Mars · natural satellite

Phobos

A sample-return destination

Grooves and the large Stickney crater mark this small, irregular moon. JAXA’s MMX mission is designed to collect material from Phobos and observe both Martian moons.

Mean diameter: 22.16 km
Mean orbital distance: 9,375 km from centre
Orbital period: 0.319 Earth days

Phobos · NASA spacecraft imagery — NASA/JPL-Caltech/University of Arizona · Image source ↗

Compared with our Moon

Phobos · 22.16 km

Moon · 3,474.8 km

One diameter scale. Circle shapes compare volume-equivalent diameters; irregular moons are not spheres.

Orbit & discovery

Surface gravity: 0.006 m/s²
Discovery: 1877
Discoverer / team: A. Hall
Provisional designation: —
JPL satellite ID: 401
Orbital eccentricity: 0.015
Inclination: 1.1 degrees

Inclination reference: Laplace. Mean-element epoch: 2000-01-01.5 TDB · MAR099.

Diameters use volume-equivalent mean radii, including for irregular bodies. Mean orbital elements describe an orbit; they are not live positions. Missing physical measurements remain unavailable.

Physical measurements & uncertainties

Mean radius · km: 11.08 ±0.04 [1]
GM · km³/s²: 0.0007087 ±0.0000006 [MAR097]
Density · g/cm³: 1.872 ±0.076 [*]

Missions in the Mars system · 101 records

52 launches · 49 linked events

These records cover the planetary system. A system mission did not necessarily visit this moon. Dedicated targets are marked separately; programme events include the journey and briefings. Launch outcomes do not establish arrival, landing success or present spacecraft operation.

Dedicated targets only

PLANETARY SYSTEM · UPCOMING

Mars Telecommunications Orbiter

Date to be confirmed

Blue Origin · New Glenn

PLANETARY SYSTEM · UPCOMING

Mars Orbiter

Date to be confirmed

Relativity Space · Terran R

PLANETARY SYSTEM · UPCOMING

ExoMars 2028 Rosalind Franklin Rover

October 2028 · date to be confirmed

SpaceX · Falcon Heavy

PLANETARY SYSTEM · UPCOMING

Mars Lander

Date to be confirmed

Relativity Space · Terran R

DEDICATED TARGET

Martian Moons eXploration (MMX)

October 19, 2026 · UTC

Mitsubishi Heavy Industries · H3-24

Compared with our Moon

Orbit & discovery

Mars Telecommunications Orbiter

Mars Orbiter

ExoMars 2028 Rosalind Franklin Rover

Mars Lander

Martian Moons eXploration (MMX)

NASA JAXA MMX Media Teleconference

NASA MAVEN Farewell Media Teleconference

EscaPADE

NASA Mars 2020 Perseverance Finding Teleconference

Ingenuity End of Mission Media Teleconference

NASA Insight & MRO Findings Media Briefing

NASA Mars 2020 Perseverance Mission Operations Briefing

NASA Insight Update Media Teleconference

NASA Mars 2020 Ingenuity 26th Flight

NASA Mars 2020 Ingenuity 25th Flight

NASA Mars 2020 Ingenuity 24th Flight

NASA Mars 2020 Ingenuity 23rd Flight

NASA Mars 2020 Ingenuity 22nd Flight

NASA Mars 2020 Ingenuity 21st Flight

NASA Mars 2020 Ingenuity 20th Flight

NASA Mars 2020 Ingenuity 19th Flight

NASA Mars 2020 Ingenuity 18th Flight

NASA Mars 2020 Ingenuity 17th Flight

NASA Mars 2020 Ingenuity 16th Flight

NASA Mars 2020 Ingenuity 15th Flight

NASA Mars 2020 Ingenuity 14th Flight

Briefing on Successful Sample Collection of Martian Rock

NASA Mars 2020 Ingenuity 13th Flight

NASA Mars 2020 Ingenuity 12th Flight

NASA Mars 2020 Ingenuity 11th Flight

NASA Mars 2020 Ingenuity Tenth Flight

NASA Mars 2020 Ingenuity Ninth Flight

NASA Mars 2020 Ingenuity Eighth Flight

NASA Mars 2020 Ingenuity Seventh Flight

NASA Mars 2020 Ingenuity Sixth Flight

Tianwen-1 Rover Landing

NASA Mars 2020 Ingenuity Fifth Flight

NASA Mars 2020 Ingenuity Fourth Flight

NASA Mars 2020 Ingenuity Third Flight

NASA Mars 2020 Ingenuity Second Flight

NASA Mars 2020 Ingenuity Post-Flight Briefing

NASA Mars 2020 Ingenuity First Flight Livestream

NASA Mars 2020 Ingenuity First Flight

NASA Mars 2020 Ingenuity Pre-Flight Press Conference

NASA Mars 2020 Perseverance Mission Images & Video Release

NASA Mars 2020 Perseverance Sol 1 Press Conference

NASA Mars 2020 Perseverance Rover Landing

Tianwen-1 Mars Orbit Insertion

Emirates Mars Mission 'Hope' Mars Orbit Insertion

Mars 2020 Post-Launch News Conference

Mars 2020 (Perseverance rover & Ingenuity helicopter)

Mars 2020 NASA Administrator & Center Director Briefing

Mars 2020 Mission Tech & Humans to Mars Briefing

Mars 2020 Sample Return Briefing

Mars 2020 Engineering & Science Briefing

Mars 2020 Pre-Launch News Conference

Tianwen-1 (Mars Global Remote Sensing Orbiter and Small Rover)

Hope (Emirates Mars Mission)

InSight, Mars Cube One 1 & Mars Cube One 2

ExoMars Trace Gas Orbiter & EDM Schiaparelli lander

MAVEN

MSL (Curiosity)

Zenit 2M | Fobos-Grunt & Yinghuo-1

Phoenix

Mars Reconnaissance Orbiter

Opportunity Rover

Spirit Rover

Mars Express

Mars Odyssey

Mars Polar Lander

Mars Climate Orbiter

Nozomi

Mars Pathfinder

Mars-96

Mars Global Surveyor

Mars Observer

Fobos-2

Fobos-1