Ultima Thule Looks Like A Frozen Peanut

It’s still a pixelated blob in this photo, but it’s the best image we’ll see today. New Horizons snapped the photo from a half million miles away, close enough to show the object’s peanut or bowling pin shape. The asteroid measures 22 miles long by 9 miles wide (35 x 15 km)NASA / JHUAPL

During a press conference this morning, the New Horizons team unveiled a new photo of the Kuiper Belt object Ultima Thule (ull-tee-muh THOO-lee) that clearly shows the Kuiper Belt object’s shape, described as bi-lobate or having two lobes like a peanut in its shell. Given the low resolution of the photo there’s a small chance the asteroid may be two separate objects in close orbit around their center of gravity.

Ultima Thule — simplified at right — appears to be rotating with its pole facing in our direction, so it spins kind like a propeller seen face-on. That would explain why it doesn’t show any changes in brightness as it rotates — we only see one side. It takes either 15 or 30 hours to make one spin around its axis, shown by the red arrow. With more data from from the spacecraft, scientists will nail the number down. NASA/JHUAPL/SwRI; sketch courtesy of James Tuttle Keane

Assuming Ultima is single object, the shape is becoming familiar to anyone who’s been keeping tabs of the various asteroid and comet flybys. There seem to be lots of bi-lobate small bodies in the solar system. Of the tiny number we’ve seen up close, there are the comets 103P/Hartley, 67P/Churyumov-Gerasimenko (the target of the European Rosetta Mission) and 19P/Borrelly, along with asteroids Kleopatra and Toutatis and even Pluto’s moon Kerberos, to name a few.

This sequence of three images, received on Dec. 31, 2018, and taken by the LORRI camera onboard New Horizons at 70 and 85 minutes apart shows the rotation of Ultima Thule. NASA/JHUAPL/SwRI

Why does this appear to bbbe a common shape? First, all of these objects are too small to crunch themselves into spheres through self-gravity, and second, they likely formed through collisions with or proximity to other small objects. Everything in the solar system started from the ground up to speak, with smaller objects forming first that later coalesced into planets, where there was enough material available. When the material was sparse or disturbed by the gravity of the growing planets, body-building never got beyond the bits-and -pieces stage.

New Horizons is now speeding past Ultima at 32,000 mph never to return, but the data is downloading across space and time — 4 billion miles and more than 6 light-hours — as you read this. Tomorrow, we’ll see the first detailed black-and-white images with low resolution color pictures later this week. The highest resolution color photos will have to wait until sometime in February.

To keep in touch with developments, go to #UltimaFlyby, #UltimaThule or #NewHorizons. Check the event schedule here. What a way to make it a Happy New Year in space! More photos tomorrow.


7 Responses

    1. astrobob

      I listened for that during the press conference but no updated figure was given. A few days before the approach, Alan Stern, the PI, gave the A-OK with the closer of the two possible trajectories, 2,200 miles from Ultima.

      1. caralex

        That’s a lot closer than the flyby of Pluto! (7,800 miles). Do you know why the team didn’t redirect New Horizons to make a much closer pass of Pluto, long before its encounter?

        1. astrobob

          Hi Carol,

          They didn’t want to go closer early on until they could rule out hazards from small moons or rings.

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