Posted on 11/24/2018 6:35:38 AM PST by ETL
Phobos’ grooves, which are visible across most of the moon’s surface, were first glimpsed in the 1970s by NASA’s Mariner and Viking missions.
Over the years, there has been no shortage of explanations put forward for how they formed.
Some planetary researchers have posited that large impacts on Mars have showered the nearby moon with groove-carving debris. Others think that Mars’ gravity is slowly tearing Phobos apart, and the grooves are signs of structural failure.
Still other scientists have made the case that there’s a connection between the grooves and the impact that created a large crater called Stickney.
In the 1970s, University of Lancaster’s Professor Lionel Wilson and Brown University’ Professor Jim Head proposed the idea that ejecta — bouncing, sliding and rolling boulders — from Stickney may have carved the grooves.
For a moon the size of the diminutive Phobos (17 miles, or 27 km, across), Stickney is a huge crater at 5.6 miles (9 km) across.
“The impact that formed it would have blown free tons of giant rocks, making the rolling boulder idea entirely plausible,” said Ken Ramsley, a researcher in the Department of Earth, Environmental and Planetary Sciences and the School of Engineering at Brown University.
“But there are also some problems with the idea. For example, not all of the grooves are aligned radially from Stickney as one might intuitively expect if Stickney ejecta did the carving And some grooves are superposed on top of each other, which suggests some must have already been there when superposed ones were created.”
“How could there be grooves created at two different times from one single event?”
(Excerpt) Read more at sci-news.com ...
Homophobos- fear of gay captured moons of mars.
Like a rolling stone...
Groovy.
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Stickney Ejecta.
Great band name.
Earf got it’s groove from the Rolling Stones!
I doubt ejecta would be spherical enough to roll around on the surface — it would be jagged and wouldn’t roll. Most ejecta is more of a splash of a semi-liquified rock rather than large roundish boulders.
With the weak gravitational attraction, a boulder would have to be very large to create enough force scar the surface of Phobos, but the small tracks indicate small boulders.
Could the boulders roll into the craters and have enough momentum to carry them up and over the opposite uphill side? I would think that much momentum would launch them off the surface.
Lastly, where are the boulders? There are none to be seen.
Miranda:
“You have the right to remain silent. Anything you say can and will be used against you in a court of law. You have the right to an attorney. If you cannot afford an attorney, one will be provided for you. Do you understand the rights I have just read to you? With these rights in mind, do you wish to speak to me?”
My theory: Phobos is a comet/asteroid that was captured by Mars. The large 'crater' is actually the head of the comet which was burning as it traveled through our solar system. The grooves paths from the burning plasma. The reason for grooves which do not follow the 'pattern' of the others is that the comet made multiple passes by the Sun and the other grooves are much older and their origin 'crater' is gone.
Here is asteroid VESTA. See the grooves ?
Some of the mysterious grooves on the surface of Mars' moon Phobos are the result of debris ejected by impacts eventually falling back onto the surface to form linear chains of craters, according to a new study.
One set of grooves on Phobos are thought to be stress fractures resulting from the tidal pull of Mars.
The new study, published August 30 in Nature Communications, addresses another set of grooves that do not fit that explanation.
"These grooves cut across the tidal fields, so they require another mechanism.
If we put the two together, we can explain most if not all of the grooves on Phobos," said first author Michael Nayak, a graduate student in Earth and planetary sciences at UC Santa Cruz.
Phobos is an unusual satellite, orbiting closer to its planet than any other moon in the solar system, with an orbital period of just 7 hours. Small and heavily cratered, with a lumpy nonspherical shape, it is only 9,000 kilometers from the surface of Mars (the distance from San Francisco to New York and back) and is slowly spiraling inward toward the planet. Phobos appears to have a weak interior structure covered by an elastic shell, allowing it to be deformed by tidal forces without breaking apart.
Tidal stresses
Coauthor Erik Asphaug, a planetary scientist at Arizona State University and professor emeritus at UC Santa Cruz, has been studying Phobos for many years. Recent computer simulations by him and NASA planetary scientist Terry Hurford showed how tidal stresses can cause fracturing and linear grooves in the surface layer. Although this idea was first proposed in the 1970s, the existence of so many grooves with the wrong orientation for such stress fractures had remained unexplained.
Nayak developed computer simulations showing how those anomalous grooves could result from impacts. Material ejected from the surface by an impact easily escapes the weak gravity of Phobos. But the debris remains in orbit around Mars, most of it moving either just slower or just faster than the orbital velocity of Phobos, and within a few orbits it gets recaptured and falls back onto the surface of the moon.
Nayak's simulations enabled him to track in precise detail the fate of the ejected debris. He found that recaptured debris creates distinctive linear impact patterns that match the characteristics of the anomalous grooves and chains of craters that cut across the tidal stress fractures on Phobos.
"A lot of stuff gets kicked up, floats for a couple of orbits, and then gets recollected and falls back in a linear chain before it has a chance to be pulled apart and disassociated by Mars' gravity," Nayak said. "The controlling factor is where the impact occurs, and that determines where the debris falls back."
The researchers used their model to match a linear chain of small craters on Phobos to its primary source crater. They simulated an impact at the 2.6-kilometer crater called Grildrig, near the moon's north pole, and found that the pattern resulting from ejected debris falling back onto the surface in the model was a very close match to the actual crater chain observed on Phobos.
With its low mass and close orbit around Mars, Phobos is so unusual that it may be the only place in the solar system where this phenomenon occurs, Nayak said.
This work was supported by NASA and the Department of Defense through a National Defense Science and Engineering Graduate Fellowship.
Nope. It was all those people from Sandusky, OH, trying to stop the Leather Goddesses...
Also not much gravity on Phobos, I would image all the ejecta blew into space.
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