The National Aeronautics and Space Administration said scientists noted that when the arm collected and released its first scoopful of soil Sunday, some of the sample stuck to the scoop.
The team instructed Phoenix Tuesday to lift another surface sample and release it, with more extensive imaging of the steps in the process. The results have not yet been announced.
"We are proceeding cautiously," said Phoenix Principal Investigator Peter Smith of the University of Arizona. "Before we begin delivering samples to the instruments on the deck, we want a good understanding of how the soil behaves."
The Phoenix mission is led by Smith at the University of Arizona with project management by NASA's Jet Propulsion Laboratory in Pasadena, Calif.