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New Horizons beyond Pluto: What is there in Ultima Thule’s realm?

An artist image of NASA’s New Horizons spacecraft will fly through the Kuiper Belt object, Ultima Thule (2014 MU69) on Jan. 1, 2019.
(Adrian Mann/All About Space)

The constellation Sagittarius, the archer, is a common sight in the winter sky, easily recognizable by the “teapot” asterism that makes up the front half. Look in the Archer’s direction and you’re staring in the centre of the milky way, the Milky way contribution from the “steam” from the teapot’s spout.

With a telescope, you might see the Lagoon Nebula in Sagittarius, or a globular cluster such as Messier 54. If you have access to millions of dollars of space telescope, however, you may discover other much smaller and weaker things.

This is exactly what happened in 2014 when the Hubble Space Telescope is a survey of the surroundings, in the hope of finding a new target for the New Horizons mission after ground-based telescopes had failed to find anything. When NASA’s mission to Pluto was still incomplete, but it was clear that the probe would be in the direction of the Archer, following its encounter with the distant dwarf planet and, as an even more distant object is found in its path, it would be able to bear and suffer that also. With a lot of plutonium dioxide on board to generate power, the probe is expected to function for many years, plenty of time to explore the outer reaches of the solar system on more than 36,040 mph (58,000 km/h). [How to Look at New Horizons’ Ultima Thule Flyby]

The object Hubble discovered was called (486958) 2014 MU69. The number in parentheses is the minor planet number — we know more than half a million, while 2014 is the year of the discovery. M is for the second half of June, and U69, it gives the 1,745 th object discovered in the two weeks. Modern techniques and space telescopes to discover a lot of objects. 2014 MU69 quickly picked up a nickname, Ultima Thule, as a result of a public vote. Thule, in the Greek and Roman literature, was the farthest north you could go, often associated with Greenland or Iceland. The later addition of the “Ultima”, which means “furthest” was used in the sense of a place outside the limits of the world.

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  • Ultima Thule
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There are many thousands of worlds that exist at the borders of our solar system outside the orbit of Neptune, but very few were in the right place to be visited by New Horizons. Known collectively as trans-Neptunian objects (TNOs), they are dimly lit and tremendously spread out, with distances of 1 astronomical unit (au) — the distance from the Earth to the sun — often between them. The best known, Pluto, is the most massive known object in a field in the space between the 30 and 55 au from the sun, known as the kuiper belt.

We know of a few other major things in the belt — with two of them classified as dwarf planets such as Pluto — and there is something heavier than Pluto, the dwarf planet Eris. But Eris is three times further from the sun than the demoted ninth planet and is not included in the Kuiper Belt object (KBO) is due to its extreme distance it falls in an area known as the Disk Spread. Many scientists also believe that the evidence is of a larger whole in the orbits of smaller ones, but that hypothetical Planet with the Nine, had not previously seen.

An object should generally have one body with a diameter of at least 186 miles (300 km) to be considered a dwarf planet. The most known KBOs are much smaller than that of Pluto (1,477 miles (2,377 km) width, however. There is Lempo, a binary system with at least one additional satellite, and a total diameter of about 249 miles (400 km), the same as Saturn’s moon Mimas. Lempo is named after the god of love from the Finnish mythology, and like a lot of KBOs appear extremely red. Then there is Drac, just 56 miles (90 km) across and named after Bram Stoker’s famous count. Drac is remarkable because the high slope and the fact the orbit is retrograde — the opposite direction of most other objects. [Dwarf Planets: Science and Facts About the solar system’s Smaller Worlds]

Ultima Thule would be a binary system, but with a diameter of only 18.6 miles (30 km) or so it is a bit difficult to make out from the Earth. It was chosen as the new target, because the position — less fuel was needed to reach it. A brighter, and thus likely to be larger object was also considered, but the fuel that is needed to achieve even less in the tank for the future maneuver.

But why worry about something that is so small and far away? The study of KBOs as this tells us about the way in which the solar system was a long time ago. “The belt is analogous to the solar system in the attic,” said New Horizons principal investigator Alan Stern, of the southwest Research Institute in Boulder, Colorado.

“It is an ancient region, far away from the sun, which has been preserved in the freezer,” Stern added. “It’s the equivalent of an archaeological dig into the history and formation of the planets. So, scientifically it’s a gold mine, and to go there with a spaceship and the observation of KBOs close-up, as we do with Ultima, we hope to learn a lot about how the beginning of the formation stages of the planets.”

And that’s not all, because the interactions of the small objects can tell us a lot about the movements of large objects. Really great. “What we know of the trans-Neptunian region is that the remaining remnants of the objects that are not in the existence of the planets,” said Michele Bannister, a post-doctoral researcher at Queen’s University Belfast, which helps in the discovery of small planets as a part of the Outer solar system Origins Survey.

“This small rock and ice worlds were formed in the first disk of material around the sun, those who never grew up in being planets in their own right,” Bannister said. “Since then, they are caused by changes in the orbital positions of the giant planets, especially Neptune.”

The idea that planets move instead of just being calm in an orbit around the sun can be difficult to process given the enormous size and mass of the outer planets, but according to the Nice model of solar system formation — named after the place in France, not only because it is a feast — as the solar system gathered together from the protoplanetary disk, everything was much closer to the sun. The outer edge of the Kuiper Belt was 30 au from the sun instead of 55, and Uranus is the outer planet in place of Neptune. There is even a hypothesis that there might be a fifth giant planet ejected from the solar system after an encounter with Jupiter.

Gravitational interactions between the four giants we know of led Neptune to move outward, beyond the orbit of Uranus, the production of the Kuiper Belt we see today. “What we see there today are the materials of this first cd,” said Bannister. “Some of them are known, such as water, ice, and rock, but a number of them are unknown, such as kitchen, cleaning chemical substances that you use under your sink, in solid form.”

And even though it is called a belt, think, but not completely flat. “Many of the objects have never had anything happen to them, they are round, flat jobs, but many of them have energy put into them,” Bannister said. “They can be much more eccentric; their jobs are long, thin ellipses, and they are tilted relative to the plane of the solar system. Some of them are in a job ballet with Neptune, called a mean motion resonance, where Neptune goes around the sun three times for every two times one of these objects is going to be around, that is the resonance with Pluto. Many of the objects in the places where they can do this, and that resonant objects exist as the spaces in between are free of objects is a signature that Neptune migrated outward in the early solar system.”

Ultima Thule is one of the less eccentric objects, and is not in resonance with Neptune. Known as a “classical” KBO, but also as part of the “cold” population, which therefore never receive energy from collisions or gravitational interactions. It’s just sitting there, doing relatively little, since the solar system formed. Much of what we know about the coming of the Hubble observations, or from occultations where the object is on a background of stars. The dip in the brightness of the star tells us about what the block and three occultations by Ultima Thule in 2017 were studied by a special group of astronomers formed by the New Horizon 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. [7 Ways to Discover Alien Planets]

“We do not know whether it is two objects, or if the binary, but we know that the shape is not round,” said Bannister. “Binary systems are very common in the population that these small the world is, and this ties directly into how they formed. A solar system begins to be made of dust and gas, and this begins with the forming of small objects, and have them in the course of about a meter in diameter and all of a sudden they are full on asteroids that could start accreting material much faster. This whole process is something people are very active to understand, but binary objects might be suggested that, when you initially make little worlds, you make them binary, so it tells us a lot about what physics to put in the simulations of how the planets formed.”

What Ultima Thule is like, New Horizons is well equipped to tell us all about it, as the surprising 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 the surface composition, search for an atmosphere, satellites, search for rings and other types of studies. And I hope that we can put together a very complete picture of what these typical Kuiper Belt object is, because not only is this the first time that an object such as this is investigated, but no one is planning another mission from the Kuiper Belt, so I think this dataset is something that is valuable scientifically for decades to come.”

How long New Horizons can contribute to the sending of this kind of outstanding data is limited by the power and the fuel on the spaceship, as well as the availability of suitable targets in the way. When you are traveling on 36,040 mph (58,000 km), to change direction is not easy.

Stern is not 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 for at least 15 years, maybe 20 years. If NASA continues to fund it, if NASA judges that it is scientifically worth, this spacecraft will be operated in the middle of the 2030s or later. It’s very much like the Voyagers who are ready with their research of the planets in the 1980s, but are still returning useful scientific data, 40 years after the launch.”

This article was provided by Space.com’s sister publication, All About Space, a print magazine dedicated to astronomy, space and the night sky. Sign up for the All Over the Space newsletter for news and subscription details! Follow us @Spacedotcom or Facebook. This version of the story published on Space.com.

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