Sunday, March 08, 2015
A look at the schedule again, with two dates in bold:
Feb 4, 2015 | OpNav #3 | 148,000 km | 68 pixels | 2.2x Hubble resolution
Feb 12, 2015 | Rotation Characterization #1 | 84,000 km | 116 pixels | 3.7x Hubble resolution
Feb 20, 2015 | Rotation Characterization #2 | 48,000 km | 226 pixels | 7x Hubble resolution
Feb 23, 2015 | Closest Approach | | Begin high-phase Approach
Feb 25, 2015 | OpNav #4 | 39,000 km | 264 pixels | 8x Hubble resolution
Mar 2, 2015 | OpNav #5 | 50,000 km | 205 pixels | 6.5x Hubble resolution
Mar 6, 2015 | Capture| | Capture into orbit
Apr 10, 2015 | OpNav #6 | 33,000 km | 300 pixels | 9.5x Hubble resolution
Apr 15, 2015 | OpNav #7 | 21,000 km | 470 pixels | 15x Hubble resolution
Why those ones in particular? Because 9.5x Hubble resolution and 15x Hubble resolution coincide perfectly with two upcoming very large telescopes:
The Giant Magellan Telescope will have a resolving power 10 times greater than that of the Hubble Space Telescope, and
the European Extremely Large Telescope, with a resolving power 16 times greater.
If you've been watching the images up until now you'll know that the bright spot on Ceres has turned out to be (at least) two, with an albedo of nearly 0.5 (Ceres is 0.09), but still not detailed enough to tell exactly what they are. They could be a result of cryovolcanism without being actual cryovolcanoes. But suffice to say that we can't tell exactly what they are at this point.
So the question is whether we will be able to with the images on 10 April and 15 April. If they turn out to be detailed enough that we can satisfactorily make some conclusions about them then 10x or 16x Hubble resolution may turn out to be enough for us to make similar conclusions about other major bodies between Mars and Jupiter, and if not...then in the early 2020s we are going to be hit with image after image of tantalizing but inconclusive features on these minor planets we want to know so much about. Given how vague these two spots still are, I'm not positive the early April pictures will tell us what we need to know.
After that there is one more distance that will be interesting: 10,000 km, the distance at which Dawn reaches the resolving power of the cancelled Overwhelmingly Large Telescope. It's no wonder that telescope was promoted as one that would provide "a planetary flyby every night".