BBC Inside Science Responding to your science questions
Apr 2, 2026
Penny Sarchet, former biologist and managing editor at New Scientist, gives plant and biology explanations. Mark Maslin, Earth System Science professor, tackles geomagnetism, plastics and noise. Catherine Heymans, Astronomer Royal for Scotland, unpacks galaxies, gravity slingshots and Martian meteorites. The trio answer listener questions on photosynthesis, magnetic reversals and why some plants are not green.
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Society, Not Life, Faces Biggest Risk From Flips
- A weakened magnetic field during a reversal would increase cosmic radiation reaching electronics and could disrupt human infrastructure.
- Biological life shows little change during past flips, but society would face significant technological impacts, says Mark Maslin.
Green Is The Default Because Chlorophyll Is Everywhere
- Nearly all land plants contain chlorophyll; non-green appearance usually comes from additional pigments like anthocyanins masking chlorophyll.
- Above-ground green tissues (stems, other parts) can photosynthesize but leaves evolved as efficient dedicated organs, says Penny Sarchet.
Expansion And Mergers Depend On Scale
- Cosmic expansion and local galaxy mergers coexist because scale matters: dark energy drives universal expansion on largest scales while gravity (including dark matter) binds nearby galaxies.
- The Milky Way–Andromeda approach is governed by mutual gravity despite overall cosmic expansion, says Catherine Heymans.