Starship Asterisk*

BDanielMayfield wrote:I think we're basically on the same page now Chris. I do realize that I likely overstated the potential depth of river carved canyons. And speaking of canyon causation, was Mars' great canyon caused by erosion, by tectonic separation or by both?

BDanielMayfield wrote:I was well aware of the need for rapid uplift for the formation of deep canyons Chris. I was also aware of physical principles like isostacy and the differing strengths of various types of rocks. The reason I chose a large continent as a setting was that I was speculating on the possibility of canyon systems in which a river (or rivers) of the size of our mighty Colorado might be mere tributaries. If this notion strains people's imaginations, well then I'll close by reminding y'all of something I believe Albert Einstein once said, "The universe is not only stranger than we imagine, it's stranger than we CAN imagine."

BDanielMayfield wrote:The grander than the Grand Canyon planet I was thinking of wouldn’t have to be all that much different than the earth Chris. As I’m sure you know the earth itself has had super continents several times in the past, so rivers with much larger watersheds than anything we have today could very well have existed even here.

neufer wrote:

Ann wrote:
The author wrote about the heights of mountains on neutron stars:

Thus, on a neutron star, we estimate h1 = 0·04 to 0·4 mm

That's not a lot.

Yes, but considering that the surface gravity is ~ 10¹¹ times that of the Earth
the energy expended climbing a 40 micron neutron star mountain
is equivalent to climbing a 4,000 km mountain on Earth.

Ann wrote:
The author wrote about the heights of mountains on neutron stars:

Thus, on a neutron star, we estimate h1 = 0·04 to 0·4 mm

That's not a lot.

P. A. G. Scheuer wrote:
The highest mountains on earth, reach ~ 4h1; since isostasy is known to occur in the earth’s crust, this is hardly surprising, but we note that the Tibetan plateau, for example, nowhere rises to heights comparable with the theoretical maximum h2 ≃ 45 km corresponding to its 1000 km horizontal extent.

Thus, on a neutron star, we estimate h1 = 0·04 to 0·4 mm

Chris Peterson wrote:

BDanielMayfeild wrote:As I love deserts and mountains and canyons, I’ve often daydreamed about what we may someday find on some distant world; a planet with a super continent largely drained by a river system much larger than anything presently on earth. Imagine a world where a river larger than the Amazon has carved through a plateau higher than Tibet. In such a place our planet’s Grand Canyon would be a mere side canyon on a main gorge perhaps ten’s of kilometers deep ...

There are natural limits on how high mountains can get, or how deep valleys can be cut. Or more precisely, on how steep the walls of mountains and valleys can get. Consider Mars: a massive mountain in Mons Olympus, an incredible canyon in Valles Marineris. Yet if you were near either, they'd seem far less impressive than many much smaller mountains on Earth, or much shallower valleys. Because in order for these to reach their heights and depths, they also had to spread out. You wouldn't be able to identify Mons Olympus as a mountain if you were at its base, and most of Valles Marineris would seem much less deep than the Grand Canyon.

A planet with geologic structures of great height or depth but similar extent to those on Earth would be a very odd planet indeed- materially nothing like a terrestrial planet, and probably with very low gravity.

BDanielMayfeild wrote:As I love deserts and mountains and canyons, I’ve often daydreamed about what we may someday find on some distant world; a planet with a super continent largely drained by a river system much larger than anything presently on earth. Imagine a world where a river larger than the Amazon has carved through a plateau higher than Tibet. In such a place our planet’s Grand Canyon would be a mere side canyon on a main gorge perhaps ten’s of kilometers deep ...

Ann wrote:

Beyond wrote:Ah yes. The ubiquitous star trails. But somehow the vista seems a lot Grander from the Grand Canyon. It just gives them extra PAZAZZ

Since I like to identify stars and constellations, I often find star trails frustrating.

But this time I was more successful! The tight grouping of trails at far right is the Alpha Persei Moving Cluster. Below and to the right of it, we have the rest of constellation Perseus, which you can also see here.

Just above the horizon is constellation Auriga. You can see another picture of Auriga here, where the pink emission nebulosity is somewhat enhanced!

It's a nice APOD! The Grand Canyon is stunning, of course. Not that I've ever been there, but it sure looks stunning in photographs.

Ann

Beyond wrote:Ah yes. The ubiquitous star trails. But somehow the vista seems a lot Grander from the Grand Canyon. It just gives them extra PAZAZZ

Greek navigators of old called Polaris; Kynosoura, which means "the Dog's Tail". The name came into our English language as Cynosure, which means "an object that serves as a focal point of attention and admiration" or "Something that serves to guide".

The Arabs also likened the constellation to a Fish, while with all that nation ... it was Al Faṣ, the Hole in which the earth's axle found its bearing.
...

Phoenice was the early Greek name, borrowed from its constellation, for this "lovely northern light" and the "most practically useful star in the heavens"; but for many centuries it has been Stella Polaris, the Pole-star, or simply Polaris, — Riccioli's Pollaris; this position seeming to be first recognized in literature by Dante when he wrote in the Paradiso:

the mouth imagine of the horn
That in the point beginneth of the axis
Round about which the primal wheel revolves.

pages 450ff