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Related Experiment Video

Updated: Jul 12, 2026

Scattering And Absorption of Light in Planetary Regoliths

Scattering And Absorption of Light in Planetary Regoliths

Published on: July 1, 2019

Phobos: preliminary results from mariner 7.

Science (New York, N.Y.)

|May 15, 1970

Summary

Phobos, a moon of Mars, is larger and darker than previously believed, with a very low albedo. New analysis suggests it was likely captured by Mars rather than forming with the planet.

Area of Science:

Planetary Science
Astronomy
Solar System Studies

Background:

Phobos is one of Mars' two moons.
Previous estimates of Phobos' size and surface properties were based on limited data.
Understanding Phobos' characteristics is key to understanding Martian history.

Purpose of the Study:

To re-evaluate the size and surface properties of Phobos.
To determine the origin of Phobos.

Main Methods:

Analysis of a specific Mariner 7 image (frame 7F91).
Measurement of the limb profile of Phobos from the image.
Calculation of the visual geometric albedo.

Main Results:

Phobos' limb profile measures 18 by 22 kilometers, indicating a larger size than previously thought.

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Last Updated: Jul 12, 2026

Scattering And Absorption of Light in Planetary Regoliths

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Optimization, Test and Diagnostics of Miniaturized Hall Thrusters

Published on: February 16, 2019

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

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Phobos has a darker surface with a visual geometric albedo of 0.065.

This albedo is lower than that of any other known solar system body.

Conclusions:

Phobos is larger and darker than previously estimated.
The low albedo and size suggest Phobos may not have formed in situ around Mars.
It is probable that Phobos was captured by Mars at a later time.