APOD: Dwarf Planet Ceres (2016 Feb 04)

[APOD Robot]

Dwarf Planet Ceres

Explanation: Dwarf planet Ceres is the largest object in the Solar System's main asteroid belt, with a diameter of about 950 kilometers (590 miles). Ceres is seen here in approximately true color, based on image data from the Dawn spacecraft recorded on May 4, 2015. On that date, Dawn's orbit stood 13,642 kilometers above the surface of the small world. Two of Ceres' famous mysterious bright spots at Oxo crater and Haulani crater are near center and center right of this view. Casting a telltale shadow at the bottom is Ceres' cone-shaped, lonely mountain Ahuna Mons. Presently some 385 kilometers above the Cerean surface, the ion-propelled Dawn spacecraft is now returning images from its closest mapping orbit.

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[ceelias]

I know that a lot of Mars atmosphere drifted off into space, and some chemically combined on the surface. How big (how much gravity) does a planet have to be (have) to retain an reasonably (capable of sustaining life) mixed atmosphere? Earth's size works well for us, but is there a lower limit? Obviously gas molecules would need to stay below escape velocity, and different chemical molecules would have different masses. I suspect the calculations have been done, but couldn't find it in a quick Google search.

[neufer]

I know that a lot of Mars atmosphere drifted off into space, and some chemically combined on the surface. How big (how much gravity) does a planet have to be (have) to retain an reasonably (capable of sustaining life) mixed atmosphere? Earth's size works well for us, but is there a lower limit? Obviously gas molecules would need to stay below escape velocity, and different chemical molecules would have different masses. I suspect the calculations have been done, but couldn't find it in a quick Google search.

Neither Mars nor Venus have significant magnetic fields and yet the CO₂ surface pressure is 15,000 times greater on Venus than it is on Mars. Surely most of that must involve a more active volcanism on Venus.

[Chris Peterson]

I know that a lot of Mars atmosphere drifted off into space, and some chemically combined on the surface. How big (how much gravity) does a planet have to be (have) to retain an reasonably (capable of sustaining life) mixed atmosphere? Earth's size works well for us, but is there a lower limit? Obviously gas molecules would need to stay below escape velocity, and different chemical molecules would have different masses. I suspect the calculations have been done, but couldn't find it in a quick Google search.

It's not just a question of mass, but of having a strong enough magnetic field to deflect solar wind that would otherwise carry away the atmosphere.

[Steve Dutch]

Dawn was fantastic from an engineering standpoint with its ion drive, orbiting two separate objects and robotic orbital insertion. And you don't know what a body will be like until you get there. But Ceres is the first completely uninteresting object we've ever visited. Mimas is a simple cratered ball, too, but it has that one huge crater. Callisto is pretty bland from one side, too, but the other side has dramatic multiple ring impact basins. Ceres has ... craters. I was thinking Ceres would be a really interesting hybrid ice/rock object but it seems to have no distinctive geologic terranes and no distinctive marker events. Win some, lose some.

[Chris Peterson]

But Ceres is the first completely uninteresting object we've ever visited.

I certainly wouldn't say that. A lack of unexpected physical features doesn't make it "uninteresting".

[Ron-Astro Pharmacist]

A question on Quora seems relevant.

Mars (planet): Would adding mass to a Mars moon stress Mars enough to release trapped gases in the interior of the planet, thus restoring a more human friendly atmosphere?

The obvious question being if Mars had a Ceres-sized moon (or larger) how much different of a place would it be?

[Gary Johnson]

Why do so many of the craters in this image appear to have the shape of hexagons?

[neufer]

Why do so many of the craters in this image appear to have the shape of hexagons?

http://asterisk.apod.com/viewtopic.php? ... 91#p113091

[MarkBour]

I know that a lot of Mars atmosphere drifted off into space, and some chemically combined on the surface. How big (how much gravity) does a planet have to be (have) to retain an reasonably (capable of sustaining life) mixed atmosphere? Earth's size works well for us, but is there a lower limit? Obviously gas molecules would need to stay below escape velocity, and different chemical molecules would have different masses. I suspect the calculations have been done, but couldn't find it in a quick Google search.

It's not just a question of mass, but of having a strong enough magnetic field to deflect solar wind that would otherwise carry away the atmosphere.

This is certainly true, and one of the great realizations of recent times. Indeed, there are a number of factors that could come into play. My quick Google search found a very interesting discussion of it here:
http://worldbuilding.stackexchange.com/ ... -time-scal
While said discussion mentions a number of possible confounding factors, it does focus in on the question you've asked. I can't actually vouch for any of its validity, I don't have time to read it right now, but it does look fun.

One might do well enough by empirical observation ... Pluto has a thin atmosphere, but you may not like that example, because you may view it like a comet ... which only has an atmosphere when it comes in close, and loses that atmosphere rapidly as it goes. On the other hand, Earth is obviously losing its atmosphere (https://en.wikipedia.org/wiki/Atmospheric_escape), if you want to get picky.

[DavidLeodis]

But Ceres is the first completely uninteresting object we've ever visited.

I certainly wouldn't say that. A lack of unexpected physical features doesn't make it "uninteresting".

If "Ceres is the first completely uninteresting object we've ever visited" then that makes it an interesting object!

[Ann]

Ceres is the first completely uninteresting object we've ever visited. Mimas is a simple cratered ball, too, but it has that one huge crater. Callisto is pretty bland from one side, too, but the other side has dramatic multiple ring impact basins. Ceres has ... craters. I was thinking Ceres would be a really interesting hybrid ice/rock object but it seems to have no distinctive geologic terranes and no distinctive marker events. Win some, lose some.

I share your feelings. But then, I also understand that it is interesting for scientists to find a celestial body that has no distinctive feature. What made Ceres so bland? Are asteroids typically bland? And if they are, why is that?

Ann

[Chris Peterson]

Ceres is the first completely uninteresting object we've ever visited. Mimas is a simple cratered ball, too, but it has that one huge crater. Callisto is pretty bland from one side, too, but the other side has dramatic multiple ring impact basins. Ceres has ... craters. I was thinking Ceres would be a really interesting hybrid ice/rock object but it seems to have no distinctive geologic terranes and no distinctive marker events. Win some, lose some.

I share your feelings. But then, I also understand that it is interesting for scientists to find a celestial body that has no distinctive feature. What made Ceres so bland? Are asteroids typically bland? And if they are, why is that?

And let's not forget, this body is being studied with a lot more than just cameras. We're very visually oriented, so we get excited by pictures. But there's a lot more information coming in, and I'll bet it's far from "bland"!

[MarkBour]

... Ceres is the first completely uninteresting object we've ever visited. ...

Okay, I'm sure you know more about what you're saying than I do, but I think that Ceres is the largest fresh water bottle in Earth's vicinity. That's just got to prove handy some day.

[BillBixby]

There are some guys that can hit a ball a fare distance. I look at today's picture and can't help but think on the other side of this small world is the word Titleist. It is almost round enough and the dimples seem about right.

[sallyseaver]

The middle-right, white-spot impact appears to show material from the impact spread out thinly like a splatter from the original collision. After contemplating Ceres last year, my guess was that the white stuff is a magnesium-based salt. Then, I read that the mission team was closing in on its conclusion that the white stuff is magnesium sulfate. Does anyone know if the mission team currently has a working conclusion about the substance responsible for Ceres' white spots?