Phobos: Irregular Shape? (APOD 3 Dec 2006)

FieryIce · Post by **FieryIce** » Sun Dec 03, 2006 5:21 am

A Mars Express image, great picture.
The First Mars Express Science Conference had four presentations specifically about the research done concerning Phobos. If you examine these presentations, which are in PDF format, you will see it stated that Phobos over the last observed 6 years has an “increased secular rate … MER Rovers see 11-12 km orbital advance … HRSC/SRC [ESA Mars Express] see 11-12 km orbital advance”, Thomas C. Duxbury et. al., JPL California Institute of Technology, 11_Duxbury.pdf.

“Phobos ahead of its predicted orbital position by approx. 1 radius, Bell Duxbury et al., Nature”… “Phobos estimated to be off its normal (JPL ephemeris) orbit by 6s (approx. 12 km) along-track; across-track position errors <1 km”, J. Oberst et al., and the HRSC Co-Investigation Team, 12_Phobos_Oberst.pdf.

In the PDF presentation by John Murray et al., the images of Phobos specifically the leading edge of Phobos does not show the leading edge crater chains to be larger than the trailing edge crater chains so their theory that Phobos flew through Mars debris or flew through ejecta debris is not valid or was not validated. But they did achieve to acquire some better imaging of the leading edge of Phobos.

What you might find even more interesting is the last presentation PDF by Severine Perrier et al., SPICAM Team on the Mars Express. They worked on the UV absorption or reflectance of Phobos and Deimos, the albedo of those two moons. What they found was a repetitive reading in the 220 um, “significant absorption feature around 220 um, similar to interstellar extinction feature … could be caused by the presence on Phobos of organic material … not compatible with the UV silicate signature (around 260 um) … similar to the extinction feature observed in the Interstellar Medium of 217.5 um” To quote them even more “Nature of ISM absorbing material? Possible organic material”.

The First Mars Express Science Conference Presentations, http://sci.esa.int/science-e/www/object ... ctid=36537

Therefore, Isoef Shmuelovich Shklovskii’s mathematics and theory of Phobos being an artificial satellite has been further substantiated by the Mars Express (JPL) MRSC/SRC investigative teams conclusions that Phobos is out of predicted position but amazingly Phobos must have some organic material.

happy@apod · Post by **happy@apod** » Sun Dec 03, 2006 2:46 pm

Why does it appear to have layers?

StACase · Post by **StACase** » Sun Dec 03, 2006 2:49 pm

happy@apod wrote:Why does it appear to have layers?

Exactly what I was going to post!

Keldor314 · Post by **Keldor314** » Sun Dec 03, 2006 3:35 pm

Perhaps some time in its past, Phobos traveled through the tail of a comet? This could explain the layered structure, since as a chunk breaks off from a comet, it would tend to disintigrate and be blown into a sort of narrow wisp by the solar wind, like a filiment. The tail of the comet would be composed of a great number of these 'filiments', each of which would leave a groove when it impacted the moon. Since they all would be streaming in the same direction - directly away from the sun - the composite effect of passing through a whole comet tail of these wisps would be to produce the layered effect we see.

As a side note, it would also explain the presence of organics on the moon, since these are fairly common in a comet.

JohnD · Post by **JohnD** » Sun Dec 03, 2006 3:53 pm

Fiery Ice seems to have misinterpeted the abstract.

Can't copy the whole, short abstract, but please go and read it for yourselves. At:
http://sci2.esa.int/Mars/MarsExpressCon ... f#page=112 paper No.110, page 112.

It includes the statement that the apex, "can be seen to be heavily grooved with orientations corresponding closely to those predicted by the last idea" ["chains of secondary craters resulting from large impacts on Mars"]. Murray et al consider this "overwhelming evidence" that validates this theory. Only their opinion, sure, but where's your evidence, FI?

John

Dr. Skeptic · Post by **Dr. Skeptic** » Sun Dec 03, 2006 4:54 pm

The Parallel Grooves of Phobos: New evidence on their Origin from HRSC Mars Express

Murray, J.B.; Muller, J-P.; Iliffe, J.C.; Neukum, G.; HRSC Co-Investigator, Team

The origin of the grooves of Phobos has been debated since they were first discovered, and there is as yet no consensus on their origin. Early hypotheses included faults or outgassing vents caused by tidal or drag forces during the capture of Phobos, and chains of secondary craters or fracturing associated with the Stickney impact. More recently, it has been suggested that they result from chains of secondary craters from large impacts on Mars. This last hypothesis predicts that the leading apex of Phobos should be the most heavily grooved, with families of parallel grooves crossing each other at all angles, but deciding between these various hypotheses has been hampered by the fact that only about half of Phobos has been imaged by previous missions with sufficient resolution and illumination to detect the grooves. Phobos has now been imaged on 5 passes by HRSC, and on two of them, the leading apex is visible at 48m and 50m resolution. Despite unfavourable vertical illumination, it can be seen to be heavily grooved, with orientations corresponding closely to those predicted by the last idea. This is overwhelming evidence that the grooves of Phobos were caused by debris ejected from large impact craters on Mars.

orin stepanek · Post by **orin stepanek** » Sun Dec 03, 2006 6:29 pm

http://antwrp.gsfc.nasa.gov/apod/ap061203.html
Could it be possible that just maybe eons ago Phobos may have been a part of a planet that may have been subjected to weathering process and later been ejected into space by some traumatic happening. Later being captured in orbit around Mars. The rigors of space may explain the craters and its present condition. Just speculating!

Orin

Andy Wade · Post by **Andy Wade** » Sun Dec 03, 2006 9:46 pm

orin stepanek wrote:http://antwrp.gsfc.nasa.gov/apod/ap061203.html
Could it be possible that just maybe eons ago Phobos may have been a part of a planet that may have been subjected to weathering process and later been ejected into space by some traumatic happening. Later being captured in orbit around Mars. The rigors of space may explain the craters and its present condition. Just speculating!
Orin

And here's me thinking that it couldn't possibly be made of sedimentary rocks, could it?

Dr. Skeptic · Post by **Dr. Skeptic** » Sun Dec 03, 2006 10:18 pm

That would be unbelievably interesting if it were sedimentary in origin!

Dezama · Post by **Dezama** » Sun Dec 03, 2006 10:32 pm

That could possibly account for the organic matter, could it not?

TimeTravel12345678 · Post by **TimeTravel12345678** » Mon Dec 04, 2006 2:07 am

Does anyone else besides me feel that the lack of a spherical structure raises questions as to the requirement for a spherical shape of a moon?

When I look at Phobos, I see a captured asteroid not a moon. I see a 1994 Comet Shoemaker Levy that came in at a different trajectory of impact possibly.

Of course the idea of a spherical moon is just the result of being accustomed to our spherical moon and other spherical moons like Titan, Ganymede, Io, Triton

I find the assumption of 10,000 years or 100,000 years before impact with Mars to be just arbitrary. Local asteroid impacts, which we are not as careful to predict, could lead to Phobos impacts earlier.

The APOD is good. You know what would be fun...a picture of like a Betelgeuse with chromatic aberration. Honest with you, me observing on Friday night at a local facility. Betelgeuse honestly looks like a firecracker. A picture of an object undergoing chromatic aberration or its natural activity would be good. You have I am sure done hundreds of such pictures.

Happy December 3rd.

Richard Pernice · Post by **Richard Pernice** » Mon Dec 04, 2006 2:55 am

Regarding the apod for Sunday, Dec 3, 2006;
I'm sure it isn't made of sedimentary rock, but does anyone know what caused those lines across the moon?

BMAONE23 · Post by **BMAONE23** » Mon Dec 04, 2006 3:15 am

Here we go again, now the IAS will need to meet to determine the requiements for a rocky body to be labeled "MOON".

orin stepanek · Post by **orin stepanek** » Mon Dec 04, 2006 3:46 am

It has to be spherical to be a planet; lets leave it at that.
Orin

harry · Post by **harry** » Mon Dec 04, 2006 7:23 am

Hello All

The lines on Phobo are quite interesting. I have seen this moon so many times and yet did not see the lines.

Could the meteorites between Mars and Jupiter form from a planet that broke up and are these rocks formed from sedimentation from that planet.
I was just thinking aloud.

Or the sedimention occcured somehow during the origin of our solar system from a supernova explotion.

I'm very interested in finding out.

FieryIce · Post by **FieryIce** » Mon Dec 04, 2006 1:30 pm

JohnD, if you look at the images of Phobos, the leading apex is as cratered as the rest of Phobos, the leading apex crater chains are not larger and trailing off as would be expected with the hypothesis suggesting “that they result from chains of secondary craters from large impacts on Mars”. Check out the Viking 1* images.

Concerning the organic material on Phobos, it is interesting in a book printed in 1980 illustrating Viking 1* images of Phobos mentions the organic surface material. This is nothing new but what was new was the position of Phobos, or the not anticipated position of Phobos.

Cosmos, page 94

*Viking 1 arrived at Mars on June 19, 1976, 30 years ago.

iamlucky13 · Post by **iamlucky13** » Mon Dec 04, 2006 5:56 pm

Does anyone know if Phobos is in tidal lock with Mars? If so, was it always (seems extremely unlikely if it was captured)?

If not, then it seems quite logical for the streaking to be well distributed around Phobos as it rotates and passes through impact debris. From the abstract Dr. Skeptic posted, I'd say this seems likely

Also, for those not familiar with the term from a chemistry perspective, organic means materials which contain carbon and hydrogen. While definitely interesting, there is nothing particularly special about the presence of organic compounds on Phobos.

The idea of the streaking being sedimentary in nature is intriguing, but I think unlikely. I have difficulty imagining such large features being retained during a breakup. If they are, I suspect they'd have to be volcanic in nature (ie, not really sedimentary). A planet breaking up where the asteroid belt is today would no doubt be too cold for liquid water to be a significant transport medium, much less leave 5 kilometers of striped geology.

Just my $0.02.

FieryIce, do you have any thoughts on the cause of Phobos' advanced orbital position. That is the most interesting part of the paper from my perspective. From the abstract book, it sounds like mostly just uncertainty in the actual orbit, but I was unsure.

Also, thanks for the link to the abstract book. It's amazing to see so many diverse papers resulting from the Mars probes of the past decade.

Galactic Groove · Post by **Galactic Groove** » Mon Dec 04, 2006 9:21 pm

It's classified as a moon because of the body it oribits. If it was still orbiting the Sun it would probably be called an asteroid (and most probably not a planet) but it is a satellite of the planet Mars... the fact that it orbits a planet is what makes it a moon. Regardless of whether or not it was originally an asteroid that got caught in Mars' gravity... its current state now is that it is a satellite. Spherical or not, once-upon-a-time an asteroid or not, it's still a satellite of a planet.

Keldor314 · Post by **Keldor314** » Mon Dec 04, 2006 9:42 pm

It does bring an interesting point, though - how small does a body have to be before it's no longer a moon? I mean, whenever they discover a new moon of a planet, it tends to be one of the smallest ones yet (since the bigger ones have already been discovered), first one with a 50 km diameter, then 25, then 10, and now a lot of the small ones are simply noted as less than 1 km. So, how small can it get and stay a moon? House sized? Car sized? Surely each rock and grain of dust in Saturn's rings cannot be called a moon, even if it IS house sized..

BMAONE23 · Post by **BMAONE23** » Mon Dec 04, 2006 10:14 pm

I believe that the large mass objects in Saturns ring system are named or numbered moons, while the dust particles remain uncatagorized as anything but rings. Hopefully this doesn't change or Saturn will be labaled "1 quintillion moons and counting"...

Galactic Groove · Post by **Galactic Groove** » Tue Dec 05, 2006 12:25 am

The size dilemma is difficult as it's basically up to personal opinion. And it's obvious that the masses will never agree to just 1 person's opinion. We just need to pick something and go with it. In the end it doesn't really matter. Heck, it'll even create more jobs for highschool kids in the summer because of all the re-cataloguing that'll need to be done!! hahaha

BMAONE23 · Post by **BMAONE23** » Tue Dec 05, 2006 2:03 pm

Could spectra be used to determine if, in fact, Mars' moons came about as a direct result of the Hellas Impact and are in fact part of the planet?

Al · Post by Al » Tue Dec 05, 2006 4:55 pm

Note that the layers of Phobos appear parallel. If the lines came from something external to the moon, I would think the layering effect would not appear so perfectly parallel.

Also note that some of the layering goes down into some (but not all) of the craters. To me this means that the layering goes down into the interior of Phobos.

All of this points toward the layering of Phobos taking place during its formation.

Al

BMAONE23 · Post by **BMAONE23** » Tue Dec 05, 2006 5:59 pm

Could Phobos be a ramnant of the Hellas Impact event? A piece of Mars that was ejected into space then recaptured by the planet?

JohnD · Post by **JohnD** » Tue Dec 05, 2006 7:17 pm

FI,
Don't agree - anyone bear me out?
There's a chain that starts about 4 o'clock, passes 'below' a very shadowed crater and then into a large, eroded and presumably older crater. It then fizzles out.
A very regular chain passes immediately 'above' that shadowed crater, to what is either a large terminal crater, or a much older, eroded crater.
And 'above' that are two irregular chains, that fizzle out among the three old eroded craters.
So several crater chains that start prominent and fade out, all leading from the lower right side of this image. I therefore presume that the leading edge of Phobos is at about 4 o'clock on this image, in the dark segment. If I'm wrong, I'm wrong.

And sedimentary? The mean diameter of Phobos is 22 kilometers, and it has stripes right through it, like Blackpool rock! The Earth's crust is between 10 and 70 kilometers thick. Is there anywhere on Earth where there is sedimentary rock, or layered volcanic deposits more than 20k thick? If not, the sedimentary, layered origin of this stone has to be doubtful.

And Al, the layering goes into craters, but only old, eroded ones. The newer, sharper ones show no 'layering'. This is entirely in line with epochs of impacts - an oldest epoch of large impacts, the craters now eroded and worn away, a later epoch of crater chaining, and a more recent one of individual impacts.

John

Starship Asterisk*

Phobos: Irregular Shape? (APOD 3 Dec 2006)

Phobos: Irregular Shape? (APOD 3 Dec 2006)

strata?

Not sedimentary

Phobos's Irregular Shape Provocative - Sphere? (3 Dec 2006)

Phobos (APOD 3 Dec 2006)

Layers of Phobos