In the book "Big Changes" (#5 in the "Alien Kids" series), Francisco is radioed by his mother, Martina. She is checking in on him and his friend Katie, who are exploring a cave system on the planet Neokosmos.
Martina is worried about them because of a recent earthquake that has caused some instability in the caves.Just as they are about to give up hope, they hear a voice cutting through the shaking. It's Francisco's mother, Martina, calling them on their communicators. She is checking in on them and worried about them because of the earthquake. She tells them to head back to the surface as soon as possible.
Francisco and Katie make their way back to the cave entrance, dodging falling rocks and debris. When they finally reach the surface, they are relieved to be out of the cave. They tell Martina that they are safe, and she tells them to stay put until she can send someone to pick them up.