# Polar orbit
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{{short description|Satellite orbit with high inclination}}
thumb|235x235px|Polar orbit on the Earth
A '''polar orbit''' is one in which a [satellite](/source/satellite) [pass](/source/pass_(spaceflight))es above or nearly above both [poles](/source/Poles_of_astronomical_bodies) of the body being [orbit](/source/orbit)ed (usually a planet such as the [Earth](/source/Earth), but possibly another body such as the [Moon](/source/Moon) or [Sun](/source/Sun)) on each revolution. It has an [inclination](/source/inclination) of about 80–90 [degree](/source/Degree_(angle))s to the body's [equator](/source/equator).[{{cite web |url = http://www.esa.int/Enabling_Support/Space_Transportation/Types_of_orbits |title=ESA - Types of Orbits |date=2020-03-30 |access-date=2021-01-10}}]
Launching [satellite](/source/satellite)s into polar orbit requires a larger [launch vehicle](/source/launch_vehicle) to launch a given payload to a given altitude than for a [near-equatorial orbit](/source/near-equatorial_orbit) at the same altitude, because it cannot take advantage of the [Earth's rotation](/source/Earth's_rotation)al [velocity](/source/velocity). Depending on the location of the [launch site](/source/Spaceport) and the [inclination](/source/Orbital_inclination) of the polar orbit, the launch vehicle may lose up to 460 m/s of [Delta-v](/source/Delta-v), approximately 5% of the Delta-v required to attain [Low Earth orbit](/source/Low_Earth_orbit).
==Usage==
Polar orbits are used for [Earth-mapping](/source/Earth_observation_satellite), [reconnaissance satellite](/source/reconnaissance_satellite)s, as well as for some [weather satellite](/source/weather_satellite)s.[Science Focus 2nd Edition 2, pg. 297]
The [Iridium satellite constellation](/source/Iridium_satellite_constellation) uses a polar orbit to provide telecommunications services.
{{anchor|nearPolarOrbit}}Near-polar orbiting satellites commonly choose a [sun-synchronous orbit](/source/sun-synchronous_orbit), where each successive orbital [pass](/source/pass_(spaceflight)) occurs at the same local time of day. For some applications, such as [remote sensing](/source/remote_sensing), it is important that ''changes'' over time are not aliased by changes in local time. Keeping the same local time on a given pass requires that the [time period](/source/frequency) of the orbit be kept as short, which requires a low orbit. However, very low orbits rapidly [decay](/source/orbital_decay) due to [drag](/source/drag_(physics)) from the atmosphere. Commonly used [altitude](/source/altitude)s are between 700 and 800 km, producing an [orbital period](/source/orbital_period) of about 100 minutes.[{{cite web |url=http://www.phy6.org/Education/wlopolar.html |title=Polar Orbiting Satellites |first=David P. |last=Stern |date=2001-11-25 |access-date=2009-01-21}}] The half-orbit on the Sun side then takes only 50 minutes, during which local time of day does not vary greatly.
{{anchor|precessingSV}}To retain a Sun-synchronous orbit as the [Earth revolves](/source/Earth's_orbit) around the Sun during the year, the orbit must [precess](/source/Nodal_precession) about the Earth at the same rate (which is not possible if the satellite passes directly over the pole).
Because of Earth's [equatorial bulge](/source/equatorial_bulge), an orbit [inclined](/source/orbital_inclination) at a slight angle is subject to a [torque](/source/torque), which causes [precession](/source/precession). An angle of about 8° from the pole produces the desired precession in a 100-minute orbit.[{{Cite journal |last1=Albrecht |first1=Simon H. |last2=Marcussen |first2=Marcus L. |last3=Winn |first3=Joshua N. |last4=Dawson |first4=Rebekah I. |last5=Knudstrup |first5=Emil |date=July 2021 |title=A Preponderance of Perpendicular Planets |journal=The Astrophysical Journal |language=en |volume=916 |issue=1 |pages=L1 |arxiv=2105.09327 |bibcode=2021ApJ...916L...1A |doi=10.3847/2041-8213/ac0f03 |doi-access=free |issn=0004-637X}}] About half of these are warm [Neptune](/source/Neptune) sized or [super-Neptune](/source/super-Neptune) sized planets.[{{Cite journal |last1=Louden |first1=Emma M. |last2=Millholland |first2=Sarah C. |date=October 2024 |title=Polar Neptunes Are Stable to Tides |journal=The Astrophysical Journal |language=en |volume=974 |issue=2 |pages=304 |arxiv=2409.03679 |bibcode=2024ApJ...974..304L |doi=10.3847/1538-4357/ad74ff |doi-access=free |issn=0004-637X}}] Examples of exoplanets with nearly polar orbits are [GJ 3470b](/source/GJ_3470_b), [TOI-858Bb](/source/TOI-858Bb), [WASP-178b](/source/WASP-178b),[{{Cite journal |last1=Czekala |first1=Ian |last2=Chiang |first2=Eugene |last3=Andrews |first3=Sean M. |last4=Jensen |first4=Eric L. N. |last5=Torres |first5=Guillermo |last6=Wilner |first6=David J. |last7=Stassun |first7=Keivan G. |last8=Macintosh |first8=Bruce |date=September 2019 |title=The Degree of Alignment between Circumbinary Disks and Their Binary Hosts |journal=The Astrophysical Journal |language=en |volume=883 |issue=1 |pages=22 |arxiv=1906.03269 |bibcode=2019ApJ...883...22C |doi=10.3847/1538-4357/ab287b |doi-access=free |issn=0004-637X}}] [HD 3167c+d](/source/HD_3167),[{{Cite journal |last1=Dalal |first1=S. |last2=Hébrard |first2=G. |last3=Lecavelier des Étangs |first3=A. |last4=Petit |first4=A. C. |last5=Bourrier |first5=V. |last6=Laskar |first6=J. |last7=König |first7=P.-C. |last8=Correia |first8=A. C. M. |date=November 2019 |title=Nearly polar orbit of the sub-Neptune HD 3167 c. Constraints on the dynamical history of a multi-planet system |url=https://ui.adsabs.harvard.edu/abs/2019A&A...631A..28D/abstract |journal=Astronomy and Astrophysics |language=en |volume=631 |pages=A28 |arxiv=1906.11013 |bibcode=2019A&A...631A..28D |doi=10.1051/0004-6361/201935944 |issn=0004-6361}}] [TOI-640b](/source/TOI-640_b),[{{Cite journal |last1=Knudstrup |first1=Emil |last2=Albrecht |first2=Simon H. |last3=Gandolfi |first3=Davide |last4=Marcussen |first4=Marcus L. |last5=Goffo |first5=Elisa |last6=Serrano |first6=Luisa M. |last7=Dai |first7=Fei |last8=Redfield |first8=Seth |last9=Hirano |first9=Teruyuki |last10=Csizmadia |first10=Szilárd |last11=Cochran |first11=William D. |last12=Deeg |first12=Hans J. |last13=Fridlund |first13=Malcolm |last14=Lam |first14=Kristine W. F. |last15=Livingston |first15=John H. |date=March 2023 |title=A puffy polar planet. The low density, hot Jupiter TOI-640 b is on a polar orbit |url=https://ui.adsabs.harvard.edu/abs/2023A&A...671A.164K/abstract |journal=Astronomy and Astrophysics |language=en |volume=671 |pages=A164 |arxiv=2302.01702 |bibcode=2023A&A...671A.164K |doi=10.1051/0004-6361/202245301 |issn=0004-6361}}] [MASCARA-1 b](/source/MASCARA-1b),[{{Cite journal |last1=Hooton |first1=M. J. |last2=Hoyer |first2=S. |last3=Kitzmann |first3=D. |last4=Morris |first4=B. M. |last5=Smith |first5=A. M. S. |last6=Collier Cameron |first6=A. |last7=Futyan |first7=D. |last8=Maxted |first8=P. F. L. |last9=Queloz |first9=D. |last10=Demory |first10=B.-O. |last11=Heng |first11=K. |last12=Lendl |first12=M. |last13=Cabrera |first13=J. |last14=Csizmadia |first14=Sz |last15=Deline |first15=A. |date=February 2022 |title=Spi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection |url=https://ui.adsabs.harvard.edu/abs/2022A&A...658A..75H/abstract |journal=Astronomy and Astrophysics |language=en |volume=658 |pages=A75 |arxiv=2109.05031 |bibcode=2022A&A...658A..75H |doi=10.1051/0004-6361/202141645 |issn=0004-6361}}] and [GJ 436b](/source/Gliese_436_b).[{{Cite journal |last1=Bourrier |first1=V. |last2=Zapatero Osorio |first2=M. R. |last3=Allart |first3=R. |last4=Attia |first4=M. |last5=Cretignier |first5=M. |last6=Dumusque |first6=X. |last7=Lovis |first7=C. |last8=Adibekyan |first8=V. |last9=Borsa |first9=F. |last10=Figueira |first10=P. |last11=González Hernández |first11=J. I. |last12=Mehner |first12=A. |last13=Santos |first13=N. C. |last14=Schmidt |first14=T. |last15=Seidel |first15=J. V. |date=July 2022 |title=The polar orbit of the warm Neptune GJ 436b seen with VLT/ESPRESSO |url=https://ui.adsabs.harvard.edu/abs/2022A&A...663A.160B/abstract |journal=Astronomy and Astrophysics |language=en |volume=663 |pages=A160 |arxiv=2203.06109 |bibcode=2022A&A...663A.160B |doi=10.1051/0004-6361/202142559 |issn=0004-6361}}]
One explanation describes the misalignment of a [circumbinary disk](/source/circumbinary_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.[{{Cite journal |last1=Chen |first1=Cheng |last2=Baronett |first2=Stanley A. |last3=Nixon |first3=C. J. |last4=Martin |first4=Rebecca G. |date=September 2024 |title=On the origin of polar planets around single stars |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=533 |issue=1 |pages=L37–L42 |arxiv=2406.16169 |bibcode=2024MNRAS.533L..37C |doi=10.1093/mnrasl/slae058 |doi-access=free |issn=0035-8711}}] 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.[{{Cite journal |last1=Petrovich |first1=Cristobal |last2=Muñoz |first2=Diego J. |last3=Kratter |first3=Kaitlin M.|author3-link=Kaitlin Kratter |last4=Malhotra |first4=Renu |date=October 2020 |title=A Disk-driven Resonance as the Origin of High Inclinations of Close-in Planets |journal=The Astrophysical Journal |language=en |volume=902 |issue=1 |pages=L5 |arxiv=2008.08587 |bibcode=2020ApJ...902L...5P |doi=10.3847/2041-8213/abb952 |doi-access=free |issn=0004-637X}}]