After Pluto: New Horizons’ Next Target is a Relict of Creation

By Eric Betz | October 18, 2016 3:45 pm

An artist’s impression of NASA’s New Horizons spacecraft flying past its next target. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Steve Gribben)

Far, far past Pluto, the most distant object humanity has ever visited, there’s a tiny world fainter than any seen in that part of our solar system. Its dark orbit reaches a billion miles beyond the former ninth planet. But 2014 MU69, as it’s labeled by astronomers, is just a few dozen miles across — too scant to be spherical.

There’s nothing particularly special about it. Thousands of similarly mysterious and icy worlds lurk in these celestial suburbs. Yet it’s precisely its banality that makes this little prince of a planet so special — 2014 MU69 is made of the very stuff of creation.

And on Jan. 1, 2019, an army of astronomers will turn their gaze to this world for a few hours, as NASA’s New Horizons spacecraft blazes by at some 8 miles per second.

At the American Astronomical Society’s Division for Planetary Sciences meeting in Pasadena, California, this week, astronomers discussed how the spacecraft’s next target is coming into focus. A team has been using the Hubble Space Telescope, which also first detected 2014 MU69 during a hunt for additional New Horizons targets, to learn more about the distant world.

“We’re going to fly past something in the solar system that is about as old as we possibly can,” says Planetary Science Institute astronomer Susan Benecchi. “And that’s exciting because it’s information we couldn’t glean otherwise.”

A Primordial World

The scientists believe 2014 MU69 is what’s called a cold, classical Kuiper Belt Object. The Kuiper Belt is a disk-shaped region of icy objects past Neptune. But Pluto isn’t part of that classical population. The distant dwarf planet crosses Neptune’s orbit, and that proximity lead it to collide with other objects — large and small — over the eons as giant gaseous worlds shuffled about our outer solar system, flinging off space rocks. So, much of Pluto’s ancient history was erased in encounters with other worlds.

And similarly, comets and asteroids, which are also excellent time capsules, have interacted with other objects and been bombarded by solar radiation.


Path of NASA’s New Horizons spacecraft toward its next potential target. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker)

But cold, classical objects like 2014 MU69 orbit further out. They are pristine, primordial remnants from the days our system began to coalesce out of the solar nebula. Primordial means that 2014 MU69 could have existed before there were dinosaurs, or trees, or eyes to see them, and before there was even a fully formed Earth or a sun to cast a dim light on its distant surface.

“This population of objects has not been perturbed for a long time,” says Benecchi. “We’re looking at a really old part of the solar system, and we’re learning something about what happened a long time ago.”

Hubble observations have helped them gain confidence that 2014 MU69 is part of that cold classical population because its surface is red. And Hubble’s catalog of thousands of other known such objects shows that the tiny object’s reddish hue is an excellent match. Its surface is redder than Pluto, but not quite so red as Mars.

“The data confirms that on New Year’s Day 2019, New Horizons will be looking at one of the ancient building blocks of the planets,” says Amanda Zangari, a researcher on the New Horizons team.

Thousands of Tiny Red Planets

That red surface color on Pluto and other redder, more primordial objects, comes from complex organic molecules that Carl Sagan called tholins.

“When you see something red in the outer solar system, generally that’s an indication the object is covered in complex organic molecules,” Northern Arizona University astronomer Stephen Tegler told me when I toured the Astrophysical Ice Laboratory before the New Horizons flyby. The lab simulated Pluto’s ice on thin films so that astronomers would better understand what they were looking at.

When sunlight reaches Pluto’s surface, blue light is absorbed, showing our eyes red.

“One of the things that can absorb really efficiently in blue are complex organic molecules,” Tegler says. “An easy way to generate them would be to take something like methane and hit it with particles or UV light; you can break it up and form more complex molecules.”

And while Pluto was known to have a red tint before New Horizons flew by, it wasn’t really considered red like many of its neighbors. So, 2014 MU69 might have a truly surprising appearance once we finally see it.

“This primordial population that is going to give us the largest lever arm for understanding the physical properties of the early solar nebula,” Benecchi says.


CATEGORIZED UNDER: Space & Physics, top posts
  • John C

    Spell check

    • Martino

      typo? where?

      • John C

        My mistake. I have never in 59 years seen the word “relict”. Derelict, relic, never relict.

        • Jeff

          Yup, just looked it up. A Relict is something left unchanged, according to the dictionary

          • OWilson

            Nuns live in a nunnery.
            Birds live in an aviary.
            Bees live in an apiary.
            Relicts live in reliquary.

  • laurele

    Please do not refer to Pluto as the “former ninth planet.” To many planetary scientists, it never stopped being a planet. Only four percent of the IAU voted on the controversial demotion of Pluto, and most were not planetary scientists but other types of astronomers. Their decision was immediately opposed in a formal petition by an equal number of professional planetary scientists. The latter prefer the geophysical planet definition, according to which a planet is any non-self-luminous spheroidal body orbiting a star, free floating in space, or orbiting another planet. If a celestial object is not a star itself and is large enough and massive enough to be rounded by its own gravity, according to this definition, it is a planet. Ceres is also a planet according to this definition, making Pluto the solar system’s tenth rather than ninth planet.

    • John Do’h

      I always thought of of Pluto sort of like a trailer home parked at the end of a row of houses. Does it count as one of the original houses? It can have an address, it is just viewed as inferior. Does Pluto count?

      So by your definition, where do you draw the line? What percentage of spheroidal shape is the cutoff? 50% and higher it’s a planet, less than 50% it’s a space rock?

      What if a smaller object just happened to have a nice spheroidal shape and it is currently orbiting the Sun. Does it count? What if some of the moons in the Solar System once orbited the Sun? Are they former planets? Captured planets? Or they are judged to be non- planets because they were lousy enough to get captured?

      What if an 12 billion year old 5000 km object came from outside our Solar System and was captured by our Sun’s gravity and established it’s own orbit? Just another planet the same as the rest?

      It all gets rather subjective. What really is wrong with having your 8 original main current planets, and then have different categories for all the other cool stuff out there? Just seems more ordered to me

      • laurele

        The geophysical definition is not about whether or not an object is spherical. It is about whether the object is shaped by its own gravity, a state known as hydrostatic equilibrium. Objects in hydrostatic equilibrium are not necessarily perfect spheres; they can be oblate spheroids. Objects must attain a certain mass in order to be in hydrostatic equilibrium. Low mass objects are shaped by their chemical bonds only. At a certain point, when an object becomes massive enough, its gravity takes over and squeezes it into a round or nearly round shape.

        There are only a small number of objects that are close to but not quite in hydrostatic equilibrium, such as Vesta, Pallas, and some of the giant planets’ moons. These borderline cases are considered proto-planets, a class between asteroids and dwarf planets. Some KBOs also fall into this category. In many cases, their masses and sizes are uncertain, meaning their status is currently unclear but hopefully will be settled once we have better telescopes to observe them, such as James Webb. There are plenty of objects outside our solar system whose classifications are also in doubt because scientists are uncertain as to their masses and therefore cannot determine whether they are giant planets or brown dwarfs (the lowest of the stellar category).

        An object that is too small to be in hydrostatic equilibrium is either an asteroid or a proto-planet. As for spherical moons, many planetary scientists already consider them to be secondary or satellite planets. They too have the complex processes and compositions that terrestrial planets have, and some are prime locations for possible microbial life. The only difference between them and spherical objects orbiting the Sun is they orbit another planet instead of orbiting the Sun directly.

        There are some objects, like Triton, that once were primary planets and were subsequently captured into orbit around gas giants (in this case, Neptune). Once captured, it went from a primary to a satellite planet. If a 5,000-km object from another star system enters orbit around our Sun, it will become a (primary) planet though there is a good chance it will not have a stable orbit.

        Viewing Pluto and any dwarf planet as somehow inferior makes no sense. The only difference between these worlds and their smaller terrestrial counterparts is their size. However, compared to Jupiter, Earth is tiny. Compared to many giant stars, the Sun is tiny. In astronomy, size is relative.

        Furthermore, there are no “eight original main planets.” The only “original” planets are the classical planets known from antiquity, which are Mercury, Venus, Mars, Jupiter, and Saturn. There is nothing that distinguishes the eight bodies you include from the ones you do not.

        Putting those eight into a single category does not even make sense. Earth has more in common with Pluto than it does with Jupiter. Both Earth and Pluto have solid surfaces; are geologically layered into core, mantle, and crust; have geology and weather; have atmospheres composed primarily of nitrogen; and have large moons formed via giant impact.

        In contrast, Jupiter (and the other gas giants) have no known solid surfaces; are composed primarily of hydrogen and helium like the Sun; and have their own “mini-solar systems” of moons and rings.

        I ask, what is wrong with having different categories of PLANETS to reflect the diversity of these objects that all share the characteristics of not being self-luminous and being in hydrostatic equilibrium? Alan Boyle proposes dividing the solar system’s planets into three subcategories: terrestrials, jovians, and dwarf planets. Once we look at exoplanets, there clearly are other subcategories such as rogue planets, super Earths, hot Jupiters, and hot Neptunes. This system of having a broad umbrella of planets under which there are many subcategories to reflect the many cool objects that share planetary characteristics seems much more ordered to me.


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