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Comment by jessriedel | Hacker News Reader

My personal favorite astronomical image of all time is this view taken by New Horizon during its retreat from Pluto:

https://en.wikipedia.org/wiki/File:PIA19948-NH-Pluto-Norgay-...

It shows atmospheric haze and the curvature of the planet in the same picture as stark terrain features. (It's a real image; not a reconstructed 3D visualization.) The Hillary Montes break into the limb (skyline) near the top of the image.

View on HN

Any idea why it appears black and white? The links say it was taken with the "Multispectral Visual Imaging Camera (MVIC)", whose description suggests it can capture in visible spectra. Is Pluto really made of grey?

Very likely the image was taken using only one MVIC filter (it has seven according to Wikipedia) [1] and is hence monochromatic.

Since this is near sunset and hence very dark, maybe they chose one of the panchromatic filters to admit as much light to the detector as possible.

Another possibility is that researchers didn't think there was any scientific value in capturing the image through multiple filters and rather saved the limited on-board memory for some other data.

[1] https://en.wikipedia.org/wiki/Ralph_(New_Horizons)#Specifica...

It's a composite of LORRI images, which is panchromatic. That means it doesn't have any filters in between, and it measures the intensity of light across all visible wavelengths (and probably a bit of near IR -- so panchromatic), that's why it's grayscale -- it's measuring the intensity of light.

I've downloaded all the mission LORRI and MVIC raw files, and I know "by eye" that MVIC isn't near as good resolution as LORRI.

Edit: after checking the linked file, then yes, this version must be an upscaled MVIC image (I saw an almost 7k by 3k image and immediately thought of LORRI). Yet, there are same views from the LORRI instrument, which are far more detailed.

Are you saying there is a version of this photo at even higher resolution? Is there anything you could tell me that would help me track it down? It's sort of a hard thing to Google for, and hunting through the raw NASA database seems like a needle in a haystack.

EDIT: Based on this, I think you might have just gotten the two cameras confused :)

> LORRI is a simple camera to understand -- it's point and shoot. It is black-and-white, with a square detector, 1024 pixels square, over an extremely narrow field of view of 0.29 degrees....Sometimes, to keep file sizes small and improve signal in low light situations, you can bin LORRI images 4x4, so the resulting pictures are 256 pixels square. That's pretty much it for LORRI....

> MVIC is quite different from LORRI...The detector is 5024 pixels wide, of which 5000 are actually photoactive, so its images are 5000 pixels wide by an arbitrary number of pixels long.

https://www.planetary.org/blogs/emily-lakdawalla/2015/091713...

Didn't confuse them, LORRI is basically a camera at the end of a long telescope, hence it gives higher resolution images.

But yeah, going over the files at the time this MVIC image was generated, LORRI took a few (very) close up images but it doesn't have any one having such a large field of view (since MVIC is not as magnified, then it's able to take such widefield images).

Edit: And after a lot of searching, I found the image: nh-p-mvic-3-pluto-v3.0/data/20150714_029918/mp2_0299181722_0x530_sci.fit.

By the way, I'm glad you threw me into this search. Having found this specific image gave me a few good ideas to work over them again, with new things I've learned since the last times I visited them.

I've now found the answer:

> Question: If MVIC is New Horizons' color camera, why is this image black-and-white?

> Answer: Either because only one channel was used to take this image, or because they have only received one channel's worth of data on the ground. To make a single color image, you have to downlink three photos, one each from three different channels; in other words, color images take three times as much data as black-and-white ones. As a matter of fact, New Horizons team member John Spencer has confirmed that only the panchromatic channel was used for this photo, because of the limited time and demands on the spacecraft during closest approach. If they were shooting in color, they wouldn't also be able to do as much with LORRI at the same time.

https://www.planetary.org/blogs/emily-lakdawalla/2015/091713...

I don't know why. My best guess is that it's low lighting, and there isn't much color information available. I think I've seen a colorized version somewhere, but can't remember if the colors were authentic. Very interested if someone could track that down.

Thanks, I had not seen that image before. It's amazing that Pluto has an atmosphere. Was this suspected before the New Horizon's mission? I seem to recall it once being presented as considered a cold rock with no interesting features or possible atmosphere.

It was indeed established that Pluto had an atmosphere before the New Horizon flyby. The atmosphere is mostly seasonal. The air freezes when Pluto is far from the sun, and sublimates again when it's near.

Thank you for reminding me how strange the universe can be sometimes.

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