How do scientists stop meteorites being contaminated?
By collecting fresh falls quickly with clean tools, storing samples in dry nitrogen or vacuum, using clean rooms, and checking isotopes to tell space chemistry from Earth contamination.
Earth is full of contamination: water, oxygen, dust, bacteria, skin oils and industrial chemicals. These can alter meteorites and confuse scientists searching for traces of space chemistry, especially organic molecules.
In the field. Fresh falls should be collected quickly, ideally within days, before rain affects them. Searchers are advised to pick up stones using clean aluminium foil or clean bags, avoid touching them with bare hands, and keep them dry. Antarctic teams collect meteorites using clean tools and sealed bags, and keep them frozen.
Storage. Many sensitive meteorites are stored in cabinets filled with dry nitrogen gas, which prevents rust and oxidation. Antarctic meteorites in the United States are kept in a dedicated curation facility in dry nitrogen. Samples from Ryugu and Bennu are kept in nitrogen or vacuum and never exposed to Earth's air.
Laboratories. Analyses for organics and isotopes are done in clean rooms with filtered air. Tools are cleaned and baked to remove organic residues. Scientists analyse 'blanks', samples of the cleaning materials and lab environment, to measure background contamination.
Detecting contamination. Scientists check for signs of Earth origin. Amino acids from life are almost entirely left-handed and have Earth-like carbon isotopes, while those from meteorites often include unusual amino acids and have isotopes enriched in carbon-13, deuterium or nitrogen-15. Weathering products, such as carbonates and sulfates formed on Earth, can be identified by their isotopes and textures.
Even with these precautions, some contamination is unavoidable, so interpreting results requires care and multiple lines of evidence.