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View Full Version : Ep. 91: The Search for Water on Mars

Fraser
2008-Jun-03, 05:40 AM
With the successful touchdown of the Phoenix Lander, NASA is continuing its quest to find evidence of past and present water on Mars. This week we discuss the geologic history of Mars, and explain why NASA thinks the story of water on Mars is so important. And how this ties into the search for life on the Red Planet.http://feeds.feedburner.com/~r/astronomycast/~4/303465676

More... (http://feeds.feedburner.com/~r/astronomycast/~3/303465676/)

clint
2008-Jul-07, 09:07 AM
Heard on this show:
Mars has only about 10% of Earth's mass. Right?

That makes me wonder:
How come an astronaut would still weigh about a third of what he weighs on Earth?

01101001
2008-Jul-07, 06:58 PM
How come an astronaut would still weigh about a third of what he weighs on Earth?

Planet radius, or distance to all the mass for someone on the surface, affects weight, too, as does the distribution of the mass within the planet.

See Exploratorium: Your Weight on Other Worlds (http://www.exploratorium.edu/ronh/weight/), and read an explanation.

clint
2008-Jul-08, 01:02 PM
Planet radius, or distance to all the mass for someone on the surface, affects weight, too, as does the distribution of the mass within the planet.

See Exploratorium: Your Weight on Other Worlds (http://www.exploratorium.edu/ronh/weight/), and read an explanation.

Nice calculator and explanation, thanks for the link!

CharlieMopps
2008-Jul-13, 01:43 PM
So, since there's water on mars, can we send my wife there?

clint
2008-Jul-28, 05:10 PM
By the way, another detail mentioned on this episode that I cannot get my head around
(is it only me, or is this a common thing listening to this show, haha - just kidding):

Why is it you cannot see the top of Olympus Mons, when standing at its base?
Did anybody understand that?
(Pamela said sth. about 'the surface of Mars curving away to fast')

CharlieMopps
2008-Jul-29, 04:41 PM
The top is beyond the curve of the horizon. Meaning, the slope of the mountain is less that how fast the planets curvature falls away from you. You could be climbing the mountain, but feel like you are walking down hill.

I believe that this is only 1 slope of the mountain though. On the other side of it, the slope is much more steep.

clint
2008-Jul-30, 10:38 AM
I still find that hard to believe.

I mean, it's easy to imagine that you might not be able to properly see the entire volcano from the surface,
and that maybe even the opposite edge might be beyond the horizon due to the planet's curvature.

But if the peak is not visible from the surface,
that should be due to the curvature of the volcano's slope rather than the planet's, shouldn't it?

Also, at the distances involved (more than 600 km across), atmospheric visibility would certainly be an issue.
(e.g. the fact that you cannot see the Alps or Rockies from 600 km away, is due to visibility rather than the planet's curvature, isn't it?)

Sovieto
2008-Jul-30, 11:19 AM
I still find that hard to believe.

I mean, it's easy to imagine that you might not be able to properly see the entire volcano from the surface,
and that maybe even the opposite edge might be beyond the horizon due to the planet's curvature.

But if the peak is not visible from the surface,
that should be due to the curvature of the volcano's slope rather than the planet's, shouldn't it?

Also, at the distances involved (more than 600 km across), atmospheric visibility would certainly be an issue.
(e.g. the fact that you cannot see the Alps or Rockies from 600 km away, is due to visibility rather than the planet's curvature, isn't it?)
Hey, I'm no expert in this at all or anything, I'm just a 15 year old student, but I'll try to explain to you what I get out of this statement. If I'm horribly wrong, please don't bash me! >.<

Okay, so Mars is way smaller than Earth.. so theres a greater curvature.. so here's a picture of how I could see this happening.

http://i130.photobucket.com/albums/p250/Conscriptt/omons.jpg

(nothing is drawn to scale)

clint
2008-Jul-31, 10:49 AM
Hey, I'm no expert in this at all or anything, I'm just a 15 year old student, but I'll try to explain to you what I get out of this statement. If I'm horribly wrong, please don't bash me! ...

Hey Sovieto, don't worry, I'm not an expert either ;)
Good idea to draw the whole thing!

http://farm4.static.flickr.com/3017/2719591240_e979a2b1b5.jpg?v=0

Green line: view from one end of the volcano to the other
(might be blocked not only by the volcano itself, but possibly also by planet's curvature
- although I'm not sure whether this still holds true for the real scales)

Blue line: view from surface to volcano peak.
(the curvature shouldn't spoil the view even at the extreme scales of your drawing)

Sovieto
2008-Aug-01, 08:08 AM
Hey Sovieto, don't worry, I'm not an expert either ;)
Good idea to draw the whole thing!

http://farm4.static.flickr.com/3017/2719591240_e979a2b1b5.jpg?v=0

Green line: view from one end of the volcano to the other
(might be blocked not only by the volcano itself, but possibly also by planet's curvature
- although I'm not sure whether this still holds true for the real scales)

Blue line: view from surface to volcano peak.
(the curvature shouldn't spoil the view even at the extreme scales of your drawing)
I'm at a lost then!

Olowkow
2008-Aug-02, 06:58 PM
Wiki does mention this, but it is more likely the cliffs surrounding the central dome that would obscure the peak.

http://en.wikipedia.org/wiki/Olympus_Mons
Both the size of Olympus Mons and its shallow slope (2.5 degrees central dome surrounded by 5 degree outer region) mean that a person standing on the surface of Mars would be unable to view the upper profile of the volcano even from a distance, as the curvature of the planet and the volcano itself would obscure it.

The attached image is a scale drawing (hope this works), and it is difficult to see how a 17 mile peak would not be visible from the outer edge due just to the curvature of the planet.

CharlieMopps
2008-Aug-03, 02:06 PM
Here's my example... this is distorted to enphasize what I mean... but you'll get the idea. I think the key difference is that mountains are not triangles. They have slopes, and that slope, combined with the planets curvature, are what put the peak out of site of the observer.

http://img397.imageshack.us/img397/9854/marsyy8.jpg

Olowkow
2008-Aug-03, 03:50 PM
Here's my example... this is distorted to enphasize what I mean... but you'll get the idea. I think the key difference is that mountains are not triangles. They have slopes, and that slope, combined with the planets curvature, are what put the peak out of site of the observer.

Your drawing is just what I pictured to be the case on reading the claim, and that is why I got on Corel and drew a scale drawing to test this hypothesis. I used the miles figures (like 4213 miles=4.213 inches, for instance for Mars' diameter),and I expected to see something like your drawing, but the curvature of Mars just is not enough compared to the diameter and height of the volcano to obscure the peak. The 16.7 mile height is pretty significant, compared to the size of the planet. The slope is said to be a combination of 2.5 and 5 degrees, but I didn't include these. The actual slope I used turned out to be about 5 degrees.

Of course I could not draw a man standing on the surface to scale, as he would be microscopic.

Sovieto
2008-Aug-05, 09:58 AM
Here's my example... this is distorted to enphasize what I mean... but you'll get the idea. I think the key difference is that mountains are not triangles. They have slopes, and that slope, combined with the planets curvature, are what put the peak out of site of the observer.

http://img397.imageshack.us/img397/9854/marsyy8.jpg
oh so i did get the general idea of it :D

Neverfly
2008-Aug-05, 10:42 AM
Your drawing is from an outside 2D kind of perspective.

Now, Imagine that you are standing on that sphere (Mars) and looking UP toward the peak of Olympus Mons.

From that perspective, the peak of the mountain is curved away from the observer, making it difficult to see (Atmospheric conditions notwithstanding.)

Instead of drawing a model on flat paper, try using a 3D simulator.

ETA: Brain fried? Somehow I missed Sovieto's post right above the first time around. Oops.
ETAČ: no, I remember reading the words in the posts- but the Pictures didn't appear. How Odd:think:
In this (http://www.bautforum.com/questions-answers/77414-can-you-identify-area-moon-please.html#post1295858) thread- the page sat for ten minutes and no images appeared. I hit reply thinking he forgot the image- only to see it's URL. Went back page and there was the image. Maybe I need to start a new thread in About BAUT>

Olowkow
2008-Aug-08, 12:00 AM
If the drawing is not to scale, it is pretty meaningless. The scale drawing (see post #12) shows that the peak is tiny compared to the curvature of Mars.