MSL - Astronomical Observations, Phobos/Deimos, planetary/celestial observations and more Options

[fredk]

What's rising?
http://mars.jpl.nasa.gov/msl-raw-images/pr...NCAM00545M_.JPG

[Zelenyikot]

Phobos in martian sky
http://www.youtube.com/watch?v=9QaQ6TCWq-0

[iMPREPREX]

Phobos in martian sky
http://www.youtube.com/watch?v=9QaQ6TCWq-0

That's awesome. I was wondering what that was! On my take of it, I enhanced the contrast and a haze can be seen. Is that indeed the atmosphere?

[Zelenyikot]

What's rising?
http://mars.jpl.nasa.gov/msl-raw-images/pr...NCAM00545M_.JPG

That line may it be a spacecraft?

Attached thumbnail(s)

 

[djellison]

That's a cosmic ray hit.

[Greenish]

That's awesome. I was wondering what that was! On my take of it, I enhanced the contrast and a haze can be seen. Is that indeed the atmosphere?

I subtracted the median of all frames and enhanced the contrast. I don't know enough to interpret it for sure, but it sure looks like very well defined clouds drifting by.

http://www.youtube.com/watch?v=AFa27WtnFHI

(if you watch in HD it has the full resolution of the original 511x511 images, although there are some compression artifacts).

[Gerald]

Sol 351 Mastcam Right thumbnail time-lapse (magnified from 64x64 to 128x128):

Deimos or Phobos?

[Zelenyikot]

Deimos or Phobos?

Transit of Phobos across Deimos

[Gerald]

Thank you very much, Zelenyikot!
The enhanced two-image gif

(based on NASA/JPL-Caltech/MSSS) makes things more obvious.

[iMPREPREX]

Wow! A few full resolution images of Deimos and Phobos have come in. Here's my take at taking out the noise and leaving the moons.

Edited to add two more: a Mastcam 34 shot and a MastCam 100 shot of Phobos.

Attached thumbnail(s)

 

[wildespace]

I think I'm seeing the large Stickney crater, and possibly Reldresal crater too. What Phobos features can you see here?

[iMPREPREX]

That most certainly, to me, looks like the Stickney crater. Man, that's awesome. Good looking out.

Attached thumbnail(s)

 

[wildespace]

Here's a Stellarium screenshot, set for the place, time, and the approximate field of view of the Mastcam shot. Some of the brighter stars are indicated, I wonder if image-processing wizards here can bring them out in the Mastcam shots.


http://www.pictureshack.us/images/87310_phobosdeimos2.jpg

Also of interest may be the saturation-enhanced closeup of Phobos. I wonder is these colours are due to how Mastcam processed the image, or are they the real subtle colour variations of the surface.

[Phil Stooke]

Sorry folks, I think you have your Phobos geography all tangled up. The clearly visible crater is Hall at the south pole, north is at left, Stickney is at the bottom, essentially invisible because the sun is shining straight into it. I will post a comparison image later when I can get to it. (turn that Viking image 180 degrees for an idea of what you're seeing, except the illumination is different)

Phil

[iMPREPREX]

I trust and believe your words, Phil. But to me it did look like it could be Stickney in the image. I'm looking forward to seeing the comparison image because I couldn't find anything on Google.

[Phil Stooke]

Here's a comparison - the map image is from here:

http://www.solarviews.com/cap/mars/phobos6.htm

(the image which Tayfun projected onto the shape model originated from USGS as the caption says, but it is the one which I had previously reprojected into modern coordinates. The USGS version was based on an experimental shape model and was badly distorted. I reprojected it cell by cell to fit Damon Simonelli's shape model from Cornell)



Hall crater is visible at the bottom. Kepler Dorsum runs horizontally just above it.

Phil

[Zelenyikot]

I used Celestia and made these images.

Attached thumbnail(s)

 

[iMPREPREX]

That's an incredible eye you have, Phil. Thank you and sorry. To the untrained eye though, you have to agree that it could be mistaken for the Stickney.

[Zelenyikot]

To the untrained eye though, you have to agree that it could be mistaken for the Stickney.

Any big crater on the Phobos is Stickney

[elakdawalla]

Remember that Phobos is synchronously rotating, just like our moon, and Stickey faces more-or-less forward along the orbit, so it's always going to be closer to the limb than to the center of the disk.

A corollary to that is that any spacecraft that either sits on the surface or is in a low, circular mapping orbit (MGS, ODY, MRO) will always only see the Mars-facing hemisphere of Phobos. Only Mars Express and earlier spacecraft have seen other sides.

[ugordan]

There's also what appears to be faint "mars-shine" illuminating Phobos if you play with image brightness:



Do we expect the original raw data to be overexposed, because the thumbnails kind of give the impression that the images are well-exposed?

EDIT: Ahh, I see now. That one full-res image corresponds to an overexposed thumbnail as well. Other shots should look pretty spectacular, then.

[mcaplinger]

Do we expect the original raw data to be overexposed, because the thumbnails kind of give the impression that the images are well-exposed?

The full-res image you're looking at is from sequence 1424 and the better-exposed thumbnails from sequence 1423, which presumably have different exposure times.

[wildespace]

Zelenyikot's images of Phobos gave me an idea to overlay colour information from the Mastcam image onto the detailed Celestia image:


For aesthtetic purpose, if anything, but I do hope to hear whether the Mastcam really picked those colours, or whether they're just an artifact.

[Phil Stooke]

I'm sorry to say they are artifacts. There are very subtle colour variations on Phobos but not like those.

Phil

[Phil Stooke]

This is a super-resolution composite of five frames from the Phobos-Deimos sequence on sol 351. Four images (in two pairs) of Deimos appear as smudges on each side - one of them shows the position of the dark limb of Phobos. The 'super-resolution' process (combining multiple views, enlarged and sharpened) is mostly just reducing the JPG artifacts here. Now Stickney can be seen at left, where it was overexposed before.

Phil



PS - I don't show it here, but if you increase the saturation in the RGB image you see some color variation - this is real color variation on Phobos, blue around Stickney, red over the northern limb. I say 'real color variation' - not 'true color'!

[fredk]

Nice!

And a quick animation of the frames so far:

[ugordan]

A few frames registered on Deimos and a few frames registered on Phobos stacked and merged. Magnified 2x, sharpened and white-balanced.

[atomoid]

..And a quick animation of the frames so far...

very nice indeed, this actually poses an interesting puzzle. So this is perhaps looking at the eastern horizon before solrise with Phobos soon to set. And it looks like Deimos is going retrograde against the background of stars and that must be due to a parallax effect of the MSL observation point sweeping underneath and overtaking Deimos' actual slower motion in the same direction as Phobos..?

hoping for a m100 transit if the cam can take it, hopefully in the right place to get one as good as the old Oppy one. Colors come out in the HiRise pics..

[jmknapp]

The moons are so tiny, I've wondered if they'd be much to look at "in person," but based on these images it looks to be a very striking sight.

BTW, the NY Times tracking map now pretty much matches the official.

[mcaplinger]

very nice indeed, this actually poses an interesting puzzle....
hoping for a m100 transit if the cam can take it...

Deimos moves E-W and Phobos moves W-E because of the rotation of Mars, so I'm not sure what your retrograde reference is to.

If you didn't like the grazing observations last year, there are more chances coming up later in the month. http://meetingorganizer.copernicus.org/EPS...PSC2012-326.pdf

[paraisosdelsiste...]

It seems Curiosity taken some pics with different exposure times at the sky during the Sol 351:



From the pointing data... could it be Regulus?

[fredk]

Regulus looks good. To bring out the fainter stars, I subtracted two ML frames, took the absolute value, and then did a linear contrast stretch. That supresses noise ("fake stars") and any real stars are visible as pairs of points, with the same separation distance and orientation for all real stars. I then generated a chart of the Regulus region at the same scale as ML (15 degrees per 1200 pix). The scale was set by hand so isn't exact. I then adjusted the one free parameter (overall orientation) until I found a match.

Here's an animation flipping between the chart and the ML difference image. There are two or three stars visible apart from Regulus (circled in the ML frame). The scale's out a bit but the fit is otherwise very good, considering there is only one free parameter here:

The stars apart from Regulus are Leo eta-30, Subra, and possibly Leo 31.

And here's a similar difference of two MR frames. You can see a few real stars (paired streaks, same orientation and separation). These stars are too faint to show up on my chart...

Crazy that Regulus is very close to the Sun now as seen from Earth, so we'd normally never see it this time of year.

[fredk]

Update to the Leo pics with one new ML frame. Now the stars are more obvious. All three previous candidates confirmed, and one new star, Leo rho-47, also spotted right where it should be:

[paraisosdelsiste...]

With the MastCam Left frames and with the advice of Fredk I made a new version of the star frames taken during Sol 351:

[fredk]

Here's a much improved attempt at extracting stars from the sol 351 ML frames. This time I took the two (positive-valued) differences of the two frames, carefully registered them (which entailed correcting for a bit of frame rotation between the two frames), averaged them, and then applied a filter with a kernel tailored to the star streaks (19 pix wide, 1 pix high). These steps were interspersed with various contrast stretches along the way.

The result now starts to look like an image of the night sky, with many stars visible. But the faintest stars I can see are only around magnitude 5.5 or 6, so they would be quite easy naked eye from a dark site. We know that mastcam was not designed to image the night sky!

It's also interesting to note that the direction of star trailing is not very different from what it would be near Regulus as seen from Earth, even though the celestial poles of Mars and Earth are quite far apart. This is because the two poles are roughly in a straight line (geodesic) with Regulus.

[atomoid]

..I'm not sure what your retrograde reference is to..

Relative to the background of stars (not horizon), both moons should be moving in the same direction. However, FredK's animation and the source files show apparent retrograde motion of Deimos relative to those stars. The time span of the sequence is only about 2 minutes which works out to something like 30 miles which doesnt seem enough for any sort of parallax effect. joes mapper says camera bearing 80.39° (E), elevation 58.64° so they arent even at zenith to mazimize that effect, I tried out a quick sim in Stellarium based on the Bradbury landing coordinates and one of the stars in the pair above could be HIP53525 with the lone one below perhaps HIP54084. But maybe these apparent 'stars' are dead pixel artifacts fixed on the frame that are masquerading as stars so there's really no apparent retrograde motion of Deimos (or perhaps most likely ive just lost my mind)

and thanks for the grazing schedule link, oh the things you can miss when you are away on vacation, looking forward to next week!

[mcaplinger]

But maybe these apparent 'stars' are dead pixel artifacts fixed on the frame...

Yes, almost certainly. Remember that exposing for the Moon/a moon is like exposing for any other (admittedly dark) sunlit object, so these exposure times were fairly short.

[iMPREPREX]

We're getting there with the moon shots!

[atomoid]

It looks like we might eventually get the full sweep between 3:02 and 3:04

So these must be stars in the 2:58 image centering on Deimos.
Then after the close in exposure optimized shots of the transit, we pull back out with long exposure and see the stars again in the 3:05 image
The stars in the long exposure shots appear to correspond perfectly with the stars in the subframe transit shots, so it appears Deimos is going the opposite direction as Phobos relative to the background stars!

[Deimos]

Deimos and Phobos both orbit in the same direction, as you know. Deimos is far enough out that it (like our moon) has an orbital period longer than the planets rotational period, and its apparent motion is in the same sense as the stars. But it lags them, and does not change directions with respect to the horizon or the stars. Remember, Deimos is moving many times faster than the rover in an inertial, Mars-centered frame. Phobos is closer and faster, so it crosses the sky in the opposite direction, but just moves faster in the same direction with respect to the stars. So if they appear to move in opposite directions with respect to something, I would speculate the 'something' is not a star. Warm/hot pixels tend to be much more observable than stars for cameras optimized for landscape photos.

[fredk]

Adding to Deimos's comments, both those MR frames you pointed to (and all the MR frames from that sequence) have the same bearing/elevation, as Joe's site shows, so they're pointing at a fixed direction in the sky, not following the stars. But the frames are minutes apart. Stars would have moved many pixels between the frames. So those are all hot pixels.

Stars are pretty hard to see with mastcam. Compare the raw Regulus shots with my heavily processed ones - how many stars can you see on the raw shots? And with short enough exposures that the stars wouldn't trail, it would be extremely hard.

[Zelenyikot]

Stellarium show it is Regulus. Sol 351

Attached thumbnail(s)

 

[atomoid]

So many hot pixels, some even masquerading as star streaks but in the wrong direction (not sure if hot pixels explains those as they should be stationary in the frame) and the only star (Regulus, as Zelenyikot points out) in these shots is the the streak going lower left Sol 351 03:09 to upper right Sol 351 03:11 (though its possible to notice a couple other extremely faint ones in similar motion).
gotta love those hot pixels though, beautiful starry colors and patterns.

[Deimos]

The hot pixels that streak in the wrong direction are bleeding down columns due to saturation. That is intrinsically colorful on a Bayer-pattern-microfilter CCD, though bland or uneven on a non-patterned CCD. The Regulus images are aimed a bit differently, so any star streaks would be somewhat different, but not column-oriented.

[Gerald]

The 17 Sol 351 Mastcam Right Phobos images available by now can be processed in a way to get a glance at the dark side of Phobos:


Processing roughly sketched:
- Calculating with double precision floating point rgb values,
- magnifying twice, interpolating subpixels,
- registering images to Phobos, iteratively by brightness barycenter of shrinking region (reducing Deimos effect), then by least squares of image deltas.
- averaging each pixel pos over main mode (accepting 20/256 delta from average) of all frames to filter out Deimos, stars, artifacts, and to reduce noise,
- subtracting background (estimated to 27/256 grey value),
- using logarithm to get bright and dark colors within 8-bit rgb range,
- additional manual stretching (brightness, saturation).

Some chromatic aberration seems to get visible this way.
Some processing artifacts (bright pixels) seem to be induced by (undefined) logarithm of 0 for pixels below 27/256, can be fixed.

I've been trying to suggest, that long exposure times can be simulated successfully by registered image sequences, and that motion blur can be limited at the same time.
So I'm optimistic, that comet observations will become possible.

[iMPREPREX]

Very nice. You've inspired me to take a crack at it (I'm more focusing on the detail on the bright side).

Full size: http://www.flickr.com/photos/84750994@N05/...254849/sizes/o/

Blown up 400%.

[Gerald]

... I'm more focusing on the detail on the bright side ...

Astonishing results!
I couldn't get much beyond this for the bright side (Sol 351 MR, 17 images):


... Beautiful panos, Damia!

[Zelenyikot]

Phobos and Deimos dance

http://www.youtube.com/watch?v=7abQLDeD0xM

[Gerald]

Sol 363 Phobos transit with available 96x96 thumbnails rather subtle yet, despite 2x magnifying and sharpening:

Hoping for full version, soon.

[Gerald]

The Sol 351 Phobos/Deimos sequence is almost complete now:

Images are roughly registered to Phobos and sharpened.

[Phil Stooke]

Revisiting the Phobos images:

http://mars.jpl.nasa.gov/msl/multimedia/images/?ImageID=5511

This is a very nice comparison of the apparent sizes of Phobos, Deimos and our Moon seen from their respective planets... but check the caption:

"The size-comparison image of Earth's moon, on the right, is also oriented with north up."

Sorry, JPL buddies, but not so - this looks like a distant Galileo encounter 2 image, and the north pole is at right, pretty much at the middle of the terminator - it's almost looking down on the pole.

Phil

[wildespace]

Interesting, the image shows that Phobos is approx as wide as the Moon in the widest part, and half as wide in the short part. Stellarium shows a much smaller Phobos as seen from Mars, 0.125 degrees or approx 1/4th of the Moon diameter, but perhaps Stellarium is not the most precise software in that regard. What is Phobos' angular size as shown in Celestia?

P.S. I plugged the numbers from the JPL link into an online calculator at http://www.1728.org/angsize.htm and the result is 0.2 degrees, slightly less than half the full moon.

[fredk]

Phobos orbits so low that its angular size varies substantially depending on how far above the horizon it is - from something like 0.14 degree at the horizon to 0.2 degree at zenith. (I'm not sure if that corresponds to an average diameter or what.)

The press image doesn't show the long axis of Phobos as wide as the moon (0.5 degrees). Look at the Marsshine images and you'll see that most (about 2/3 or 3/4) of the length of Phobos is in sunlight in this image. So it shows the long axis at roughly 0.3 degrees wide.

[Deimos]

I wonder how this happened?

http://mars.jpl.nasa.gov/msl/multimedia/images/?ImageID=5511

Thanks to Phil Stooke, wildespace, fredk (and Doug E). Note that the image of Phobos and Deimos that is used is enlarged to 2x MCAM-100 resolution. That has a 5 deg field of view spanned by 1200 pixels. The roughly N-S axis of Phobos is, in fact, nearly 0.2 deg in the image.

[djellison]

this looks like a distant Galileo encounter 2 image,

Ahh - just saw Marc's post

Yeah - whacked out a little render of the moon to fit the job

https://solarsystem.nasa.gov/multimedia/dis...amp;IM_ID=17749


Doug

[stevesliva]

Sorry, JPL buddies, but not so - this looks like a distant Galileo encounter 2 image, and the north pole is at right, pretty much at the middle of the terminator - it's almost looking down on the pole.

[Moon] Atlas did not shrug.

[Gerald]

The first reasonably resolved Sol 363 Phobos transit (eclipse) images are available, e.g. this and this MR image.
Enhanced regions (blur with radius 0.3, brightness stretched):

[fredk]

We caught what appears to be a serious wind gust on sol 368. Notice how the near foreground darkens in the first frame, then the distant slope darkens, before everything brightens up again. That suggests a huge dusty gust blowing roughly north to south. It has to be huge to darken such a large region. This is half-resolution, to fit all frames into 1MB:

[fredk]

Full resolution view of the big gust, cropped and including only the first four frames to fit (there is very little change after the fourth frame):

[Gerald]

Full resolution view of the big gust, cropped and including only the first four frames to fit (there is very little change after the fourth frame):

If you are right, this may be the first successful triggering of a Hazcam sequence by a REMS event.
Great observation! Like Ed, I first assigned it to some unusual exposure fluctuation, but I think you've got it.
It may look large, as it probably moved straight over MSL.

[fredk]

I didn't realize they could trigger from REMS. Very cool. It is hard to say how large it is. All we have to go on is that the entire visible slope of the central mound darkens in frame 2, including the little peak way off to the left. But the visible local horizon doesn't darken noticably. So the dust must be beyond the local horizon, which, given the extent of the darkening, suggests it is very large. Presumably from the timing and some estimate of wind speed we could get an estimate of the size.

Ed - I can't see any way this could be exposure variations. Between the first two frames, eg, the central mound darkens while the foreground stays about the same brightness. Exposure variations would brighten/darken everything uniformly, or maybe in some nonlinear way accounting for lut's and stretching. But whatever the details, all pixels with some particular pixel value must be mapped to the same pixel value after the exposure change (if the scene remains the same, of course). You shouldn't see some parts of the frame with some shade of grey mapped to different shades of grey than other parts with the same original shade of grey.

I'd add one more change to Ed's list. For the first two frames, the sky is brighter than in the other frames. This is all consistent with a gust passing over. The extra dust in the gust would brighten the sky as it passes over, while shading the ground.

[Gerald]

All we have to go on is that the entire visible slope of the central mound darkens in frame 2, including the little peak way off to the left. But the visible local horizon doesn't darken noticably. ...

Similar effects can also be obtained by color filtering.
As example, based on this Sol 364 ML image, switching between the brightness and the blue channel, brightness adjusted.
A local dust cloud may work like a color filter, brightness adjustment by exposure time.

[dvandorn]

Must it have been a dust cloud? The air at Gale has been getting clearer and less dusty lately, I thought.

What are the possibilities of either clouds or one of the larger-size dust devils casting these shadows?

-the other Doug

[Deimos]

REMS cannot currently be used to trigger imaging. The general idea does go way back, but I don't know of any MSL related implementation. Any other images document the event time frame?

[PaulH51]

We caught what appears to be a serious wind gust on sol 368.....

Could this 'event' have been caused by the transit of Phobos? By reducing the light level (when the darkened HazCam was captured) or by the reduced lighting causing an abrupt fluctuation in the air temperature?

Note: the MastCam 100 was taking a sequence of images of such a transit at the same time as the 'event'. Sol 308 Midnight Planets

[dvandorn]

Are you saying that we could have been seeing the shadow of Phobos passing over the terrain?

Cooool!!!

-the other Doug

[Gerald]

First, for a better illustration of the filtering effect of an assumed dd-related local dust cloud, I've combined an rgb image from two Sol 368 grey-scale Rear Hazcam Left B images (red from one image, green and blue from the other, so actually just two color channels) :


Local dust devils don't necessarily increase the overall dust in the atmosphere, as long as there isn't a local or regional dust storm. So there is no contradiction to the air becoming clearer at Gale, in general. It was just a short event of the order of a minute.

A relation to the Phobos transit should be very unlikely, it was sol 363, i.e. 5 sols earlier.

Edit: There was again a transit, very convincing explanation, Paul! So it will have been a shadow of Phobos, instead of a dd.

Interesting, that the channel combination did work, nevertheless.

[elakdawalla]

No, dude, check it out: there was an eclipse, a good one, happening at the same time as those Hazcam images. Super duper cool. Nicely done, @Deimos!

[fredk]

Yeah, this image was simultaneous with the RLB sequence. Very cool indeed! Was this never done with MER?

The darkening moving over to the mound makes sense - the shadow (penumbra) of Phobos is on the order of the size of Phobos, ie 20-odd km. (Actually the penumbra will be somewhat wider.) The mound is several km away.

[Explorer1]

Chalk up another amazing one for the team; feels like Spirit and the dust devils all over again!
Next August is another season of transits; by then Curiosity could be on Mount Sharp itself and right in the path... a chance for MAHLI movies?

[jmknapp]

Are you saying that we could have been seeing the shadow of Phobos passing over the terrain?

Cooool!!!

Per SPICE, here's the ground track of the center of Phobos' shadow (red line) during the transit:



The two red dots are the position at the time of two of the HAZCAM shots. The wedge shows the field of view of the rear HAZCAM.

How wide would the shadow be?

[EdTruthan]

The eclipse thumbnails appear to indicate a maximum conjunction at almost precisely the 03:22:00 P.M. LMST mark, the exact time of the RLB darkening event. Way cool catch by the imaging team.

And speaking of cool - Sol 369 tracks anaglyph - gotta love that repeated JPL Morse Code track. Easy to judge distance too, I believe it's about 1.5 meters per rotation if I'm not mistaken. (50cm wheel diameter x 3.14 = 157cm or 1.57 meters).

[atomoid]

scroll down to get an idea about the size of Phobos' shadow on Mars' surface, i had no idea it was imaged by Viking lander/orbiter as well! stunning!

hopefully more pics will stream in, i suppose there are more hazcam frames and they werent clustered at the very end of the transit as it currently appears. with everything else going on im wondering if it wass technically feasible to stage a navcam sequence as well?

[Deimos]

MER never imaged the ground while imaging a transit. Partly, this is the sheer scale of the event--maybe 60 km diameter, but no sharp edges. Partly it is that there is not a straight line from the science requirements to taking those images. Once in a while, maybe you do something just because you can. There didn't look like a good chance at Endeavor this year, but in principle right Pancam images can be taken in parallel with left RHAZ or FHAZ. You could do the same with NAV, but of course you couldn't point away from the Sun while also imaging the transit. And the sequencing on MER for that seems complex, given the hoops we jump through to get 3 sec/image out of Pancam.

Maybe next year hazcam could be kicked off earlier in the video. There are sequencing constraints, but boundaries aren't usually pushed hard the first time.

You could consider Navcam of a near-miss transit -- but of course the event center is >30 km away. That's a tough sell given the implications of the specific transit timing constraints on sequencing a sol. That's especially true with Opportunity's power limitations, but transits (and near-misses) don't wait for drives or comm passes ... and are less important than either, in general.

[Gerald]

"How wide would the shadow be?"

There is no umbra of Phobos on the Martian surface.
The size of Phobos is 26,8 × 22,4 × 18,4 km, average 22.2 km, distance from the surface 6,000 km.
Diameter of the Sun 1,392,684 km, average distance Sun-Mars 228 million km.
Apparent diameter of Phobos relative to Sun therefore (22.2/6,000) / (1.4/228)=0.61.

Therefore the antumbra will be about 14.2 km (remaining 39% of Sun's apparent diameter).
The whole penumbra adds a tiny bit more than the diameter of Phobos around the antumbra, i.e. 22.2 km, together 14.2 + 2 * 22.2 = 58.6 km.
That's a rough approximation based on average values at noon.
The eclipse was in the afternoon, so we get a roughly elliptical shadow, with the apparent diameter of Phobos a little smaller. Irregular shape of Phobos is to be added.

See also Transit of Phobos from Mars on Wikipedia,
Phobos, Sun, Distance Sun-Mars.

[fredk]

MER never imaged the ground while imaging a transit.

Thanks for the info, Deimos. I see now that what I was thinking of was that we fantasized about this years ago with MER - see Doug's post and my reply. We talked about how cool it would've been to do this from the top of Husband Hill. Maybe we'll get another chance from Oppy or MSL showing the shadow racing across the landscape from a high vantage point...

[vikingmars]

Yeah, this image was simultaneous with the RLB sequence. Very cool indeed! Was this never done with MER?

No with MER, but yes with Viking Lander 1.
Here is the image taken ("rescan" mode) on its mission Sol 423 : the darkening of the Phobos shadow flying above its Chryse Planitia site can be seen easily also. Cheers !

[Gerald]

In the meanwhile, six of the Sol 363 MR eclipse images are there. Here a 10x time-lapsed gif:

(based on NASA/JPL-Caltech/MSSS)

Well, the Sol 368 eclipse will be much cooler, as Emily pointed out.

[fredk]

Well, the Sol 368 eclipse will be much cooler

The sol 369 transit looks not bad too - in fact, it looks very close to central:
http://mars.jpl.nasa.gov/msl-raw-images/ms...0784Q1_DXXX.jpg

[Gerald]

Bullseye!

[fredk]

Here's what I dreamed of doing 7 years ago - I've subtracted the average of the 8 post-transit RLB hazcam frames from each transit frame, then added 128 and did a small symmetrical stretch. So neutral grey means the same as after the transit, dark grey means darker, and light grey lighter than after transit:

As the transit ends, everything goes to neutral grey, with the last bit of shadow fading off into the east. The sky looks brighter during the transit (first two frames) than after, which can't be true of course. So what's probably happening is that different exposures, or more likely just different auto-stretching, are being applied. We'll have to wait for PDS (or a press release) to see how much the sky darkened during the transit...

[mcaplinger]

Bullseye!

All we had to do was get the sun in the field of view at the right time, Phobos did the rest.

[elakdawalla]

Point a camera with a 5-degree FOV at a moving speck crossing a moving spot from a rover that was only briefly paused in the middle of DRIVING ACROSS ANOTHER FREAKING PLANET??? Pshaw, that's nothing

[PaulH51]

Point a camera with a 5-degree FOV at a moving speck crossing a moving spot from a rover that was only briefly paused in the middle of DRIVING ACROSS ANOTHER FREAKING PLANET??? Pshaw, that's nothing

Hats off to the team

[DeanM]

Quoting Emily: "Point a camera with a 5-degree FOV at a moving speck crossing a moving spot from a rover that was only briefly paused.."

This can have been no easy feat!

Indeed, how is such precise 'pointing' achieved: gravity provides one vector but Mars (now) has no magnetic field to provide a second.

Dean

[Gerald]

A gyro could do the job.

[Deimos]

Indeed, how is such precise 'pointing' achieved: gravity provides one vector but Mars (now) has no magnetic field to provide a second.

Sun images show the Sun's position and (optionally) direction of motion in the rover's frame. These allow a full attitude solution or a yaw-only solution. Initial measurement units (gyro-based) update attitude between sun images. MER used a subset of Pancam Sun images. MSL uses Navcam Sun+sky images. The IMU propagates attitude forward, but error builds with drive-time. So the attitude, especially for Sun aims, is precise after a Sun update and before the next drive, and degrades until the next Sun update. The midnight planets page for sol C/369 shows such an update after the drive (and mid-drive imaging). Sol B/3387 shows an update for Opportunity. (In both cases, look for the Sun image/images after "driving...".)

[fredk]

MSL uses Navcam Sun+sky images.

I didn't realize that - I had assumed MSL used mastcam. Why navcam? Surely it's harder to pinpoint the sun's position in a navcam frame, or in other words the uncertainty on the sun's position would be much larger in a navcam frame than a mastcam frame. That's both because of the lower resolution of navcam, but also because of the overexposure due to lack of solar filter. (I guess you could pinpoint the position from navcam pretty well in one direction, due to the CCD bleeding.)

FredK: "Subtracted the average..." Brilliant idea... just freaking brilliant.

Thanks a lot Ed, but I have to say I was inspired by what we did several years ago with Spirit's dust devil images. I have no idea who started differencing the images to show DD's more easily.

[john_s]

Why navcam? Surely it's harder to pinpoint the sun's position in a navcam frame, or in other words the uncertainty on the sun's position would be much larger in a navcam frame than a mastcam frame.

I presume it's simply that Navcam has a much wider field of view, so you can find the sun even if the accumulated error in the rover's orientation is quite large.

John

[mcaplinger]

I presume it's simply that Navcam has a much wider field of view...

On MER they do sun-finding with Pancam, which has the same FOV as the 34mm Mastcam.

It was more a political/requirements-driven issue related to Mastcam being a non-JPL instrument. Mastcam could be used if needed but Navcam is completely sufficient.

[Gerald]

Why navcam? Surely it's harder to pinpoint the sun's position in a navcam frame, or in other words the uncertainty on the sun's position would be much larger in a navcam frame than a mastcam frame. That's both because of the lower resolution of navcam, but also because of the overexposure due to lack of solar filter. (I guess you could pinpoint the position from navcam pretty well in one direction, due to the CCD bleeding.)

Here a graphical sketch, how a good reference point can be determined from this NRB image:

[fredk]

good

The question is how good. Being able to image the sun's un-overexposed disc means you will be able to pinpoint it's position considerably better with mastcam (or pancam).

But mcaplinger has answered this - the accuracy from navcam is sufficient. One thing I suppose they can do is calibrate - image the sun simultaneously with mastcam and navcam, and use that to create a model for the sun's true position in the navcam overexposed blob. There will still be uncertainties due to differing tau, dust on optics, etc. All of these effects could distort the shape of the overexposed "blob".

[mcaplinger]

The question is how good.

In the accuracy stackup, the uncertainty in the actual RSM pointing from gear backlash, encoder/resolver precision, etc, is probably many times larger than any centroiding error from sun overexposure.

[Deimos]

I don't know if any flight Mastcam/Navcam tests have been done on the engineering side. I do know that many test images were acquired with the MERs, starting long before MSL's launch. These were used for development and validation, and probably include a decent sampling of atmospheric conditions.

[Gerald]

Begin and end of the Sol 369 eclipse:

(magnified 4x by nearest neighbour, blur radius 2, brightness stretched)
They probably downlinked those images first, because they are of highest value for retrieving orbital data (extrapolating the two instants, when Phobos' "disk" is externally tangent to the Sun, compare contacts I and IV of the 2012 Venus transit).

[Deimos]

Personally, I'd love to have the cool images down fast, and they are of high long term interest as well. But the first and last contacts have a special property that is relevant to planning: they segregate data worth keeping from data that can be deleted. That's the sort of thing one likes to be sure of, and cannot see perfectly in the thumbnails.

[Gerald]

Phobos silhouette inferred from 3 Sol 369 MR images, so not yet quite free of aliasing and jpg artifacts:

[Airbag]

What did you do to that image??? The original was just fine.

Airbag

[Gerald]

Squeezing out details which are not visible in a single image. It works better with more images available.
Of course the raw images are great!

[Phil Stooke]

This is my version of combining the three transit frames, only this time I cropped the solar disk out from two of them.

Phil