Talk:Phobos (moon)

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Former good article nominee Phobos (moon) was a Natural sciences good articles nominee, but did not meet the good article criteria at the time. There are suggestions below for improving the article. Once these issues have been addressed, the article can be renominated. Editors may also seek a reassessment of the decision if they believe there was a mistake.
March 5, 2007 Good article nominee Not listed
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Orbital Speeds[edit]

Would it be possible to provide maximum and minimum orbital speeds in addition to just the average?

Discovery Dates[edit]

Is it not appropriate to state that Jonathan Swift wrote about the two hurtling moons of Mars in Gulliver's Travels in 1726, in Part 3, Chapter 3 (the "Voyage to Laputa") more than a 150 years before Hall found them? — Preceding unsigned comment added by (talk) 05:19, 11 September 2011 (UTC) Fact checking is crucial, guys. This U.S. Naval Observatory page has a detailed account of the discovery of Phobos and Deimos:

Within we can read that "[...] I found a faint object on the following side and a little north of the planet. [...] This was at half past two o'clock on the night of the 11th." (discovery of Deimos on August 12). And later: "On August 17th while waiting and watching for the outer moon, the inner one was discovered." (discovery of Phobos on August 17, possibly 18).

Urhixidur 12:32, 2004 Jul 8 (UTC)

Oops, sorry, I went and changed it to August 11 before reading this.
The key is here: [1] (for Deimos, and click on "Next page" for Phobos).
For Deimos, we have first observation at "August 11 14h40m Washington M.T."
For Deimos, we have second observation at "August 16 13h07m Washington M.T."
For Phobos, we have first observation at "August 17 16h06m Washington M.T."
W.M.T. means "Washington meridian time". US Naval Observatory (Washington) (before 1893) is observatory code 787 (787 282.9494 0.77934 +0.62451 U.S. Naval Obs., Washington (before 1893)) [2] That's 77.0506°W longitude, or 5 hours, 8 minutes, 12 seconds time difference from Greenwich Meridian Time.
They weren't using time zones yet, and definitely they weren't using daylight saving time yet, and obviously they were using the old astronomical convention of the day beginning at noon.
A quick check: to find moons, they were observing Mars at its opposition. Mars was reaching its highest point in the sky at the meridian about 2 am at night. Mars was at about -10° declination at the 1877 opposition, so they were making their observations while Mars was not too far from peak altitude of about 40° from the horizon.
So you are probably right, times of discovery were August 12 at 02:40 local time and August 18 at 04:06 local time. Add 5 hours 8 minutes to convert to UTC.
We can play with
to try to get a view of what Mars and satellites looked like at the time in question. I'd like to get an exact match with Hall's reported position angles and separations, then we can be sure.
We could try
but it won't compute positions of Phobos or Deimos before 1976.
-- Curps 21:44, 8 Jul 2004 (UTC)
I've changed the discovery time from UTC to GMT. UTC is based on TAI, which was only defined in 1955. UTC did not exist in 1877. The discussion above leads me to believe the calculation is correct even if the label was not. (I assume that "Greenwich Meridian Time" is intended to mean "Greenwich Mean Time.") Peter 03:12, 18 Aug 2004 (UTC)

Next trick[edit]

(moved to Talk:Timeline of natural satellites)

Surface Gravity[edit]

I'm going to switch the mm/s² back to m/s². Granted, if this were an independent article mm/s² would be preferable, but it is not; it is part of a large series of articles, and sticking to a single unit (m/s²) is necessary for comparison purposes.

Urhixidur 12:34, 2004 Jul 12 (UTC)

Surface dust impossible?[edit]

How can it have surface dust if it's inside its Roche Limit? Wouldn't tidal forces tend to cause the dust to lift from the surface and either dissipate into space, or fall toward Mars? --Doradus 19:17, 27 Aug 2004 (UTC)

I'll take a stab at it: Tidal "forces" aren't really forces, they're more like a difference of force. Let's say I could grab Phobos by two ends and pull it towards me. If I pulled harder on the side nearer to me, Phobos would feel as if it were being pulled apart. This is what Mars's gravity is doing. The force from gravity is weaker on the far side of Phobos because it's farther away from the planet. The apparent force between two sides of Phobos is much larger than parts of Phobos which are near each other. Dust lying on the surface feels a minimal tidal "force" with respect to the surface it is near because they are close. The collective gravity of Phobos, however, will keep the dust on the surface. If Mars had stronger gravity, though, it could pull the dust right off the surface. Peter 00:07, 28 Aug 2004 (UTC)
That doesn't seem right since being within the Roche limit should mean the tidal force at the inner and outer tips are strong enough to overcome Phobos' gravity, by the definition of "Roche limit". I'll take another stab. The tidal force is strongest at the point closest to Mars and the point farthest away from Mars; it falls off to nothing at the "middle" of the moon. So perhaps the dust is only present in a belt around the midsection of the moon, with dust-free "peaks" at the two tips. Bryan 00:35, 28 Aug 2004 (UTC)
I like that explanation. Because Phobos is tidally locked, dust could indeed settle at the midsection. It would be interesting to know whether measurements confirm this. Also, while the tidal force is a repulsive force at the near and far ends of Phobos, I think it is mildly attractive at the midsection, which might help the dust to settle there. (If you imagine the force vectors at the two opposite limbs of Phobos, they are not parallel, but both point toward Mars' center.) --Doradus 03:32, 28 Aug 2004 (UTC)
There does seem to be quite a lot of dust on Phobos (according to the page), so it's probably not impossible. Let's say Phobos is like a stretched spring with one end always pointing towards Mars. The tension on the spring is the tidal "force". The greater the tidal "force", the longer the spring will be stretched. But, let's say we look at only the first half of the spring. How much tidal "force" is there? I think it will be half as strong. If we pursue this exercise down to the scale of dust, the forces will be quite small relative to that applied to the moon as a whole. In the case of Phobos, this force is apparently less than the force of gravity attracting the dust to the moon. Peter 04:50, 28 Aug 2004 (UTC)
No, I still don't think this is right. If this was the case then passing the Roche limit would never result in a body being broken up by tidal force. The cause of this "force" is the difference between the velocity of a particle on the moon's surface and the velocity of a stable orbit at that distance - the stuff on the inner end of the moon is moving slower than it "should" and the stuff on the outer end is moving faster. Remove the influence of the moon forcing them to follow the moon's orbit and those particles would move off into different paths. It has nothing to do with the size of the particle. Bryan 07:47, 28 Aug 2004 (UTC)
Maybe there's another force between the dust particles, like static electricity or some kind of adhesion. Failing that, perhaps Phobos is not inside its roche limit after all. Or maybe we all misunderstand the roche limit. --Doradus 12:39, 28 Aug 2004 (UTC)
I don't believe Phobos is within its Roche limit. It may well be within what the Roche limit would be if it were a liquid moon, but it is less prolate than a liquid moon would be at the Roche limit- using the formulae on the Wolfram page, at the Roche limit the ratio between the semimajor and both semiminor axes would be 1.952- Phobos isn't a perfect prolate spheroid, and the ratio between its largest and smallest axis length is only 1.45. I have a reference from Icarus from 2001 which states that "...assuming a typical friction angle of 30°,it is clearly nowhere near a tidal limit for a MC body, although it may be at the (fluid) Roche limit depending on the exact value for its density." MC appears to be "zero-cohesion Mohr-Coulomb". If Phobos is a 'rubble pile' it would need an 'angle of friction' of at least 7.1° for stability at its current orbit of 2.76 R. (R is the radius of Mars) Assuming a 'typical friction angle of 30°' Phobos should remain tidally stable until its orbit gets as close as 2.12 R.

I may make some significant edits at this point, I think the Phobos page as it stands is in error. Does anyone have any citations (preferably in another peer-reviewed academic journal) which states that Phobos is within its Roche limit? --Noren 21:28, 1 Sep 2004 (UTC)

(William M. Connolley 09:08, 3 Sep 2004 (UTC)) Tidal forces don't fall to zero at the "middle" - they are attractive there. See Image:Tidal-forces-calculated.png from tidal force.

I'm not sure if this was added after or before you guys had this disucssion, but it says in the artilce "it has been calculated that Phobos is stable with respect to tidal forces, but it is estimated that Phobos will pass the Roche Limit for a rubble pile of its description when its orbital radius drops to about 8400 km, and will likely break up soon afterwards." So, basically, it is not inside the Roche Limit yet.
The page as it existed during most of the above discussion claimed that Phobos was within its Roche limit. I added the phrase you quote to the main page shortly after posting the above to this discussion, the 8400 km figure used on the page was derived from the 2.12 R (mars) given in the above reference. I initially wanted to be sure I wasn't missing any evidence to the contrary by asking for it here... shortly after that I decided to go ahead and be bold and edit it myself. --Noren 17:47, 4 Oct 2004 (UTC)

Millisecond precision in orbit period[edit]

Yes, we do know it to about 1 ms. See Remember that you can observe over a great number of revolutions and the divide by that number, so precision grows with time.

Urhixidur 17:12, 2004 Sep 2 (UTC)

I believe we can time a single revolution to that accuracy. Will subsequent orbits vary by less than 1ms? Surely Mars is not that uniform, perturbation by Jupiter must be on that order of magnitude. Unfortunately I don't know how to calculate either of those effects, so I guess I'll take your word for it. --Doradus 19:11, 2 Sep 2004 (UTC)

I agree with Urhixidur. The reverse or the above is true- I expect we can't time a single revolution to that accuracy(I doubt the position is known that well), but we can time many of them and take the average, just as Urhixidur describes. The orbital period should be quite uniform, I believe. Mars' gravity should be the same during each orbit- no change in period resulting from there- and the gravity gradient from Jupiter should be extremely small. The constant component of any pull from Jupiter or another body will effect both Mars and Phobos equally, and thus cannot influence the period. Diemos might conceivably be relevant, however, though I think the orbit period is by definition an average anyhow. --Noren 20:34, 2 Sep 2004 (UTC)
I think you're right about Jupiter's pull. I disagree on the other points, but not strongly enough to kick up a fuss.  :-) --Doradus 04:25, 3 Sep 2004 (UTC)


I am having trouble getting the formatting to work on 800x600 resolution. That image in the middle kind of mucks things up. I kept tweeking with it and got it to work for this resolution, but don't know the impact at other resolutions.

Mass in Earths[edit]

is given by 1.07 × 1016 kg (1.8 µEarths).

There seems to be a misscalculation here. I'm getting 50.58 nano Earths.

Could someone please check this and either correct the article or my calculation? Thanks 09:38, 13 Mar 2005 (UTC)

Well, I also did the same calculation and came up with yet another result, namely 1.8 nanoEarths. I went ahead and put this in the article; if I'm mistaken then it should be reedited, of course.
-Noren 06:02, 15 Mar 2005 (UTC)
I confirm Noren's result.
Urhixidur 13:07, 2005 Mar 15 (UTC)

In a related change, the volume in Earths was also mistakenly expressed in microearths rather than nanoearths. (As something of a sanity check, I expected comparative volume and mass to be of the same order of magnitude, and they previously were not.) -Noren 00:36, 19 Mar 2005 (UTC)


I had added the alternate pronunciation fob'-us, but it's pretty rare, so I'm taking it out. It's given as an alternate pronunciation in Gayley's Classic Myths in English Literature and in Art. In the OED, not even the much more common cognate "phobic" has a variant with that vowel. Put it back if you like... --kwami 07:52, 7 Apr 2005 (UTC)

The adjectival form Phobian is fairly common, and consistant with the Greek. kwami 2005 June 30 06:19 (UTC)

As seen from...[edit]

"As seen from Phobos, Mars would be 6400 times larger and 2500 times brighter than the full Moon as seen from Earth" it isn't supposed to be as seen from Mars, Phobos...?

No. Phobos looks tiny as seen from Mars. Mars looks huge as seen from Phobos. So it's correct. The Singing Badger 01:04, 19 Apr 2005 (UTC)

The table on the side[edit]

I was looking at this website and I realized that the table on the side of this page is a little hard to read. If somebody could please change the format of this, seeing as I don't know how, I, along with many others I'm sure, would greatly appreciate it. Thank you very much

What exactly do you have trouble with? Font? Text size? Lines between cells (or lack thereof)? Something else?
Urhixidur 20:56, 2005 May 11 (UTC)
I'm guessing that their problem is that there's no gridlines. It does make it hard to read. Ravenswood 21:41, 17 May 2005 (UTC)


That "Pre-discovery" section is bereft of any references and hard facts. "It is said that he saw them in a dream"? Who said that? When? What was the source? What does "some accuracy" mean? All I see is a subjective narative that doesnt deserve to be featured so prominently in this article. I am removing it with the expectation that if someone wants to include it, they actually find some content to go with it as well. Asteron ノレツァ 18:28, August 18, 2005 (UTC)

This is a fairly well-known bit of astronomical lore (see for instance [3]), though written in a rather odd way. I've rewritten it and moved it to the bottom of the page as "trivia" (and likewise on the Deimos page). -- Curps 19:39, 18 August 2005 (UTC)

View from Mars[edit]

I can't find a clear statement, or number that tells me if Phobos (or Deimos for that matter) appears larger from the surface of mars than our moon appears from the surface of earth. Considering how close Phobos is, I initially believed it to be larger, but because of its small size, I may be smaller. If we could get some sort of photograph of it in the sky, that would be great. The current one of Phobos passing by the sun doesn't give you a good idea of what it looks like to a person on mars.--Ikiroid 17:16, 2 December 2005 (UTC)

Hi there! Since Mars is about 1.5 times further from the Sun than Earth, so the Sun seen in the Phobos eclipse movie is also 1.5 times smaller than that seen from the Earth. On Earth, the moon is almost exactly the same angular size as the Sun. That gives a scale. Personally I can't think of a better photo than the eclipse movie to give a sense of scale. In this respect, check out also moon illusion. Deuar 20:09, 2 December 2005 (UTC)
Thank you for the response, I'll add that into the article if it hasn't been done already.--Ikiroid 05:24, 11 December 2005 (UTC)
Remember that the Moon's apparent size is about the same as the Sun's, when viewed from Earth's surface (this is what makes solar eclipses so interesting). From Mars, the Sun appears smaller, since Mars is further away. And then the transit images clearly show Phodos does not eclipse the Sun entirely, hence Phobos appears considerably smaller (to a Martian observer) than the Moon does (to an Earth observer). Urhixidur 18:08, 26 March 2007 (UTC)

Is Phobos even a moon?[edit]

Should we note that Phobos is clearly not a moon in the sense that Luna, Umbriel, etc. are? I mean, it's traditionally been called a moon, but it's incredibly small (its mass is equivalent to 1.8 billionth Earths) and, more importantly, it isn't even spherical and is probably an asteroid, or possibly a chunk of Mars ejected from a collision with a planetoid.

Any natural body orbiting another natural body is a moon, no matter the size. Just because it is small doesn't mean it's not a moon. Moons like our own, Titan, Charon, Ganymede, etc., are moons in hydrostatic equilibrium.
so Saturn has billions of moons?
Technically speaking, yes, Saturn has billions of moons, though it is common to call them moonlets. Since Mars has only 2 natural objects orbiting it, it is logical to call them moons. -- Kheider (talk) 23:55, 18 August 2010 (UTC)

Swift's 'Prediction'[edit]

I suggest that if anyone has any sourced info, including published speculations, on that issue, to go ahead and insert it. I reverted what I felt was an unsourced WP:OR. If we end up with multiple sourced explanations, we may possibly need to present all of them. Thanks, Crum375 21:05, 6 August 2006 (UTC)

I have added a section to the "Literature" section noting Swift's mention of two moons of Mars in Gulliver's visit to Laputa. The naming of features after characters from Gulliver is clearly a reference to this association. There is no evidence whatsoever that Swift had any knowledge of Phobos and Deimos, but it is a sufficiently striking literary parallel that it was taken into account by the IAU --APRCooper (talk) 18:15, 12 August 2008 (UTC)

As for whether Swift had any knowledge of Phobos and Deimos -- as I understand it, he did and he didn't. Carl Sagan writes in The Cosmic Connection that Johannes Kepler predicted that Mars would have two moons, based on a complete guess (interpolating between Venus' zero moons, Earth's one moon, and Jupiter's four then-known moons). Sagan says that as Kepler was so well respected, his speculation was assumed to be correct and that Swift's inclusion of the moons is due to Kepler. That Mars would later be found to actually have two moons basically comes down to good fortune. --JB Gnome (talk) 01:08, 3 September 2011 (UTC)


In the list of features page (separate) there are these craters:

Clustril   Character in Gulliver's Travels
D'Arrest        Heinrich Louis d'Arrest
Drunlo          Character in Gulliver's Travels
Flimnap         Character in Gulliver's Travels
Gulliver        Main character of Gulliver's Travels
Hall            Asaph Hall
Limtoc          Character in Gulliver's Travels
Reldresal       Character in Gulliver's Travels
Roche           Édouard Roche
Sharpless       Bevan Sharpless
Skyresh         Character in Gulliver's Travels
Stickney        Angeline Stickney
Todd            David Peck Todd
Wendell         Oliver Wendell

could we get some kind of map or labelled picture to show where they are? GB 01:59, 26 February 2007 (UTC)

GA review[edit]

Overall, the article is in pretty good shape. Here are my comments.

  • Technical notes:
    • Use {{cite_journal}} instead of {{cite_web}} where applicable (e.g., for the first note which is from The Observatory).
    • The formatting of the quote from Asaph Hall could be better. It should be indented or set off in some other way (consider using a different quotation template), and it should have line breaks between paragraphs. The picture on the left may make it difficult to distinguish the indenting, however, so a box should be considered.
    • Are the red links likely candidates for their own articles? If not, they should be unlinked.
    • The article might be added to more categories.
    • Deimos shouldn't appear in the "See also" section.
    • The headings use both single and double scare quotes. Pick one.
  • Stylistic notes:
    • The article uses the passive voice too much. Rephrase to active voice.
    • Asaph Hall's full name needn't be repeated. "Hall" is fine after the first usage.
    • The quotation from Hall is a bit long, not particularly necessary, and redundant with the non-quoted text. It should be reduced to a pithy or particularly interesting part and/or be summarized in non-quoted prose.
    • The last sentence under "Death of a moon" is rather unwieldy. It should be rephrased and perhaps broken in two.
    • Sentences can be a little choppy. For instance, consider combining one or more short sentences in this passage:
Asaph Hall also discovered Deimos, Mars' other moon. At the time, he was deliberately searching for Martain moons. Hall had previously seen what appeared to be a Martian moon on August 10. Due to bad weather, he did not definitively identify them until later.
  • Content notes:
    • I'd prefer the etymology that gives a bit more explanation and is in the active voice. E.g., "Henry Madan (1838–1901), Science Master of Eton, suggested the names based on book XV of the Iliad in which Ares, who corresponds to the Roman god Mars, summons his sons Dread (Deimos) and Fear (Phobos)."
    • Regarding Swift's prediction, the article says, "This is regarded as a fascinating coincidence." First this is in the passive voice, which should be avoided, and it doesn't cite it's sources (cf. also words which editorialize with respect to "fascinating").
    • Obviously, the {{original research}} tag under "Orbital characteristics" needs to be rectified.
    • "Secular acceleration" is not defined/wikilinked.
    • Some other features listed in the previous section on this talk page could be added without becoming too "listy."

I'm going to fail this nomination primarily because of the original research and the passive voice, but I think these could be corrected after which the article should be renominated. --Flex (talk|contribs) 22:15, 5 March 2007 (UTC)

The Hurtling moons of Barsoom[edit]

The first ever time I recall hearing about the moons of Mars, and specifically Phobos, I was told the story of how Phobos generated the names "The Hurtling moons of Barsoom" by Edgar Rice Burroughs. To this day I still think of Phobos in this way. Does anybody feel this is notable for the page on Phobos?

"In 1912 Edgar Rice Burroughs published a story entitled "Under the Moons of Mars" (printed in book form in 1917 as 'A Princess of Mars') in which he referred to the "hurtling moons of Barsoom" (Barsoom being the "native" word for Mars in the fictional account). Burroughs was inspired by the fact that Phobos, having an orbital period of slightly less than 8 hours, would appear from Mars to rise in the west and set in the east only five and a half hours later. "

Or perhaps under Phobos and Deimos in fiction...

Beeawwb 02:04, 8 May 2007 (UTC)

Meaning of name[edit]

At the recent Phobos Deimos conference, Steven Dick (the NASA historian), surprised many of us by telling us that Phobos means flight and Deimos means fear. I found this reference backing him up, but are there any greek experts to confirm this? We should change this in the article if this is true. Jespley 22:01, 12 November 2007 (UTC)

See Gazetteer of Planetary Nomenclature. It states that Phobos also means "flight" (in addition to fear?) and that Deimos means fear (Panic is a sudden fear). But I know nothing about nomenclature. -- Kheider 23:16, 12 November 2007 (UTC)

That's the kind of flight that's related to flee, in case anyone didn't get that. —Tamfang (talk) 03:07, 31 May 2009 (UTC)

surface gravity (again)[edit]

Because of its shape alone, the gravity on its surface varies by about 210%; the tidal forces raised by Mars more than double this variation (to about 450%) ....

210% and 450% of what? Is the maximum (1+4.5) × the minimum, or is the minimum (1-4.5) × the maximum, or is the range (1±2.25) × the mean? Two of these are of course absurd, but with no reference stated they're all logically valid. I'd prefer the form local gravity varies by a factor of x.y, not only because of that ambiguity but because the known numbers don't appear to justify using three digits (one reason I dislike percentage expressions in general). —Tamfang (talk) 20:38, 16 February 2009 (UTC)

that is cool —Preceding unsigned comment added by (talk) 17:07, 10 April 2009 (UTC)


  • The reference to support the claim that grooves on Phobos "must have been excavated by material ejected into space by impacts on the surface of Mars" refers to "closely-spaced overlapping pits with raised rims." Where is the photographic evidence to support the claim that the overlapping pits actually have raised rims? A lack of raised rims would be consistent with pits caused by subsidence rather than impact.
  • It is conceivable that ejecta from a Martian impact could have formed streams of molten rock (among other things) by the interaction of high pressure plasma of the impact with surrounding material. Such a stream could have formed globules of the right size to make craters such as seen on Phobos, but that every set of craters neatly overlaps and there is no linear set of craters with spaces between them in twelve instances of Martian impacts is a little much to believe.
  • The complicated treatment of data using Gauss-Jackson integration reminds me of the epicyclical formulas that fit planetary observations to an Earth-centered theory of the planets. It could be the theory of grooves from impacts is perfectly sound and just beyond me, but that does not explain the lack of photographic evidence for those raised rims.
  • The Wikipedia article is no better than the reference it cites. FARTHERRED-- (talk) 19:04, 23 May 2009 (UTC)
  • There are craters with raised rims scattered about Phobos. It is the chains of craters with raised rims that lack photographic evidence. What the cited paper directly supports is the statement that researchers in the field believe that the grooves have been excavated by material ejected into space by impacts on the surface of Mars. The paper fails to support the authors' beliefs with photographic evidence. Therefore the reference does not support the statement.FARTHERRED-- (talk) 03:46, 28 May 2009 (UTC) I edited the article to correspond with this discussion on the 29th of June.--Fartherred (talk) 19:16, 19 August 2009 (UTC)


Today an anonymous editor added a quote by Buzz Aldrin about there being a "monolith" on Phobos, with a Youtube link to prove it. I found out what he is referring to — it's an object at about 15°N, 14°W, a few km east of Stickney. It is big enough to be seen in our infobox photo at full resolution. You can see it more easily here in this Global Surveyor photo, a bit left of center. I found out that a Canadian team is considering landing a spacecraft near there so I thought that might be a good way to add context to the quote, rather than linking to some of the speculative amateur sites that are out there. --Cam (talk) 01:45, 28 July 2009 (UTC)

tidal locking[edit]

I'm doubtful about this recent change:

Due to Phobos's low rotational rate relative to its orbital rate, tidal locking is decreasing its orbital radius at the rate of about 20 meters per century.

The ratio of rotation to revolution is the same for Phobos as for Earth's Moon, which is receding with tidal effects! —Tamfang (talk) 18:20, 5 August 2009 (UTC)

But Phobos orbits Mars more quickly than Mars rotates, whereas the Moon orbits Earth more slowly that Earth rotates: the effects are therefore opposite. To put it non-mathematically: each satellite creates in its respective primary planet a slight tidal bulge immediately beneath the satellite, which due to its enhanced proximity produces a slightly larger gravitational pull on the satellite than the undistorted primary would have had (the corresponding tidal bulge on the opposite side of the primary is further away and so has less effect).
  1. Earth rotates beneath the Moon faster than the Moon is moving, so the bulge tends to move ahead of the Moon and its gravity pulls the Moon forward in its orbit, thus adding orbital kinetic energy, which results in the Moon spiralling outwards.
  2. Mars rotates beneath Phobos slower than Phobos is moving, so the bulge tends to lag behind Phobos, and its gravity drags Phobos backwards in its orbit, thus subtracting orbital kinetic energy, so Phobos is spiralling inwards. (talk) 07:15, 20 August 2009 (UTC)

Quite so. Now: what has any of this to do with "Phobos's low rotational rate"? —Tamfang (talk) 07:31, 20 August 2009 (UTC)

Everybody's right here. But it should be made clear that although Phobos is fully tide-locked, it is exerting a miniscule tidal locking effect on Mars, increasing Mars' rate of rotation infinitesimally and losing orbital velocity in return. We're all in agreement, but looking at it in different ways. I think it'd be good to explain more clearly in the article. And yes, Tamfang, the part about Phobos' rotational rate vs. its orbital rate (which are equal!) seems to have already gone away.Steve Hyland (talk) 15:43, 23 November 2009 (UTC)

Update: I've (hopefully) clarified the article; further refinement is welcomed. Steve Hyland (talk) 16:23, 23 November 2009 (UTC)

I lack the mathematical sophistication to show why Phobos will spiral in to the Roche Limit and form a ring . I cannot solve for the time this will take, but some things are intuitively obvious to me. For instance, the statement in the article that the ring system will continue to spiral slowly into Mars is somewhat misleading. The tidal bulge raised by the ring will be equatorial and radially symmetric. There will not be a transfer of momentum between the ring and Mars. However, the ring will crash into Mars because it will spread out as a result of mutual gravitational interactions between ring particles. Thus, the inner edge of the ring will be continually dropping off into Mars' atmosphere. A reference to the eventual fate of the ring would be a plus. This all presupposes no artificial alteration of the situation.--Fartherred (talk) 19:52, 23 November 2009 (UTC)

Regolith retention, cause?[edit]

The article currently states that "Recent images from Mars Global Surveyor indicate that Phobos is covered with a layer of fine-grained regolith at least 100 meters thick; it is believed to have been created by impacts from other bodies, but it is not known how the material stuck to an object with almost no gravity." Could electrostatic charges have anything to do with this? I'm reminded of electrostatic accretion every time I think about regolith on the surface of an object too small to be in hydrostatic equilibrium. Anyone know where you might find info about this (one way or the other)? Sakkura (talk) 00:38, 12 August 2009 (UTC)

Instead of resolving the electrostatic attraction question, I will raise another. The slow disintegration of Phobos' material by the evolution of volatile substances could result in the powdery surface without the powder ever having to fall down onto Phobos.--Fartherred (talk) 20:03, 23 November 2009 (UTC)

Orbital resonance with Deimos?[edit]

The animation of these two moons' orbits (also present in the Deimos article) appears to show Phobos orbiting exactly 4 times for every orbit of Deimos. The figures listed for their respective Orbital periods, however, show a slight discrepancy:

Phobos - 0.31891023d x 4 = 1.27564092d
Deimos - 1.26244d
difference - 0.01320d, or about 19 minutes.

The orbits are therefore not in exact 4:1 resonance. Doubtless it would be difficult to make the animation more accurate, but perhaps a note should be added lest anyone draw this erroneous conclusion. Perhaps also the main text should mention that the two are not quite in resonance, and whether or not (if this be known) they are tending that way. I will attempt to find out if this question has been addressed, and if successful will return to post further information here. (talk) 06:43, 20 August 2009 (UTC)

The period of Phobos is getting shorter, so they will eventually reach resonance. You're right, they can't be shown correctly (without skips) in an animated .gif —Tamfang (talk) 07:27, 20 August 2009 (UTC)
On another hand, if the animation showed 24 orbits of Deimos to 95 orbits of Phobos (24:95 being the next rational approximation after 1:4), the illusion of resonance would be less blatant. —Tamfang (talk) 20:35, 27 August 2009 (UTC)

Exploration section[edit]

Regarding the Russian Phobos missions, it says --

the second returned documented, unusual data and images

What are "documented" data, much less "unusual" data...? -- Syzygy (talk) 11:53, 20 August 2009 (UTC)

... of human design[edit]

A lander bound for Mars would need to be capable of atmospheric entry and subsequent in-situ return to orbit without any support facilities (a capacity which has never been attempted in a manned spacecraft of human design) ...

Isn't that a somewhat unnecessary qualifier? Or have we attempted such feats in spacecraft of non-human design? —Preceding unsigned comment added by (talk) 15:47, 27 August 2009 (UTC)

We have not attempted it, but we don't know who else may or may not have done so. Heh. —Tamfang (talk) 20:37, 27 August 2009 (UTC)
We know there are no spacecraft of non-human design capable of atmospheric entry to any planet available to human use. The designers of such would not have left the craft for human use without having left signs of their being present in the solar system. While this knowledge is not absolute in the logical sense, it is more certain than many things included in Wikipedia and more certain than much scientific knowledge. Implying the possible existence of non-human designed spacecraft within the solar system is like suggesting God may have created the universe. God is much more likely, but neither is suitable for an article that purports to deal with objective scientific fact.--Fartherred (talk) 00:09, 8 September 2009 (UTC)--Fartherred (talk) 20:15, 22 September 2009 (UTC)
The redundant language is now gone.--Fartherred (talk) 03:30, 16 October 2009 (UTC)

Fred Singer[edit]

The bit about Fred Singer supporting the idea of Phobos being a hollow artificial structure does not appear to be legitimate. Singer supposedly made some comments in a journal called Astronautics, but, this journal does not appear to exist, and the given ref doesn’t actually link to anything. The possibility that Singer ever supported Shklovsky is rather dubious. This stuff was removed from Singer’s BOLP, and should be removed from this article as well. Any objections?--CurtisSwain (talk) 07:44, 16 April 2010 (UTC)

Done.--CurtisSwain (talk) 21:04, 18 April 2010 (UTC)
Undone. Apparently, the publication did exist. It's just not available online. I should have been more carefull.--CurtisSwain (talk) 04:50, 22 April 2010 (UTC)

I have a question: He said that it is undeniable that phobos is an artificial structure with the measurements that existed to this point. So if it really is artificial, and makes an effort to look like a moon, doesn't it make sense for the "controlroom" of phobos to adjust the orbit, so it stays undetected? Or am i wrong? Not trying to pitch a conspiracy, just honest interest if anybody considered this. I guess the only way we can prove it to be artificial is to send a probe to dig through the 100m of regolit dust... but the russian spacecraft didn't make it. — Preceding unsigned comment added by (talk) 06:11, 9 October 2014 (UTC)

Contradiction: decrease in orbital radius[edit]

  • Singer's critique was justified when earlier studies were later discovered to have used an overestimated value of 5 cm/yr for the rate of altitude loss, which was later revised to 1.8 cm/yr.
  • tidal deceleration is decreasing its orbital radius at the rate of about 20 metres (66 ft) per century.

These are contradictory because 1.8 cm/yr = 1.8 m/century, not 20 m/century. -- B.D.Mills  (T, C) 02:13, 18 August 2010 (UTC)

Thanks for noting. Both claims are referenced, but both references are somewhat dubious: The ref. for the first value is a paper by Singer which neither Google nor Google Scholar knows; and the ref. for the second is an ArXiv article (i.e. not peer-reviewed) which is obviously not a real scientific paper (they use this Wikipedia article as a reference, among others).--Roentgenium111 (talk) 17:45, 18 August 2010 (UTC)
With the edit of Hamiltonstone on the 20th of September 2010 the contradiction is now gone. The 20 m/century rate has been deleted. I also removed the contradict template. --Fartherred (talk) 16:05, 20 September 2010 (UTC)
Unfortunately, that edit was reverted by an IP just three days later [4] without an argument, and the contradiction has remained since then. --Roentgenium111 (talk) 21:15, 19 February 2013 (UTC)

Is the density of Phobos inconsistent with a hollow shell theory?[edit]

Iron has a density of 7.874. Phobos has a density of 1.876. To be made of iron and have a size and density of Phobos, an object would merely need to have a hollow volume within the shell equal to 76.175% of the whole. Observations of Phobos are inconsistent with a hollow iron shell, but not merely because of observed density. The statement in the article does not claim mere inconsistency between the density and a hollow iron shell theory, but inconsistency with a hollow shell in general. The vary next paragraph refers to the possibility of Phobos being hollow. So it seems to me the claim of inconsistency between the density of Phobos and the hollow shell theory should be removed. --Fartherred (talk) 03:09, 9 September 2010 (UTC)

I don't really see a problem since Phobos is constantly compared to C and D type asteroids throughout the article. But I suppose you could state that the density is consistent with typical asteroids. Certainly there is no proof that Phobos has an iron shell covered with interplanetary dust. -- Kheider (talk) 04:15, 9 September 2010 (UTC)
There is no need to mention in the article that there is no proof that Phobos has an iron shell covered with dust; just as there is no mention in the article on Saint Paul, Minnesota that there is no proof of a network of caves under the city currently infested by the mafia. The article just mentions the Wabasha Street Caves with a link and leaves it at that. --Fartherred (talk) 15:22, 19 September 2010 (UTC)
I never read Shklovsky's work suggesting a hollow sheet metal Phobos, so I assume I would find no fault with it if I did. No one can know everything. Even if there were reasons to suspect the data pointing to a hollow Phobos in Shklovsky's time, it was probably reasonable to publish and bring the matter to the attention of others. People should resist the urge to prove whacky notions wrong. Just pointing out a lack of convincing evidence to support whacky notions should be enough. Especially making a false statement in attempt to prove a whacky notion wrong is harmful, because then the supporters of the strange claim can point out the falseness of opposition argument and gain an appearance of respectability for their claim. --Fartherred (talk) 22:43, 19 September 2010 (UTC)


Patrick Moore states in one of his standard text books that when he asked Shklovsky about the hollow Phobos claim, Shklovsky claimed that it had originally been intended to be a hoax. It seems that like all good hoaxes, this hoax had taken on a life of its own.AT Kunene (talk) 08:41, 6 March 2011 (UTC)

It seems to me we really should drop the whole section on the Hollow Phobos notion on notability grounds. It was never taken very seriously, quickly refuted (not that it is "possible", but that the current drastically improved orbit data is evidence for it), and disavowed by Shklovsky. Or, if anyone thinks it needs to survive, put it into a separate article. It seems to have no place in an article giving the current best understanding of Phobos. Wwheaton (talk) 23:36, 5 August 2014 (UTC)

Taking off from Phobos[edit]

The gravity of Phobos is small so the reaction control system (RCS) thrusters of the Mars Transfer Vehicle could be used to power the take off.

For a spacecraft massing 200 tonne including propellant with a Phobos thrust to weight ratio of 1.2 : 1 . (Ratio used by Earth LV.)

F = m a = 200,000 kg * 0.0084 m/s2 * 1.2 = 2016 N (or 453 lbf)

Larger thrusters will have a shorter burn time, particularly during landing.
Andrew Swallow (talk) 20:00, 1 July 2011 (UTC)

Calculating the strength of thrusters needed by a spacecraft to achieve a Phobos escape velocity of 11.3 m/s2 in 5 seconds
v = u + a t giving a = (v - u) / t
a = (11.3 - 0)/5 = 2.26 m/s2
Add in Phobos's gravity of 0.0084 m/s2
2.26 + 0.0084 = 2.2684 rounds to 2.27 m/s2
F = m a, for a 200 tonne spacecraft
F = 200000 * 2.27 = 454,000 N (or 102,000 lbf)
Andrew Swallow (talk) 18:27, 10 August 2011 (UTC)

Location of Stickney crater[edit]

Dave Alama just got it wrong in edits of the 16th of August. Stickney (crater) is the big one on the right edge of image. Will fix. Fartherred (talk) 01:20, 22 August 2011 (UTC)

Phobos template map[edit]

FWIW - added a newly created {{PhobosCraterNames}} imagemap template (and related Image:USGS-Phobos-MarsMoon-Map.png) to the article - tried to label the crater and region locations as best as possible at the moment - (labels can be hyperlinked to relevant articles, like the label for Stickney (crater)) - some locations are "best-guesses" and are noted with a question mark (?) for now - the Phobos usgs pdf map seemed helpful - any further help with this template project would be welcome of course - in any case - Enjoy! :) Drbogdan (talk) 01:55, 19 August 2013 (UTC)

I hadn't noticed this image template's appearance in the article. The names with question marks are incorrect. The crater labeled "Öpik?" is actually an unnamed crater at about +15° latitude, 2° longitude. Compare crater Flimnap, whose western edge is roughly at 0° longitude, and Reldresal, whose center is at 39° longitude. The real crater Öpik is not visible but would be in shadow in the upper left of the photo. Thus Laputa Regio and crater Shklovsky east of Öpik are not visible at all here. Crater Wendell is some 83 degrees west of Stickney, so is not visible at this angle.--Cam (talk) 21:40, 30 April 2014 (UTC)

Surface area seems way off.[edit]

With a mean radius of 11.1 kms, and surface area of a sphere = 4π*r^2, shouldn't the surface area be something in the realm of 1548.3 km^2? Even if Phobos wasn't rounded at all, dimensions of 26.8 km by 22.4 km by 18.4 should put an upper limit of its surface area at ((26.8*22.4*2)+(26.8*18.4*2)+(22.4*18.4*2)) = 3011.2 kms^2? — Preceding unsigned comment added by (talk) 02:08, 28 November 2013 (UTC)

Thanks for noticing. It seems the diameter had been used as if it were the radius. I've fixed it. --

JorisvS (talk) 09:09, 28 November 2013 (UTC)

Maybe you should fix the other sentences that comment on that surface area? I went ahead and removed where it used to say that the surface area was similar to that of Delaware. --

Inclination figures[edit]

Phobos infobox says that Phobos is inclined 1.093° (to Mars's equator) and 26.04° (to the ecliptic). Mars infobox says its inclined 1.850° to ecliptic. I don't understand how the 26.04 ecliptic inclination is derived. Please correct or cite source. Twang (talk) 16:46, 16 January 2015 (UTC)

Mars's orbit is inclined ~1.850° to the ecliptic. Mar's equator—entirely different thing—is inclined 25.19° to the ecliptic, comparable to Earth's (~23.5°). Phobos's orbital plane is close to Mars's equator, and its rotation axis is is essentially perpendicular to its orbital plane. Wwheaton (talk) 03:42, 23 March 2015 (UTC)
Mars's orbit is tilted 1.85° relative to the ecliptic, i.e. Earth's orbit. Mars's rotation is tilted 25.19° to its orbit actually (it wasn't mentioned in the article until just now, so it took a little digging). Phobos's orbit is titled 1.093° to Mars's equator. Not knowing Mars's rotational orientation, this could give it an axial tilt relative to the ecliptic of 25.19±1.85±1.093°, or any value between 22.25° and 28.13°, depending on the orientation of their orbits and Mars's rotational axis. --JorisvS (talk) 10:06, 23 March 2015 (UTC)

Ring formation - new source to add[edit]

[5] : After 20-40 million years all but some stronger chunks will break up and disperse into a planetary ring. Zerotalk 02:15, 24 November 2015 (UTC)

Mariner 9[edit]

In the exploration history, Mariner 9's observations are not mentioned. -anon. — Preceding unsigned comment added by (talk) 19:07, 22 February 2016 (UTC)