02 August 2004
NASA Set to Launch Orbiter to Mercury
MESSENGER to investigate the most mysterious terrestrial planet
By Cheryl Pellerin
Washington File Staff Writer
Washington -- Bad weather forced NASA to cancel the scheduled August 2 launch of MESSENGER, the first mission to Mercury in 30 years. The space agency's window to begin the mission extends to August 14.
MESSENGER -- a name drawn from a description of its scientific goals, MErcury Surface, Space ENvironment, GEochemistry, and Ranging -- will be an exploration by spacecraft of Mercury, the least explored of the terrestrial, or rocky, planets. Earth, Mars and Venus are also terrestrial planets.
Named for the Roman god of commerce, travel and thievery, Mercury has the shortest year and, as the closest planet to the sun, is exposed to more solar radiation than any planet. It is the smallest and densest terrestrial planet, and its surface may be one of the oldest in the solar system, according to NASA background material on the mission. At its hottest, about 450 degrees Celsius, the surface temperature would melt lead. At night, its --212 Celsius temperatures could turn oxygen from gas to liquid. A very thin layer of gas called an exosphere surrounds the plant.
"Our missions to Mars and Venus have produced exciting data and new theories about the processes that formed the inner planets," says Orlando Figueroa, director of the Solar System Exploration Division at NASA Headquarters, Washington. "Yet Mercury still stands out as a planet with a fascinating story to tell. MESSENGER should complete the detailed exploration of the inner solar system, our planetary backyard, and help us to understand the forces that shaped planets like our own."
MESSENGER is designed to find out about Mercury's geologic history, the structure and state of its massive iron core, the nature of its magnetic field, and the unusual-looking materials (possibly water ice) at its poles. The mission will also examine which molecules in its exosphere are important, and why Mercury is so dense.
When weather conditions allow during this 13-day window, the spacecraft will launch aboard a Boeing Delta II rocket from Cape Canaveral Air Force Station, Florida. MESSENGER will travel more than 6.5 years before it starts to orbit Mercury in 2011.
After launch, MESSENGER will match Mercury's orbit by flying once past Earth, twice past Venus, and three times past Mercury, each time using the planet's gravity to adjust its path. The Mercury flybys will provide pictures and measurements of the planet's uninvestigated side that are critical for the study, which will last four Mercury years, or one Earth year.
Most of what is known about Mercury comes from three flyby visits by the Mariner 10 spacecraft in 1974 and 1975. Mariner 10 was launched in 1973, then flew past Venus in February 1974 and got the first close-up images of that planet's smooth upper layers of clouds. Mariner then headed for Mercury in an orbit around the Sun that took the craft past the same side of the planet three times while Mercury was at its farthest point from the Sun.
The MESSENGER mission will bring NASA knowledge about the processes that also produced Earth, Venus and Mars. Learning how Mercury turned out to be the densest planet will reveal much about planetary formation. Discovering why Mercury still has a magnetic field -- when Mars lost an earlier field and Venus has no field and no record of a past field -- will help explain magnetic-field generation on Earth.
Mercury must be explored from space because the planet is too far from Earth and too close to the Sun to make good astronomical observations from the ground. Mercury is only visible from Earth just after sunset or before sunrise, and astronomers have trouble seeing it with telescopes through the haze of Earth's atmosphere. Even Hubble Space Telescope operators will not risk a viewing Mercury because the Sun might damage the telescope.
After MESSENGER, the next mission planned to Mercury is the 4.2-year BepiColumbo project of the European Space Agency and Japan's Institute of Space and Astronautical Science. Two separate planetary orbiters will launch in 2012 to study the planet, the origin of its magnetic field and its magnetosphere, its exosphere and other questions.
The mission is named for Professor Giuseppe (Bepi) Colombo (1920-1984), a mathematician and engineer from the University of Padua, Italy, who was first to see that an unsuspected resonance was responsible for Mercury's rotation on its axis three times for every two revolutions around the Sun. He also suggested to NASA how to use a gravity-assist swing-by of Venus to put the Mariner 10 spacecraft in a solar orbit that would allow it to fly by Mercury three times in 1974-75.
MESSENGER and BepiColombo scientists have held several discussions and expect that there will be opportunities for cooperation involving data exchange, targeting of observations during the missions, sharing of ground resources and collaborative scientific analysis of joint datasets.
After traveling 7.9 billion kilometers from launch until beginning orbit around Mercury in March 2011 and another 39.9 million kilometers around Mercury, the spacecraft will eventually crash into Mercury's surface several years after the mission officially ends and spacecraft operators lose the ability to maintain MESSENGER's minimum altitude.
Further information is available at:
http://messenger.jhuapl.edu/
http://sci.esa.int/science-e/www/area/index.cfm?fareaid=30
(The Washington File is a product of the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)
This page printed from: http://usinfo.state.gov/xarchives/display.html?p=washfile-english&y=2004&m=August&x=20040802161021lcnirellep0.1903955&t=livefeeds/wf-latest.html
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