New close-up images of Ceres

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

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Cerealia Facula on Ceres

Cool image time! The image on the right, cropped and reduced in resolution to post here, is one of two images released today by the Dawn science team of the double bright spots found in Occator Crater, taken from the spacecraft’s tight final orbit above Ceres. This image shows what they have dubbed Cerealia Facula. The second image shows Vinalia Faculae.

This mosaic of Cerealia Facula is based on images obtained by NASA’s Dawn spacecraft in its second extended mission, from an altitude as low as about 21 miles (34 kilometers). The contrast in resolution obtained by the two phases is visible here, reflected by a few gaps in the high-resolution coverage. This image is superposed to a similar scene acquired in the low-altitude mapping orbit of the mission from an altitude of about 240 miles (385 km).

Inset of Cerealia Facula

The second image on the left is a crop at full resolution of the area in the white box above. This gives you a taste of the many interesting things found in the full resolution image. For example, the bright spots scattered throughout this image suggest they are recent upwellings from below. The ridgelines in the upper right are either the remains of the water-ice volcano they think once stood here but subsequently slumped back down to form a depression, or pressure ridges being pushed up by later upwellings.

The full image has lots more. So does the image of Vinalia Faculae. Check them out.


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  • Localfluff

    The landing site for the next Ceres mission has been well mapped.

  • Andrew

    It is hard to believe an object as small as Ceres can have “geology” as we understand it on Earth but after reading the JPL website it apparently does.

    I wonder what the lower bound on the mass of a rocky object that can have a volcano would be?

    Ceres would be a great place for basketball. I could dunk like MJ in that gravity!

  • wayne

    Great Question! (..lower bound on mass of object for volcanic activity…)
    [I only play space-volcanologist on the interweb.]

    If I’m not mistaken, there is evidence of volcanic activity (past or current) for all the rocky planets, so that gives us at least some direction.
    A concurrent Question might also be: Is there a relationship between Mass and length-in-time, for active volcanic activity?
    back to your specific ponder:
    I would tend to think– ‘depends on the amount of heat produced in the core of the object and the composition of the immediate outer layers. The point at which the core (or extreme gravity swings) doesn’t produce enough heat to differentially melt the overlying rocky minerals.

    Pivoting totally tangentially:
    a question:
    How much bigger would the Earth have to be, to render our chemical-rockets incapable of launching us off the Earth??
    At what Mass does the force of gravity exceed the thrust we can produce with chemical rockets?
    (I’m under the impression, for example, we could never launch our rockets if we had the same gravity as the gas giant size planets.)

  • wayne asked, “How much bigger would the Earth have to be, to render our chemical-rockets incapable of launching us off the Earth??”

    This is a great question. I am not the one to answer it. I will note that there are many variables. For the analogy to really work the planet has to be an Earthlike terrestrial planet with an actual surface. We’d want to create a super-earth that life could form on, but the physics of chemical rocketry is insufficient to reach orbit.

    Any engineer or scientist out there willing to do the math?

  • wayne

    Yes, please!
    given current rocket technology and no absurd solutions.

    –I’m under the impression it’s ‘not a whole lot bigger,’ but I’ve never heard a solid number. I know there is point where the lines on the graph cross.

  • Localfluff

    The surface gravity of a planet increases linearly with the radius, since the gravity decreases with the distance to the center of mass, but the volume=mass increases with the cube. However, the density likely increases with volume with higher pressure compacting the internal, so it should increase a bit more. Planets larger than about 2 to 2½ Earth radii are expected to collect a large envelope of hydrogen and helium and become “mini-Neptunes” (although such an envelope could blow away if near a near a star). I suppose that the rocket equation gives that the energy required to get of a higher surface gravity increases as the exponent of e=2.72, so that would require 7 to 12 times more energy on the largest expected Earth-like planet, so about a factor of ten. One would need a Falcon Heavy to launch a crew like the Soyuz does today. So it would be harder, but still doable.

    (I’m sure I’ve missed some stuff in this estimate)

  • Localfluff

    Typo correction first sentence:

    The surface gravity of a planet increases linearly with the radius, since the gravity decreases with *THE SQUARE* of the distance to the center of mass,

  • Edward

    A nice analysis from Localfluff, for the same density the gravity does increase linearly with the radius.

    I have heard that if the Earth were 10% larger we could not get into space the way that we do with chemical rockets.

    This seems reasonable, considering that a rocket payload is less than 10% of the rocket weight. In fact, the rocket equation shows that the propellant is about 80% to 90% of the total mass of a fueled rocket with payload.

    Doing the math is a little difficult, because I have to make a few assumptions, and this is the first time I have tried the math. The delta-v from the surface, including climb and atmospheric drag, is 9.7 km/sec. Orbital speed is about 8 km/sec, so my assumption is that 1.7 km/second is a increases with the increase in planet size, ignoring the atmospheric drag.

    The velocity of an orbit is related to the square root of the mass divided by the radius, and these two are related in a square root sort of way, similar to Localfluff’s note.

    My calculation shows that for a 90% mass for the propellant and the rest being rocket and payload, a two stage rocket can still reach orbit with a planet that is about 23% more massive than the Earth.

    This does not feel right to me, so I may have messed up the math.

    Here is an example that I followed:

    Because orbital velocity is related to escape velocity, I used this example for finding the relation between orbital velocity and mass:

  • Edward: I wonder if the use of multiple stages on a heavier Earth could solve the problem. We manage with two, but why not five or six?

  • Edward

    Robert asked: “I wonder if the use of multiple stages on a heavier Earth could solve the problem. We manage with two, but why not five or six?

    It may work, but the engines are heavy. Each stage would need an engine, unless the stages were merely fuel tanks that fell away as they were exhausted and a single, common engine were located at the top of the stack of upper stages/drop tanks. Perhaps the tanks would be doughnut shaped so that the engine could remain aligned with the center of mass as it thrusted through the doughnut holes.

    I’m sure that if we were on a heavier planet we would have worked on other ways to get into space. As it is, we have difficulty using the obvious best way, the reusable single stage to orbit rocket.

    We have messed up the space environment with too much orbital junk to successfully use the more preferred space elevator.

  • wayne

    Localfluff- thank you.
    Edward- I was hoping you would tackle this.
    Mr. Z., you would still need to lift stages 3, 4, and 5.

    Escape Velocity Chart of the Planets
    (the Sun btw, is 618 Km/s)

  • wayne

    so… a back of the envelope number might be 23%, and we’d be stuck on Earth, no matter how brilliant or sophisticated we were.

    this guy has a lot of factoids that might be enlightening: (I’m sure you know this these)

    The tyranny of the rocket equation
    Don Pettit
    TEDxHouston 2013
    — go to the 6:30 mark for mass percent propellant, payload, and rocket-structure factoids.

  • Edward

    Thanks for the link, wayne. I enjoyed it.

    I had seen that one years ago, and I recall discussing one or two of the charts with my father. I think we were comparing rockets with explosives. The rocket engine is said to be a controlled explosion, and that is literally true, due to the definition of explosion: “a violent expansion or bursting with noise.”

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