Mariner 9, which in November will become the first man-made object to orbit another planet, has travelled more than 120 million miles since it was launched toward Mars 74 days ago.
Meanwhile Mars has moved in its orbit to a point closer to Earth than it has been in the past 47 years and for the remainder of this century. Today, Mars and Earth are 34.9 million miles apart. In 1924, the two planets were separated by 34.66 million miles. When Earth and Mars are on opposite sides of the sun, the distance can be as great as 250 million miles.
Close approached of the two planets occur every 25 months, but the miss distance varies greatly. In 1969, Earth and Mars were 45 million miles apart.
Because Mars is farther from the sun than Earth, the entire lighted side of the planet faces the dark side of Earth. Each night, the planet's path forms a low arc across the southern horizon from east to west and is visible for about 10 hours.
The biennial event affords astronomers and physicists an excellent opportunity to study Mars with telescopes and other instruments from Earth. This week, a NASA jet aircraft in Hawaii is carrying scientists and their instruments each night to altitudes above 99 per cent of Earth's atmospheric water vapor for a clearer look at Mars.
When Mariner 9 reaches Mars on November 13, the planet will be 75 million miles from Earth. The spacecraft will orbit the planet, mapping the surface with TV cameras and other instruments for about ayear. It's highest resolution pictures will be taken from less than 800 miles altitude.
Engineers at the Jet Propulsion Laboratory in Pasadna, which manages the Mariner Project for NASA, report that Mariner 9, now nearly 16 million miles from Earth, is operating normally.
The Mariner 9 spacecraft reached its 86th day of travel in its 167 day journey to Mars today and is 18,299,000 miles from Earth.
Since launch on May 30, the spacecraft has traveled 131,305,000 miles on a curving path around the Sun headed for Mars intercept on November 13, 1971. The current velocity, relative to Earth, is 16,756 MPH.
A small course correction is planned for late October to prepare the spacecraft for a precise injection into orbit at Mars on November 13.
Basic objective of the mission is 90 days in orbit and mapping of about 70% of the Martian surface with two television cameras. Other experiments will record atmospheric and surface data.>
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