MER-B Dimes images

In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
slightly diffuse dark circular shadow about half a crater width to its
left. Is this the shadow of the spacecraft? I had thought the sunlight
incidence angle was lower since it is supposed to be around 2PM local time
at Meridiani. This seems to be directly below the spacecraft as it
descends. So maybe it is something else.

The 3 DIMES images are at:

http://marsrovers.jpl.nasa.gov/galle...20040125b/MER-
B_DIMES_1404m-B22R3.jpg

http://marsrovers.jpl.nasa.gov/galle...20040125b/MER-
B_DIMES_1690m-B22R3.jpg

http://marsrovers.jpl.nasa.gov/galle...20040125b/MER-
B_DIMES_1986m-B22R3.jpg

Mark

Mark asks:

In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
slightly diffuse dark circular shadow about half a crater width to its
left. Is this the shadow of the spacecraft?

JPL says that it's the shadow of the parachute. The bright ring around the
shadow is of course caused by the diffraction of sunlight around the parachute.

Wirt Atmar

mlm writes:

In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
slightly diffuse dark circular shadow about half a crater width to its
left. Is this the shadow of the spacecraft?

Highly unlikely, since this photo is almost certainly being taken from a
quite high altitude, and your alleged "shadow" is a substantial fraction
of the large crater's diameter --- whereas even the lander's parachute
is quite small compared to the diameter of a typical aregraphical feature !!!

Downloading the image and tweaking the image's intensity curve using the
image editing tool 'xv' clearly brings out an ejecta blanket surrounding
your dark spot, and gradations in intensity within said spot, that strongly
suggest to me that your "shadow" is merely a deep, relatively "fresh" crater,
and that the limited contrast range of a typical color monitor simply can't
easily display the full dynamic contrast range in this image.

Once this image has been processed a bit to "dodge out" the "over-exposed"
crater rim and "burn in" the darker regions away from the main crater
and within the dark, deep crater you've noticed, this picture will become
MUCH more photogenic, and the nature of its various features quite obvious.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In sci.astro Wirt Atmar wrote on 26 Jan 2004 22:49:46 GMT:
:WA Mark asks:

In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
slightly diffuse dark circular shadow about half a crater width to its
left. Is this the shadow of the spacecraft?

:WA JPL says that it's the shadow of the parachute. The bright ring around the
:WA shadow is of course caused by the diffraction of sunlight around the parachute.

Yes, that is the shadow of the parachute/spacecraft, but the bright
halo around it is caused by the opposition affect, not by diffraction
of sunlight around the parachute. It is the backscattering of
sunlight near the zero phase angle that can also be seen in the
abnormal brightening of asteroids near opposition, or even of the
full moon. The full moon, for example, is much more than twice as
bright as the first quarter moon appears. You can also see the same
affect from an airplane if you look on the ground opposite the sun
where the shadow of the plane should be - you'll see a bright area
on the ground.

Jim.

Jim Scotti
Lunar & Planetary Laboratory
University of Arizona
Tucson, AZ 85721 USA http://www.lpl.arizona.edu/~jscotti/

mlm wrote in message ...
In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
slightly diffuse dark circular shadow about half a crater width to its
left. Is this the shadow of the spacecraft? I had thought the sunlight
incidence angle was lower since it is supposed to be around 2PM local time
at Meridiani. This seems to be directly below the spacecraft as it
descends. So maybe it is something else.

The 3 DIMES images are at:

http://marsrovers.jpl.nasa.gov/galle...20040125b/MER-
B_DIMES_1404m-B22R3.jpg

http://marsrovers.jpl.nasa.gov/galle...20040125b/MER-
B_DIMES_1690m-B22R3.jpg

http://marsrovers.jpl.nasa.gov/galle...20040125b/MER-
B_DIMES_1986m-B22R3.jpg

Mark
I think it is. Interestingly on the first of 3 DIMES in the lower
right quadrant you can see a black dot/line. This looks suspiciously
like the heatshield as seen on DIMES image from Spirit. Oh hell why
not speculate even more. My bet is that it the lander is in one of
the two craters down to the lower left of the larger crater that are
side by next vertically in the image. There's not a lot more that I
would call candidates. By the way I also think you can see a dimmer
version of the shadow in the second DIMES image. RN

On Mon, 26 Jan 2004 08:00:42 -0600, mlm wrote:

In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
slightly diffuse dark circular shadow about half a crater width to its
left. Is this the shadow of the spacecraft? I had thought the sunlight
incidence angle was lower since it is supposed to be around 2PM local time
at Meridiani. This seems to be directly below the spacecraft as it
descends. So maybe it is something else.


They said in the press conference it's the shadow of the parachute.


Bill Cherepy
Grayson, GA

mlm wrote:

In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
snip
Can you, or anyone, explain the bright ring? It does not seem to cross
from the inside to the outside at the 2 points where the solar rays
would be tangent to the ridgeline. It looks as if it is lit from the
outside all the way around.

Mitchell Timin
--
"Many are stubborn in pursuit of the path they have chosen, few in
pursuit of the goal." - Friedrich Nietzsche

http://annevolve.sourceforge.net is what I'm into nowadays.
Humans may write to me at this address: zenguy at shaw dot ca

Gordon D. Pusch wrote:
:WA Mark asks:


In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
slightly diffuse dark circular shadow about half a crater width to its
left. Is this the shadow of the spacecraft?

Highly unlikely, since this photo is almost certainly being taken from a
quite high altitude, and your alleged "shadow" is a substantial fraction
of the large crater's diameter --- whereas even the lander's parachute
is quite small compared to the diameter of a typical aregraphical feature !!!

He isn't referring to the large dark area on the crater floor. He is refering
to a small dark dot with a diffuse bright area around it which sits just to
the lower left of the bright rim of the large crater (see the following image:
http://marsrovers.jpl.nasa.gov/galle...m-B22R3_br.jpg
I believe that it may indeed be the shadow of the parachute and spacecraft
since the chute is quite large (somewhere around 17 or 18 meters in diameter)
and the altitude is only 1404 meters. It can also be vaguely glimsed in the
two other images which were taken at somewhat higher altitudes. The area
around the dark dot is lighter, which is consistent with it being a shadow
when viewed from above with light backscattered from the surface of Mars in
the area immediately around the shadow. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Highly unlikely, since this photo is almost certainly being taken from a
quite high altitude, and your alleged "shadow" is a substantial fraction
of the large crater's diameter --- whereas even the lander's parachute
is quite small compared to the diameter of a typical aregraphical feature!

Unlikely. If you take the series as a sequence, you'll notice the feature
is absent from the first frame taken at 1986 m of height, quite near to
the crater and dimmer on the second taken at 1690 m of height, and has
moved again from the crater and become more distinct and larger on the
third taken at 1404 m of height.

Jan

(Wirt Atmar) wrote in
:

Mark asks:

In 1 of the 3 DIMES images taken by Opportunity on its approach to the
surface (at 1404m), there is a brightly ringed crater and a distinct,
slightly diffuse dark circular shadow about half a crater width to its
left. Is this the shadow of the spacecraft?

JPL says that it's the shadow of the parachute. The bright ring around
the shadow is of course caused by the diffraction of sunlight around
the parachute.

Wirt Atmar


Wirt, how did you find this out from JPL?

Mark