After failure of the second fourth-stage burn, the probe assembly re-entered the Earth's atmosphere, breaking up over a 320 km (200 mi) long portion of the Pacific Ocean, Chile, and Bolivia.

Mars 96, the only Soviet/Russian lunar or planetary probe in the 1990s, was an ambitious mission to investigate the evolution of the Martian atmosphere, its surface, and its interior.

The entire spacecraft comprised an orbiter, two small autonomous stations, and two independent penetrators.

The mission included a large complement of instruments provided by France, Germany, other European countries and the United States.

The scientific goal of the mission was to study the evolutionary history of the planet's surface, atmosphere, and inner structure.

Studies of the atmosphere were to include the climate, abundance of certain elements, ions, and chemicals such as water, carbon dioxide, ozone, and others, general global monitoring, pressure variations over time, and characterization of aerosols.

Each Surface Station also carried a compact disc which contained science fiction stories, sound, and art that have inspired Mars exploration.

This is a four-stage rocket in a configuration which had flown only twice before, both times to launch Phobos spacecraft towards Mars in 1988.

The fourth stage, called the Blok D-2, would then ignite to place it and the spacecraft into a parking orbit around the Earth.

After the fourth stage shut-down, the spacecraft was to separate, deploy its antennae, and use its propulsion unit to complete the burn.

Four to five (preferably five) days before arrival, the spacecraft was to release both Surface Stations to land at two separate sites in the northern hemisphere.

At the appropriate moment, with the main engine of the propulsion unit facing the direction of flight, the spacecraft would make a burn to slow down and enter Mars orbit.

The window to land the Penetrators would be seven to twenty-eight days after Mars orbit insertion.

The primary science phase of the orbiter could not begin until after both Penetrators were released and the propulsion unit was jettisoned.

The propulsion unit would get in the way of the deployment of the LWR instrument and ARGUS platform and has to be jettisoned before the primary science phase can begin.

Unfortunately, without the fourth stage burn, the spacecraft lowered its perigee back into the Earth's atmosphere causing reentry.

The failure occurred at the second ignition of the Proton Blok D-2 upper stage, while the spacecraft was out of range of Russian ground stations.

[4] It was originally believed that the Mars 96 assembly burnt up in the atmosphere and the debris fell into the Pacific Ocean.

[3] However, in March 1997, the United States Space Command admitted that it had miscalculated the satellite's path of re-entry.

"We were aware of a number of eyewitness accounts of the re-entry event via the media several weeks after the re-entry occurred," wrote Major Stephen Boylan, Chief of the Media Division at the United States Space Command in Colorado Springs, Colorado.

Despite this and the fact that the four assemblies carried a combined total of 200 grams of plutonium-238 for fuel, the Russians have not mounted any recovery effort to date.