Phobos
A confirmed moon in the Mars system.
Physical measurements
- Mean radius
- 11.08 ± 0.04 kmmeasured · Source estimate; uncertainty is the source-reported standard error when available.
- GM · gravitational parameter
- 0.0007087 ± 6e-7 km³ s⁻²measured · Source estimate; uncertainty is the source-reported standard error when available.
- Mass
- ≈ 1.0618e+16 ± 8.9929e+12 kgderived · GM/G; independent standard uncertainties combined in quadrature. No uncertainty is invented when the source omits GM uncertainty.
- Mean density
- ≈ 1.872 ± 0.076 g cm⁻³derived · JPL derives density from GM and volume-equivalent radius.
Orbit descriptions
Mean elements describe an average orbit. They are not positions for a chosen date.
MAR099 · Laplace plane · 2000-01-01.5 TDB
- Semimajor axis
- 9,375 km
- Sidereal period
- 0.3187 days
- Eccentricity
- 0.015
- Inclination to reference plane
- 1.1°
- Argument of periapsis
- 216.3°
- Mean anomaly
- 189.7°
- Ascending node
- 169.2°
- Apsidal / nodal precession periods
- 1.1 / 2.3 years
- Reference-plane pole RA / Dec
- 317.7 / 52.9°
- Plane tilt to parent equator
- 0°
- Reference center
- Not specified in this summary sourceThe summary table identifies a parent system but does not explicitly specify the reference center for each solution. Do not infer a physical-primary center, especially for Pluto’s circumbinary moons.
Orientation
NAIF-pck00011 supplies a modeled pole and prime meridian in the J2000 frame. A dated sky also needs compatible trajectories.
- Pole right ascension
- 317.67071657, -0.10844326, 0
- Pole declination
- 52.88627266, -0.06134706, 0
- Prime meridian
- 35.1877444, 1128.84475928, 9.536137031212154e-9
- Reference epoch
- JD 2451545 TDB
Periodic corrections
RA and prime-meridian corrections multiply sine; declination corrections multiply cosine. Each row uses the same angle polynomial for its three corrections.
- Term 1 · angle coefficients
- 190.72646643, 15917.10818695, 0RA: -1.78428399° · Dec: -1.07516537° · meridian: 1.42421769°
- Term 2 · angle coefficients
- 21.4689247, 31834.27934054, 0RA: 0.02212824° · Dec: 0.00668626° · meridian: -0.02273783°
- Term 3 · angle coefficients
- 332.86082793, 19139.89694742, 0RA: -0.01028251° · Dec: -0.0064874° · meridian: 0.00410711°
- Term 4 · angle coefficients
- 394.93256437, 38280.79631835, 0RA: -0.00475595° · Dec: 0.00281576° · meridian: 0.00631964°
- Term 5 · angle coefficients
- 189.6327156, 41215158.1842005, 12.711923222RA: 0° · Dec: 0° · meridian: -1.143°
Identity & availability
- Stable catalog ID
- phobos
- JPL / NAIF satellite ID
- 401
- Names & designations
- Phobos
- Discovery / rediscovery years
- 1877A. Hall
No validated dated trajectory admitted in catalog 1.0.0. Mean elements are not ephemerides.
No image or global texture admitted in this catalog release.No environment measurements admitted in this catalog release.
Sources & evidence
- JPL discovery circumstancestable tr[2] (zero-based); mars / Phobos · References: IAU WGPSN
- JPL physical parameters#sat_phys_par; Mars / Phobos / NAIF 401; mean radius · References: 1
- JPL physical parameters#sat_phys_par; Mars / Phobos / NAIF 401; GM · References: MAR097
- NIST CODATA 2022Table of universal constants, Newtonian constant of gravitationVerified numeric transcription; see acquisition notes in the download.
- JPL physical parameters#sat_phys_par; Mars / Phobos / NAIF 401; density · References: *
- JPL mean orbital elements#sat_elem row ID=1; Mars / Phobos / NAIF 401 · References: 7
- NAIF PCK 00011BODY401_POLE_RA/POLE_DEC/PM/NUT_PREC_*; BODY4_NUT_PREC_ANGLES; active data blocks
- NAIF PCK 00011BODY401_RADII; active data block
Full catalog, uncertainty and source manifests · All Mars moons · Moon model limits