Short answers, pulled from the story.
Ernest Rutherford discovered the proton in 1919 when he fired alpha particles at nitrogen gas and detected scintillations on a zinc sulfide screen. This experiment marked the first artificial disintegration of an atom and proved that the hydrogen nucleus was a fundamental constituent of all heavier atomic nuclei.
The proton is a composite particle consisting of three valence quarks held together by the strong force. Two of these quarks are up quarks with a charge of plus one elementary charge, and the third is a down quark with a charge of minus one.
The CODATA recommended value for the proton's charge radius is approximately 0.84 femtometers. This measurement has been subject to the proton radius puzzle due to discrepancies between electron-proton scattering and muonic hydrogen experiments.
Researchers reported in 2018 that the pressure inside the proton is on the order of 10 to the power of 35 pascals. This pressure is maximum at the center of the proton and becomes negative or attractive at greater distances.
Free protons make up about 90 percent of the total particle flux in galactic cosmic rays. These protons often have higher energy than solar wind protons and travel through the universe as cosmic rays.
The number of protons in the nucleus is known as the atomic number and determines the chemical element to which the atom belongs. For example, the atomic number of chlorine is 17, meaning that each chlorine atom has 17 protons.