Mars Close Approach
The latest Mars rover, Opportunity, launched July 7th, and its sister rover, Spirit, which was launched on June 10th, have begun challenging trips to act as robotic geologists. The twin launches began journeys leading to an eventual three months of exploration on the martian surface in January. To help scientists determine whether there was ever enough water on Mars to sustain life, the motorized explorers will send back images of sediment and mineral deposits.
A primary reason for this summer flurry of Mars missions is a unique close approach between Earth and Mars. Mars is approaching Earth in what is the closest the planets have been in 73,000 years–a confluence set officially for 5:46 AM, Wednesday, August 27, 2003. Tonight, the Red Planet will be the brightest object in the sky as it reaches its closest Earth encounter, or opposition, at 34,646,418 miles.
|Mars Opposition, Summer 2003. While Mars and Earth will be closest at the end of August, the complex orbital paths required to land on the Red Planet make early summer launches optimal.|
At opposition Mars will be as close as it has been since September 12, 57,537 B.C., or one-third closer than the average opposition. The next approach this close is August 28, 2287 A.D at 34,620,000 miles.
The planet’s bright magnitude should begin August 20 and continue through September 2 but fades rapidly thereafter as Earth pulls ahead of it and the Moon begins to grow full.
Cornell University Professor Steve Squyres, lead principal investigator of the Athena science packages on NASA’s Mars Exploration Rovers, noted one advantage of this orbital closeness is faster communication: "At closest approach, the one-way transmission time is around 11 minutes." [In contrast, Viking in 1976-77 took around 19 minutes for one-way transmission].
Ten times bigger than the highly successful 1997 Sojourner rover, these twin vehicles are equipped to traverse the planet’s surface over a daily distance of about a football field. With 6,000 miles separating the two landing locations on Mars, both surface missions will begin in January, 2004 and continue for three months through April, 2004.
Nozomi, a Japanese (ISAS) Mars probe, has also completed its final Earth swingby operation on June 19 (JST), and is on its way to Mars. Nozomi, which means Hope, passed within 18,000 km of the Earth in a manuever designed to use the planet’s gravity to slingshot the probe toward Mars. Nozomi, launched in July 1998, is Japan’s first attempt to explore Mars. Its mission is to orbit Mars and gather data on the Martian atmosphere and its interaction with solar wind for up to two years.
|Artist conception of Pathfinder’s dramatic airbag landing Credit: NASA.|
The European Space Agency, ESA, launched its own probe June 2nd, called the Mars Express, with a lander, named after the famous voyage, Beagle, that carried Englishman Charles Darwin on his world tour in search of how life evolved on Earth. With a landed mass of less than 30 kg, Beagle 2 represents the most ambitious science payload-to-systems mass ratio ever attempted. Almost a third of the payload will carry out various types of analysis or be used to manipulate and collect samples for study on the surface of Mars. One of its main tasks will be the step-wise heating of martian soil in a kind of oven, to determine the elemental composition of any volatiles including organic compounds.
Each of the quartet of current Mars missions has its own challenges and rewards. Beagle is smaller and will perform some of the first biology detection experiments since the 1976 Vikings first injected microbial nutrients in hopes of seeing evolved gases and byproducts of martian metabolism. Beagle will be less mobile, relying on a mole-like digging tool to burrow for its soil samples just below the dusty top-layers. The Mars Exploration Rovers, Opportunity and Spirit, will have panoramic cameras and much greater mobility to travel beyond where they initially come to rest. Late this year and early next will give focus to the international science effort to explore whether the ‘wetter and warmer’ Mars can be viewed up close.
In looking back on the success of the 1997 Mars rover, Pathfinder project scientist, Dr. Matthew Golombek, of the Jet Propulsion Laboratory, reflected that: "Power for a solar spacecraft must be managed very carefully. Managing the lag in knowledge from one day to the next is also important. Better autonomy placing instruments against rocks and targets and more autonomous roving could help look at more materials on the surface and visit more sites. For deep space missions, all it takes is one mistake for the mission to fail. Every launch has a 5 times out of 100 chance of blowing up. Part of exploration is confronting the unknown and risk can never be removed completely. In cases like Pathfinder taking a little risk can result in an enormous payoff."
JPL, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Additional information about the project is available from JPL and from Cornell University, Ithaca, N.Y.