View Full Version : Analysis of Mars Global Surveyor

2002-Dec-19, 10:17 PM
The images on this page can difficultly be associated with natural formations.You`ll be the judges.If someone as a logical explanation?In particular about the -tunnels-.


<font size=-1>[ This Message was edited by: Aldrin on 2002-12-19 17:21 ]</font>

The Bad Astronomer
2002-Dec-19, 10:36 PM
Those pictures don't load for me. Is this about the "glass tunnels"? I get a lot of email about them. Here is my standard reply:

I have seen these images and read all the furor about them, including Arthur C. Clarke's unfortunate statements. Normally,
I wouldn't argue with someone of his stature, but in this case he (and Richard Hoagland who is also trumpeting the 'tubes' as evidence of life on Mars) is quite wrong.

They're not tubes; they're valleys. They look raised due to a peculiar illusion. We expect light to come from above, and we interpret shadows that way. If the light is coming from below in an image, it throws our brains off, making depressions look raised and vice-versa. The illusion is very strong,
making craters on the Moon look like raised domes, for example.

A good example of this can be found at
http://isaac.exploratorium.edu/~pauld/summer_institute/summer_day1perception/crater_illusion.html. In this case, we see the valley as if it were raised up, but it's not real. Those aren't slices cut through a raised tube; they are raised dunes in a valley!

The glassy part of the image is very striking, but it too is an illusion. When a digital image is displayed, the contrast
(the difference between how light and dark parts are displayed) must be chosen. In this case, the people at Malin Space Science (who take all thse Mars images; see them at http://www.msss.com) chose a contrast that made bright features white as well as somewhat immer features look white too.

It's almost as if the image were overexposed. In this image, it makes the tube look shiny, as if it is reflecting
light the way glass would. But had they displayed the image with less contrast, those parts would not have been so white,
and might have been a bit grayer. That would destroy the illusion pretty well.

For more about this, go to the Straight Dope Message board at http://boards.straightdope.com/sdmb/showthread.php?threadid=69117 and scroll down to the message from Podkayne (I posted there as well a bit later).

So in conclusion, those are valleys with dunes, not glass tubes with etchings. The moral here is that image interpretation is very difficult, and takes practice. What you see initially may not be what's really there.

Phil Plait
The Bad Astronomer

<font size=-1>[ This Message was edited by: The Bad Astronomer on 2002-12-19 17:36 ]</font>

2002-Dec-20, 02:06 AM
Some of the "glass tube" photos are very persuasive, but the same sorts of rows of dunes can be seen in just about any MGS photograph. The "conspiracists" just pick out the best examples and ignore the other images that make it clear that this is just geology.

2002-Dec-20, 03:31 AM
Check this out:

Far out, eh?