Mercury MESSENGER CRAFT (APOD 10 Jul 2008)

[royalpalms6]

THE MESSENGER CRAFT SENT A PHOTO BACK SHOWING TWO COLORS, BLUE AND (GOLD EXPLAINED COLOR OF). WHAT ABOUT THE "BLUE", IS IT TITANIUM DEPOSITES OR SOMETHING UN KNOWN?[img](APOD,%20July%2010,%2008)[/img]

[orin stepanek]

http://apod.nasa.gov/apod/ap080710.html

No outposts! It would be bragging rights if there were.

Orin

[iamlucky13]

The APOD caption says it is an "enhanced color" image (meaning natural colors have simply been brightened) but it looks to me like it is false color.

I'm not sure what minerals we might be seeing, but apparently that is discussed in some of the papers that were written based on data from that flyby.

There's a little bit more information at the link below, but not a whole lot that is useful to your question:

http://www.jhuapl.edu/newscenter/pressr ... 080703.asp

[apodman]

According to this link from the caption, the imaging system uses 12 filters in visible and near infrared wavelengths. It doesn't say how many of each. The infrared "colors" are surely false rather than enhanced, huh? Maybe the enhancement is overlaying false colors in hand-picked intensities on a monochrome photo. If what we are looking at is mostly from infrared filters, it is basically a thermal image. Thermal imaging would make sense in the case of the presumptive volcanic vents, and maybe the basin heats in sunlight or cools in darkness faster or more slowly than the surrounding terrain.

[iamlucky13]

Yes, infrared would be false color. I couldn't discern from the links or from the Messenger pages which wavelengths were actually used to construct this image and what colors they corresponded to. However, they did say they used a "statistical method" to enhance the colors. I presume they implying they either picked the most predominant colors or the colors that already showed the most variation and increased the saturation of those.

The Messenger site says the MDIS instrument covers a range from 395 nm to 1040 nm. Visible light is about 400 to 750 nm, so about half of the filters are probably visible light, and it doesn't go very far into the infrared.

It wouldn't really be considered a thermal image, as thermal radiation is generally considered to start at the long end of that range and go on out to about 14,000 nm, and normally refers to emitted radiation rather than reflected radiation.

That's somewhat technical, I know. There's some more information, and more importantly, some cool pictures on wikipedia:

http://en.wikipedia.org/wiki/Thermal_imaging

[henk21cm]

The Messenger site says the MDIS instrument covers a range from 395 nm to 1040 nm. Visible light is about 400 to 750 nm, so about half of the filters are probably visible light, and it doesn't go very far into the infrared.

It wouldn't really be considered a thermal image, as thermal radiation is generally considered to start at the long end of that range and go on out to about 14,000 nm, and normally refers to emitted radiation rather than reflected radiation.

I browsed in Pointons Introduction to statistical mechanics and found the solution Max Planck has derived for the energy of a black body:

     E(λ) = 8 π h c / [λ^5 {exp(hc/(λkT))-1}] (equation 4.21)

h is the Planck constant (6.64E-34 Js), c is the velocity of light (3E8 m/s), k is the Boltzmann constant (1.38E-23 JK) and λ is the wavelength of light.

To find the maximum wavelength at a specific temperature, differentiate E(λ) with respect to λ and demand that the derivative is 0:

     ∂E(λ)/∂λ = 8 π h c {5-(hc)/(λkT)}/[λ^6 {exp(hc/(λkT))-1}] = 0

That leaves us with: 5-(hc)/(λ_max kT) = 0, so

     λ_max = hc / (5 kT) ≈ 2.89E-3 / T

When we apply this formula for increasing temperatures (one decade per step), we arrive at the table below:

Code: Select all

T[K]     λ_max            Object
3        960 µm           Big Bang remnant
30       96 µm            Dark molecular cloud
300      9.6 µm           Earth, planet
3000     960 nm           Cool star  (IR)
30000    96 nm            Hot star  (UV)
300000   9.6 nm           Hot burst (far UV)
3000000  0.96 nm          Coronal discharge (X-ray)

Thermal images, as meant in oncological research, are usually focussed in the range of 10 µm. The old geostationary wheather satellites have two distinct IR band sensors: 6.2 µm (water vapour) and 10.8 µm (cloud temperatures). The newer satelites employ a 3.9 µm sensor as well. From the table it becomes clear why they use precisely these wavelengths: it is where the peak in the (thermal) black body radiation is located.