DOES MARS HAVE RINGS?
Since from our childhood we know the characteristics of planets in our solar system like jupiter is the largest , saturn has rings , mercury is the closest and venus is also called morning star but have you ever thought about mars and its rings. but it is clear that it has no rings now. but in future?
In order to justify this first we need to understand about natural satellite (moons) of mars and its orbiting axis.
PHOBOS
Phobos is a small, irregularly shaped object with a mean radius of 11 km (7 mi) and is seven times as massive as the outer moon, Deimos. Phobos is named after the Greek god Phobos, a son of Ares (Mars) and Aphrodite (Venus) and the personification of fear (phobia).
DEIMOS
Phobos isn’t nearly the size of a planet, but many of the same mechanisms will drive its destruction. Its companion moon Deimos is about 7.8 miles (12.6 kilo meters) in diameter and orbits Mars at an average distance of 14,580 miles (23,460 km), far enough away to avoid Phobos’ fate. Phobos is 13.8 miles (22.2 km) in diameter. It circles the planet at an average distance of 5,827 miles (9,377 km). With an orbital period of just 7 hours, 39.2 minutes, Phobos is one of only 18 of the 181 known moons in the solar system whose orbital period is less than its planet’s rotation period.
Since from our childhood we know the characteristics of planets in our solar system like jupiter is the largest , saturn has rings , mercury is the closest and venus is also called morning star but have you ever thought about mars and its rings. but it is clear that it has no rings now. but in future?
In order to justify this first we need to understand about natural satellite (moons) of mars and its orbiting axis.
MOONS OF MARS
Mars have two moons phobos and deimos.PHOBOS
Phobos is a small, irregularly shaped object with a mean radius of 11 km (7 mi) and is seven times as massive as the outer moon, Deimos. Phobos is named after the Greek god Phobos, a son of Ares (Mars) and Aphrodite (Venus) and the personification of fear (phobia).
Phobos orbits 6,000 km (3,700 mi) from the Martian surface, closer to its primary body than any other known planetary moon. It is so close that it orbits Mars much faster than Mars rotates, and completes an orbit in just 7 hours and 39 minutes. As a result, from the surface of Mars it appears to rise in the west, move across the sky in 4 hours and 15 minutes or less, and set in the east, twice each Martian day.
Deimos the smaller and outermost of the two natural satellites of the planet Mars, the other being Phobos. Deimos has a mean radius of 6.2 km (3.9 mi) and takes 30.3 hours to orbit Mars. Deimos is 23,460 km (14,580 mi) from Mars, much further than Mars's other moon, Phobos.It is named for Deimos who in Greek mythology is the twin brother of Phobos, and personifies terror.
both the moons are fine as of now and they are orbiting mars in orbital axis , but in future ?
The theory put forth by NASA-funded scientists at Purdue University, Lafayette, Indiana, whose findings were published in the journal Nature Geoscience. David Minton and Andrew Hesselbrock developed a model that suggests that debris that was pushed into space from an asteroid or other body slamming into Mars around 4.3 billion years ago alternates between becoming a planetary ring and clumping together to form a moon.
That’s one of a few reasons why Phobos is doomed. “There are four factors in action,” explains Mittal. “The tidal force of Mars; the centrifugal forces on Phobos, which is rotating; the gravity of Phobos; and the strength of Phobos. There’s a balance among these. Tidal and rotational stresses act to pull Phobos apart; self-gravity and [tensile] strength act to hold Phobos together.”
Just as our own Moon’s gravity raises tides in both Earth’s oceans and landmasses, Phobos creates a tiny tidal bulge in Mars. The bulge moves as the moon circles Mars, just as the Moon-caused tidal bulge moves around Earth. Because Phobos has an orbital period faster than the martian day, the tidal bulge lags behind Phobos and acts to gradually slow it in its orbit, sending Phobos slowly spiraling in toward the martian surface. The rate is about 0.79 inch (2 centimeter) per year. for that we need to know one atronomical term roche limit.
ROCHE LIMIT
The distance within which the gravitational field of a large body is strong enough to prevent any smaller body from being held together by gravity.
“As Phobos gets closer to Mars,” says Mittal, “the tidal stresses increase.” The moon’s self-gravity and tensile strength oppose the tidal forces, but eventually Phobos will drop to a distance called the Roche limit where the martian gravity is greater than moon's self gravity. Several studies confirm that Phobos’ inward spiral will lead to its destruction in 25 million to 75 million years.
Phobos could resist if it were a dense body, more able to resist the pull of gravity past the Roche limit. Unfortunately, data from the European Space Agency’s Mars Express orbiter show that the moon has a density of just 1.9 grams per cubic centimeter. Mars Express also revealed that Phobos is porous, likely containing large voids.
In addition, Phobos’ makeup is similar to carbonaceous chondrite meteorites . These primitive meteorites are made of a bevy of loose, easily broken materials, including magnetite, olivine crystals, phyllosilicates, and complex organic molecules such as amino acids, and are about 10 percent water, formed in oxygen-rich regions of the early solar system.
Then there’s Stickney Crater, the giant impact basin on Phobos. Sometime in its past, Phobos was hit by an object that left a crater 5.6 miles (9km) wide — nearly half the moon’s diameter. The impact surely fractured much of Phobos’ interior, leaving it even weaker. From there, billions of years of meteoroid impacts have churned the surface of Phobos into a layer of fine dust about a hundred meters deep. Given the extremely weak surface gravity (escape velocity for Phobos is a mere 4.56 feet per second), the rock making up the rubble pile just barely stays put.
Black and Mittal used a numerical geotechnical model designed for large underground construction projects to estimate what they call the moon’s “rock mass strength.” The results place the finale for Phobos between 20 million and 40 million years from now, and give more details on its violent end.
As Phobos reaches its Roche limit, about 3,400 miles (5,470km) from the martian surface, tidal forces will start pulling Phobos apart. It will happen quickly: In as little as a week, the dust will spread into a ring circling Mars, the moon no more.
FUTURE RING
Is it possible that Mars possessed a ring system in itspast? “We’re not certain,” says Black, “but it would be worth investigating whether past migrating moons may have existed. Some fraction of moons might be expected to have an orbital configuration similar to that of Phobos and Mars.”
Some planetary scientists think Mars once did have more than two moons. Researchers have identified 258 elliptical craters on Mars formed by objects hitting the surface at grazing angles. At least some of them could well have been made by oblique impacts of ancient martian moons. If so, others may have broken up before hitting the atmosphere, leaving short-lived rings of rocks and dust around Mars.
EARTH PAST RING:THEIA
Earth did, though, for an extremely brief period during the formation of the Moon 4.5 billion years ago when our planet was struck by a Mars-sized body Theia. Much of Theia merged with Earth, but the “Big Splash” would have blown the remaining material into space. Computer simulations indicate about 20 percent of Theia’s mass would have gone into orbit around Earth as a ring. About 10 percent of the ring’s material then quickly coalesced into the Moon, with the rest eventually falling back to Earth. The ring would not have lasted long, perhaps as little as a month but probably no more than 100 years.
Curiously, our Moon also could end as it began, the fate of Earth as the Sun expands into a red giant, it is found that the Moon stood a chance of becoming a ring around Earth.
The Moon is receding from Earth at a rate of about 1.6 inches (4 cm) per year. Left unchecked, the Moon will eventually migrate out to a distance where it will take 47 days to orbit Earth. By then, Earth’s rotation also will have slowed to 47 days. The two will then keep the same face to each other,
Before this happens, though, some 5 billion years from now, the Sun will enter its red giant phase. It will start expanding in size, and swallow up Mercury and Venus. As the Earth-Moon system orbits through the Sun’s expanded outer atmosphere, drag forces will cause the Moon’s orbit to begin decaying. The Sun probably will continue to expand, and destroy both Earth and the Moon. On the other hand, if the Sun should blow off about 20 percent of its mass first, the Moon will continue to spiral down to its Roche limit. Tidal forces will tear it apart, just as they will destroy Phobos.
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