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

The moment of truth: 
the New Horizons probe arrives to the very distant asteroid informally

named Ultima Thule

(31/12/2018)

Ultima Thule, the far away asteroid destination of the New Horizons mission, is one of the less eccentric objects in the Kuiper Belt (zone of the Solar System that is very distant from the Sun where there are a great number of objects and dwarf planets).

Known as a "classical" KBO (Kuiper Belt Object), Ultima Thule it's also part of the "cold" population, which means it has never received any energy from collisions or gravitational interactions. It's just been sitting there, doing relatively little, since the solar system formed. Much of what we know about it comes from Hubble observations, or from occultations where the object passes in front of a background star. The dip in the star's brightness tells us about what's blocking it, and three occultations by Ultima Thule in 2017 were studied by a special group of astronomers formed by the New Horizons team. This study of occultations is the same process that is often used to observe exoplanets around distant stars, but even with this data Ultima Thule remains a mystery.
We will probably find out if there is and what type of organic matter is present, and perhaps, if there are viable microorganisms o spores, confirming the panspermia hypothesis.
 "We don't know if it's two objects, or if it's binary, but we know its shape is not round," said Bannister. "Binary systems are very common in the population to which this little world belongs, and this ties directly into how they formed. A solar system starts off being made of dust and gas, and this starts forming little objects, and they have to get over about a meter in diameter and suddenly they're full-on asteroids that can start accreting material much, much faster. This whole process is something people are very actively working to understand, but binary objects might be implying that, when you initially make little worlds, you make them binary, so it tells us a lot about what physics to put into simulations of how planets are formed." 

Whatever Ultima Thule is like, New Horizons is well equipped to tell us all about it, as the startling images of red-and-white plains and mountains on Pluto showed. "We have a very powerful set of seven scientific instruments," Stern said. "They will map its surface composition, search for an atmosphere, search for satellites, search for rings and make other kinds of studies. And I hope that we put together a very complete picture of what this typical Kuiper Belt object is like, because not only is this the first time that an object like this has been explored, but nobody's planning another mission out to the Kuiper Belt, so I think that this dataset is something that's going to be valuable scientifically for decades to come."

How long New Horizons can carry on sending back this kind of remarkable data is limited by the power and fuel supplies on the spacecraft, as well as the availability of suitable targets in its path. When you're travelling over 36,040 mph (58,000 kilometres), changing direction isn't easy. 

Stern isn't worried about the future, however. "We have a very healthy spacecraft," he said. "We have the fuel and the power in our nuclear battery to run it for at least 15 years, maybe 20 years. If NASA continues to fund it, if NASA judges that it's scientifically worthwhile, this spacecraft will be operated into the mid-2030 or later. It's very much like the Voyagers which finished their exploration of the planets in the 1980s, but are still returning useful scientific data 40 years after launch." 

Author: Ian Evenden

Reference:

https://www.space.com/42860-new-horizons-beyond-pluto-ultima-thule.html

The New Horizons probe is approaching Ultima Thule, an  extremely far away, frigid cold, mysterious and very small piece of rock/ice/organic matter

"As the New Horizons spacecraft closes in on its target, Ultima Thule is getting brighter and brighter in the LORRI optical navigation images," New Horizons project scientist Hal Weaver, from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said im a statement. "It's now standing out much more clearly among the sea of background stars."

New Horizons took the picture 33 hours before performing a record-setting engine burn to refine its course toward Ultima. The burn — the most distant ever conducted by a spacecraft — lasted 105 seconds and changed New Horizons' velocity by about 2.2 mph (3.5 km/h), mission team members said.

(486958) 2014 MU69 also known as Ultima Thule, is a trans-Neptunian object from the Kuiper belt located in the outermost regions of the Solar System. It was discovered by astronomers using the Hubble Space Telescope on 26 June 2014. The irregular shaped classical Kuiper Belt objecti a suspected is a suspected contact binary or close binary system and measures approximately 30 kilometers (19 miles) in diameter.

In August 2015, this object was selected as the next target for the New Horizonsprobe shortly after it had visited Pluto. The flyby will occur on 1 January 2019, which will make it the farthest object in the Solar System ever to be visited by a spacecraft. After four course changes in October and November 2015, New Horizons is on course toward 2014 MU69

On 13 March 2018, NASA announced that (486958) 2014 MU69 would receive the nickname Ultima Thule. The decision was based on the results of a public voting campaign. Ultima Thule, or Ultima for short, serves as an unofficial name for the object until the discovery team proposes an official name to the IAU that is consistent with existing naming guidelines. The New Horizons team has decided not to go forward with the formal naming process until after the flyby, when the properties of (486958) 2014 MU69 are known well enough to choose a suitable name.

The probe remains on course to cruise within just 2,200 miles (3,500 km) of Ultima Thule (which is officially known as 2014 MU69) at 12:33 a.m. EST (0533 GMT) on Jan. 1. That's more than three times closer than New Horizons got to Pluto during the spaceraft's epic flyby of the dwarf planet on July 14, 2015. 

That encounter showed Pluto to be a complex world with a stunning diversity of landscapes, from tall water-ice mountains to vast nitrogen-ice plains to "bladed" terrain similar to the penitente fields of the high Andes. 

New Horizons' encounter with Ultima, which lies about 1 billion miles (1.6 billion km) beyond Pluto, should be similarly revealing. Astronomers have estimated Ultima's size — about 23 miles (37 km) wide — but they know little else about the object. Indeed, it's unclear if Ultima is a single body or a close-orbiting pair.

New Horizons launched in January 2006, tasked with returning the first-ever up-close looks at Pluto. The Ultima Thule flyby is the centerpiece of the probe's extended mission.