APOD: A High Cliff on Comet... (2021 Nov 28)

[APOD Robot]

A High Cliff on Comet Churyumov-Gerasimenko

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 featured here, 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.

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[orin stepanek]

300px-Comet_67P_on_19_September_2014_NavCam_mosaic.jpg (10.86 KiB) Viewed 4336 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!

[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.

[Chris Peterson]

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. :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!)

[Jim Armstrong]

This (or the other one) is one of my favorite APOD images.

[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.

[Chris Peterson]

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.)

[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?

Ann

[neufer]

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.

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).

[How craggy]

At last, an alien landscape that looks like an alien landscape.

[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.

[neufer]

Click to play embedded YouTube video.

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.

---

[neufer]

Click to play embedded YouTube video.

At last, an alien landscape that looks like an alien landscape.

[Chris Peterson]

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.