.

Additionally, some of the images in this mosaic overlap with flyby data acquired by the Mercury Atmospheric and Surface Composition Spectrometer and Mercury Laser Altimeter instruments, resulting in the first time that these three instruments have gathered data of the same area of Mercury. The combination of these three datasets will enable unprecedented studies of this region of Mercury's surface.

The image at right WAC image acquired about 89 minutes before the craft's closest approach to Mercury, resembles the optical navigation images taken leading up to the flyby. The resolution of this image is somewhat better than that obtained by the final optical navigation image set, and the surface visible is newly imaged terrain that was not previously seen by either Mariner 10 or during MESSENGER's first flyby.

However, the added resolution is not the main scientific advancement that will be provided by this image. This WAC image is one of 11 viewed through different narrow-band color filters, the set of which will enable detailed color studies of this newly imaged area. In addition, the Narrow Angle Camera (NAC) acquired a high-resolution mosaic of most of this thin crescent view of Mercury at a resolution better than 0.5 kilometers/pixel (0.3 miles/pixel) that will enable the MESSENGER team to explore this newly imaged region of Mercury's surface in more detail.

About 58 minutes before MESSENGER's closest approach to Mercury, the NAC captured a close-up image of a portion of Mercury's surface imaged by spacecraft for the first time
Mercury flyby. See the second image at right. It is one of 44 in a high-resolution NAC mosaic taken of the approaching crescent-shaped Mercury, as seen at lower resolution in the optical navigation images and the approach WAC color image set.

As the MESSENGER team is busy examining this newly obtained view, data from the flyby continue to stream down to Earth, including higher resolution close-up images of this previously unseen terrain. Collectively, these images and measurements made by other MESSENGER instruments will soon provide a broad range of information for understanding the formation and geologic history of the innermost planet.

Additional information and features from this encounter will be available online, so check back frequently to see the latest released images and science results!

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and after flybys of Earth, Venus, and Mercury will start a yearlong study of its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.


NASA returned to Mercury for the first time in almost 33 years on January 14, 2008, when the MESSENGER (MErcury Surface, Space ENvironment, Geochemistry, and Ranging) spacecraft made its first flyby of the Sun's closest neighbor, capturing images of large portions of the planet never before seen.

The probe made its closest approach to Mercury at 200 kilometers (124 miles) above its surface. This encounter provided a critical gravity assist needed to keep the spacecraft on track for its 2011 orbit insertion around Mercury.

"The MESSENGER Science Team is extremely excited about this flyby," said Dr. Sean C. Solomon, MESSENGER principal investigator, from the Carnegie Institution of Washington prior to the flyby. "We are about to enjoy our first close-up view of Mercury in more than three decades, and a successful gravity assist will ensure that MESSENGER remains on the trajectory needed to place it into orbit around the innermost planet for the first time."

During the flyby, the probe's instruments made the first up-close measurements of the planet since Mariner 10's third and final flyby of Mercury on March 16, 1975, and  gathered data essential to planning the MESSENGER mission's orbital phase. MESSENGER's seven scientific instruments began to address the mission goals of:

  • mapping the elemental and mineralogical composition of Mercury's surface;
  • imaging globally the surface at a resolution of hundreds of meters or better;
  • determining the structure of the planet's magnetic field;
  • measuring the planet's gravitational field structure; and
  • characterizing exospheric neutral particles and magnetospheric ions and electrons.
A Close-up of Mercury

The cameras onboard MESSENGER will take more than 1,200 images of Mercury from approach through encounter and departure. "When the Mariner 10 spacecraft did its flybys in the mid-1970s, it saw only one hemisphere - a little less than half the planet," notes Dr. L. M. Prockter, instrument scientist for the Mercury Dual Imaging System, and a scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.  "During this flyby we will begin to image the hemisphere that has never been seen by a spacecraft and at resolutions that are comparable to or better than those acquired by Mariner 10 and in a number of different color filters so that we can start to get an idea of the composition of the surface."

One site of great interest is the Caloris basin, an impact feature about 1,300 kilometers (808 miles) in diameter and one of the largest impact basins in the solar system. "Caloris is huge, about a quarter of the diameter of Mercury, with rings of mountains within it that are up to 3 kilometers high," says Prockter. "Mariner 10 saw a little less than half of it. During this first flyby, we will image the other side of Caloris. These impact basins act like giant natural drills, pulling up material from underneath the surface and spreading it out around the crater. By looking through different color filters, we can start to understand what the composition of the Caloris basin may be and learn something about the subsurface of Mercury."

MESSENGER instruments will provide the first spacecraft measurements of the mineralogical and chemical composition of Mercury's surface. The visible-near infrared and ultraviolet-visible spectrometers will measure surface reflectance spectra that will reveal important mineral species. Gamma-ray, X-ray, and neutron spectrometer measurements will provide insight into elemental composition.

During the flyby, Doppler measurements will provide the first glimpse of Mercury's gravity field structure since Mariner 10. The long-wavelength components of the gravity field will yield key information on the planet's internal structure, particularly the size of Mercury's core.

The encounter provides an opportunity to examine Mercury's environment in ways not possible from orbit because of operational constraints. The flyby will yield low-altitude measurements of Mercury's magnetic field near the planet's equator. These observations will complement measurements that will be obtained during the later orbital phase.

The flyby is an opportunity to get a jump start on mapping the exosphere with ultraviolet observations and documenting the energetic particle and plasma population of Mercury's magnetosphere. In addition, the flyby trajectory enables measurements of the particle and plasma characteristics of Mercury's magnetotail, which will not be possible from Mercury orbit.

MESSENGER is slightly more than halfway through a 4.9-billion mile (7.9-billion kilometer) journey to Mercury orbit that includes more than 15 trips around the Sun. It has already flown past Earth once (August 2, 2005) and Venus twice (October 24, 2006, and June 5, 2007). Three passes of Mercury, in January 2008, October 2008, and September 2009, will use the pull of the planet's gravity to guide MESSENGER progressively closer to Mercury's orbit, so that orbit insertion can be accomplished at the fourth Mercury encounter in March 2011.

"The complexity of this mission, with its numerous flybys and multitude of maneuvers, requires close and constant attention," says MESSENGER project manager P. D. Bedini, of APL. "MESSENGER is being driven by a team of extremely talented and dedicated engineers and scientists who are fully engaged and excited by the discoveries before them."

The MESSENGER project is the seventh in NASA's Discovery Program of low-cost, scientifically focused space missions.  Solomon leads the mission as principal investigator; APL manages the mission for NASA's Science Mission Directorate and designed, built, and operates the MESSENGER spacecraft.  MESSENGER's science instruments were built by APL; NASA Goddard Space Flight Center, Greenbelt, Md.; University of Michigan, Ann Arbor; and the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder; with the support of subcontractors across the United States and Europe.  GenCorp Aerojet, Sacramento, Calif., and Composite Optics Inc., San Diego, Calif., respectively, provided MESSENGER's propulsion system and composite structure.

MESSENGER: A NASA Discovery mission to conduct the first orbital study of the innermost planet
The Johns Hopkins University Applied Physics Laboratory

Notes from the Holocene
Notes from the Holocene

In four thoughtful chapters titled after the Greek classical elements Earth, Water, Air and Fire science writter Dorion Sagan re-examines theories of creation (cosmogony) and philosophies of life in light of recent scientific discoveries.

Using humor, science fiction, and a personal knowledge of sleight-of-hand magic, Sagan investigates some significant posers like:
  • Why do we drink water?
  • Can we save the Earth from global warming?
  • Are human beings central and special?
  • Is it possible that we've arisen by pure chance?
  • Is the Earth an organism?
  • Does God exist?
  • What is the nature of ultimate reality?
In an Afterword, at the back of the book, Sagan briefly recaps his asnwers to twelve such question,  including:

Why does life exist?

I have said that life exists to spread energy in accord with the second law of thermodynamics. The process we call life is unusual but natural, a growing system that cycles matter in a region of energy flow. Global society's focus on energy is a reflection of life's natural energetic purpose.

back out there