• We have updated the guidelines regarding posting political content: please see the stickied thread on Website Issues.

The Moons Of Mars: Deimos & Phobos

re: Mars and Phobos (above):

The Roche limit (pronounced /ʁoʃ/ in IPA, similar to the sound of rosh), sometimes referred to as the Roche radius, is the distance within which a celestial body, held together only by its own gravity, will disintegrate due to a second celestial body's tidal forces exceeding the first body's gravitational self-attraction.[1] Inside the Roche limit, orbiting material disperses and forms rings whereas outside the limit material tends to coalesce. The term is named after Édouard Roche, who is the French astronomer who first calculated this theoretical limit in 1848.

etc...

https://en.wikipedia.org/wiki/Roche_limit
 
Do you think there are moonquakes on Phobos and Deimos?

My guess is "yes."

This would be especially true for Phobos, which is believed to have a loose structure of agglomerated "rubble" and is subject to tidal forces.
 
Of course the tidal forces onPhobos are small, because it is such a small object. Tides are dependent on the difference in gravity at each end of the object, and Phobos is only 23km long. But it is tidally locked, so tidal forces are significant enough to affect its rotation. Eventually it will get torn apart, or enter the atmosphere, or both.
 
... But it is tidally locked, so tidal forces are significant enough to affect its rotation. Eventually it will get torn apart, or enter the atmosphere, or both.

Phobos references I've seen unanimously claim it's doomed, with estimates of its demise ranging from 2 million years (in the future) upward.
 
... Phobos will eventually disintegrate and form a ring around the red planet. ...

Newly published research suggests this wouldn't be the first time there was a ring around Mars. For one thing, both the Phobos and Deimos of today may have coalesced from a prior ring - perhaps more than once.
We Just Got Even More Evidence Mars Once Had a Ring

New research provides even more evidence that a rubbly ring once circled the Red Planet.

The new clue lies in Deimos, the smaller of the two Martian moons. It's orbiting Mars at a slight tilt with respect to the planet's equator - and this could very well be the result of the gravitational shenanigans caused by a planetary ring.

Ring systems aren't actually all that uncommon. When you think about ring systems, your mind immediately leaps to Saturn, no doubt - but half the planets in the Solar System have rings, Saturn, Uranus, Neptune, and Jupiter. Dwarf planet Haumea, and centaurs Chiron and Chariklo also have rings.

In 2017, a pair of researchers theorised that Mars, too, once had a ring. They conducted simulations of the larger of the two Martian moons, Phobos, and found that it could have formed after an asteroid slammed into Mars, sending debris flying into space, forming a ring that then clumped together into an earlier form of Phobos that was much more massive than it is today.

Now this new research has added Deimos into the mix - and the findings are in total agreement with the previous model.

"The fact that Deimos's orbit is not exactly in plane with Mars's equator was considered unimportant, and nobody cared to try to explain it," said astronomer Matija Ćuk of the SETI Institute.

"But once we had a big new idea and we looked at it with new eyes, Deimos's orbital tilt revealed its big secret." ...

But there is something screwy going on with Phobos. It's much closer to Mars, on an orbit of 7 hours and 39 minutes, and it's getting closer to Mars by 1.8 centimetres a year.

Within 100 million years, it's expected that Phobos will reach the Roche limit, the distance from Mars at which the planet's tidal forces tear the moon apart.

Much of the debris could form a ring that rains down on Mars; but some of it could re-form into a smaller, newer Phobos that gets pushed outwards as the ring is pulled in.

This, according to the 2017 research, could have happened several times in the past. And this is where Deimos comes in.

Using numerical simulations, Ćuk and his team attempted to model how such an outward-moving proto-Phobos would have affected Deimos' orbital inclination. And they arrived at a proto-Phobos 20 times the moon's current mass, which would have entered a 1:3 orbital resonance with Deimos at a distance of 3.3 Mars radii that pushed the latter's orbit into a slight tilt.

This neatly produced the Deimos orbit we see today, which then remained relatively unchanged for billions of years. ...

FULL STORY:
https://www.sciencealert.com/the-weird-orbit-of-mars-moon-suggests-the-red-planet-once-had-a-ring

INFO ABOUT THE DRAFT REPORT ACCEPTED FOR PUBLICATION:
https://arxiv.org/abs/2006.00645
 
Newly published research suggests this wouldn't be the first time there was a ring around Mars. For one thing, both the Phobos and Deimos of today may have coalesced from a prior ring - perhaps more than once.


FULL STORY:
https://www.sciencealert.com/the-weird-orbit-of-mars-moon-suggests-the-red-planet-once-had-a-ring

INFO ABOUT THE DRAFT REPORT ACCEPTED FOR PUBLICATION:
https://arxiv.org/abs/2006.00645
That might explain why the moons aren't nice and smooth.
 
May not explain the odd 'striations' though.
 
But not on both moons.
 
I meant that the striations are only on one moon.

Wouldn't one expect them both to be similar.
 
Not necessarily. They are different sizes, in different orbits, and may have differing overall compositions. Small differences between bodies can result in very significant differences in behavior over millions of years. Yet another reason to study them more closely.
They'd also make good bases for early human Mars missions, being easier to land on and take off from. Natural observation platforms and way stations.
 
Not necessarily. They are different sizes, in different orbits, and may have differing overall compositions. Small differences between bodies can result in very significant differences in behavior over millions of years. Yet another reason to study them more closely.
They'd also make good bases for early human Mars missions, being easier to land on and take off from. Natural observation platforms and way stations.

As envisaged by K M Robinson in his Mars trilogy.
 
Newly published research results are claimed to demonstrate that Deimos and Phobos are the remnants of a single larger Martian moon that disintegrated long ago - probably as a result of a collision.
Researchers Say They’ve Solved the Puzzling Mystery of the Moons of Mars

Phobos and Deimos are the remains of a larger Martian moon that was disrupted between 1 and 2.7 billion years ago, say researchers from the Institute of Geophysics at ETH Zurich and the Physics Institute at the University of Zurich. In collaboration with the U.S. Naval Observatory, they reached this conclusion using computer simulations and seismic recordings from the InSight Mars mission. ...

“Phobos and Deimos look more like asteroids than natural moons.” ...

This led people to suspect that they might in fact be asteroids that were captured in Mars’s gravity field. “But that’s where the problems started,” Bagheri says. Captured objects would be expected to follow an eccentric orbit around the planet, and that orbit would be at a random inclination. In contradiction to this hypothesis, the orbits of the Martian moons are almost circular and move in the equatorial plane of Mars. So, what is the explanation for the current orbits of Phobos and Deimos? ...

“The idea was to trace the orbits and their changes back into the past” ... As it turned out, the orbits of Phobos and Deimos appeared to have crossed in the past. “This means that the moons were very likely in the same place and therefore have the same origin” ... The researchers concluded that a larger celestial body was orbiting Mars back then. This original moon was probably hit by another body and disintegrated as a result. “Phobos and Deimos are the remainders of this lost moon” ...

... {The} researchers ran hundreds of computer simulations to track the orbits of the moons backward in time until they reached the intersection – the moment Phobos and Deimos were born. Depending on the simulation, this point in time lies between 1 and 2.7 billion years in the past. “The exact time depends on the physical properties of Phobos and Deimos, that is, how porous they are” ...

Another thing their calculations show is that the common ancestor of Phobos and Deimos was further away from Mars than Phobos is today. While the smaller Deimos has remained in the vicinity of where it came into being, tidal forces are causing the larger Phobos to approach Mars ... It seems Deimos will move away from Mars very slowly, just as our Moon is slowly receding from Earth. Phobos, however, will crash into Mars in less than 40 million years or be torn apart by the gravitational forces as it nears Mars. ...

FULL STORY: https://scitechdaily.com/researchers-say-theyve-solved-the-puzzling-mystery-of-the-moons-of-mars/
 
Here are the bibliographic details and abstract of the newly published research report.

Bagheri, A., Khan, A., Efroimsky, M. et al.
Dynamical evidence for Phobos and Deimos as remnants of a disrupted common progenitor.
Nat Astron (2021).
https://doi.org/10.1038/s41550-021-01306-2

Abstract
The origin of the Martian moons, Phobos and Deimos, remains elusive. While the morphology and their cratered surfaces suggest an asteroidal origin1,2,3, capture has been questioned because of potential dynamical difficulties in achieving the current near-circular, near-equatorial orbits4,5. To circumvent this, in situ formation models have been proposed as alternatives6,7,8,9. Yet, explaining the present location of the moons on opposite sides of the synchronous radius, their small sizes and apparent compositional differences with Mars2 has proved challenging. Here, we combine geophysical and tidal-evolution modelling of a Mars–satellite system to propose that Phobos and Deimos originated from disintegration of a common progenitor that was possibly formed in situ. We show that tidal dissipation within a Mars–satellite system, enhanced by the physical libration of the satellite, circularizes the post-disrupted eccentric orbits in <2.7 Gyr and makes Phobos descend to its present orbit from its point of origin close to or above the synchronous orbit. Our estimate for Phobos’s maximal tidal lifetime is considerably less than the age of Mars, indicating that it is unlikely to have originated alongside Mars. Deimos initially moved inwards, but never transcended the co-rotation radius because of insufficient eccentricity and therefore insufficient tidal dissipation. Whereas Deimos is very slowly receding from Mars, Phobos will continue to spiral towards and either impact with Mars or become tidally disrupted on reaching the Roche limit in ≲39 Myr.

SOURCE: https://www.nature.com/articles/s41550-021-01306-2
 

Mars moon mystery: Strange structures found inside 'fearful' Phobos


Europe's Mars Express spacecraft has peered deeper into the subsurface of the Martian moon Phobos than ever before, finding hints of unknown structures that could be clues as to the moon's origin.

Mars Express, which is a 19-year-veteran spacecraft in orbit around Mars, came within 51.6 miles (83 kilometers) of Phobos on Sept. 22, 2022 and was able to probe beneath the moon's surface using upgraded software on its MARSIS instrument (Mars Advanced Radar for Subsurface and Ionosphere Sounding).

MARSIS involves a 40-meter-long antenna beaming low frequency radio waves down to the surface. Most of the radio waves are reflected directly back from the surface, but some penetrate deeper, where they encounter transitions between layers of different composition and structure, and are reflected back by these boundaries. The stronger the reflection in the resulting 'radargram', the brighter the returning radio signal.

The radargram from across a narrow track on Phobos shows a bright line, split into two and labeled A–C and D–F respectively. The A–C section was captured using the old MARSIS software to compare with D–F, which utilizes the new software and which shows much more detail. The main bright line is the reflection from the surface of Phobos, but beneath that there is evidence for fainter lines that could just be interference, or 'clutter,' from features on the surface, but they could also be caused by structures below the surface.

https://www.space.com/phobos-radar-unknown-structures-mars-express

maximus otter
 
Back
Top