CEPS Mercury Research

Understanding Mercury

Mercury is the smallest and least explored terrestrial planet. In 1974 and 1975, Mariner 10 captured images of one hemisphere of Mercury in three encounters. Thus there was an entire hemisphere of Mercury that was never seen by a spacecraft until MESSENGER spacecraft arrived for its first flyby in early 2008. Orbiting the Sun in only 88 days, Mercury was named for the swift messenger god of Roman mythology. With a rotation period of 59 days, the planet rotates exactly three times while it orbits the Sun twice. Mercury is unique among the planets in many ways. A remarkable characteristic of Mercury is its high average density. Even though Mercury is only one-third the size of the Earth and only a little larger than the Moon, its average density (5.4 g/cm3) is just slightly less than Earth's. This high density suggests that as much as 65% of the interior of the planet is made up of a metal-rich core. This is greater than any other terrestrial planet, about two times greater than Earth.

At first glance, the surface of Mercury looks similar to the Moon. Much of the imaged portion of the surface is made up of heavily cratered terrain. One large impact basin, the Caloris basin, is 1,300 km across and like impact basins on the Moon it has been flooded by volcanic material. Plains units are also common on the surface, but little is known about the composition of the plains material. Intercrater plains occur in and around ancient cratered terrain and smooth plains are found predominately surrounding the Caloris basin. The plains are thought to be either volcanic or impact in origin. Color data obtained from Mariner 10 images of Mercury reflect different chemical and physical properties of the surface materials. In some areas the colors define surface units with the characteristics of volcanic material that has flowed into and around impact craters. This suggests that at least some of the mercurian smooth plains are the product of volcanism.

One of the most extraordinary characteristics of the surface of Mercury imaged by Mariner 10 is the presence of hundreds of landforms that indicate crustal deformation. Evidence of deformation is reflected by landforms described as lobate scarps, high-relief ridges, and wrinkle ridges. Lobate scarps occur throughout the broad intercrater plains and smooth plains materials, and are interpreted to be the surface expression of thrust faults. Less common high-relief ridges, that often transition into lobate scarps, may be the results of high-angle reverse faulting. Wrinkle ridges, interpreted to be a combination of folding and thrust faulting, deform interior plains and the surrounding smooth plains. Narrow linear troughs in the interior plains are interpreted to be fractures or graben. Extensional features are largely absent elsewhere on the planet. Researchers in CEPS are actively studying tectonic features on Mercury.

Mercury Research in CEPS

Critical to the study of the tectonic features and other aspects of geologic evolution of Mercury is topography. New topographic data for Mercury is being generated using Mariner 10 stereo image coverage. Using digital stereo techniques, digital terrain models (DEM) are being derived from approximately 1700 stereo pairs. Techniques are being developed to create regional topographic maps by mosaicing many overlapping individual DEMs. Regional-scale DEMs reveal long wavelength topographic trends such as broad, shallow depressions that may reflect buried ancient impact basins.

Even with the application of modern processing techniques, there is only so much information that can be obtained from the Mariner 10 images and data. MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) launched in August, 2004, promises to provide new and exciting data. After two encounters with Venus, MESSENGER made the first of two encounters with Mercury in 2008, revealing views of the unseen hemisphere of Mercury. Then in 2011, MESSENGER will enter Mercury orbit and begin a mapping phase that will extend over four Mercury years. MESSENGER will obtain global image cover of Mercury at resolutions better than highest resolution images returned by Mariner 10. MESSENGER will determine the elemental and mineral makeup of the crustal material exposed at the surface. Global topography will be obtained by a laser altimeter and from global stereo coverage. Tom Watters at the Center for Earth and Planetary Studies is a member of MESSENGER’s Science Team and is involved in the mission's outreach efforts.

Learn more at the MESSENGER Web site.

List of Mercury Research Projects