Explanation: This high cliff occurs not on a planet, not on a moon, but on a comet. It was discovered to be part of the dark nucleus of Comet Churyumov-Gerasimenko (CG) by Rosetta, a robotic spacecraft launched by ESA that rendezvoused with the Sun-orbiting comet in 2014. The ragged cliff, as featuredhere, was imaged by Rosetta in 2014. Although towering about one kilometer high, the low surface gravity of Comet CG would likely make it an accessible climb -- and even a jump from the cliff survivable. At the foot of the cliff is relatively smooth terrain dotted with boulders as large as 20 meters across. Data from Rosetta indicates that the ice in Comet CG has a significantly different deuterium fraction -- and hence likely a different origin -- than the water in Earth's oceans. Rosetta ended its mission with a controlled impact onto Comet CG in 2016. Comet CG has just completed another close approach to Earth and remains visible through a small telescope.
300px-Comet_67P_on_19_September_2014_NavCam_mosaic.jpg (10.86 KiB) Viewed 4083 times
Comet Churyumov-Gerasimenko; The Comet looks
like a ferocious beast to me ! The rugged terrain
makes it look look like it was torn off from a mountain
of some planet! I think the ice looks like fallen snow! Just my vivid imagination worki8ng OT!
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Sun Nov 28, 2021 3:54 pm
by E Fish
and even a jump from the cliff survivable.
Yikes! Survivable or not, I don't know that I could bring myself to jump off a cliff.
Yikes! Survivable or not, I don't know that I could bring myself to jump off a cliff. :shock:
From the base, a jump of less than a meter per second would take you right to the top, and then you'd fall back down, landing at that same low speed. (FWIW, you hit the ground at about 1 m/s when you fall from a height of 5 cm!)
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Sun Nov 28, 2021 4:51 pm
by Jim Armstrong
This (or the other one) is one of my favorite APOD images.
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Sun Nov 28, 2021 5:39 pm
by DL MARTIN
Thanks for qualifying for me what a comet actually looks like. I grew up thinking it was just a ball of ice that shed crystals as it encountered the heat from the Sun - thus the tail.
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Sun Nov 28, 2021 5:57 pm
by Chris Peterson
DL MARTIN wrote: âSun Nov 28, 2021 5:39 pm
Thanks for qualifying for me what a comet actually looks like. I grew up thinking it was just a ball of ice that shed crystals as it encountered the heat from the Sun - thus the tail.
Some are. They range from dirty snowballs to snowy dirtballs. Pristine comets making their first pass are probably close to what you imagined. Those that are in short period orbits and have made many orbits are more like asteroids. Some have lost all of their volatiles and can only be distinguished from asteroids by their orbits (sometimes).
(And, of course, their mass is important in determining just how regular or irregular their shape is. High mass comets are closer to spherical, while low mass ones are likely to be highly irregular.)
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Sun Nov 28, 2021 8:32 pm
by Ann
It sure looks like a mythical beast of some sort!
Attack on the left, surrender at right. I mean, you can see the two heads, right?
Yikes! Survivable or not, I don't know that I could bring myself to jump off a cliff.
From the base, a jump of less than a meter per second would take you right to the top, and then you'd fall back down, landing at that same low speed. (FWIW, you hit the ground at about 1 m/s when you fall from a height of 5 cm!)
Click to play embedded YouTube video.
Astronaut John Young (commander of the Apollo 16 lunar landing mission) was able to leap about a foot above an object with 73.5 billion (=[4190]3) times the mass of 'Cherry-Geary' and survived the fall back intact.
Ergo: He could have lept about 4190 feet high on 'Cherry-Geary' and survived the fall back (assuming he misses the flag pole).
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Sun Nov 28, 2021 11:45 pm
by How craggy
At last, an alien landscape that looks like an alien landscape.
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Mon Nov 29, 2021 6:56 am
by Newtownian
Will the outgassing increasingly make the comet spin and as it shrinks into rubble help it take on a spherical shape?
Related to this is there any particular reason why we have seen at least two of these rubble residues take on a near Octahedral shape instead of one of the other polyhedrons? Might we expect to see other Platonic solid rubble balls in the future? depending on spin v. gravity.
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Mon Nov 29, 2021 1:32 pm
by neufer
Click to play embedded YouTube video.
Newtownian wrote: âMon Nov 29, 2021 6:56 am
Will the outgassing increasingly make the comet spin and as it shrinks into rubble help it take on a spherical shape? Related to this is there any particular reason why we have seen at least two of these rubble residues take on a near Octahedral shape instead of one of the other polyhedrons? Might we expect to see other Platonic solid rubble balls in the future? depending on spin v. gravity.
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Mon Nov 29, 2021 1:36 pm
by neufer
Click to play embedded YouTube video.
How craggy wrote: âSun Nov 28, 2021 11:45 pm
At last, an alien landscape that looks like an alien landscape.
Re: APOD: A High Cliff on Comet... (2021 Nov 28)
Posted: Mon Nov 29, 2021 1:38 pm
by Chris Peterson
Newtownian wrote: âMon Nov 29, 2021 6:56 am
Will the outgassing increasingly make the comet spin and as it shrinks into rubble help it take on a spherical shape?
It's already a rubble pile. Just how much the shape will change depends on how much of that rubble consists of volatiles.