On The Origin Of Phobos’ Groovy Mystery

Phobos

Mars’ natural satellites – Phobos and Deimos – have been a mystery since they were first discovered. While it is widely believed that they are former asteroids that were captured by Mars’ gravity, this remains unproven. And while some of Phobos’ surface features are known to be the result of Mars’ gravity, the origin of its linear grooves and crater chains (catenae) have remained unknown.

But thanks to a new study by Erik Asphaug of Arizona State University and Michael Nayak from the University of California, we may be closer to understanding how Phobos’ got its “groovy” surface. In short, they believe that re-accretion is the answer, where all the material that was ejected when meteors impacted the moon eventually returned to strike the surface again.

Naturally, Phobos’ mysteries extend beyond its origin and surface features. For instance, despite being much more massive than its counterpart Deimos, it orbits Mars at a much closer distance (9,300 km compared to over 23,000 km). It’s density measurements have also indicated that the moon is not composed of solid rock, and it is known to be significantly porous.

(a) Spacecraft image of Phobos (photo credit: ESA/Mars Express) showing the observed catena of interest (red arrows); (b) reimpact map for a primary impact at Grildrig, azimuth ?? [0: ) rendered in three dimensions. Relative sizes and orientations between a and b are similar and may be correlated from Drunlo, Clustril, Grildrig, Gulliver and Roche craters, respectively. From the correlation, the highlighted catena likely originates from sesquinary ejecta from Grildrig.
Image of Phobos showing the observed catena of interest (left) and reimpact map for a primary impact at Grildrig (right). Credit: ESA/Mars Express
Because of this proximity, it is subject to a lot of tidal forces exerted by Mars. This causes its interior, a large portion of which is believed to consist of ice, to flex and stretch. This action, it has been theorized, is what is responsible for the stress fields that have been observed on the moon’s surface.

However, this action cannot account for another common feature on Phobos, which are the striation patterns (aka. grooves) that run perpendicular to the stress fields. These patterns are essentially chains of craters that typically measure 20 km (12 mi) in length, 100 – 200 meters (330 – 660 ft) in width, and usually 30 m (98 ft) in depth.

In the past, it was assumed that these craters were the result of the same impact that created Stickney, the largest impact crater on Phobos. However, analysis from the Mars Express mission revealed that the grooves are not related to Stickney. Instead, they are centered on Phobos’ leading edge and fade away the closer one gets to its trailing edge.

For the sake of their study, which was recently published in Nature Communications, Asphaug and Nayak used computer modeling to simulate how other meteoric impacts could have created these crater patterns, which they theorized were formed when the resulting ejecta circled back and impacted the surface in other locations.

Credit: ESA/DLR/FU Berlin-Neukum
Image showing the Stickney crater (left) and how ejecta from an impact can form patterns (right) and crater chains (catenae). Credit: ESA/DLR/FU Berlin-Neukum

As Dr. Asphaug told Universe Today via email, their work was the result of a meeting of minds that spawned an interesting theory:

“Dr. Nayak had been studying with Prof. Francis Nimmo (of UCSC), the idea that ejecta could swap between the Martian moons. So Mikey and I met up to talk about that, and the possibility that Phobos could sweep up its own ejecta. Originally I had been thinking that seismic events (triggered by impacts) might cause Phobos to shed material tidally, since it’s inside the Roche limit, and that this material would thin out into rings that would be reaccreted by Phobos. That still might happen, but for the prominent catenae the answer turned out to be much simpler (after a lot of painstaking computations) – that crater ejecta is faster than Phobos’ escape velocity, but much slower than Mars orbital velocity, and much of it gets swept up after several co-orbits about Mars, forming these patterns.”

Basically, they theorized that if a meteorite stuck Phobos in just the right place, the resulting debris could have been thrown off into space and swept up later as Phobos swung back around mars. Thought Phobos does not have sufficient gravity to re-accrete ejecta on its own, Mars’ gravitational pull ensures that anything thrown off by the moon will be pulled into orbit around it.

Once this debris is pulled into orbit around Mars, it will circle the planet a few times until it eventually falls into Phobos’ orbital path. When that happens, Phobos will collide with it, triggering another impact that throws off more ejecta, thus causing the whole process to repeat itself.

The streaked and stained surface of Phobos. (Image: NASA)
The streaked and stained surface of Phobos, with the Stickney crater shown in the center. Credit: NASA/JPL/Mars Express

In the end, Asphaug and Nayak concluded that if an impact hit Phobos at a certain point, the subsequent collisions with the resulting debris would form a chain of craters in discernible patterns – possibly within days. Testing this theory required some computer modeling on an actual crater.

Using Grildrig (a 2.6 km crater near Phobos’ north pole) as a reference point, their model showed that the resulting string of craters was consistent with the chains that have been observed on Phobos’ surface. And while this remains a theory, this initial confirmation does provide a basis for further testing.

“The initial main test of the theory is that the patterns match up, ejecta from Grildrig for example,” said Asphaug. “But it’s still a theory. It has some testable implications that we’re now working on.”

In addition to offering a plausible explanation of Phobos’ surface features, their study is also significant in that it is the first time that sesquinary craters (i.e. craters caused by ejecta that went into orbit around the central planet) were traced back to their primary impacts.

The many faces of Mars inner moon, Phobos (Credit: NASA)
Mosaic of space images showing the many “faces” of Mars inner moon, Phobos. Credit: NASA

In the future, this kind of process could prove to be a novel way to assess the surface characteristics of planets and other bodies – such as the heavily cratered moons of Jupiter and Saturn. These findings will also help us to learn more about Phobos history, which in turn will help shed light on the history of Mars.

“[It] expands our ability to make cross-cutting relationships on Phobos that will reveal the sequence of geologic history,” Asphaug added. “Since Phobos’ geologic history is slaved to the tidal dissipation of Mars, in learning the timescale of Phobos geology we learn about the interior structure of Mars”

And all of this information is likely to come in handy when it comes time for NASA to mount crewed missions to the Red Planet. One of the key steps in the proposed “Journey to Mars” is a mission to Phobos, where the crew, a Mars habitat, and the mission’s vehicles will all be deployed in advance of a mission to the Martian surface.

Learning more about the interior structure of Mars is a goal shared by many of NASA’s future missions to the planet, which includes NASA’s InSight Lander (schedules for launch in 2018). Shedding light on Mars geology is expected to go a long way towards explaining how the planet lost its magnetosphere, and hence its atmosphere and surface water, billions of years ago.

Further Reading: Nature Communications

How Close Can Moons Orbit?

The Moon is great and all, but I wish it was closer. Close enough that I could see all kinds of detail on its surface without a telescope or a pair of binoculars. Close enough that I could just reach up and grab enough cheese for a lifetime of grilled cheese sandwiches.

Sure, there would be all kinds of horrible problems with having the Moon that much closer. Intense tides, a total lack of good dark nights for stargazing, and something else… Oh right, the total destruction of life on Earth. On second thought the Moon can stay right where it is, thank you very much.

The Earth’s Moon is located an average distance of 384,400 kilometers away. I say average because the Moon actually follows an elliptical orbit. At its closest point, it’s only 362,600 km, and at its furthest point, it’s 405,400 kilometers.

Still, that’s so far that it takes light a little over a second to reach the Moon, traveling almost 300,000 km/s. The Moon is far.

But what if the Moon was much closer? How close could it get and still be the Moon?

Many of the features on the moon are named as oceans. Credit: NASA
The Moon isn’t actually getting closer. It just looks that way because it’s on your computer screen. Credit: NASA

Once again, I need to remind you that this is purely theoretical. The Moon isn’t getting closer to us, in fact, it’s getting further. The Moon is slowly drifting away from us at a distance of almost 4 centimeters per year.

Let’s go back to the beginning, when the young Earth collided with a Mars-sized planet billions of years ago. This catastrophic encounter completely resurfaced planet Earth, and kicked up a massive amount of debris into orbit. Well, a Moon’s worth of debris, which collected together by mutual gravity into the roughly spherical Moon we recognize today.

Shortly after its formation, the Moon was much closer, and the Earth was spinning more rapidly. A day on Earth was only 6 hours long, and the Moon took just 17 days to orbit the Earth.

The Earth’s gravity stopped the Moon’s relative rotation, and the Moon’s gravity has been slowing the Earth’s rotation. To maintain the overall angular momentum of the system, the Moon has been drifting away to compensate.

This conservation of momentum is very important because it works both ways. As long as a moon takes longer than a day to orbit its planet, you’re going to see this same effect. The planet’s rotation slows, and the moon drifts further to compensate.

But if you have a scenario where the moon orbits faster than the planet rotates, you have the exact opposite situation. The moon makes the planet rotate more quickly, and it drifts closer to compensate. This can’t end well.

Once you get close enough, gravity becomes a harsh mistress.

Reaching the Roche limit can ruin your day. Credit: Hazmat2. Original Image Credit: Theresa Knott. CC-SA 3.0
Reaching the Roche limit can ruin your day. Credit: Hazmat2. Original Image Credit: Theresa Knott. CC-SA 3.0

There’s a point in all gravitational interactions called the Roche Limit. This is the point at which an object held together by gravity (like the Moon), gets close enough to another celestial body that it gets torn apart.

The exact point depends on the mass, size and density of the two objects. For example, the Roche Limit between the Earth and the Moon is about 9,500 kilometers, assuming the Moon is a solid ball. In other words, if the Moon gets within 9,500 kilometers or so, of the Earth, the gravity of the Earth overwhelms the gravity holding the Moon together.

The Moon would be torn apart, and turned into a ring. And then the pieces of the ring would continue to orbit the Earth until they all came crashing down. When that happened, it would be a series of very bad days for anyone living on Earth.

Get too close to the sun and a comet could be torn apart. Credit: NASA/JPL-Caltech

If an average comet got within about 18,000 km of Earth, it would get torn to pieces. While the Sun can, and does, tear apart comets from about 1.3 million km away.

This sounds purely theoretical, but this is actually going to happen over at Mars. Its largest moon Phobos orbits more quickly than a Martian day, which means that it’s drifting closer and closer to the planet. In a few million years, it’ll cross the Roche Limit, tear into a ring, and then all the pieces of the former Phobos will crash down onto Mars. We did a whole article on this.

Phobos, the larger of Mars' two moons, with the Stickney crater seen on the right side. Credit: HiRISE, MRO, LPL (U. Arizona), NASA
Phobos will eventually break apart from reaching the Roche limit, which will leave Deimos as Mars’ only moon. Credit: HiRISE, MRO, LPL (U. Arizona), NASA

Now you might be wondering, wait a second. I’m a separate object from the Earth, why don’t I get torn apart since I’m definitely within the Earth’s Roche Limit.

You do have gravity holding you together, but it’s insignificant compared to the chemical bonds holding you together. This is why physicists consider gravity to actually be a pretty weak force compared to all the other forces of the Universe.

You’d need to go somewhere with really intense gravity, like a black hole, for the Roche Limit to overcome the forces holding you together.

So that’s it. Bring the Moon within 9,500 kilometers or so and it would no longer be a Moon. It would be torn apart into a ring, a Halo ring, if you will, capable of wiping out all life on a planet infected by the flood. All the moons we see in the Solar System are are least at the Roche Limit or beyond, otherwise they would have broken up long ago… and probably did.

Time For NASA To Double Down On Journey To Mars

Since the Authorization Act of 2010, NASA has been pushing ahead with the goal of sending astronauts to Mars by the 2030s. The latter part of this goal has been the subject of much attention in recent years, and for good reason. Sending crewed missions to the Red Planet would be the single-greatest initiative undertaken since the Apollo era, and the rewards equally great.

However, with the scheduled date for a mission approaching, and the upcoming presidential election, NASA is finding itself under pressure to show that they are making headway. Despite progress being made with both the Space Launch System (SLS) and the Orion Multi-Purpose Crew Vehicle, there are lingering issues which need to be worked out before NASA can mount its historic mission to Mars.

One of the biggest issues is that of assigned launched missions that will ensure that the SLS is tested many times before a crewed mission to Mars is mounted. So far, NASA has produced some general plans as part of it’s “Journey to Mars“, an important part of which is the use of the SLS and Orion spacecraft to send a crew beyond low-Earth orbit and explore a near-Earth asteroid by 2025.

NASA's Journey to Mars. NASA is developing the capabilities needed to send humans to an asteroid by 2025 and Mars in the 2030s. Credit: NASA/JPL
NASA’s Journey to Mars. NASA is developing the capabilities needed to send humans to an asteroid by 2025 and Mars in the 2030s. Credit: NASA/JPL

This plan is not only intended to provide their astronauts with experience working beyond LEO, but to test the SLS and Orion’s capabilities, not to mention some vital systems – such as Solar Electric Propulsion (SEP), which will be used to send cargo missions to Mars. Another major step is  Exploration Mission 1 (EM-1), the first planned flight of the SLS and the second uncrewed test flight of the Orion spacecraft (which will take place on September 30th, 2018).

However, beyond this, NASA has only one other mission on the books, which is Exploration Mission 2 (EM-2). This mission will involve the crew performing a practice flyby of a captured asteroid in lunar orbit, and which is scheduled for launch in 2023. This will be the first crewed test of the Orion spacecraft, and also the first time American astronauts have left low-Earth orbit since the Apollo 17 mission in 1972.

While significant, these mission remain the only two assigned flights for the SLS and Orion. Beyond these, dozens more have been proposed as part of NASA’s three phase plan to reach Mars. For instance, between 2018 and the 2030s, NASA would be responsible for launching a total of 32 missions in order to send the necessary hardware to near-Mars space before making crewed landings on Phobos and then to Mars.

In accordance with the “Evolvable Mars Campaign” – which was presented last year by NASA’s Human Exploration and Operations Mission Directorate (HEOMD) – Phase One (the “Earth Reliant” phase) of this plan would involve two launches in 2028, which would be responsible for transporting a habitation module, an SEP module, and a exploration vehicle to cis-lunar space.

This would be followed by two SLS flights in 2029, bringing the Trans-Earth Injection (TEI) stage to cis-lunar space, followed by a crew to perform the final checks on the Phobos Hab. By 2030, Phase Two (known as the “Proving Ground” phase) would begin with the last elements – the Earth Orbit Insertion (EOI) stage and taxi elements – being launched to cis-lunar orbit, and then all the equipment being sent to near-Mars space for pre-deployment.

By 2031, two more SLS missions would take place, where a Martian Hab would be launched, followed in 2032 by the launches of the Mars Orbit Insertion (MOI) and Trans-Mars Injection (TMI) stages. By 2033, Phase Three (the “Earth Independent” phase) would begin, where the Phobos crew would be transported to the Transit Hab, followed by the final crewed mission to the Martian surface.

Accomplishing all of this would require that NASA commit to making regular launches over the next few years. Such was the feeling of Bill Gerstenmaier – NASA’s Associate Administrator for Human Exploration and Operations – who recently indicated that NASA will need to mount launches at least once a year to establish a “launch cadence” with the SLS.

Mission proposals of this kind were also discussed at the recent Aerospace Safety Advisory Panel (ASAP) meeting – which meets annually to discuss matters relating to NASA’s safety performance. During the course of the meeting, Bill Hill – the Deputy Associate Administrator for Exploration Systems Development (ESD) in NASA’s Human Exploration and Operations Mission Directorate (HEOMD) – provided an overview of the latest developments in NASA’s planned mission.

The many faces of Mars inner moon, Phobos (Credit: NASA)
The many faces of Mars inner moon, Phobos. Credit: NASA

By and large, the meeting focused on possible concepts for the Mars mission, which included using SEP and chemical propellants for sending hardware to cis-lunar space and near-Mars space, in advance of a mission to Phobos and the Martian surface. Two scenarios were proposed that would rely to these methods to varying extents, both of which called for a total of 32 SLS launches.

However, the outcome of this meeting seemed to indicate that NASA is still thinking over its long-term options and has not yet committed to anything beyond the mission to a near-Earth asteroid. For instance, NASA has indicated that it is laying the groundwork for Phase One of the Mars mission, which calls for flight testing to cis-lunar space.

However, according to Hill, NASA is currently engaged in “Phase 0” of the three phase plan, which involves the use of the ISS to test crew health via long duration space flight. In addition, there are currently no plans for developing Phases Two and Three of the mission. Other problems, such as the Orion spacecraft’s heatshield – which is currently incapable of withstanding the speed of reentry coming all the way from Mar – have yet to be resolved.

Another major issue is that of funding. Thanks to the Obama administration and the passage of the Authorization Act of 2010, NASA has been able to take several crucial steps towards developing their plan for a mission to Mars. However, in order to take things to the next level, the US government will need to show a serious commitment to ensuring that all aspects of the plan get the funding they need.

And given that it is an election year, the budget environment may be changing in the near future. As such, now is the time for the agency to demonstrate that it is fully committed to every phase of its plan to puts boots on the ground of Mars.

On the other hand, NASA has taken some very positive strides in the past six years, and one cannot deny that they are serious about making the mission happen in the time frame it has provided. They are also on track when it comes to proving key concepts and technology.

In the coming years, with flight tests of the SLS and crewed tests of the Orion, they will be even further along. And given the support of both the federal government and the private sector, nothing should stand in the way of human boots touching red soil by the 2030s.

Artist's concept image of a boot print on the moon and on Mars. Credit: NASA/JPL-Caltech
Artist’s concept image of a boot print on the moon and on Mars. Credit: NASA/JPL-Caltech

Further Reading: NASA Spaceflight.com

How Many Moons Does Mars Have?

Many of the planets in our Solar System have a system of moons. But among the rocky planets that make up the inner Solar System, having moons is a privilege enjoyed only by two planets: Earth and Mars. And for these two planets, it is a rather limited privilege compared to gas giants like Jupiter and Saturn which each have dozens of moons.

Whereas Earth has only one satellite (aka. the Moon), Mars has two small moons: Phobos and Deimos. And whereas the vast majority of moons in our Solar System are large enough to become round spheres similar to our own Moon, Phobos and Deimos are asteroid-sized and misshapen in appearance.

Size, Mass and Orbit:

The larger moon is Phobos, whose name comes from the Greek word which means “fear” (i.e. phobia). Phobos measures just 22.7 km across and has an orbit that places it closer to Mars than Deimos. Compared to Earth’s own Moon — which orbits at a distance of 384,403 km away from our planet — Phobos orbits at an average distance of only 9,377 km above Mars.

This produces an orbit of short duration, revolving around the planet three times in a single day. For someone standing on the planet’s surface, Phobos could be seen crossing the sky in only 4 hours or so.

Phobos, the larger of Mars' two moons, with the Stickney crater seen on the right side. Credit: HiRISE, MRO, LPL (U. Arizona), NASA
Phobos, the larger of Mars’ two moons, with the Stickney crater seen on the right side. Credit: HiRISE, MRO, LPL (U. Arizona), NASA

Mars’ second moon is Deimos, which takes its name from the Greek word for panic. It is even smaller, measuring just 12.6 km across, and is also less irregular in shape. Its orbit places it much farther away from Mars, at a distance of 23,460 km, which means that Deimos takes 30.35 hours to complete an orbit around Mars.

When impacted, dust and debris will leave the surface of the moon because they do not have enough gravitational pull to retain the ejecta. However, the gravity from Mars will keep a ring of this debris around the planet in approximately the same region that the moon orbits. As the moon revolves, the debris is redeposited as a dusty layer on its surface.

Like Earth’s Moon, Phobos and Deimos always present the same face to their planet. Both are lumpy, heavily-cratered and covered in dust and loose rocks. They are among the darker objects in the solar system. The moons appear to be made of carbon-rich rock mixed with ice. Given their composition, size and shape, astronomers think that both of Mars’ moons were once asteroids that were captured in the distant past.

However, it appears that of these two satellites, Phobos won’t be orbiting the Red Planet for very much longer. Because it orbits Mars faster than the planet itself rotates, it is slowly spiraling inward. As a result, scientists estimate that in the next 10-50 million years or so, it will get so low that the Martian gravity will tear Phobos into a pile of rocks. And then a few million years later, those rocks will crash down on the surface of Mars in a spectacular string of impacts.

The Martian Moon of Deimos, as pictured by the Mars Reconnaissance Orbiter. Credit: HiRISE/MRO/LPL (U. Arizona)/NASA
The Martian Moon of Deimos, as pictured by the Mars Reconnaissance Orbiter. Credit: HiRISE/MRO/LPL (U. Arizona)/NASA

Composition and Surface Features:

Phobos and Deimos both appear to be composed of C-type rock, similar to blackish carbonaceous chondrite asteroids. This family of asteroids is extremely old, dating back to the formation of the Solar System. Hence, it is likely that they were acquired by Mars very early in its history.

Phobos is heavily cratered from eons worth of impacts from meteors with three large craters dominating the surface. The largest crater is Stickney (visible in the photo above). The Stickney crater is 10 km in diameter, which is almost half of the average diameter of Phobos itself. The crater is so large that scientists believe the impact came close to breaking the moon apart. Parallel grooves and striations leading away from the crater indicate that fractures were likely formed as a result of the impact.

Much like Phobos, it’s surface is pockmarked and cratered from numerous impact. The largest crater on Deimos is approximately 2.3 km in diameter (1/5 the size of the Stickney crater). Although both moons are heavily cratered, Deimos has a smoother appearance caused by the partial filling of some of its craters.

Origin:

Compared to our Moon, Phobos and Deimos are rough and asteroid-like in appearance, and also much smaller. In addition, their composition (as already noted) is similar to that of C-type asteroids that are common to the Asteroid Belt. Hence, the prevailing theory as to their origin is that they were once asteroids that were kicked out of the Main Belt by Jupiter’s gravity, and were then acquired by Mars.

 

History of Observation:

Phobos and Deimos were originally discovered by American astronomer Asaph Hall in August of 1877. Ninety-four years after the moons’ discovery, NASA’s Mariner 9 spacecraft got a much better look at the two moons from its orbit around Mars. Upon viewing the large crater on Phobos, NASA decided to name it after Hall’s wife – Stickney. Subsequent observations conducted by the HiRISE experiment, the Mars Global Surveyor, and the Mars Reconnaissance Orbiter have added to our overall understanding of these two satellites.

Someday, manned missions may be going to Phobos and Deimos. Scientists have discussed the possibility of using one of the Martian moons as a base from which astronauts could observe the Red Planet and launch robots to its surface, while shielded by miles of rock from cosmic rays and solar radiation for nearly two-thirds of every orbit.

Here’s an article about how Phobos is going to crash into Mars in the future. And here are some great images of both Phobos and Deimos.

Here’s NASA’s fact sheet on Mars, including information about the moons, and additional info from Starry Skies.

Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.

Sources:

Mars’ Moon Phobos Undergoing ‘Structural Failure’

We’ve said it before: Mars’ moon Phobos is doomed. But a new study indicates it might be worse than we thought.

One of the most striking features we see on images of Phobos is the parallel sets of grooves on the moon’s surface. They were originally thought to be fractures caused by an impact long ago. But scientists now say the grooves are early signs of the structural failure that will ultimately destroy this moon.

“We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves,” said Terry Hurford, from NASA’s Goddard Space Flight Center.

Why is Phobos falling apart?

Two words: tidal forces.

Phobos orbits closer to its planet than any moon in the Solar System. As it orbits just 6,000 km (3,700 miles) above Mars, and the planet’s gravity is pulling Phobos in closer and closer; it is also tearing Phobos apart. Scientists estimate the ultimate destruction of this tiny moon (22 kilometers/13.5-miles in diameter) might take place in about 30 to 50 million years.

It only take about 7.5 hours for Phobos to complete an orbit around the planet, while Mars takes almost 25 hours to complete one rotation on its axis. So Phobos travels three times around the planet for every Martian day. And as Fraser explains in this video, this is a problem.

Mars’ gravity is pulling in Phobos closer by about 2 meters (6.6 feet) every hundred years. The orbit will get lower and lower until it reaches a level known as the Roche Limit. This is the point where the tidal forces between the two sides of the moon are so different that it gets torn apart.

Hurford and his colleagues, who presented their latest findings at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society this week, also delivered other bad news about the interior of Phobos – which could ultimately speed up the demise of the moon. Phobos’ insides are likely to be just a big pile of rubble — barely holding together — surrounded by a layer of powdery regolith about 100 meters (330 feet) thick.

“The funny thing about the result is that it shows Phobos has a kind of mildly cohesive outer fabric,” said Erik Asphaug of the School of Earth and Space Exploration at Arizona State University in Tempe and a co-investigator on the study. “This makes sense when you think about powdery materials in microgravity, but it’s quite non-intuitive.”

Phobos' Stickney Crater
Phobos’ Stickney Crater. Credit: NASA.

Phobos’ grooves have long been an issue up for debate. As mentioned previously, one idea is that the grooves were associated with the impact that formed Stickney Crater, a big 10 km-wide crater that dominates one side of Phobos. However, scientists eventually determined that the grooves don’t radiate outward from the crater itself but from a focal point nearby. Another idea is they came from Phobos moving through streams of debris thrown up from impacts 6,000 km away on the surface of Mars, with each ‘family’ of grooves corresponding to a different impact event.

But new modeling by Hurford and his team supports the idea that the grooves are more like “stretch marks” that occur when Phobos gets deformed by tidal forces.

The team said that stress fractures predicted by their model coincide with the grooves seen in images of Phobos. This explanation also fits with the observation that some grooves are younger than others, which would be the case if the process that creates them is ongoing.

Huford also said the same fate may await Neptune’s moon Triton, which is also slowly falling inward and has a similarly fractured surface. The work also has implications for extrasolar planets, according to researchers.

“We can’t image those distant planets to see what’s going on, but this work can help us understand those systems, because any kind of planet falling into its host star could get torn apart in the same way,” said Hurford.

Here’s a video showing Mars Express images of Phobos over the last 10 years. The images show the grooves running across the small moon:

Source: NASA

How Could We Destroy the Moon?

What would it take to destroy our moon, and eliminate the enemy of stellar astronomy for all time?

In the immortal words of Mr. Burns, “ever since the beginning of time, man has wished to destroy the Sun.” Your days are numbered, Sun.

But supervillains, being the practical folks they are, know that a more worthy goal would be to destroy the Moon, or at least deface it horribly. Nothing wrecks a beautiful night sky like that hideous pockmarked spotlight. What would it take to destroy it and eliminate the enemy of stellar astronomy for all time?

Crack out your Acme brand blueprint paper and white pencils, it’s Wile E. Coyote time.

The energy it takes to dismantle a gravitationally held object is known as its binding energy, we talked about it in a Death Star episode and inventive ways to overcome it.

For example, the binding energy of the Earth is 2.2 x 10^32 joules. It’s a lot. The binding energy of a smaller object, like our Moon is a tidy little 1.2 x 10^29 joules. It takes about 1800 times more energy to destroy the Earth than it takes to destroy the Moon.

It’s 1800 times easier. That’s downright doable, isn’t it? That’s almost 2000 times easier. Which, on the scale of easy to less easy, is definitely closer to easy.

Take the event that created the Caloris Basin on Mercury. It’s a crater, 1,500 km across. Astronomers think that a big fat asteroid, a fatsteroid(?) around 100 km in diameter crashed into Mercury billions of years ago. This event released 1.3 x 10^26 joules of energy, carving out this giant pit. It’s a thousandth of the binding energy of the Moon. We’ll need something more.

Our Sun produces 3.8 x 10^26 joules of energy every second, the equivalent of about a billion hydrogen bombs. If you directed the full power of the Sun at the Moon for 15 minutes, it’d tear apart.

That’s quite a superweapon you’ve got there, perhaps you’ll want to mount that on a space station and take it for a cruise through a galaxy far far away?

If that scene took that long, we’d have fallen asleep. It’s as if millions of voices gradually became a little hoarse from crying out for a quarter of an hour. There’s another way you could tear the Moon apart that doesn’t require an astral gate accident: gravity.

Astronomers use the Roche Limit to calculate how close an object – like a moon – can orbit another object – like a planet.

This is the point where the difference between the tidal forces on the “front” and “backside” are large enough that the object is torn apart, and if this sounds familiar you might want to look up “spaghettification”.

Spaghettification. Credit: Streeter
Spaghettification. Credit: Streeter

This is all based on the radius of the planet and the density of the planet and moon. If the Moon got close enough to the Earth, around 18,000 km, it would pull apart and be shredded into a beautiful ring.

And then the objects in the ring would enter the Earth’s atmosphere and rain down beautiful destruction for thousands of years.

Fortunately or unfortunately, depending your position in this “Die Moon, Die” discussion, the Moon is drifting away from the Earth. It’ll never be closer than it is right now, at almost 400,000 km, without a little nudge.

Phobos, the largest moon orbiting Mars is slowly approaching the planet, and astronomers think it’ll reach the Roche Limit in the next few million years.

It turns out that if we really want to destroy the Moon, we’ll need to destroy all life on Earth as well.

Now we know your new supervillain project, what’s your supervillain name? Tell us your handle in the comments below.

Dazzling Gallery From India’s MOM Mars Orbiter Camera

Spectacular 3D view of Arsia Mons, a huge volcano on Mars, taken by camera on India’s Mars Orbiter Mission (MOM). Credit: ISRO
Story updated with more details and imagery[/caption]

India’s first ever robotic explorer to the Red Planet, the Mars Orbiter Mission, more affectionately known as MOM, has captured an absolutely dazzling array of images of the fourth rock from the Sun.

The Indian Space Research Organization (ISRO), India’s space agency, has recently published a beautiful gallery of images featuring a variety of picturesque Martian canyons, volcanoes, craters, moons and more.

We’ve gathered a collection here of MOM’s newest imagery snapped by the probes Mars Color Camera (MCC) for the enjoyment of Martian fans worldwide.

The spectacular 3D view of the Arsia Mons volcano, shown above, was “created by draping the MCC image on topography of the region derived from the Mars Orbiter Laser Altimeter (MOLA), one of five instruments on board NASA’s Mars Global Surveyor (MGS) spacecraft.

The Arsia Mons image was taken from Mars orbit on 1 April 2015 at a spatial resolution of 556 meters from an altitude of 10707 km. Volcanic deposits can be seen located at the flanks of the Mons, according to ISRO.

The view of Pital crater below was released in late May and taken on 23 April 2015. Pital is a 40 km wide impact crater located in the Ophir Planum region of Mars and the image shows a chain of small impact craters. It is located in the eastern part of Valles Marineris region, says an ISRO description. MCC took the image from an altitude of 808 km.

Pital crater is an impact crater located in Ophir Planum region of Mars, which is located in the eastern part of Valles Marineris region. This  image is taken by Mars Color Camera (MCC) on 23-04-2015 at a spatial resolution of  ~42 m from an altitude of 808 km. Credit: ISRO
Pital crater is an impact crater located in Ophir Planum region of Mars, which is located in the eastern part of Valles Marineris region. This image is taken by Mars Color Camera (MCC) on 23-04-2015 at a spatial resolution of ~42 m from an altitude of 808 km. Credit: ISRO

It is an odd shaped crater, neither circular nor elliptical in shape, possibly due to “regional fracture in the W-E trending fracture zone.”

A trio of images, including one in stunning 3D, shows various portions of Valles Marineris, the largest known canyon in the Solar System.

Three dimensional view of Valles Marineris center portion from India’s MOM Mars Mission.   Credit: ISRO
Three dimensional view of Valles Marineris center portion from India’s MOM Mars Mission. Credit: ISRO

Valles Marineris stretches over 4,000 km (2,500 mi) across the Red Planet , is as much as 600 km wide and measures as much as 7 kilometers (4 mi) deep.

Valles Marineris from India’s Mars Mission.   Credit: ISRO
Valles Marineris from India’s Mars Mission. Credit: ISRO

For context here’s a previously taken global image of the red planet from MOM showing Valles Marinaris and Arsia Mons, which belongs to the Tharsis Bulge trio of shield volcanoes. They are both near the Martian equator.

Olympus Mons, Tharsis Bulge trio of volcanoes and Valles Marineris from ISRO's Mars Orbiter Mission. Note the clouds and south polar ice cap.   Credit: ISRO
Olympus Mons, Tharsis Bulge trio of volcanoes and Valles Marineris from ISRO’s Mars Orbiter Mission. Note the clouds and south polar ice cap. Credit: ISRO

Valles Marineris is often called the “Grand Canyon of Mars.” It spans about as wide as the entire United States.

A gorgeous view of Phobos, the largest of Mars’ two tiny moons, silhouetted against the surface is shown below.

Phobos, one of the two natural satellites of Mars silhouetted against the Martian surface.  Credit: ISRO
Phobos, one of the two natural satellites of Mars silhouetted against the Martian surface. Credit: ISRO

MOM’s goal is to study Mars atmosphere, surface environments, morphology, and mineralogy with a 15 kg (33 lb) suite of five indigenously built science instruments. It is also sniffing for methane, a potential marker for biological activity.

MOM is India’s first deep space voyager to explore beyond the confines of her home planets influence and successfully arrived at the Red Planet after the “history creating” orbital insertion maneuver on Sept. 23/24, 2014 following a ten month journey from Earth.
MOM swoops around Mars in a highly elliptical orbit whose nearest point to the planet (periapsis) is at about 421 km and farthest point (apoapsis) at about 76,000 km, according to ISRO.

It takes MOM about 3.2 Earth days or 72 hours to orbit the Red Planet.

Higher resolution view of a portion of Valles Marineris canyon from India’s MOM Mars Mission.   Credit: ISRO
Higher resolution view of a portion of Valles Marineris canyon from India’s MOM Mars Mission. Credit: ISRO

MOM was launched on Nov. 5, 2013 from India’s spaceport at the Satish Dhawan Space Centre, Sriharikota, atop the nations indigenous four stage Polar Satellite Launch Vehicle (PSLV) which placed the probe into its initial Earth parking orbit.

The $73 million MOM mission was expected to last at least six months. In March, ISRO extended the mission duration for another six months since its healthy, the five science instruments are operating fine and it has sufficient fuel reserves.

And with a communications blackout between Mars and Earth imminent as a result of natures solar conjunction, it’s the perfect time to catch up on all things Martian.

Solar conjunctions occur periodically between Mars and Earth about every 26 months, when the two planets line up basically in a straight line geometry with the sun in between as the two planets travel in their sun-centered orbits.

Since Mars will be located behind the Sun for most of June, communications with all the Terran spacecraft at the planet is diminished to nonexistent.

“MOM faces a communication outage during June 8-25,” according to The Hindu.

Normal science operations resume thereafter.

“Fuel on the spacecraft is not an issue,” ISRO Satellite Centre Director M. Annadurai told The Hindu.

Image of Tyrrhenus Mons in Hesperia Planum region taken by Mars Color Camera (MCC) on 25-02-2015 at a spatial resolution of 166m from an altitude of 3192km.  Tyrrhenus Mons is an ancient martian volcano and image shows its timeworn gullies and wind streaks.  Credit: ISRO
Image of Tyrrhenus Mons in Hesperia Planum region taken by Mars Color Camera (MCC) on 25-02-2015 at a spatial resolution of 166m from an altitude of 3192km. Tyrrhenus Mons is an ancient martian volcano and image shows its timeworn gullies and wind streaks. Credit: ISRO

Including MOM, Earth’s invasion fleet at the Red Planet numbers a total of seven spacecraft comprising five orbiters from NASA, ESA and ISRO as well as the sister pair of mobile surface rovers from NASA – Curiosity and Opportunity.

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer

Weekly Space Hangout – May 15, 2015: Finding, Studying and Visiting Other Worlds!

Host: Fraser Cain (@fcain)

Guests:
Jolene Creighton (@jolene723 / fromquarkstoquasars.com)
Brian Koberlein (@briankoberlein / briankoberlein.com)
Dave Dickinson (@astroguyz / www.astroguyz.com)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Alessondra Springmann (@sondy)
Continue reading “Weekly Space Hangout – May 15, 2015: Finding, Studying and Visiting Other Worlds!”

Is Phobos Doomed?

What fate awaits Phobos, one of the moons of Mars?

“All these worlds are yours except Europa, attempt no landing there.”

As much as I love Arthur C. Clarke and his books, I’ve got to disagree with his judgement on which moons we should be avoiding. Europa is awesome. It’s probably got a vast liquid ocean underneath its icy surface. There might even be life swimming down there, ready to be discovered. Giant freaky Europa whales or some kind of alien sharknado. Oh man, I just had the BEST idea for a movie.

So yea, Europa’s fine. The place we should really be avoiding is the Martian Moon Phobos. Why? What’s wrong with Phobos? Have I become some kind of Phobo…phobe? Is there any good reason to avoid this place?

Well first, its name tells us all we need to know. Phobos is named for the Greek god of Horror, and I don’t mean like the usual gods of horror as in Clive Barker, John Carpenter or Wes Craven, I mean that Phobos is the actual personification of Fear… possibly with a freaky lion’s head. And… there’s also the fact that Phobos is doomed.

Literally doomed. Living on borrowed time. Its days are numbered. It’s been poisoned and there’s no antidote. It’s got metal shards in its heart and the battery on it’s electro-magnet is starting to brown out. More specifically, in a few million years, the asteroid-like rock is going to get torn apart by the Martian gravity and then get smashed onto the planet.

The streaked and stained surface of Phobos. (Image: NASA)
The streaked and stained surface of Phobos. (Image: NASA)

It all comes down to tidal forces. Our Moon takes about 27 days to complete an orbit, and our planet takes around 24 hours to complete one rotation on its axis. Our Moon is pulling unevenly on the Earth and slowing its rotation down.

To compensate, the Moon is slowly drifting away from us. We did a whole episode about this which we’ll link at the end of the episode. On Mars, Phobos only takes 8 hours to complete an orbit around the planet. While the planet takes almost 25 hours to complete one rotation on its axis. So Phobos travels three times around the planet for every Martian day. And this is a problem.

It’s actually speeding up Mars’ rotation. And in exchange, it’s getting closer and closer to Mars with every orbit. The current deadpool gives the best odds on Phobos taking 30 to 50 million years to finally crash into the planet. The orbit will get lower and lower until it reaches a level known as the Roche Limit. This is the point where the tidal forces between the near and far sides of the moon are so different that it gets torn apart. Then Mars will have a bunch of teeny moons from the former Phobos.

Mars with rings of moon dust after the fall of one of its moons, Phobos. (Photo Credit: © Hive Studios)
Mars with rings of moon dust after the fall of one of its moons, Phobos.
(Photo Credit: © Hive Studios)

And then good news! Those adorable moonlets will get further pulverized until Mars has a ring. But then bad news… that ring will crash onto the planet in a cascade of destruction to be described as “the least fun balloon drop of all time”. So, you probably wouldn’t want to live on Mars then either.

Count yourself lucky. What were the chances that we would exist in the Solar System at a time that Phobos was a thing, and not a string of impacts on the surface of Mars.

Enjoy Phobos while you can, but remember that real estate there is temporary. Might I suggest somewhere in the alien sharknado infested waters of Europa instead?

What do you think. Did Arthur C Clarke have it wrong? Should we explore Europa?

And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!

Curiosity Rover Snaps Photos of Comet Siding Spring, Giant Sunspot and Mars-shine

NASA’s Curiosity Rover spends most of its time staring at the ground, but like humans, it looks up once in a while too. As reported earlier, NASA ground controllers pointed the rover’s Mast Camera (mastcam) skyward to shoot a series of photos of Comet Siding Spring when it passed closest to the Red Planet on October 19th.  Until recently, noise-speckled pictures available on the raw image site confounded interpretation. Was the comet there or wasn’t it?  In these recently released versions, the fuzzy intruder is plain to see, tracking from right to left across the field of view. 

Remember the monster sunspot group on bold display during last month's partial solar eclipse. It was the largest group of the current solar cycle. Here it is again - returning for a second time - as seen by Curiosity on November 10th. Credit: NASA/JPL-Caltech
Remember the monster sunspot group on bold display during last month’s partial solar eclipse? It was the largest group of the current solar cycle and largest recorded in 24 years. Here it is again (lower left) – returning for a second time – as seen by Curiosity on November 10th. Click for raw version. Credit: NASA/JPL-Caltech

Ten exposures of 25 seconds each were taken between 4:33 p.m. and 5:54 p.m. CDT on October 19th to create the animation.  The few specks you see are electronic noise, but the sharp, bright streaks are stars that trailed during the time exposure. Curiosity’s Mastcam camera system has dual lenses –  a 100mm f/10 lens with a 5.1° square field of view and a 34mm, f/8 lens with a 15° square field of view. NASA didn’t include the information about which camera was used to make the photos, but if I had to guess, the faster, wide-angle view would be my choice. Siding Spring was moving relatively quickly across the Martian sky at closest approach.

Sunspot region 2192 (lower left) has returned for an encore in this photo taken by NASA's Solar Dynamics Observatory. The same group is visible in images taken 4 days earlier from Mars. Credit: NASA/SDO
Sunspot region 2192 (lower left) has returned for an encore in this photo taken by NASA’s Solar Dynamics Observatory. The same group is visible in images taken 4 days earlier from Mars. Credit: NASA/SDO

Prowling through the Curiosity raw image files, I came across this photo of the Sun on November 10th. Three dark spots at the left are immediately obvious and a dead-ringer for Active Region 2192, now re-named 2209 as it rounds the Sun for Act II.  You’ll recall this was the sunspot group that nearly stole the show during the October 23rd partial solar eclipse. From Mars’ perspective, which currently allows Curiosity to see further around the solar “backside”, AR 2209 showed up a few days before it was visible from Earth.

Mars Earth line of sight nov 10 final V2
Because of Mars’ position relative to the Sun, Curiosity saw the return of sunspot group 2192 before it was visible from Earth. The Sun had to rotate about another 4 days to carry the group into Earth’s line of sight. Source: Solarsystemscope with additions by the author

Although it’s slimmed down in size, the region is still large enough to view with the naked eye through a safe solar filter. More importantly, it possesses a complex beta-gamma-delta magnetic field where magnetic north and south poles are in close proximity and ripe for reconnection and production of M-class and X-class flares. Already, the region’s crackled with three moderate M-class flares over the past two days. In no mood to take a back seat, AR 2209 continues to dominate solar activity even during round two.

Phobos is very small but big enough for someone on the surface to see its shape with the naked eye, especially when the moon is high in the sky and closest to the observer. Then, it spans 1/3 the diameter of our Moon. Credit: NASA/JPL-Caltech
Phobos is very small but orbits close enough for someone on the surface to see its shape with the naked eye, especially when it’s high in the sky and closest to the observer. Phobos is about 1/3 the size of our Moon. This photo was taken by Curiosity on October 20th and shows the moon’s largest crater, Stickney, at top.  Credit: NASA/JPL-Caltech with toning by the author to bring out details

Mars possesses two small moons, Deimos and Phobos. Curiosity has photographed them both before including an occultation Deimos (9 miles/15 km) by the larger Phobos (13.5 miles/22 km). Phobos orbits closer to Mars than any other moon does to its primary in the Solar System, just 3,700 miles (6,000 km). As a result, it moves too fast for Mars’ rotation to overtake it the way Earth’s rotation overtakes the slower-moving Moon, causing it to set in the west overnight. Contrarian Phobos rises in the western sky and sets in the east just 4 hours 15 minutes later. When nearest the horizon and farthest from an observer, it’s apparent size is just 0.14º. At the zenith it grows to 0.20º of 1/3 the diameter of the Moon.

Phobos occults Deimos in real time photographed by the Curiosity Rover on August 1, 2013. Credit: NASA/JPL-Caltech
Phobos occults Deimos in real time photographed by the Curiosity Rover on August 1, 2013. Credit: NASA/JPL-Caltech

One longish observing session on the planet would cover a complete rise-set cycle during which Phobos would first appear as a crescent and finish up a full moon a few hours later. All this talk about Phobos is only meant to direct you to the picture above taken by Curiosity on October 20, 2014 when the moon was a thick crescent. As on Earth, where Earthshine fills out the remainder of the crescent Moon, so too does Mars-shine provide enough illumination to see the full outline of Phobos.

Four-wheel drive only. Curiosity took this photo showing a sea of dark dune from the Pahrump Hills outcrop on November 13th. Credit: NASA/JPL-Caltech
Four-wheel drive only! Curiosity took this photo showing a sea of dark dunes from the Pahrump Hills outcrop on November 13th. Credit: NASA/JPL-Caltech

Curiosity has also photographed Earth, sunsets and transits of Phobos across the Sun while rambling across the dusty red landscape since August 2012. Before we depart, it seems only fair to aim our gaze Mars-ward again to see what’s up. Or down. The rover’s been doing a geological “Walkabout” in the Pahrump Hills outcrop at the base of Mt. Sharp in Gale Crater since September. Earlier this fall it drilled and sampled rock there containing more hematite than at any of its previous stops. Hematite is an iron oxide that’s often associated with water.

The mission may spend weeks or months at the outcrop looking for and drilling new target rocks before moving further up the geological layer cake better known as Mt. Sharp.