APOD: Martian Moon Phobos Crosses the Sun (2019 Apr 10)

[APOD Robot]

Martian Moon Phobos Crosses the Sun

Explanation: What's that passing in front of the Sun? It looks like a moon, but it can't be Earth's Moon, because it isn't round. It's the Martian moon Phobos. The featured video was taken from the surface of Mars late last month by the Curiosity rover. Phobos, at 11.5 kilometers across, is 150 times smaller than Luna (our moon) in diameter, but also 50 times closer to its parent planet. In fact, Phobos is so close to Mars that it is expected to break up and crash into Mars within the next 50 million years. In the near term, the low orbit of Phobos results in more rapid solar eclipses than seen from Earth. The featured video has been sped up -- the actual transit took about 35 seconds. A similar video was taken of Mars' smaller and most distant moon Diemos transiting the Sun. The videographer -- the robotic rover Curiosity -- continues to explore Gale crater, most recently an area with stunning vistas and unusual rocks dubbed Glen Torridon.

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[bcj_sf_nm]

Really cool pic, but please, please, please, would people stop saying something is 150 times, or some such, smaller than something else? That is nonsensical. It may be 1/150th the size or Luna may be 150 times larger than Phobos. Thank you.

[Nitpicker]

The phrase "150 times smaller than Luna" is not at all nonsensical. I suspect more people would have trouble understanding "1/150th the size of Luna". But I cannot say with any certainty whether either form is discouraged in any style guide.

The phrase "50 times closer" is similarly fine in my book.

[Nitpicker]

I suppose a scientific paper might be written as "Phobos, at 1.15x10^4 meters across, is 6.67x10^-3 times the diameter of Luna". Quite revolting. I'm glad the APOD captions aren't written like scientific papers.

[Nitpicker]

And never mind that Phobos actually has dimensions of 27×22×18 km ... its mean diameter of 22.5 km is 150 times smaller than Luna's.

[De58te]

I know that today's young people have the attention span of less than a goldfish, 13 seconds, but, was it really necessary to speed up the original transit time of 35 seconds to 2 seconds? I wouldn't have minded to have watched the entire original 35 seconds. After all that is just a wee bit longer than one super bowl commercial.

[orin stepanek]

I for one; don't mind that Starship Asterisk; gave us the figures of size and distance comparison between the two planets and there moons!

[Indigo_Sunrise]

I just wanted to say that I think this video is pretty amazing.

[JohnD]

Interesting. Never thought of Mars' moons doing a solar transit.

The video of a Deimos transit at https://photojournal.jpl.nasa.gov/archive/PIA23134.gif (link in blurb) is a very much smaller (20 times?? He-he) image. But it looks as though I can see the moon rotating as it goes. Illusion, or real?
JOhn

[Chris Peterson]

Interesting. Never thought of Mars' moons doing a solar transit.

The video of a Deimos transit at https://photojournal.jpl.nasa.gov/archive/PIA23134.gif (link in blurb) is a very much smaller (20 times?? He-he) image. But it looks as though I can see the moon rotating as it goes. Illusion, or real?
JOhn

Deimos is tidally locked (i.e., its period is synchronous with its orbit), so... illusion. Phobos also has synchronous rotation.

[BDanielMayfield]

I know that today's young people have the attention span of less than a goldfish, 13 seconds, but, was it really necessary to speed up the original transit time of 35 seconds to 2 seconds? I wouldn't have minded to have watched the entire original 35 seconds. After all that is just a wee bit longer than one super bowl commercial.

I agree. Many astronomical events are far too slow (or, even too fast) to be viewed in real time by humans, but this event was timed perfectly by nature. It would be nice to see it as it would have appeared if one was actually standing on Mars.

Bruce

[geckzilla]

I know that today's young people have the attention span of less than a goldfish, 13 seconds, but, was it really necessary to speed up the original transit time of 35 seconds to 2 seconds? I wouldn't have minded to have watched the entire original 35 seconds. After all that is just a wee bit longer than one super bowl commercial.

You definitely could have written this without the ageism.

[neufer]

.

Curiosity's real-time view of Phobos passing Deimos

---

I know that today's young people have the attention span of less than a goldfish, 13 seconds, but, was it really necessary to speed up the original transit time of 35 seconds to 2 seconds? I wouldn't have minded to have watched the entire original 35 seconds. After all that is just a wee bit longer than one super bowl commercial.

You definitely could have written this without the ageism.

• Or Deimos's De58te's need to carp on Cypriniformes

Fancy Celestial eye goldfish

---

Busting the attention span myth
By Simon Maybin BBC World Service, More or Less

<<It turns out that there is no evidence that goldfish - or fish in general - have particularly short attention spans or memories, despite what popular culture suggests.

I spoke to Prof Felicity Huntingford, who has spent almost half a century studying fish behaviour and just delivered a series of public lectures under the title, How Smart Are Fish? "Goldfish can perform all the kinds of learning that have been described for mammals and birds," she says. "And they've become a model system for studying the process of learning and the process of memory formation, exactly because they have a memory and because they learn."

She says there have been literally hundreds of scientific papers over the decades on goldfish learning and memory. I found a reference to a study on fish memory as early as 1908. "That a species that's used by neuro-psychologists and scientists as a model for studying memory formation should be the very species that has this reputation - I think that's an interesting irony," she says.>>

[Nitpicker]

Starship discussions are so wonderfully broad: grammarism, sizeism, timelapseism, ageism and goldfishism.

Re the timelapseism, it is possible that only a limited number of individual frames were recorded, so it was sped up to provide a smoother animation.

[MarkBour]

Because of my last name, some unkind people have occasionally given me the nickname of "goldfish".
... But anyway, what were we talking about?



Oh yes. Slowing down the video of Phobos.

If you follow the second linked word "Phobos" in the APOD caption, it leads to Wikipedia's Phobos article, https://en.wikipedia.org/wiki/Phobos_(moon). If you look down in that article under the section "Origin", at the right is a bit of media that Curiosity took quite a while ago, on 2013-08-20. It is satisfyingly slow, so Bruce and De58te, you might like it ... I do. It also repeats at 6x at the same stately speed. The direct reference to the video is: https://upload.wikimedia.org/wikipedia/ ... p.vp9.webm

The enlarged version shows the same kind of pixelation that caused JohnD to wonder if the Diemos video showed rotation. I agree, it certainly did look a lot like rotation, but as Chris pointed out, that cannot be. The above referenced video helps one confirm that it was an illusion, as the pixelation effects are consistent between this video and the Diemos video.

[orin stepanek]

When Phobos finally comes down to Mars! Will it be a crash or maybe a landing? Since it is in orbit; is it possible it may come in parallel to Mars surface and pretty much roll along the landscape until it comes to a stop? Still I'm sure there would be much damage! I know; just a crazy thought on my part!

[BDanielMayfield]

Because of my last name, some unkind people have occasionally given me the nickname of "goldfish".
... But anyway, what were we talking about?



Oh yes. Slowing down the video of Phobos.

If you follow the second linked word "Phobos" in the APOD caption, it leads to Wikipedia's Phobos article, https://en.wikipedia.org/wiki/Phobos_(moon). If you look down in that article under the section "Origin", at the right is a bit of media that Curiosity took quite a while ago, on 2013-08-20. It is satisfyingly slow, so Bruce and De58te, you might like it ... I do. It also repeats at 6x at the same stately speed. The direct reference to the video is: https://upload.wikimedia.org/wikipedia/ ... p.vp9.webm

The enlarged version shows the same kind of pixelation that caused JohnD to wonder if the Diemos video showed rotation. I agree, it certainly did look a lot like rotation, but as Chris pointed out, that cannot be. The above referenced video helps one confirm that it was an illusion, as the pixelation effects are consistent between this video and the Diemos video.

Thanks Mark! I'm old and slow enough, so I enjoyed the entire event.

Bruce

[neufer]

When Phobos finally comes down to Mars! Will it be a crash or maybe a landing? Since it is in orbit; is it possible it may come in parallel to Mars surface and pretty much roll along the landscape until it comes to a stop? Still I'm sure there would be much damage!

<<Tidal deceleration is gradually decreasing the orbital radius of Phobos by ~2 meters every one hundred years (as compared to our own Moon's orbital radius increase by ~3.8 meters every hundred years). Scientists estimate that Phobos will be destroyed in approximately 30–50 million years. Given Phobos's irregular shape and assuming that it is a pile of rubble (specifically a Mohr–Coulomb body), it will eventually break up when it reaches approximately 2.1 Mars radii (from it's current 2.76 Mars radii). When Phobos is eventually torn apart by tidal forces, a fraction of the debris will likely form a planetary ring around Mars, which may last from one million to one hundred million years.

Phobos' grooves were long thought to be fractures caused by the impact that formed the Stickney crater. Other modelling suggested since the 1970s support the idea that the grooves are more like "stretch marks" that occur when Phobos gets deformed by tidal forces, but in 2015 when the tidal forces were calculated and used in a new model, the stresses were too weak to fracture a solid moon of that size, unless Phobos is a rubble pile surrounded by a layer of powdery regolith about 100 m thick. Stress fractures calculated for this model line up with the grooves on Phobos. The model is supported with the discovery that some of the grooves are younger than others, implying that the process that produces the grooves is ongoing.>>

[BDanielMayfield]

When Phobos finally comes down to Mars! Will it be a crash or maybe a landing? Since it is in orbit; is it possible it may come in parallel to Mars surface and pretty much roll along the landscape until it comes to a stop? Still I'm sure there would be much damage!

<<Tidal deceleration is gradually decreasing the orbital radius of Phobos by ~2 meters every one hundred years (as compared to our own Moon's orbital radius increase by ~3.8 meters every hundred years). Scientists estimate that Phobos will be destroyed in approximately 30–50 million years. Given Phobos's irregular shape and assuming that it is a pile of rubble (specifically a Mohr–Coulomb body), it will eventually break up when it reaches approximately 2.1 Mars radii (from it's current 2.76 Mars radii). When Phobos is eventually torn apart by tidal forces, a fraction of the debris will likely form a planetary ring around Mars, which may last from one million to one hundred million years.

Phobos' grooves were long thought to be fractures caused by the impact that formed the Stickney crater. Other modelling suggested since the 1970s support the idea that the grooves are more like "stretch marks" that occur when Phobos gets deformed by tidal forces, but in 2015 when the tidal forces were calculated and used in a new model, the stresses were too weak to fracture a solid moon of that size, unless Phobos is a rubble pile surrounded by a layer of powdery regolith about 100 m thick. Stress fractures calculated for this model line up with the grooves on Phobos. The model is supported with the discovery that some of the grooves are younger than others, implying that the process that produces the grooves is ongoing.>>

So, if you're a Mars' colonist in the distant future don't settle directly under the path of Phobos, the fear moon. 8 to 80 million minutes years of terror is in the forecast.

[rstevenson]

Really cool pic, but please, please, please, would people stop saying something is 150 times, or some such, smaller than something else? That is nonsensical. It may be 1/150th the size or Luna may be 150 times larger than Phobos. Thank you.

I agree. I find it distractingly odd to read something like "150 times closer". This may be due to my speaking a particular subset of English, or to my being a grumpy old man -- I can't tell. But I do feel that reductions should be expressed as fractions or percentages, and expansions as multiples. Using a multiple to express a reduction is just wrong. It says so right here in Rob's Book of Style.

Rob

[Chris Peterson]

Really cool pic, but please, please, please, would people stop saying something is 150 times, or some such, smaller than something else? That is nonsensical. It may be 1/150th the size or Luna may be 150 times larger than Phobos. Thank you.

I agree. I find it distractingly odd to read something like "150 times closer". This may be due to my speaking a particular subset of English, or to my being a grumpy old man -- I can't tell. But I do feel that reductions should be expressed as fractions or percentages, and expansions as multiples. Using a multiple to express a reduction is just wrong. It says so right here in Rob's Book of Style.

Rob

Your Book of Style is 10 times smaller than mine.

[rstevenson]

Really cool pic, but please, please, please, would people stop saying something is 150 times, or some such, smaller than something else? That is nonsensical. It may be 1/150th the size or Luna may be 150 times larger than Phobos. Thank you.

I agree. I find it distractingly odd to read something like "150 times closer". This may be due to my speaking a particular subset of English, or to my being a grumpy old man -- I can't tell. But I do feel that reductions should be expressed as fractions or percentages, and expansions as multiples. Using a multiple to express a reduction is just wrong. It says so right here in Rob's Book of Style.

Rob

Your Book of Style is 10 times smaller than mine.

Yes but I'm close to sea level, where the denser atmosphere allows for greater understanding of such niceties.

Rob

[Chris Peterson]

I agree. I find it distractingly odd to read something like "150 times closer". This may be due to my speaking a particular subset of English, or to my being a grumpy old man -- I can't tell. But I do feel that reductions should be expressed as fractions or percentages, and expansions as multiples. Using a multiple to express a reduction is just wrong. It says so right here in Rob's Book of Style.

Rob

Your Book of Style is 10 times smaller than mine.

Yes but I'm close to sea level, where the denser atmosphere allows for greater understanding of such niceties.

Rob

Too much oxygen is toxic. My thinking always gets fuzzy when I descend to sea level.

[Nitpicker]

I offer this:
https://www.nytimes.com/2007/10/28/opin ... 81659.html

[JohnD]

As this thread has become hopelessly diverted...
Chris,
Too LITTLE oxygen is toxic, and to little babies too much can be, to their retinas.

But in coming down from Cloudbait, have you considered the nitrogen? Divers breathing air who go below 100ft (30m) start to experience 'nitrogen narcosis' as the partial pressure of nitrogen in air rises to about 2400mmHg. Experiments have been done at sea level to wash out as much nitrogen as possible by breathing pure oxygen that showed a marginal increase in cognition. So your confusion on descending from your eyrie is due to the nitrogen!
John