Are There Any Planets That Don't Rotate or Revolve in Our Solar System and the Universe?

The Rotation of Planets in Our Solar System

It is a well-known fact that all planets within our Solar System both rotate on their axes and revolve around the Sun. However, the rate and characteristics of this rotation can vary significantly among the planets. For example, Venus has a very slow rotation, taking about 243 Earth days to complete a rotation on its axis. It rotates in the opposite direction, also known as retrograde rotation, compared to most planets in the Solar System, which rotate in a prograde direction. Uranus, on the other hand, is unique due to its rotational axis being nearly horizontal, with an axial tilt of approximately 98 degrees. This makes it rotate on its side.

Planets in Our Solar System

Venus's rotation is particularly notable due to its extremely slow speed, making it a celestial body with a unique rotational pattern. Uranus, with its almost horizontal axis, serves as another interesting case study. It is important to note that while no known planets in our Solar System are completely stationary (i.e., not rotating or revolving), some celestial bodies, such as certain moons or dwarf planets, may exhibit very slow or unusual rotation patterns. Mercury, for instance, is tidally locked with the Sun, meaning it always shows the same face to the Sun. It is important to distinguish between tidally locked bodies and planets with zero rotation relative to a distant star.

Beyond the Solar System

When considering the broader universe, theoretically, it is possible for celestial bodies to exist that do not rotate or revolve, especially in certain gravitational conditions. However, no such bodies have been identified yet. Most celestial bodies, due to the conservation of angular momentum from their formation, will exhibit some degree of rotation and revolution. Understanding the reasons behind the rotation of these bodies involves the precise dynamics of their formation and the impact of external forces such as collisions or gravitational interactions.

Rogue Planets and Planetary Dynamics

Rogue planets, these celestial bodies that were ejected from their planetary systems at or soon after their formation, may also have unique rotational dynamics. Studies suggest that our Solar System may have lost as many planets as it currently has, predating its formation. The rotation of a planet is influenced by the physics involved in the collisions that may take place, and these collisions can either slow down or stop a planet’s rotation completely.

Mercury's Tidal Locking

Mercury is tidally locked to the Sun, meaning it always shows the same face to the Sun. All other planets in our Solar System exhibit some degree of rotation relative to the Sun. While Mercury does not rotate in a conventional sense, it still completes one rotation over the course of two orbits around the Sun. Other tidally locked bodies, such as our Moon and Mercury, always show the same face to the body they orbit.

Could a Planet Be Completely Stationary Relative to a Star?

Theoretically, it is possible for a planet to grow and suffer impacts that add or subtract from its rotational velocity such that it is precisely zero with respect to a distant star. However, this scenario would be extremely rare. Planets form from tiny particles that stick together, eventually growing into larger planetoids. The early Earth, for instance, was impacted by a Mars-sized body that likely gave us not only our Moon but also a day that was initially only 6 to 10 hours long. Over time, tidal forces from the Moon slowed the Earth's rotation to the 24-hour day we have today.