U.S. embassy and consulate websites or www.state.gov.
We’ve gone social!
Follow us on our facebook pages and join the conversation.
01 February 2008
Flyby Prepares NASA Vessel To Orbit Mercury in 2011
Spacecraft returns images of cliffs, impact craters, spider-like feature
Washington -- NASA’s Messenger spacecraft flew past Mercury January 14 on the first of three passes that will prepare the instrumented craft to orbit the closest planet to the sun for one year beginning March 18, 2011.
After a journey of more than 3.2 billion kilometers, Messenger’s cameras and other sophisticated instruments collected more than 1,200 images, close-up measurements and other observations. Instruments also provided a topographic profile of craters and other geological features on Mercury’s night side.
The images showed that Mercury has huge cliffs with structures snaking hundreds of kilometers across the planet's face. The cliffs preserve a record of patterns of fault activity from early in the planet's history.
As Messenger’s science payload of seven instruments gathered data from the planet, “We were continually surprised,” principal investigator Sean Solomon of the Carnegie Institution of Washington said during a January 30 NASA briefing. “It was not what we expected, it was not the moon, it’s a very dynamic place that’s changing very rapidly. Features we saw with the Messenger camera haven’t been seen on any other planet.”
The spacecraft also returned images of a feature scientists call "the spider" that lies in the middle of the Caloris Basin -- one of the solar system’s largest impact craters measuring about 1,545 kilometers from rim to rim -- and consists of more than 100 narrow, flat-floored troughs radiating from a complex central region.
SCIENTIFIC QUESTIONS
Only one other spacecraft has visited Mercury -- NASA’s Mariner 10 examined less than half the planet’s surface during three flybys in 1974 and 1975.
Mercury is one of four terrestrial (rocky, Earth-like) planets that are the solar system’s innermost planets. The other three terrestrial planets --Venus, Earth and Mars -- have significant atmospheres. Mercury’s atmosphere is very thin, and it is the only inner planet other than Earth that has a global magnetic field.
The other four planets -- Jupiter, Saturn, Uranus and Neptune -- are called Jovian (Jupiter-like) planets because they are all gigantic compared with Earth and, like Jupiter, are more gaseous than solid. They also are called gas giants, although some or all might have small solid cores.
The name Messenger is derived from “Mercury surface, space environment, geochemistry and ranging.” Its mission -- to answer scientific questions about the planet’s density, geologic history, magnetic field, core structure and unusual polar materials -- began with an early morning launch in August 2004 from Cape Canaveral Air Force Station in Florida.
On its journey, Messenger looped through the inner solar system in a series of close flybys of Earth and Venus to change its trajectory and get a gravity boost for the rest of the trip.
UNDERSTANDING MERCURY
Understanding Mercury and the forces that shaped the planet is fundamental to understanding the terrestrial planets and their evolution. One feature that Mercury and Earth, alone among the terrestrial planets, have in common is a magnetic field and a resulting magnetosphere.
Earth’s magnetosphere, controlled by the magnetic field and extending far into space, is full of streaming particles, electromagnetic radiation and constantly changing electric and magnetic fields.
On Earth, Solomon said, “We owe our lives to this magnetosphere. It is a protective bubble around our planet that keeps cosmic rays and energetic particles from the sun from impacting the surface and doing genetic damage to anything living here on Earth. But we know that the Earth’s magnetic field changes and we know that space weather modifies our magnetosphere. The only other example in our solar system of an Earth-like magnetosphere and magnetic field is tiny Mercury.”
Magnetic fields and magnetospheres are generated by electrical dynamos in the form of a liquid metallic outer core deep in the planet's center. A similar mechanism is expected for Mercury's magnetic field but the nature of its field and time scales for internal changes are unknown. The next two flybys (October 2008 and September 2009) and the yearlong orbital phase will shed more light on these processes.
The spacecraft's suite of instruments also has provided insight into the mineral makeup of the surface terrain and detected ultraviolet emissions from sodium, calcium and hydrogen in Mercury's exosphere -- the region high up in the planet’s atmosphere where atoms and molecules escape into space.
Of the magnetosphere, the atmosphere and the surface, Solomon said, “all of those aspects of the planet Mercury are closely interlinked. It’s a very dynamic planet with an awful lot going on.”
More information about Messenger and Mercury is available Johns Hopkins University Applied Physics Laboratory Web site.
