SAN FRANCISCO — Initial analysis of Martian soil by the full suite of instruments aboard NASA’s Curiosity rover is not yielding any particular surprises for project scientists so far, who are trying to manage expectations of how quickly the $2.5 billion Mars Science Laboratory (MSL) mission might report a breakthrough in the search for signs of past or present life.

“You have to be careful of what you say and how you say it,” said MSL Chief Scientist John Grotzinger of the California Institute of Technology when he learned about early enthusiasm for Curiosity. The mission’s website recorded more than 500 million hits in just the first month after the spacecraft landed last August.

“The major discovery we’ve made so far is that we landed on an ancient river bed,” added MSL Program Scientist Michael Meyer of NASA Headquarters, in another “let’s be patient” response about science breakthroughs. They joined others on Curiosity’s science team in a Dec. 3 address at the American Geophysical Union in San Francisco.

A eureka moment would be the discovery of organic compounds, says Ralf Gellert of the University of Guelph in Ontario, principal investigator for the Alpha Particle X-Ray Spectrometer.

Instead, five 4-centimeter-wide samples of windblown, red-gray dust and sand scooped from the so-called Rocknest area of the Gale Crater have turned up little that was not well understood from previous missions, including the 1970s Viking landers, Gellert says.

But that is good. “This is what we were looking for,” he explained. Seeing common soils again allows the science team to verify the granular precision of their instrument suite against known results.

Had the mission turned up unusual samples this early in its life, they would be difficult to evaluate because the science team would not yet have established a good baseline for their observations.

Initial sampling showed about half common volcanic minerals and half non-crystalline materials, such as glass. While Curiosity has detected water molecules in the region, the finding does not indicate a wet area, merely one where water molecules have bonded to grains of sand, which is not unusual.

One concern is how much Curiosity, manufactured on Earth, might contaminate the samples it gathers on Mars. The rover found perchlorate, a reactive chemical that NASA’s Phoenix lander also detected, and performed a laboratory test on it that produced chlorinated methane compounds. The chlorine is of Martian origin, but it is possible the carbon might have been carried to Mars by Curiosity.

One unanswered question is how much of the water, oxygen, carbon dioxide and sulfur dioxide levels in the Martian atmosphere are indigenous and how many were introduced from space, such as from micrometeorite bombardments.