This term is commonly used in astronomy to describe planets that share these characteristics, particularly when they are part of the same planetary system.

Here are some examples:

* Kepler-36b and Kepler-36c: These two exoplanets are very close in size and mass, orbiting a star about 1,200 light-years from Earth.

* Earth and Venus: These planets have relatively similar sizes and masses, though they have very different atmospheres and surface conditions.

It's important to note that "twins" is a loose term in astronomy. While two planets may be similar in mass and size, they can still have significant differences in other characteristics, like their composition, atmosphere, or orbital properties.