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Headshot of Emily Lakdawalla

New Dawn images of Ceres: comparable to Hubble

Posted by Emily Lakdawalla

20-01-2015 9:06 CST

Topics: pretty pictures, Dawn, asteroid 1 Ceres

The Year of the Dwarf Planet is off to a great start! Yesterday the Dawn mission released its latest photos of Ceres, taken from 383,000 kilometers away -- roughly the same as the distance from Earth to the Moon. The original pictures were 27 pixels across, and I'm surprised by the amount of detail that is visible. There are circular features that might (or might not!) turn out to be craters, and a noticeable bright spot. Other markings are not obviously circular. It's hazardous to try to read these images too closely -- but they are awfully cool, showing Ceres beginning to come into focus! Our other dwarf planet mission, New Horizons, will get photos of Pluto that are about 27 pixels across at the very end of June. I'm so glad we have Dawn approaching Ceres to satisfy our mini-world curiosity right now, because it will be hard to wait for comparable Pluto images for so long.

Dawn optical navigation sequence on Ceres, January 13, 2015


Dawn optical navigation sequence on Ceres, January 13, 2015
Dawn took the 20 images for this animation on January 13, 2015, in its first lengthy optical navigation sequence on asteroid 1 Ceres. Dawn was 383,000 kilometers away at the time. The images in this animation have been aligned and contrast-adjusted.

Here I've separated the frames out of the animation so you can examine them individually:

Montage of Dawn Ceres optical navigation images taken January 13, 2015

NASA / JPL / UCLA / MPS / DLR / IDA / Emily Lakdawalla

Montage of Dawn Ceres optical navigation images taken January 13, 2015

One of the Hubble images was taken from a very similar perspective, and it also contains the bright dot and some of the darker areas visible in the Dawn images. I'll leave it as an exercise for you to find other similarities! The Hubble images from January 2004 have slightly better resolution than these Dawn photos, but they were taken from a lower phase angle. That enhances color variety, but it's tough to see any topographic detail because there are few shadows. Some of the features we are seeing in the Dawn images of Ceres must be topographic ones, especially close to the terminator (near the bottom of the images), where shadows are most dramatic.

Hubble view of Ceres, January 23, 2004

NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), L. McFadden (University of Maryland, College Park), and M. Mutchler and Z. Levay (STScI)

Hubble view of Ceres, January 23, 2004

If you look at the Dawn animation again, you may notice a striking flickering. I thought that was a telltale sign that the camera was cycling through different color filters as it took the photos, and I made a color version of the photo, but I've been told by a member of the Dawn team that the flickering was not due to filter choices, but just due to lack of calibration, so I've taken out the color picture. Sorry about the confusion!

See other posts from January 2015


Or read more blog entries about: pretty pictures, Dawn, asteroid 1 Ceres


Alderamin: 01/20/2015 09:31 CST

Hi Emily, thanks for your excellent reports about Dawn (and also the other space missions)! For a distance of just 383,000 km, I find the resolution of the above images to be quite low compared to e.g. what Cassini achieves from a couple of million kilometers away. Even a DSLR with a zoom lens should be able to capture more detail on the Moon from the same distance (ok, Ceres is only 1/4 the diameter of the Moon, but still...). Can the probe do better with a different camera? Or was it designed to use such a low resolution because it will eventually orbit the dwarf planet much closer anyway?

Michael Richmond: 01/20/2015 10:48 CST

Alderamin, This image of Ceres was taken with Dawn's Framing Camera, which is a relatively small instrument: with an aperture of 20 mm and a focal length of 150 mm, it is more like an ordinary telephoto lens than a telescope. The camera yields a plate scale of about 19 arcseconds per pixel. If we used it from the Earth's surface to look at the Moon, we'd see an image of the Moon about 93 pixels across. Not very impressive. Cassini, on the other hand, has an impressive instrument: the Narrow Angle Camera has an aperture of 200 mm (ten times larger than Dawn's) and a focal length of 2000 mm (13 times larger than Dawn's); if you saw this instrument, you'd call it a telescope rather than a telephoto lens. Its images have a plate scale of about 1.2 arcseconds per pixel, much more detailed than Dawn's. If you stood on the Earth's surface and took a picture of the Moon with the NAC, it would make an image about 1460 pixels across.

Messy: 01/21/2015 09:33 CST

The problem is, is that the Hubble pics are pretty bad, so getting better than those isn't that hard. What we need, (assuming I haven't missed it) is a schedule of when the photos will be taken prior to getting into orbit. With the exception of the "great white splotch" there are very few actual details to be seen. When will the images be as clear as those of some of the lesser moons from Voyager? Ceres is orange. When will we get a non-mosaic image that is clear enough to make a poster out of? etc...

Emily Lakdawalla: 01/21/2015 10:02 CST

Space cameras are built for specific purposes -- Hubble's is designed to look at objects that are very far away; Cassini's, for a middle distance; and Dawn's for global mapping of an object that it will eventually orbit quite close to. The angular resolution of Dawn's FC is 98 microradians, which is comparable to the wide-angle cameras of Voyager (53 microradians) and Cassini (60 microradians), but unlike Voyager and Cassini there's no corresponding narrow-angle camera. Dawn doesn't need one; it'll eventually be orbiting 1000 times closer to Ceres. Messy, regarding the schedule: Read Marc Rayman's posts, he's detailed it all in there. Or you can read an article I wrote about Dawn at Ceres that is just now going to press in Sky & Telescope.

Jonathan Ursin: 01/21/2015 11:32 CST

Now is the time to make wild guesses on what the white spot is. My guess is it is the ice covered tip of a hydrovolcano.

Steven Taylor: 01/21/2015 02:25 CST

I am getting confused re Pixels. I assumed that if you halve the distance to Ceres, the number of pixels would quadruple in an image. However, the NASA Ceres Approach Timeline has First OpNav JAN13 - 379,000 km 26 pixels, and OpNav 4 - FEB25 - 39,000 as 264 Pixels. I would assume as Dawn is approx 10 times nearer, the image would contain 100 more Pixels, not 10 more. What am I missing?

Steven Taylor: 01/21/2015 03:26 CST

Re my above email, I have just realised that you have answered my question, namely,"The original pictures were 27 pixels across", so obviously the number of pixels quoted does not relate to the area, just apparent diameter. Making more sense now.

mercury3488 : 01/21/2015 06:19 CST

That bright spot? Fresh impact crater with rays, like Heimdall Crater on Callisto. So far, 1 Ceres is looking more like the Uranus moon Oberon with large flat floored craters. We'll see soon.

StevenTaylor: 01/23/2015 03:54 CST

Apropos the `White Spot`, has anyone estimated its albedo?

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