Starship Asterisk*

Flase wrote:
What's more, what is the point of such a mission? Obviously scientific data is one important reason, but what is the point of science? Surely it's for the whole human race, including laypeople.

http://en.wikipedia.org/wiki/Color_blindness wrote:
<<About 8 percent of males, but only 0.5 percent of females, are color blind in some way or another, whether it is one color, a color combination, or another mutation. The reason males are at a greater risk of inheriting an X linked mutation is that males only have one X chromosome (XY, with the Y chromosome carrying altogether different genes than the X chromosome), and females have two (XX); if a woman inherits a normal X chromosome in addition to the one that carries the mutation, she will not display the mutation. Men do not have a second X chromosome to override the chromosome that carries the mutation. If 5% of variants of a given gene are defective, the probability of a single copy being defective is 5%, but the probability that two copies are both defective is 0.05 × 0.05 = 0.0025, or just 0.25%.>>

Flase wrote:Well it's a shame. Most of the pictures of Mars that you get are recreated from computer models and just don't look right.

Flase wrote:Poo. A $150 digital camera from Dick Smith can take pictures in colour. Couldn't they just gaffertape one of them on? Also, one of these articles mentions that the framing camera has only a million pixels. A cheap digital camera nowadays can do 8 megapixels. Surely you just need a USB port on the probe and you can upload better results. No?

Flase wrote:
A $150 digital camera from Dick Smith can take pictures in colour.
Couldn't they just gaffertape one of them on?

Flase wrote:Thanks but I'm still confused. The example in the article has only black and white and false colour. It also seems to imply that filters are only used as scientific instruments and not to create true-colour images. Certainly when I test the hex value of colours in a Vesta image, they are all mathematically precisely grey, although the image isn't grey-scale. Are any of Dawn's photos in true colour?

Flase wrote:
Thanks but I'm still confused. The example in the article has only black and white and false colour. It also seems to imply that filters are only used as scientific instruments and not to create true-colour images. Certainly when I test the hex value of colours in a Vesta image, they are all mathematically precisely grey, although the image isn't grey-scale. Are any of Dawn's photos in true colour?

http://dawn.jpl.nasa.gov/multimedia/imageoftheday/image.asp?date=20111026 wrote:

[b][color=#0000FF]Vesta’s northern and equatorial regions in simulated true color Image Credit: NASA/ JPL-Caltech/ UCLA/ ASI/ INAF/ IASF/ IFSI[/color][/b]

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<<This composite image is a simulated true color image of Vesta’s northern and equatorial regions. It was produced by combining images obtained by the Visible and Infrared Imaging Spectrometer (VIR) instrument aboard NASA’s Dawn spacecraft. The VIR instrument can image Vesta in many different wavelength regions, called bands, in the near ultraviolet, visible and infrared parts of the electromagnetic spectrum, which corresponds to a wavelength range of 300nm to 5000nm. This is an RGB composite image where red is set as the 700nm band, green is set as the 550nm band and blue is set as the 440nm band. The wavelength of red light is around 700nm, of green light is around 550nm and of blue light is around 440nm, so this image approximates what the human eye would see looking at Vesta. It is an approximation because the human eye can see many more wavelengths than the three used here. This image shows the diverse colors of Vesta’s surface: the left and middle parts of the image are dominated by reddish hues and the right part of the image is more blue in color.

NASA’s Dawn spacecraft obtained the images used to make this composite image with its Visible and Infrared Imaging Spectrometer on July 23rd 2011. The distance to the surface of Vesta is 5200km and the average image resolution is 1.5 kilometers per pixel.>>

Flase wrote:
I have a question. Are Dawn's photos black'n'white ? I have been trying to use photoshop to increase the saturation in some pictures and I haven't found even subtle hints of colour. Even the moon has more colour in it.

http://www.universetoday.com/90374/rainbow-of-colors-reveal-asteroid-vesta-as-more-like-a-planet/#more-90374 wrote:
Rainbow of Colors Reveal Asteroid Vesta as More Like a Planet
by Ken Kremer on December 7, 2011

[b][color=#0000FF]This mosaic uses color data obtained by the framing camera aboard NASA's Dawn spacecraft and shows Vesta's southern hemisphere in false color, centered on the Rheasilvia impact basin, about 290 miles (467 kilometers) in diameter with a central mound reaching about 14 miles (23 kilometers) high. The black hole in the middle is data that have been omitted due to the angle between the sun, Vesta and the spacecraft. The green areas suggest the presence of the iron-rich mineral pyroxene or large-sized particles. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA[/color][/b]

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<<The giant Asteroid Vesta is among the most colorful bodies in our entire solar system and it appears to be much more like a terrestrial planet than a mere asteroid, say scientists deciphering stunning new images and measurements of Vesta received from NASA’s revolutionary Dawn spacecraft. The space probe only recently began circling about the huge asteroid in July after a four year interplanetary journey.

Vesta is a heavily battered and rugged world that’s littered with craters and mysterious grooves and troughs. It is the second most massive object in the Asteroid Belt and formed at nearly the same time as the Solar System some 4.5 Billion years ago.

“The framing cameras show Vesta is one of the most colorful objects in the solar system,” said mission scientist Vishnu Reddy of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany. “Vesta is unlike any other asteroid we have visited so far.”

Scientists presented the new images and findings from Dawn at the American Geophysical Union meeting this week in San Francisco.

“Vesta is a transitional body between a small asteroid and a planet and is unique in many ways,” Reddy said. “We do not know why Vesta is so special.” Although many asteroids look like potatoes, Reddy said Vesta reminds him more of an avocado.

Asteroid Vesta is revealed as a ‘rainbow-colored palette’ in a new image mosaic (above) showcasing this alien world of highly diverse rock and mineral types of many well-separated layers and ingredients. Researchers assigned different colors as markers to represent different rock compositions in the stunning new mosaic of the asteroid’s southern hemisphere. The green areas in the mosaic suggest the presence of the iron-rich mineral pyroxene or large-sized particles, according to Eleonora Ammannito, from the Visible and Infrared (VIR) spectrometer team of the Italian Space Agency. The ragged surface materials are a mixture of rapidly cooled surface rocks and a deeper layer that cooled more slowly.

[b][color=#30A000]An avocado in simulated true color[/color][/b]

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“The surface is very much consistent with the variability in the HED (Howardite-Eucritic-Diogenite) meteorites,” Prof. Chris Russell, Dawn Principal Investigator (UCLA) told Universe Today in an exclusive interview. “There is Diogenite in varying amounts.” “The different colors represent in part different ratios of Diogenite to Eucritic material. Other color variation may be due to particle sizes and to aging,” Russell told me.

No evidence of volcanic materials has been detected so far, said David Williams, Dawn participating scientist of Arizona State University, Tucson. Before Dawn arrived, researchers expected to observe indications of volcanic activity. So, the lack of findings of volcanism is somewhat surprising. Williams said that past volcanic activity may be masked due to the extensive battering and resultant mixing of the surface regolith.

“More than 10,000 high resolution images of Vesta have been snapped to date by the framing cameras on Dawn,” Dr. Marc Rayman told Universe Today. Rayman is Dawn’s Chief Engineer from NASA’s Jet Propulsion Lab (JPL) in Pasadena, Calif.

Dawn will spend a year in orbit at Vesta and investigate the asteroid at different altitudes with three on-board science instruments from the US, Germany and Italy. The probe will soon finish spiraling down to her lowest mapping orbit known as LAMO (Low Altitude Mapping Orbit), approximately 210 kilometers above Vesta’s surface. “Dawn remains on course to begin its scientific observations in LAMO on December 12,” said Rayman.>>

JohnD wrote:What is the slope of the 'cliff'?

JohnD wrote:
This has been an interesting thread diversion!

• Diversion

JohnD wrote:
de Vet et al, http://adsabs.harvard.edu/abs/2010AGUFM.P53A1510D found that,
"static angle of repose increases about 5 deg with decreasing g (from 1 to 0.1 g)"

Only for the finest glass beads in air

http://adsabs.harvard.edu/abs/2010AGUFM.P53A1510D wrote:
<<Angular materials had time-averaged angles of about 40 deg and rounded materials about 25 deg for all g, except the finest glass beads in air, which is explained by static electricity. For all materials, the static angle of repose increases about 5 deg with decreasing g (from 1 to 0.1 g), whereas the dynamic angle decreases with about 10 deg. Consequently, the avalanche size increases with decreasing g.>>

JohnD wrote:
On the other hand, this theoretical study http://ascelibrary.org/aso/resource/1/j ... horized=no found no gravity effect in a 2D model.

But this student group found a definite effect - "On Earth, that dust settles at almost a 45-degree angle," Martin said. "In lunar gravity, we were watching the drum and just seeing the angle go up, and up, and up, until it was almost at a 90-degree angle."

JohnD wrote:
A seems logical that AoR would be changed by gravity. The angle of repose reflects a balance between the shear strength of the material and gravity pulling it downwards. At some angle, the downslope vector of gravity becomes less than the force necessary to pull the particles past each other and slippage stops. As shear strength weakens, the AoR will become less and less - wet, sticky sand piles higher than dry sand - and conversely as gravity weakens, a higher pile should be possible.

If wet, sticky sand is observed anywhere in the solar system
we will immediately send a Viking there to invade!

http://www.tulane.edu/~sanelson/geol111/masswasting.htm wrote:
Mass-Wasting
Prof. Stephen A. Nelson Tulane University

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<<Mass-wasting is the down-slope movement of Regolith (loose uncemented mixture of soil and rock particles that covers the Earth's surface) by the force of gravity without the aid of a transporting medium such as water, ice, or wind. Still, as we shall see, water plays a key role.

In order for regolith to move in a mass wasting process it must be on a slope, since gravity will only cause motion if the material is on a slope. On a slope, the force of gravity can be resolved into two components: a component acting perpendicular to the slope, and a component acting tangential to the slope. The perpendicular component of gravity, g_p, helps to hold the object in place on the slope. The tangential component of gravity, g_t, causes a shear stress parallel to the slope and helps to move the object in the down-slope direction. On a steeper slope, the shear stress or tangential component of gravity, g_t, increases, and the perpendicular component of gravity, g_p, decreases. Another force resisting movement down the slope is grouped under the term shear strength and includes frictional resistance and cohesion among the particles that make up the object. Down-slope movement is favored by steeper slope angles (increasing the shear stress) and anything that reduces the shear strength (such as lowering the cohesion among the particles or lowering the frictional resistance.

Although water is not directly involved as the transporting medium in mass-wasting processes, it does play an important role. Think about building a sandcastle on the beach. If the sand is totally dry, it is impossible to build a pile of sand with a steep face like a castle wall. If the sand is somewhat wet, however, one can build a vertical wall. If the sand is too wet, then it flows like a fluid and cannot remain in position as a wall. Dry unconsolidated grains will form a pile with a slope angle determined by the angle of repose. The angle of repose is the steepest angle at which a pile of unconsolidated grains remains stable, and is controlled by the frictional contact between the grains. In general, for dry materials the angle of repose increases with increasing grain size, but usually lies between about 30 and 37º. Slightly wet unconsolidated materials exhibit a very high angle of repose because surface tension between the water and the grains tends to hold the grains in place. When the material becomes saturated with water, the angle of repose is reduced to very small values and the material tends to flow like a fluid. This is because the water gets between the grains and eliminates grain to grain frictional contact.>>

JohnD wrote:
If anything on Vesta, Art, is lying at an angle of repose, it's that slumped terrain below the 'cliff'.
Material that has slid, being stirred and mixed like falling sand, off the cliff.

And the Wiki article ignores 'g'. Under low gravity, you can expect a higher AoR.
http://www.mendeley.com/research/determ ... nt-method/
So the slope of that slumped terrain will be closer to the slope of the 'cliff' than it would be on Earth.

. .

http://www.mendeley.com/research/determining-angle-repose-sand-under-lowgravity-conditions-using-discrete-element-method/ wrote:
The gravity effects on the angle of repose of the sand were negligible.

JohnD wrote:
How steep is that 'cliff'?
What is its angle to a vertical, a line towards the centre of gravity of Vesta?

I ask, because it's diffciult to visualise that from the picture, AND there are rather small and faint craters in the cliff, almost dead centre to the pic, that show the same shadowing as craters in the scarp below and on the plateau above the cliff. So these craters must be in surfaces that are at a very similar angle to the Sun. In other words, the 'cliff' isn't that steep, it's more like this: http://www.photovanbeek.com/blog/?p=1849 No. 20 from the top - "about 2000m of smooth rock at an angle of about 45 degrees."

http://en.wikipedia.org/wiki/Angle_of_repose wrote:

<<The angle of repose or, more precisely, the critical angle of repose, of a granular material is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is in the range 0°–90°. When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The internal angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area and shapes of the particles, and the coefficient of friction of the material. Material with a low angle of repose forms flatter piles than material with a high angle of repose.>>

Here is a list of various materials and their angle of repose.
All measurements are approximated and not exact.

Code: Select all

Material (condition) 	Angle of Repose (degrees)
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Sand (wet) 	                 45°
Flour (wheat)               	45°
Bark (wood refuse) 	         45°
Chalk 	                      45°
Coconut (shredded) 	         45°
Coffee bean (fresh)  	    35–45°
Earth 	                   30–45°
Gravel (loose dry) 	      30–45°
Asphalt (crushed) 	       30–45°
Malt 	                    30–45°
Bran 	                    30–45°
Ashes 	                      40°
Granite 	                 35–40°
Clay (dry lump) 	         25–40°
Sand (dry) 	                 34°
Gravel (natural w/ sand) 	25–30°
Sand (water filled) 	     15–30°
Clover seed 	                28°
Wheat                	       28°
Clay (wet excavated) 	       15°