Janell's

//My Jobs: I will be taking care of Voyage of this mission//

//**Voyage:**// A description of the voyage and arrival. Details must include:  Total distance traveled  Time the voyage will take (using speed formula)  Space objects encountered on the way

[] The space agency has sent orbiters to five planets — Mercury, Venus, [|Mars], Jupiter and Saturn — but it will most likely be another decade or two before a spacecraft enters orbit around [|Uranus] or Neptune. (A study on future planetary missions put a Uranus orbiter on the wish list.) NASA does have a spacecraft, New Horizons, that will zoom past [|Pluto] in 2015, but, alas, [|Pluto] is no longer counted as a planet. Mercury has been seen close up, albeit briefly, in half a dozen flybys by NASA probes: three by the Mariner 10 in the 1970s and three by the Messenger in the last three years. But now that the Messenger has pulled into an orbit of Mercury, planetary scientists will be able to get their first long look at the smallest of the eight planets. The day side of Mercury can broil at 800 degrees Fahrenheit; the night side drops to minus 300 degrees. Particularly intriguing, scientists say, are the shadows in craters near Mercury’s poles. There, the Sun never shines, and in the frigidity, some scientists expect that the Messenger will find frozen water. The Messenger arrived at its final destination after a 6.5-year loop the loop through the inner solar system. A 15-minute engine burn slowed the spacecraft sufficiently for it to be captured by Mercury’s gravity. By design, the Messenger loops around the planet on a highly elliptical orbit, dipping down as close to 160 miles to Mercury’s surface and rising as far up as 9,300 miles. Since its arrival, engineers have been checking out the orbiter’s systems and gear. Finding everything in working order, they turned on the instruments, including the camera. The first picture, showing a bright crater called Debussy, was taken early Tuesday. By the end of Thursday, 1,500 photographs will have been taken. More than 75,000 are planned over the next year. The spacecraft’s seven instruments have also begun measuring emissions of neutrons, X-rays and gamma rays, which will allow scientists to deduce many of the minerals of the surface. The extended observation will help them understand how Mercury, which is half the mass of Mars, still has a magnetic field — presumably generated by a molten outer core — while Mars does not.

[]

Messenger spent nearly seven years in transit and traveled about five billion miles. It will spend one Earth-year studying the mineralogy of Mercury, mapping its surface and magnetic and gravitational fields, and trying to identify the substance covering the planet’s north pole. All the while, a ceramic-fabric sunshade will be protecting Messenger from the ferocious heat of the nearby Sun and the solar reflection from Mercury. The craft will eventually plummet into the planet. It’s hard to know just what we will learn about Mercury. Like all scientific missions and experiments, this is a journey to a more refined sense of what we don’t yet know.

Mariner 10's [|ultraviolet] observations have established an upper bound on the exospheric surface density at about 105 particles per cubic centimeter. This corresponds to a surface pressure of less than 10−14 [|bar] (1 [|nPa]).[|[][|19][|]] The temperature of the Hermian exosphere depends on species as well as geographical location. For exospheric atomic hydrogen, the temperature appears to be about 420 K, a value obtained by both Mariner 10 and MESSENGER.[|[][|10][|]] The temperature for sodium is much higher, reaching 750–1500 K on the equator and 1,500–3,500 K at the poles.[|[][|20][|]] Some observations show that Mercury is surrounded by a hot corona of calcium atoms with temperature between 12,000 and 20,000 K.[|[][|15][|]]

[[|edit]] Tail
Because of Mercury's proximity to the Sun, the pressure of Solar light is much stronger than at Earth's location. Solar radiation pushes neutral atoms away from the Sun, creating a comet-like tail behind Mercury.[|[][|21][|]] The main component in the tail is sodium, which has been detected as far as 56,000 km (about 23 RM) from the planet.[|[][|21][|]] This sodium tail expands rapidly to a diameter of about 20,000 km at a distance of 17,500 km.[|[][|22][|]] In 2009 MESSENGER also detected calcium and magnesium in the tail, although these elements were only observed at distances less than 8 RM from the planet.[|[][|21][|]]

[[|edit]] Origin
Mercury's exosphere is constantly escaping into space, implying that some process resupplies its constituents. The main source of hydrogen and helium is likely to be the Solar wind. Other atomic and molecular species are thought to originate from the Hermian crust through three main processes: vaporization of surface material by [|meteoritic impacts]; [|sputtering] by energetic charged particles from the Solar wind; and photo- and electron-induced [|desorption] of [|alkali metal] atoms. Mercury's orbit has a significant [|eccentricity], which causes a strong variation in the Solar light and particle fluxes reaching the planet. [|Solar flares] contribute additional variation. As a result the Hermian exosphere is extremely changeable: its atomic concentrations can fluctuate by orders of magnitude within a few hours.[|[][|23][|]]

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