Apolar orbit is one in which asatellitepasses above or nearly above bothpoles of the body beingorbited (usually a planet such as theEarth, but possibly another body such as theMoon orSun) on each revolution. It has aninclination of about 80–90degrees to the body'sequator.[1]
Launchingsatellites into polar orbit requires a largerlaunch vehicle to launch a given payload to a given altitude than for anear-equatorial orbit at the same altitude, because it cannot take advantage of theEarth's rotationalvelocity. Depending on the location of thelaunch site and theinclination of the polar orbit, the launch vehicle may lose up to 460 m/s ofDelta-v, approximately 5% of the Delta-v required to attainLow Earth orbit.
Polar orbits are used forEarth-mapping,reconnaissance satellites, as well as for someweather satellites.[2]TheIridium satellite constellation uses a polar orbit to provide telecommunications services.
Near-polar orbiting satellites commonly choose asun-synchronous orbit, where each successive orbitalpass occurs at the same local time of day. For some applications, such asremote sensing, it is important thatchanges over time are not aliased by changes in local time. Keeping the same local time on a given pass requires that thetime period of the orbit be kept as short, which requires a low orbit. However, very low orbits rapidlydecay due todrag from the atmosphere. Commonly usedaltitudes are between 700 and 800 km, producing anorbital period of about 100 minutes.[3] The half-orbit on the Sun side then takes only 50 minutes, during which local time of day does not vary greatly.
To retain a Sun-synchronous orbit as theEarth revolves around the Sun during the year, the orbit mustprecess about the Earth at the same rate (which is not possible if the satellite passes directly over the pole).Because of Earth'sequatorial bulge, an orbitinclined at a slight angle is subject to atorque, which causesprecession. An angle of about 8° from the pole produces the desired precession in a 100-minute orbit.[3]
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A misalignment between host star rotation plane and orbital plane of the planet is calledobliquity and is usually measured with theRossiter-McLaughlin effect. Around 10% of exoplanets have a misalignment between 80 and 125°.[4] About half of these are warmNeptune sized orsuper-Neptune sized planets.[5] Examples of exoplanets with nearly polar orbits areGJ 3470b,TOI-858Bb,WASP-178b,[6]HD 3167c+d,[7]TOI-640b,[8]MASCARA-1 b,[9] andGJ 436b.[10]
One explanation describes the misalignment of acircumbinary disk that forms the planets. When the central binary merges into a single star, the disk and any planets that have formed remain in a polar orbit.[11] A study has shown that circumbinary disks are aligned with binaries that have a short orbital period of less than 20 days. Circumbinary disks around binaries with an orbital period of more than 30 days showed a wide range of alignments, including polar disks.[6] The other explanation describes how a Neptune-sized planet might get into a polar orbit at the end of the planet formation. This happens due to aresonance with aprotoplanetary disk in a system with an additional outer planet.[12][5]
In April 2025 astronomers usingESO's UVES instrument on theVery Large Telescope announced strong evidence for acircumbinary planet orbiting the brown dwarf pair2M1510AB. The planet is called 2M1510(AB)b, or just 2M1510b. The orbit of the planet is unusual as it is a polar orbit around a binary system, the first such case that was discovered. The discovery was made with the help ofradial velocity measurements that showedretrogradeapsidal precession of the brown dwarf pair, which could not be explained by the outer companion.
