The Speed of Planets: An Exploration from Earth to the Cosmos

The laws of gravity determine that a planet’s speed in its orbit is directly proportional to its closeness to its star. For instance, Earth, our home planet, travels along its orbit at an average speed of 29.8 kilometers (18.5 miles) per second. However, Mercury, the nearest planet to the sun in our solar system, outpaces Earth with a top speed of 59 kilometers (37 miles) per second.

Yet, these speeds are relatively modest when compared to the fastest planets in our galaxy, known as Ultra-Short Period Planets (USPPs). These celestial bodies complete their orbits in just a few hours. The fastest known USPP, Kepler-70b, is believed to be the exposed solid core of a planet that was once akin to Jupiter. It orbits its star at an impressive average speed of 272 kilometers (169 miles) per second.

Planets cannot naturally form in such extreme orbits. Therefore, astronomers theorize that these gas giants initially formed much further out in their solar systems and then spiraled inward due to interactions with residual planet-forming material. Some of these ‘hot Jupiters’ meet a catastrophic end by colliding into their parent stars.

Rogue planets, which are ejected from their planetary systems through the same process that creates hypervelocity stars, can also reach impressive speeds. These planets offer fascinating insights into the dynamic and complex nature of our universe.

In conclusion, the velocities of planets vary greatly, from the relatively leisurely pace of Earth to the breakneck speeds of USPPs and rogue planets. These differences offer fascinating insights into the diverse processes that shape planetary systems.