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MESSENGER Spacecraft Will Be First to Orbit Planet Mercury

   Jessica Berman | Washington  March 17, 2011
   An  artist's  concept  shows  the MESSENGER spacecraft in orbit around
   Mercury

Photo: NASA

   An  artist's  concept  shows  the MESSENGER spacecraft in orbit around
   Mercury

   The U.S. space probe MESSENGER is poised to enter orbit around Mercury
   early  Friday,  Universal time, capping a nearly seven-year journey to
   the  solar systemâs innermost planet.  Scientists with the U.S. space
   agency,  NASA,  hope  the  orbiting  probe  will  greatly  expand  our
   knowledge  of Mercury, and provide news clues to the origins of Earth,
   as well. Â
   MESSENGERâs  orbital  rendezvous  with Mercury is the final stage of a
   breathtaking  journey that has taken it billions of kilometers through
   the  inner  solar system, including half dozen photographic fly-bys of
   Earth, Venus and Mercury itself for gravitational assists.
   "Those  were  all hor dâoeuvres for the banquet weâre about to enjoy,"
   said Sean Solomon of the Carnegie Institution of Washington D.C. , who
   is  the  MESSENGER missionâs principal investigator.  "Once MESSENGER
   is  in orbit around Mercury, it will be the first spacecraft to do so,
   we  will  have the first global observatory at the innermost planet of
   the solar system."
   The  last  close-up data on Mercury was collected by NASAâs Mariner 10
   in a fly-by mission in the mid-1970s.
   Fifteen  minutes  before  insertion into Mercury orbit, MESSENGER will
   begin  firing  its  main thruster engine, burning off one-third of its
   propellant.    That burn will slow the spacecraft down by 862 meters
   per second for the orbit insertion maneuver.
   Scientists  say  it  will  be  an hour before they are able to confirm
   whether MESSENGER is securely in orbit around Mercury.
   MESSENGER  will  circle  the  tiny planet, roughly the size of Earthâs
   Moon,  every  12 hours, traveling over the planetâs polar regions just
   200 kilometers above the rocky surface.
   MESSENGER  will  be a mere 46 million kilometers from the Sun.  Built
   to  withstand  the  blistering  heat, the spacecraft is carrying seven
   scientific  instruments  that  mission investigator Solomon hopes will
   help  answer  some  intriguing  questions  about  the  solar  systemâs
   inner-most planet.
   For  example,  Solomon  says  there appears to be ice in the floors of
   impact craters at Mercuryâs poles, which are in permanent shadow.
   "Thatâs  pretty  astonishing  because  at  the equator of Mercury, the
   temperature  varies  between day and night by 600 degrees centigrade,"
   he said. "So, the notion that there might be permanent repositories of
   water ice at the poles of Mercury seems to fly in the face of the fact
   that  this is a planet closest to the Sun and has extraordinarily high
   daytime temperatures."
   Solomon  says  MESSENGER  wonât  begin returning any images of Mercury
   until April.
   MESSENGERâs  orbital  mission  is  scheduled  to  last one year.  But
   Solomon   is   hopeful  there  will  be  enough  fuel  to  extend  its
   observations of Mercury into a second year.

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