Nature highlights

Key research and analysis from this week's Nature magazine.

• Stem cells: Purification from the adult brain
  
• Prion diseases: Antibodies block PrP^Sc formation in vitro
• Origin of the Moon: Computing the collision
• Lava flow: Geology en croûte
• Astronomy: Hunt the hydrogen
• Particle physics: Crystalline ion beams
• Molecular sieves: Gas gate
• Photosynthesis: Hard times