Polar orbit

A polar orbit is a specific path that a satellite follows around a celestial body. This body might be a planet like Earth, or it could be a Moon or the Sun. On every single revolution, the satellite passes directly over or very near both poles. This path has a steep inclination relative to the equator. Specifically, the inclination is about 80 to 90 degrees. These orbits are essential for many modern technologies and scientific observations.

Launching a satellite into this path is more difficult than a standard equatorial launch. Most rockets rely on the Earth's rotational velocity to help them reach orbit. However, a polar orbit cannot take advantage of this spinning motion. This means the launch vehicle must provide more energy to reach the same altitude. Depending on the launch site and the specific inclination, a vehicle may lose up to 460 m/s of Delta-v. This loss represents approximately 5% of the Delta-v required to reach Low Earth orbit.

Scientists use polar orbits for several important purposes on Earth. They are vital for Earth-mapping and reconnaissance satellites. Some weather satellites also utilize these paths to monitor the planet. The Iridium satellite constellation uses polar orbits to provide global telecommunications services. Many of these near-polar satellites use a specialized type of path called a sun-synchronous orbit. This allows each successive pass to occur at the same local time of day.

Maintaining a sun-synchronous orbit requires very specific conditions. For remote sensing, it is important that data is not affected by changing local times. To keep the timing consistent, the satellite must maintain a low orbit. Common altitudes for these satellites are between 700 and 800 km. At this height, the orbital period is about 100 minutes. The half-orbit on the Sun side takes only 50 minutes. During this time, the local time of day does not vary much.

To keep this sun-synchronous timing as Earth moves around the Sun, the orbit must undergo precession. Precession is a slow rotation of the orbital plane itself. This is achieved by using the Earth's equatorial bulge. Because the Earth is wider at the equator, it exerts a torque on the orbit. This torque causes the orbit to precess at the correct rate. An angle of about 8 degrees from the pole produces the desired precession for a 100-minute orbit.

We also see unusual orbits in deep space around other stars. About 10% of exoplanets have a misalignment between their orbital plane and their host star. This misalignment is known as obliquity. Scientists measure this using the Rossiter-McLaughlin effect. Many of these planets are Neptune-sized or even larger, called super-Neptunes. Several specific exoplanets have been identified with nearly polar orbits. These include GJ 3470b, TOI-858Bb, WASP-178b, HD 3167c+d, TOI-640b, MASCARA-1 b, and GJ 436b.

Astronomers have proposed different reasons for these strange planetary paths. One theory involves the misalignment of a circumbinary disk, which is a disk of material around two stars. If the central binary stars merge into one, the disk and its planets might stay in a polar orbit. Another theory suggests a Neptune-sized planet might enter a polar orbit through resonance. This happens when a planet interacts with a protoplanetary disk and an additional outer planet.

In April 2025, a major discovery was announced using the Very Large Telescope. Astronomers used the UVES instrument to find evidence of a unique planet. This planet, named 2M1510b, orbits a pair of brown dwarfs known as 2M1510AB. It is the first discovered case of a planet in a polar orbit around a binary system. Researchers found it by measuring radial velocity. This showed a retrograde apsidal precession in the brown dwarf pair that could not be explained by other companions.