As New Horizons and its scientists prepare for the end of a solar conjunction in two days and the resumption of science data downlink from the craft of its historic flyby of 2014 MU69 on New Year’s Day, Alan Stern and his team are busy analyzing the first few datasets returned from the spacecraft before the solar conjunction began on 4 January.
New Horizons current status:
As viewed from Earth, New Horizons is now directly behind the Sun in an alignment known as a solar conjunction. During this period, communications with the spacecraft are not possible due to radio interference produced by the Sun’s atmosphere.
The cessation of communications was known well in advance of the New Year’s Day flyby of 2014 MU69, with the New Horizons science teams understanding they would only get a small amount of data back before all communication with the craft stopped for five days.
The solar conjunction and communications blackout period will end Thursday, 10 January, at which point the steady stream of data from New Horizons will resume. “The data will start to come back down again and begin this long 20-month period in which we’ll be emptying the solid-state recorder of all the different kinds of data we’ve taken – literally hundreds of images and spectra and other data types,” said Dr. Alan Stern, New Horizons Principal Investigator.
But just because data is not flowing back from the spacecraft right now doesn’t mean the team is relaxing. On the contrary, New Horizons’ science teams are hard at work analyzing the data already returned from the spacecraft.
The moons of 2014 MU69?
It might sound like a funny thing. One of the first things the New Horizon science team is looking for around MU69 is evidence of a moon or moons orbiting the small body.
2014 MU69 is only 21 miles long and significantly smaller in width, and looking for moons might seem counterintuitive. But in fact it is quite vital in terms of understanding the interior composition of this Kuiper Belt Object (KBO).
The importance of understanding 2014 MU69’s interior lies with the body’s importance of understanding the early formation of the solar system and would reveal what was present in the stellar disk of dust and material surrounding the Sun after its birth – the disk from which almost everything we see in the solar system today was created or formed from.
In turn, this would tell us if our current models of solar system formation and development are accurate or if they need to be adjusted based on what 2014 MU69 tells us about what was present in the earliest days of the solar system.
“@NASANewHorizons is like a time machine, taking us back to the birth of the solar system. We are seeing a physical representation of the beginning of planetary formation, frozen in time." #UltimaThule https://t.co/BzlsY81EiL pic.twitter.com/gAFaTEsKYD
— Johns Hopkins APL (@JHUAPL) January 7, 2019
If there are moons orbiting MU69, and those moons were observed by New Horizons for long enough to determine their orbits, that information would be crucial to understanding the interior composition of MU69 because an object’s internal characteristics can be determined from a satellite’s orbit by observing how the orbit is changed by fluctuating gravity of the parent body – in this case 2014 MU69.
While the initial returns from New Horizons reveals no moons, Dr. Mark Showalter, a New Horizons Co-Investigator from the SETI Institute, and his team have already used approach imagery of MU69 to preclude the possibility of a moon 1 mile across at a distance of 500 miles or more from the KBO.
Already returned images of the MU69 flyby have allowed the team to tighten that search and eliminate the possibility of a moon within 100 miles of the surface of this primordial remnant of the solar system.
But that still leaves a 400-mile gap around nearly the entirety of MU69 to search. Despite the sheer amount of space left to explore, Dr. Showalter is confident that if a moon or moons exist, New Horizons will have likely observed it/them during the flyby.
For 2014 MU69, the presence of a moon or moons would not just help scientists understand and categorize the object’s interior but would also help explain its current slow rate of rotation at 15 hours +/- 1 hour.
According to Dr. Showalter, when 2014 MU69 formed as a contact binary, the object was likely rotating at a speed of 3-4 hours per rotation.
That’s much faster than the current observed rate of rotation, and the most natural way to explain such a rapid and significant decrease in the rotation rate of a solar system object is if a permanently orbiting companion were affecting its spin rate.
A closer-to-home example of how a natural satellite can slow a solar system body’s rotation can be found on Earth, where tidal interactions with the Moon have slowed Earth’s rotation from 21 hours 600 million years ago to the 24 hour rotation we enjoy today.
For 2014 MU69, the question for Dr. Showalter of how the bilobate object’s rotation slowed from 3-4 hours to 15 hours comes down to the same understanding we have of Earth’s rotation: the best way to understand this is if there “was a moon or two or three orbiting the system. Essentially, what those moons would do is put the brakes on [MU69], slow [it] down, and as a result the small moons would spiral outward a little bit but not necessarily very far.
In terms of other information already released regarding 2014 MU69 is its surface coloration.
As Dr. Silvia Protopapa related, MU69 is a cold classical member of the Kuiper Belt – a term that does not refer to the object’s temperature but rather its status as a primitive object of the early solar system.
The cold classical KBOs reside in a tightly grouped ring with a low inclination relative to the solar system’s plane – which again connects MU69 and the other cold classical objects to the very formation of the solar system from the protoplanetary disk of dust and gas.
My new sketch of @NewHorizons2015’s small Kuiper Belt object, #MU69! It’s a glimpse into the discussions going on behind the scenes: what do the shapes and colors mean and what geologic processes are at play? We will soon find out! @NASANewHorizons @JHUAPL #UltimaFlyby pic.twitter.com/4gyXY4forD
— James Tuttle Keane (@jtuttlekeane) January 3, 2019
The cold classicals have thus far all been observed as redder than the rest of the Kuiper Belt population, and MU69’s observed color is “well within the average color displayed by the cold classical Kuiper Belt Objects,” says Dr. Protopapa.
Moreover, the observed color of both lobes, Ultima and Thule, are the same – lending further evidence that the two objects formed from the same general clump of material before coming together as the bilobate object we see today.
Presently, New Horizons is 9 million miles deeper into the Kuiper Belt than 2014 MU69.
Flyby observations officially concluded on 3 January before New Horizons transitioned to its first post-flyby command load given to it by the science team.
During the solar conjunction, New Horizons is “making observations of the deeper environment of the Kuiper Belt,” related Dr. Stern, and the craft will also make additional observations of other KBOs once its MU69 data transmission resumes.
Before the end of January, Dr. Stern anticipates releasing more information of “this wondrous place in this wondrous scientifically valuable region of the solar system: the Kuiper Belt.”