Rover spectrometer connects with Yogi.

After a 5-day delay, the roving field geologist Sojourner has finally obtained a spectrum of Yogi, a meter-wide Martian rock. Sojourner and its mother ship, Mars Pathfinder, landed on Mars July 4; the rover drove onto Martian soil 2 days later (SN: 7/12/97, p. 20).

Yogi has a higher concentration of magnesium than its rough-hewn neighbor Barnacle Bill, which Sojourner examined last week. The magnesium content suggests that Yogi has undergone far fewer cycles of heating and cooling than Barnacle Bill, says James P. Greenwood of the University of Tennessee, Knoxville.

At a press briefing at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., Greenwood noted that the composition of Yogi resembles that of basalts on Earth. Such rocks line Earth's oceans.

Sojourner's spectrometer also found that three soil samples from different parts of the landing site have similar compositions and resemble soil sampled by the two Viking landers in 1976. This suggests that global winds on Mars have distributed the surface soil evenly, says spectrometer investigator Rudolph Rieder of the Max Planck Institute for Chemistry in Mainz, Germany.

Recording and transmitting Yogi's spectrum has proven something of a bear. On July 9, the rover overshot its target, and its front wheels climbed onto the rock before halting. Then, on July 10, 11, and 13, Pathfinder's computer reset in the middle of receiving commands, abruptly terminating the downlink with Earth.

Observations with the Hubble Space Telescope reveal that the amount of dust in the atmosphere around the landing site changed dramatically in less than 2 weeks. Images taken June 27 show a cloudy, dustfree environment with a dust storm confined to a canyon 1,000 kilometers to the south. New pictures, taken July 9 through 11, show that the storm abated and that some of the dust may have migrated to the Pathfinder area. This dovetails with Pathfinder's observations that its surroundings are dusty, similar to conditions encountered by the Viking craft.

A color panorama is expected to be available on the Internet shortly, and a high-resolution image taken with 12 color filters is scheduled to be completed within 2 weeks.