It’s a contact binary, two different spherical rocks permanently touching each other and bound together by each other’s gravity. And that’s just the tip of the proverbial iceberg when it comes to 2014 MU69, the small little red world in the center of the Kuiper Belt that NASA’s New Horizons spacecraft flew by for close-range exploration less than two days ago.
New Horizons begins to unlock 2014 MU69’s mysteries:
With less than 1% of the total data accumulated during the flyby sequence returned, the small amount of data has already allowed scientists to begin unlocking the mysteries surrounding the small little world 2014 MU69 that is receiving – as is the New Horizons science team – its moment of fame.
Yesterday, Principal Investigator Alan Stern said that if he had to bet, his money would be on 2014 MU69 being a single object – a prediction agreed to by others on the panel.
But two new images of the Kuiper Belt world taken from a no-closer distance of 50,000 km by New Horizons reveal 2014 MU69 to be a contact binary, meaning it is composed of two spherical objects that formed separately before gently easing together to form the object we see today.
This easing together of the two lobes of 2014 MU69 occurred over 4 billion years ago at speeds between 1 to 2 miles per hour, according to Jeff Moore of the geography and geophysics investigation teams for New Horizons.
A primordial element from the formation of our solar system, the bilobate 2014 MU69 took a few hundred thousand years to a million years to form from a scattering of small rocky objects gravitationally swirling around each other that gradually formed two large spherical rocks.
These two rocks were then pulled together by the extremely weak gravitational forces of each other, nudging together at such slow speeds that initial observations from New Horizons do not reveal any stress fractures or damage from the “collision”.
So gentle was the initial contact between the two lobes of MU69 that Mr. Moore related it to getting into a fender bender car accident that produces no damage; you wouldn’t bother filling out the insurance claim.
Mr. Moore confirmed that the two lobes are “soundly bound” to each other, with Alan Stern adding that their mutual gravity holds the two together.
What is perhaps most exciting about the final confirmation that 2014 MU69 is a contact binary is that it begins to solidify models of solar system formation and planetary accretion.
For quite some time, this model has relied heavily on the theory that small pieces of dust in the protoplanetary nebula surrounding the Sun after its birth collided with each other and stuck together to form larger specs of dust.
Those larger specs then continued to clump together until objects greater than 1 kilometer in size formed and began attracting each other with their gravity… and so on to form the larger objects in our solar system today.
“This is what we need to move the models of planetary formation forward,” said Alan Stern. “This is how science works. The theorists have ideas, they do computer modeling, they think hard about problems. They take the available data. And different models produce different outcomes.
“But then you need more data in order to distinguish between those models. And in the last 36 hours, NASA and New Horizons have collected more data about the formation of the solar system, in particular the planetesimals in the Kuiper Belt, that now let us choose between models or tell which models are more likely to be right than others.”
While contact binaries have been observed in the solar system already, what’s exciting about 2014 MU69 is that we know definitively that this is how it formed, as a contact binary, and not what it was shaped into via interactions with planets, the Sun, or through sublimation and structural collapse changes.
The known specifics:
With the obvious warning that with only 1% of the data in-hand that some of this will change, here’s what we currently know about 2014 MU69 based on those initial science returns.
The object is composed of two distinct lobes in contact with each other, with a 3-1 ratio in terms of their respective size. The larger lobe is the “bottom” sphere and the smaller lobe is the “upper” sphere.
The team has nicknamed the larger lobe “Ultima” and the smaller lobe “Thule” – much the same way they gave unofficial names to the regions and features of Pluto and Charon before submitting the names for formal approval to the International Astronomical Union.
The New Horizons team has also been able to determine a rough calculation for 2014 MU69’s rotation period at 15 hours +/- 1 hour, meaning that more than half of the object was in daylight as New Horizons passed and was therefore observed.
The Kuiper Belt body also has an extremely low surface reflectivity, with the New Horizons team likening it to dark potting soil in a garden.
Pre-flyby observations made by the Hubble Space Telescope indicated that MU69’s surface was red in color, and that has proven true – with the reddish hue indicating the presence of tholins, which are processed volatile ices.
Exactly what ices – methane, nitrogen, or something else – is not yet known.
The less-red areas near 2014 MU69’s neck – the connection point between the two lobes – carries a higher albedo or reflectivity than the rest of the so-far-observed rockey world, indicating the presence of fine grain particles in the neck region.
The neck area is also sloped enough that objects and fine grain elements can tumble or roll down the slopes and settle in the valley where the two lobes meet – something which likely explains the higher albedo seen in the data thus far returned from New Horizons.
While much higher-resolution images will provide a better sense of the topography and geography of 2014 MU69, what is currently known is that the bottom, larger lobe (“Ultima”) contains changes in elevation greater than one kilometer and that the upper, smaller lobe (“Thule”) may contain a plateau feature.
Also interesting in the returned images is the lack of observable craters.
“Theoretical studies suggesting what the crater rate in this part of the solar system might be suggest that MU69 could be very underpopulated with small craters compared to the asteroids or something in the inner solar system,” said Jeff Moore. “We may discover that it doesn’t have many craters and we may very well find that most of the surface texture is dominated by the slow accretion processes and not the high-energy impacts that cause craters.”
Alan Stern cautioned, though, that this might change and sought to lay out why we might not be seeing craters just yet.
“Unfortunately the approach images we’re showing you that came down first just aren’t conducive to determining whether there are craters on the surface or not,” said Mr. Stern. “We’re not saying there aren’t craters. What we’re saying is that the lighting geometry on approach with the Sun behind the spacecraft’s back makes it hard to see whether the features on the surface are craters are not.”
Mr. Stern added that images acquired when New Horizons flew around the side of 2014 MU69 will create a better phase angle between the Surface and the sunlight and should allow the team to make a “definitive determination and ultimately will count the number of craters” on MU69.
Additional information will be released at 14:00 EST (1900 UTC) Thursday, 3 January 2019 by the New Horizons team.