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Phobos viewed from Mars

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#1 jimlake

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Posted 06 March 2021 - 05:23 PM

Please look at this video: https://www.youtube....h?v=vOvP12-hDTg taken by Perseverance.

 

At 11:46 - 12:00, and at several other spots in the video, you can see a spherical object in the sky.  Note that this object pans with the background as the camera pans, which tells me that the object is not dirt on the lens. It is an object in the sky. Some commentators have postulated that this object is Phobos (or Deimos). JPL has not commented, as far as I know.

 

I do not believe that the Martian moons would look dark when viewed from the surface in the Martian daylight because they can only be seen via reflected sunlight. Therefore, in the bright Martian daylight, a Martian moon should be brighter than the sky or not visible at all. But, I admit that I have never seen one of the moons from the surface of Mars, so I do not know for sure.  

 

Someone here may have a better idea on how to determine the provenance of the object in the sky. What are your opinions?

 

Also, is anyone here able to analyze Phobos' orbit? It seems that we should be able to determine conclusively whether the object is one of the moons by plotting its orbit with respect to Jezero crater (18.38°N 77.58°E). I would think that just knowing its latitude would answer the question. The orbit parameters are listed on Wikipedia   https://en.wikipedia.../Phobos_(moon).

 

 

 


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#2 johnsoda

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Posted 06 March 2021 - 05:28 PM

Astronomy on Mars is fascinating.  To me, the most amazing thing is the you would be able to see both the Earth and the Moon with your naked eye!


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#3 TOMDEY

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Posted 06 March 2021 - 06:04 PM

Those are post-scans of digital still shots, just for engaging presentation to the public. The two little artifacts are undoubtedly motes in the imaging train, not spherical objects in the sky.  At that range, true video clips would be profoundly wasteful of the comm-link precious bandwidth. [I worked imint for decades. Part of my job was to ident, locate, and eliminate artifactuals.]   Tom



#4 rblackadar

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Posted 06 March 2021 - 06:23 PM

Also, think what it would mean to see a dark moon against a bright sky. The moon would have to be blocking the scattered light from that sky, i.e. it would have to be *in* the atmosphere and very near to the ground. Our moon doesn't do that, and neither would Phobos if seen in daytime.


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#5 chrysalis

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Posted 06 March 2021 - 07:09 PM

Also, think what it would mean to see a dark moon against a bright sky. The moon would have to be blocking the scattered light from that sky, i.e. it would have to be *in* the atmosphere and very near to the ground. Our moon doesn't do that, and neither would Phobos if seen in daytime.

TOMDEY right on the money. Also, rblackadar is 100% correct - they should be bright, not dark.



#6 caleuche

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Posted 06 March 2021 - 07:23 PM

Please look at this video: https://www.youtube....h?v=vOvP12-hDTg taken by Perseverance.

 

At 11:46 - 12:00, and at several other spots in the video, you can see a spherical object in the sky.  Note that this object pans with the background as the camera pans, which tells me that the object is not dirt on the lens. It is an object in the sky. Some commentators have postulated that this object is Phobos (or Deimos). JPL has not commented, as far as I know.

 

I do not believe that the Martian moons would look dark when viewed from the surface in the Martian daylight because they can only be seen via reflected sunlight. Therefore, in the bright Martian daylight, a Martian moon should be brighter than the sky or not visible at all. But, I admit that I have never seen one of the moons from the surface of Mars, so I do not know for sure.  

 

Someone here may have a better idea on how to determine the provenance of the object in the sky. What are your opinions?

 

Also, is anyone here able to analyze Phobos' orbit? It seems that we should be able to determine conclusively whether the object is one of the moons by plotting its orbit with respect to Jezero crater (18.38°N 77.58°E). I would think that just knowing its latitude would answer the question. The orbit parameters are listed on Wikipedia   https://en.wikipedia.../Phobos_(moon).

You can set a viewing location in Stellarium at the current position of the Mars 2020 rover and view it that way. As I type this, Phobos is setting from the point of view of the lander and the Sun is still in the sky. It rose at magnitude -8 or so at March 06 20:40 UTC (at least that is when it was out of eclipse and became visible). I think we'd need to know when the image were taken, but it something darker than the surrounding sky won't be a moon.

 buEW1GA.png


Edited by caleuche, 06 March 2021 - 11:43 PM.


#7 jimlake

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Posted 06 March 2021 - 08:43 PM

Cosmos et al, 

What you say makes sense, but when I look at the supposed live stream from Perseverance today:

 https://www.youtube....h?v=UA1-izKmeJc

 At 16:09:54:48, the same object appears in the sky. Same size, same color, same contrast as the first video. Check it out.

 

If this is some random glitch or some piece of crud, why does it appear in sky in multiple images on different days? Does anyone know if the original images available online?



#8 caleuche

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Posted 06 March 2021 - 11:08 PM

jimlake, the raw image for that appears to be this: https://mars.nasa.go...M00015_034085J 

 

Phobos rises almost directly in the west (262º) and sets almost directly in the east (97º). It is hard to tell the orientation of the image from local terrain, but I think it is toward the south. The mean solar time they mention does not appear to line up, though - but whatever the case if the image is pointing southward it could not be Phobos. 

 

Edit: converting the local mean solar time at the landing site to UTC, I think it is March 2, 2021 at 4:10:30 AM (UTC). Both Phobos and Deimos were below the horizon at that point. 


Edited by caleuche, 06 March 2021 - 11:38 PM.


#9 jimlake

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Posted 07 March 2021 - 01:13 PM

I have looked at all of the original images as they came from the rover. This one:

 

https://mars.nasa.go...AM00015_034085J

 

appears to be the image that was used to make the video. You can tell by looking at the shadows and comparing with the video. The object is also in this original image from the rover. Can we conclude that the object is not an artifact that came about through the image processing process after it arrived here on earth? 

 

So, the object is in the original image and it's not one of the moons. What other possibilities remain.... Besides the possibility that someone has dropped by the check out the new rover.



#10 jimlake

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Posted 07 March 2021 - 02:24 PM

I loaded the image containing the object into PS and zoomed on the object. This is the result: 

 

I don't what would cause it, but there appears to be distortions in the atmosphere surrounding the object.

Mars_Perseverance_ZLF_0011_0667930008_064FDR_N0030000ZCAM00015_034085J.png

 

It looks an interference pattern. I zoomed in on other parts of the photo as well, and while I see pixilation, I don't see that distortion pattern. Perhaps its a digital artifact I am not familiar with. 



#11 caleuche

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Posted 07 March 2021 - 02:26 PM

I have looked at all of the original images as they came from the rover. This one:

 

https://mars.nasa.go...AM00015_034085J

 

appears to be the image that was used to make the video. You can tell by looking at the shadows and comparing with the video. The object is also in this original image from the rover. Can we conclude that the object is not an artifact that came about through the image processing process after it arrived here on earth? 

 

So, the object is in the original image and it's not one of the moons. What other possibilities remain.... Besides the possibility that someone has dropped by the check out the new rover.

It is probably a compression artifact generated by the image compression on the rover itself, from some kind of spike in the data on the sensor (internal reflection in the optical stack, or something). I don't think the images sent from Mars are raw image data, but are compressed on-site. There's not much bandwidth to spend on thousands of raw images, but who knows.



#12 caleuche

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Posted 07 March 2021 - 02:27 PM

I loaded the image containing the object into PS and zoomed on the object. This is the result: 

 

I don't what would cause it, but there appears to be distortions in the atmosphere surrounding the object.

 

It looks an interference pattern. I zoomed in on other parts of the photo as well, and while I see pixilation, I don't see that distortion pattern. Perhaps its a digital artifact I am not familiar with. 

That distortion is a compression artifact, and hints at the kind of compression. 

 

Edit: check that. possibly an image compression artifact: https://en.wikipedia...ging_artifacts 

 

It could also result optically from an object outside of the focus range (such as something present on the lens or camera shield or within the optical stack). It's kind of hard to speculate, but I don't think this represents a physical object in the sky. 


Edited by caleuche, 07 March 2021 - 02:30 PM.


#13 jimlake

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Posted 07 March 2021 - 03:27 PM

Caleuche: The identifier for the image is this :

 

 

<iframe src="https://mars.nasa.go...AM00015_034085J" width="500" height="500" scrolling="no" frameborder="0"></iframe>

 

This states that it is a raw image. That suggests there is no compression, unless I am reading it wrong.



#14 jimlake

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Posted 07 March 2021 - 03:30 PM

 

<iframe src="https://mars.nasa.go...AM00015_034085J" width="500" height="500" scrolling="no" frameborder="0"></iframe>

The descriptor didn't display correctly in the last post. Here is the quote:



#15 caleuche

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Posted 07 March 2021 - 10:49 PM

The descriptor didn't display correctly in the last post. Here is the quote:

The camera sensors are 11-bit per pixel (per color for color images) so if it were really uncompressed straight from the lander would be more like a 6 MB image. Also the PNG data is 8-bit, so we know that at least some compression was performed somewhere. The specifications for the camera are here: https://live-mastcam...ras/tech-specs/ - I think NASA saying "raw" just means "not color-processed", not that they are uncompressed. 



#16 caleuche

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Posted 28 March 2021 - 03:00 AM

Revisiting this, an image of Phobos as taken from Curiosity was posted on the 19th, which may have included Deimos as well. Phobos is just about to set over Mt Sharp, while Deimos and all of the other object in the sky in this frame would be rising. https://i.imgur.com/XeEQTf1.jpg (posting as link rather than as image as the image format itself is large). This is raw and not demosaiced. 

 

Phobos was about 9º altitude and Deimos about 19.5º, and -8 and -4.7 apparent visual magnitudes, respectively. The sun was -3º (below the horizon) so this would be local civil twilight, if this were on Earth. 




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