The temperature of outer space is 2.7 Kelvin (-270.5° Celcius) (-454.9° Fahrenheit). This is the baseline temperature of space, as set by the CMB (cosmic background radiation). This is not the coldest temperature in the universe. There are liquids colder than outer space.
The liquid helium can be colder than outer space. The Large Hadron Collider’s electromagnets are cooled down by liquid helium. The cryogenic system of the Large Hadron Collider operates at -456.3° Fahrenheit (-271.3° Celcius) (1.9 Kelvin), colder than the temperature of outer space.
Outer space contains hydrogen – with a density of approximately one hydrogen atom per cubic meter – and helium atoms mostly in plasma form (electrons stripped), as well as electromagnetic radiation (CMB is electromagnetic radiation), magnetic fields, neutrinos, dust and cosmic rays (energetic elementary particles). And…the Higgs field, of course! The Higgs field pervades the entire universe. The space/universe also contains the “vacuum.” Other than the Higgs field and the other fields theorized by the Quantum Field Theory we know very little about the “vacuum.” In my opinion, the “vacuum” should be thought of as the “internal space” and the space as the “external space.” The space also contains “dark matter” and “dark energy.” We are aware of their existence but we have no idea what “dark matter” and “dark energy” are.
Going back to what is colder than outer space, helium is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas. Helium transforms into liquid form at -269 degrees Celsius (about 4 Kelvin or -452.2 degrees Fahrenheit). At the Large Hadron Collider they keep it a little colder at -456.3 degrees Fahrenheit so that helium does not evaporate as it circulates in the largest cryogenic system in the world.
In the nucleus of the Helium atom there are two protons and 2 neutrons.
Hydrogen is the lightest element. It has only 1 proton and no neutron in its nucleus. Hydrogen is also the most abundant element in the universe because it is the easiest to form. One proton and one electron. That’s it.
Helium is the second lightest element and is the second most abundant element in the universe because it is the second easiest to form. Two protons, 2 neutrons and two electrons.
You can learn more about Helium at the following links