In situ: the Latin phrase used in more than 910,000 scientific papers
In situ simply means in the place, but the phrase does heavy lifting across science. It describes a probe sampling the Sun's atmosphere, concrete poured where the wall will stand, cancers that have not spread, and chemicals made inside the reaction mixture because they would fall apart if isolated. By 2022 over 910,000 papers had used it.
The phrase joins in with situ, a form of situs, meaning place. Classical Roman authors never used it; it first shows up in Late Latin, in the writings of Augustine of Hippo, who lived from 354 to 430 AD, and spread through Medieval Latin. English borrowed it by 1648, when William Molins used it in an anatomy text called Myskotomia. Scientific use climbed from the late 19th century, first for measurements inside living bodies and oil wells. Artists adopted it in the late 1960s and 1970s for works made for one particular space, and materials scientists picked it up in the mid-1980s for catalysis. As of August 2022 it had appeared in more than 910,000 publications since 1874, against over 29,000 for its opposite, ex situ, since 1958.
The core idea is that moving a specimen can destroy the context that explains it. Astronomers send instruments to the object itself: the Parker Solar Probe samples the Sun's atmosphere, and Cassini–Huygens examined Saturn's magnetosphere. Some theorists even argue that planets such as Earth formed in situ, in their present orbits. Cell biologists use in situ hybridization, attaching fluorescent or radioactive tags to probe strands that latch onto matching genetic sequences, to show exactly where those sequences sit inside intact tissue.
Chemists make fragile or dangerous ingredients on the spot. One-pot sequences avoid isolating hazardous azide intermediates, and the Corey–Chaykovsky reagent, a highly reactive sulfur ylide, is generated in the flask by stripping a proton from a sulfonium salt with a strong base, since it would decompose if stored. NMR, Raman spectroscopy and mass spectrometry let researchers watch such short-lived species without disturbing the reaction. Electrochemists hold an electrode at a fixed potential with a potentiostat so the interface stays as it would in real operation.
Engineers use the phrase in their own ways. In situ concrete is poured at its final position rather than prefabricated, and geotechnical engineers distinguish undisturbed native soil from relocated fill. Aircraft parts can be checked in place with infrared thermography, shearography or ultrasound. Mission planners hope to live off the land: the Mars Direct plan would use the Sabatier reaction to turn Martian carbon dioxide and hydrogen into methane and water.
Source: In situ
