Themisto

A confirmed moon in the Jupiter system.

Named · Jupiter XVIII · S/1975 J 1

Snapshot 2026-09-09 · catalog 1.0.0

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Physical measurements

Mean radius
— No value in the admitted source set.
GM · gravitational parameter
— No value in the admitted source set.
Mass
— Mass requires an admitted GM estimate.
Mean density
— No value in the admitted source set.

Orbit descriptions

Mean elements describe an average orbit. They are not positions for a chosen date.

JUP347 · ecliptic plane · 2000-01-01.5 TDB
Semimajor axis
7,397,000 km
Sidereal period
129.968 days
Eccentricity
0.257
Inclination to reference plane
44.3°
Argument of periapsis
236.3°
Mean anomaly
289.1°
Ascending node
202.7°
Apsidal / nodal precession periods
626.4 / 648.5 years
Reference-plane pole RA / Dec
— / —°
Plane tilt to parent equator
—°
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

No supported orientation model in the admitted PCK source.

Identity & availability

Stable catalog ID
themisto
JPL / NAIF satellite ID
518
Names & designations
Themisto · S/1975 J 1 · S/2000 J 1
Discovery / rediscovery years
1975, 2000C.T. Kowal, E. Roemer (1975), S.S. Sheppard, D.C. Jewitt, Y.R. Fernandez, G. Magnier (2000)

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

  1. JPL discovery circumstancestable tr[22] (zero-based); jupiter / Themisto · References: IAUC 7525
  2. MPC planetary satellite listitems[17]; Jupiter 18
  3. MPC satellite namesitems[150]; Jupiter 18
  4. JPL mean orbital elements#sat_elem row ID=20; Jupiter / Themisto / NAIF 518 · References: 47

Full catalog, uncertainty and source manifests · All Jupiter moons · Moon model limits