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Creation 40(3):50–51, July 2018

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Mars moons mystery

How did Phobos and Deimos get to where they are?



It wasn’t until 1877 that the two moons of Mars were discovered.

American astronomer Asaph Hall, acting on suspicions that Mars had at least one moon, had conducted a night-by-night methodical search using the telescope facility at the U.S. Naval Observatory in Washington, D.C. Frustrated at not finding anything, he was about to give up but his wife Angelina urged him to continue. The following night, 12 August, he discovered Deimos, closer in to the red planet than anyone had thought of looking before, orbiting just 23,000 km away.

 (By way of comparison, our Moon is about 384,000 km from Earth.1) Six nights later, Hall discovered Phobos, even closer in—only about 9,000 km from Mars.2

Their close proximity to Mars and relatively small size had kept the moons hidden in the glare from the red planet until Asaph Hall’s dogged persistence finally found them. It helped that he had a much larger, and thus light-gathering, telescope than that available to astronomers like Galileo—26 inches (66cm) in diameter. He named them from Homer’s ancient poem, The Iliad, in which Phobos (Gk. = fear) and Deimos (Gk. = flight, as in fleeing after defeat) were the twin sons of Ares (Mars in the Roman pantheon), accompanying him into battle.

Over the next century, as more information came to light about the two Martian moons, there was much to fascinate astronomers. Phobos is about 22 km in diameter, while potato-shaped Deimos is even smaller, being about 12 km across at most. While our Moon takes a leisurely month to orbit the Earth, Deimos takes about 30 hours to go around Mars, in a nearly perfectly circular orbit around its equator. Meanwhile the remarkable Phobos goes around Mars in only eight hours, i.e. about three times per Martian day. Being faster than the red planet’s rotation, Phobos would appear to an observer on Mars to rise in the west and set in the east, with that moon passing through all its phases in a few hours.

The biggest puzzle in the minds of many cosmologists, however, concerns theories about the formation of the moons.

Deimos bears more resemblance to an asteroid than to any of the other moons in the solar system. This and other factors led many to suggest that both Deimos and Phobos might hail from the asteroid belt, pushed from there by Jupiter then captured by the gravity of Mars. But the near-circular orbit of both moons does not sit well with that idea. Also, the atmosphere on Mars is so thin that it “would have a hard time providing the necessary braking to settle the pair into their present-day orbits.”2 And the moons are less dense than objects in the asteroid belt.

Other ideas—that the moons formed around Mars through dust and rock being drawn together there by gravity, or that they originated as a result of something colliding with Mars—also have serious problems. So the ‘captured asteroid’ theory remains the most popular, despite the awkward facts already mentioned and that “the capture mechanism is unknown and the scenarios unlikely”.3

A major challenge for the various formation theories about Phobos and Deimos concerns the constraints in timing. The difficulty in a nutshell: Deimos is inexorably spiralling away from Mars (just as our Moon is moving away from Earth), and Phobos is ‘doomed’ in the other direction—it is progressively being drawn closer to the red planet. Spiralling inward at a rate of about 1.8 metres per century, Phobos is on track to crash into Mars within 50 million years2—“an eyeblink in [evolutionary] astronomical terms”.4

That is why formation theories for the Martian moons have to try to come up with an origins scenario that is substantially younger than the billions-of-years evolutionary age ascribed to Mars.

The problem is so stark, and the unusual characteristics and decaying orbit of Phobos in particular so distinctive, that in the 1950s and 1960s “reputable scientists”, including the science advisor to USA President Eisenhower, suggested that Phobos had been put there artificially.2 I.e. that it was a “hollow artificial satellite” deliberately lofted into position from the Martian surface by intelligent beings living there.

However, when subsequent data and imaging definitively showed the rocky characteristics of both moons, the idea of them being artificial satellites was abandoned.

Note however that the original primary reason for invoking an artificial origin to explain the mystery hasn’t gone away, i.e. the distinctive motion of the moons. The conclusion of the scientists that it pointed to intelligent placement was perfectly reasonable—but they were wrong in thinking that it was ‘Martian Intelligence’ that had thwarted naturalistic origins theories. Rather, the Intelligence was (is!) eternal, and revelatory:

The heavens declare the glory of God, and the sky above proclaims His handiwork.” (Psalm 19:1)

References and notes

  1. Redd, N.T., Deimos: Facts about the smaller Martian moon, space.com, 21 June 2016. Return to text.
  2. Redd, N.T., Phobos: Facts about the doomed Martian moon, space.com, 21 June 2016. Return to text.
  3. Dick, S.J., Under the moons of mars, nasa.gov, 19 November 2007. Return to text
  4. The rate of our Moon’s recession from Earth raises huge difficulties for evolutionary timelines there, too.
    See: Sarfati, J., The moon—the light that rules the night, Creation 20(4):36–39, creation.com/moonReturn to text.

Readers’ comments

Miss Yvonne R.
Thank you to the dedicated people at Creation Ministries Intl. Comparing what GOD has done with evolutionary theories irritates me. I understand why this comparison is presented but for me, my need is to see through the eyes of GOD as is possible to so do. Job 9:8 HE alone stretches out the Heavens and treads on the waves of the sea. 9 HE is the MAKER of the Bear and the Orion, the Pleiades and the constellations of the south 10 HE performs wonders that cannot be fathomed, miracles that cannot be counted. Praise to GOD for what HE has done - Glory to HIS NAME
Dan B.
Having come to post a couple of ideas of my own, I'd like first to give a hearty Amen to Rodney P's contribution above. Yes, it's highly telling to stand back from time to time and view the big picture of evidence, now that 50+ years of space exploration have failed to uncover a single feature that positively looks > 4 billion years old, and often quite the opposite, multiple indications of much younger upper limits (meaning the true ages are younger still). As far as astronomy goes, it's time for 21st century astronomers to proceed to operate without paying the blindest bit of notice to the ideas of 19th century geologists who never even heard of Mars' moons, nor Pluto or many other objects which have now thrown up massive problems for such.

Now to the point I came here to make ;) It's stated that Deimos is (1) further from Mars and receding, and (2) nearer to Mars and approaching. Given that both orbit it around the equator in virtually circular paths, how far back in time can we go before we get to the point where their orbits would no longer be stable because they'd either collide or interact in such a way as to end the circularity of their orbits, or indeed either to throw either one out of orbit or else on a collision course with the host planet? I doubt it would be anything like long enough for evolutionists, seeing that our moon is so much further away from us yet 1.3 billion years ago would have been at the Roche limit. That's about 360,000 km of orbital radius change cf. the mere 14,000 km difference between the orbital radii of Mars' moons. Maybe someone at CMI could crunch the numbers for us?
Rodney P.
Fascinating how all of the latest discoveries - in astronomy, in paleontology, in geology, etc, etc - seem to "surprise" the evolutionists, and pose a new "problem", and are "anomalies" (their own words) to their beliefs. Another example is the red blood cells and DNA found in dinosaur bones, etc, etc. But they won't admit that the "problem" is with their beliefs, their worldview, not with the latest discoveries which refute their beliefs. I picture the situation like this: Their worldview is like a weak, old rickety structure, and the latest discoveries are like heavy stones being piled up on top of this about-to-collapse structure one by one. We stand back wondering how many more stones will be piled on before it all collapses.

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