Some highlights from the 28th May blog http://dawnblog.jpl.nasa.gov/2015/05/28/dawn-journal-may-28-2015/#more-2754

Ceres has shrunk a bit. Before Dawn arrived it was estimated to have an equatorial diameter of 975 km, now that’s shrunk to 963 km. Mass down by about 1%. Ceres still contains about 30% of the entire mass of the asteroid belt.

Upon concluding its first mapping orbit, Dawn powered on its remarkable ion propulsion system on May 9 to fly down to a lower altitude “survey orbit”. By the time it completes this descent, the probe will be at an altitude of 4,400 kilometers, orbiting Ceres every 3.1 days. Dawn will reach the lower orbit on June 3, but it will not be ready to begin its next science observations then. Rather, as in the other new mapping orbits, the first order of business will be for navigators to measure the new orbital parameters accurately.

The orbit is over the poles. On the day side, Dawn will aim its camera and spectrometers at the lit ground, filling its memory to capacity with the readings. On the night side, it will point its main antenna to distant Earth in order to radio its findings home. At Dawn’s altitude, Ceres will appear twice as wide as the camera’s view. The views there will be three times as sharp as in the previous orbit.

It turns out that leaving survey orbit three days later shifts a significant amount of the following work off weekends, making it more comfortable for the team members. (LOL) Three days is one complete revolution.

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(This part from an earlier dawn blog is also worth repeating.)

Ceres apparently formed far enough from the sun under conditions cool enough for it to hang on to water molecules. Indeed, scientists have good reason to believe that water (mostly in the form of ice) may make up an astonishing 30 percent of its mass. Ceres probably contains more water than the whole of Mars or any other body in the inner solar system except Earth.

Radioactive elements incorporated into Ceres when it was forming would supply it with some heat, and its great bulk would provide thermal insulation, so it would take a very long time for the heat to escape into space. As a result, there may be some deep water warm enough to be liquid. This distant, alien world may have lakes or even oceans of liquid water deep underground. What a fantastic possibility!

>This distant, alien world may have lakes or even oceans of liquid water deep underground

Certainly not what we traditionally expect of asteroids, even great big ones.

Bubblecar said:

>This distant, alien world may have lakes or even oceans of liquid water deep underground

Certainly not what we traditionally expect of asteroids, even great big ones.

True, even at that size the central temperature ought to be way too cold by now. If it has buried uranium or thorium or potassium radioactives then they could perhaps be keeping pockets of solute-laden water liquid, but that’s unlikely.

On the same topic, consider Ceres vs Mars from an ‘origin of life’ perspective.

Life on Earth is made primarily from elements H, C, N, O together with Na, S, Cl.

Mars is a huge ball made primarily from elements O, Si, Fe, Ni. It contains only small amounts of H and even smaller amounts of C. There is more carbon on our Moon than there is on Mars.

Ceres is a huge ball made primarily from elements H, C, N, O together with Na, S, Cl. In other words, when Ceres was hotter it was a perfect example of a huge Miller-Urey experiment, perfect for the origin of carbon-based life. Mars isn’t and never was a suitable environment for the origin of carbon-based life. That life on Ceres is almost certainly dead by now, but if it once existed there it would be very worthwhile finding out, to see how it resembles life on Earth. The core of Ceres once was much hotter than it is now, hot enough to melt iron, and this would have originally kept its mantle of organic chemicals comfortable warm.

mollwollfumble said:

Bubblecar said:

>This distant, alien world may have lakes or even oceans of liquid water deep underground

Certainly not what we traditionally expect of asteroids, even great big ones.

True, even at that size the central temperature ought to be way too cold by now. If it has buried uranium or thorium or potassium radioactives then they could perhaps be keeping pockets of solute-laden water liquid, but that’s unlikely.

On the same topic, consider Ceres vs Mars from an ‘origin of life’ perspective.

Life on Earth is made primarily from elements H, C, N, O together with Na, S, Cl.

Mars is a huge ball made primarily from elements O, Si, Fe, Ni. It contains only small amounts of H and even smaller amounts of C. There is more carbon on our Moon than there is on Mars.

Ceres is a huge ball made primarily from elements H, C, N, O together with Na, S, Cl. In other words, when Ceres was hotter it was a perfect example of a huge Miller-Urey experiment, perfect for the origin of carbon-based life. Mars isn’t and never was a suitable environment for the origin of carbon-based life. Life on Ceres is almost certainly dead by now, but if it once existed there it would be very worthwhile finding out, to see how it resembles life on Earth. The core of Ceres once was much hotter than it is now, hot enough to melt iron, and this would have originally kept its mantle of organic chemicals comfortable warm.

Just checking wikipedia. Six of the seven largest asteroids are Ceres-like in composition. The exception is Vesta, which is more Mars-like. This may be because Vesta has an orbit closer to the Sun than all of the other large asteroids.

Solar system objects further from the Sun of roughly similar composition to Ceres include Pluto and sixteen of the eighteen (not Io or Europa) spherical moons of Jupiter, Saturn, Uranus, Neptune and Pluto.

“ Six of the seven largest asteroids are Ceres-like in composition. The exception is Vesta, which is more Mars-like. This may be because Vesta has an orbit closer to the Sun than all of the other large asteroids.”

This where astronomy and real-estate intersect: it’s all about location.

captain_spalding said:

“ Six of the seven largest asteroids are Ceres-like in composition. The exception is Vesta, which is more Mars-like. This may be because Vesta has an orbit closer to the Sun than all of the other large asteroids.”

This where astronomy and real-estate intersect: it’s all about location.

I agree, and that’s one example of how the recent crazy “Jupiter moving orbit” theory is easily shown to be rubbish. If Jupiter’s orbit had ever been closer to the Sun than it is at present then all the well-defined families of asteroids, see figure, would have become jumbled up.

Dawn View from OpNav9

This image of Ceres is part of a sequence taken by NASA’s Dawn spacecraft on May 23, 2015, from a distance of 3,169 miles (5,100 kilometers). Resolution in the image is about 1,565 feet (477 meters) per pixel.