As 2018 ended and 2019 began, NASA's New Horizons flew past its first target after Pluto: 2014 MU69.

Ultima Thule is barely a blip in images from the New Horizons spacecraft. The remote world stands out more when the stars have been removed (right); the dark blobs are artifacts from imperfect star subtraction. Yellow crosshairs mark Ultima’s position. Until just a few days before its arrival, 2014 MU69 (Ultima Thule) was no more than a single pixel in New Horizons' detectors.

Nicknamed Ultima Thule, it's transformed from a single pixel in our detectors to a red-hued, mottled snowman.

The first color image constructed (via a composite from New Horizons data) of 2014 MU69: Ultima Thule. The reddish color is likely due to tholins: the same reddish color visibly present on the surface of Charon.

The first three weeks of data have revealed spectacular details concerning this distant world.

Multiple images of Ultima Thule (2014 MU69) as New Horizons approached it reveal a body that's rotating and tumbling, but also reveal additional details about the object, as the distance from the camera decreased from 500,000 km down to 28,000 km: a decrease of 94%.NASA/JHUAPL

Aside from its inactivity, it conforms perfectly to our expectations of cometary nuclei.

Many comets have had their nuclei imaged by a variety of spacecraft, revealing two main classes of cometary nuclei: a single-object nucleus and a contact binary nucleus. 2014 MU69 appears to be of the contact binary type, and marks the first time we've ever imaged such an object before it's ever developed a tail or lost some of its volatiles.

Its now-legendary snapshots and movies of comet 67P/Churyumov-Gerasimenko show offgassing, plumes, and even snow.

The sun-facing sides of comets heat up first, with the presence of easily-sublimated ices leading to offgassing, the release of pressure, and the loss of material. The longer comets spend in close proximity to the Sun, the faster they evaporate. For objects still in the Kuiper belt, evaporation should be negligible.ESA/ROSETTA/NAVCAM

Volatile, icy materials are abundant on these comets, and change phase rapidly when they're exposed to sunlight.

The most spectacular movie from ESA's Rosetta mission shows what the surface of comet 67P/Churyumov-Gerasimenko looks like, including the volatile ices that sublimate and re-freeze when they're in sunlight or shadow, respectively, causing this snow-like behavior.

Ultima Thule is currently rotating and tumbling in a similar fashion to these known, close-in comets.

The only difference? It's still incredibly distant from the Sun, causing its ices to remain intact.

https://www.forbes.com/sites/startswithabang/2019/01/21/new-horizons-big-reveal-on-mu69-ultima-thule-is-a-typical-future-comet/#7892c4d831e0