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Emily LakdawallaFebruary 8, 2019

Looking Back at MU69

Hamburger Patty-Shaped World

The New Horizons team released this stunning crescent view of 2014 MU69 today. I love crescent views so much. They mean so much.  You have to be farther from the Sun than a place in order to get a crescent view. New Horizons did it; it's beyond this distant solar system world, as it's beyond so many others.

MU69's crescent


MU69's crescent
New Horizons took the images for this crescent view of 2014 MU69 from a position 8,862 kilometers beyond it. To see such a thinly lit crescent so far from the Sun required long exposures, and the original images were blurred. Team members stacked 10 exposures and processed the result to remove the motion blur and present this sharp view.

This photo was from an observation that shows MU69 moving against background stars. That observation has revealed something remarkable and confusing and amazing: MU69's shape isn't that of a snowman, it's flat, like two hamburger patties smushed together. (Yes, "smush" is a technical term.) Who ordered this?? Nobody, that's who.

Shape model for 2014 MU69


Shape model for 2014 MU69
The two lobes of 2014 MU69 are roughly circular in cross-section, so the simplest assumption was that they were spherical. Following New Horizons' flyby, it became clear that they are very non-spherical. The larger lobe is extremely flat, like a hamburger, and the smaller lobe is also squashed. The blue dotted lines indicate the uncertainty in the shape estimate; it could be less flat than the figure depicts, but still very flat.

This is just bonkers, and is going to be, I think, the major scientific accomplishment of the MU69 flyby. Geophysicists did not predict this. Back to the drawing board! Isn't that fun?

You can read more about the discovery and observations at the New Horizons website, but I want to take the rest of this post to enjoy other weird-shaped space crescents.

New Horizons has taken a couple of other good ones. Here's a crescent Nix. Not many pixels, but a funky looking crescent!

Crescent Nix

NASA / JHUAPL / SwRI / Emily Lakdawalla

Crescent Nix
This is a stack of 16 images taken by New Horizons about 3 hours after closest approach. Nix's outline is very faint but clear. The resolution of this image, which has been enlarged by a factor of 3 from the original, is 310 meters per pixel, and the phase angle is 158 degrees.

Or how about this crescent Io? Io has a hat. (It's actually not a hat, it's a fiery fountain of lava. Do not touch Io's hat.)

Io's crescent


Io's crescent
New Horizons captured this photo of Io with its Long Range Reconnaissance Imager (LORRI) as it sped away from the Jupiter system on March 3, 2007 at 06:11 UTC.

Here's a cool crescent Ceres from Dawn. I love how the extreme lighting really shows that Ceres is on the edge of being a lumpy, not round, world.

Skinny crescent Ceres

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Skinny crescent Ceres
Dawn took this photo of Ceres from the dwarf planet's night side on April 29, 2015. It has a phase angle of 155.6 degrees.

Let's contrast that with a photo of Enceladus. Enceladus is half the diameter of Ceres and so much smoother! I love the specular (mirror-like) reflection off the edge at upper right. Smooth as ice. Smooth and ice.

Enceladus’ crescent in natural color (17 January 2005)

NASA / JPL-Caltech / SSI

Enceladus’ crescent in natural color (17 January 2005)
Cassini captured the images for this portrait of Enceladus on 17 January 2005, through red, green, and blue filters.

Let's see, where else can we go? How about some lumpy worlds. Here's a crescent Phobos.

Crescent Phobos from Mars Express, 25 May 2007

ESA/DLR/FU Berlin (G. Neukum) / Emily Lakdawalla

Crescent Phobos from Mars Express, 25 May 2007
Mars Express captured this view of a crescent Phobos on May 25, 2007. The view is looking down on the northern hemisphere, with the equator toward the top. A bright splash of material on the upper right limb is the west rim of the giant crater Stickney.

How about crescent Hyperion?

High-Resolution Mosaic of a Crescent Hyperion, 25 August 2011

NASA / JPL-Caltech / SSI / mosaic by Emily Lakdawalla

High-Resolution Mosaic of a Crescent Hyperion, 25 August 2011
As Cassini approached Hyperion for a close encounter on 25 August 2011, it snapped a three-image mosaic of the sponge-like moon at a crescent phase. The mosaic did not quite cover the entire visible crescent, so a wide-angle image (with a resolution 10 times lower than the other images) was used to fill in a small area on the "nose."

Here's a crescent Lutetia (this is one of two asteroids Rosetta visited on the way to Churyumov-Gerasimenko).

Lutetia's crescent, in color

ESA / MPS / UPD / LAM / IAA / RSSD / INTA / UPM / DASP / IDA / Daniel Machacek

Lutetia's crescent, in color
A parting view of Lutetia as Rosetta sped away on July 7, 2010.

Speaking of Rosetta, here's comet 67P. Comets have a slightly different way of doing the crescent thing.

Backlit comet

ESA / Rosetta / Navcam

Backlit comet
Single frame enhanced NavCam image taken on 27 March 2016, when Rosetta was 329 km from the nucleus of Comet 67P/Churyumov-Gerasimenko. The scale is 28 m/pixel and the image measures 28.7 km across.

Especially when we smack them really hard, intentionally.

Deep Impact


Deep Impact "lookback" image of Tempel 1
This "lookback" image was captured by Deep Impact's high-resolution imager as it receded from its flyby of comet Tempel 1 on 4 July 2005. The bright spot is not an incandescent flare; it represents dust in the ejecta curtain spraying out from the comet, which is backlit by the Sun.

I hope you've enjoyed all these lookback views! There are a lot more in our image library!

Read more: trans-neptunian objects, New Horizons, pretty pictures, 486958 Arrokoth (2014 MU69)

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
Read more articles by Emily Lakdawalla

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