Ultima Thule Update – high res images and science results


When New Horizons flew past Ultima Thule
on New Year’s Day, we got our very first look at a classical Kuiper belt object.
It was unlike anything we’d ever seen before – a contact binary that resembled a
dark red snowman. Those initial images were incredible, but they were also low
res thumbnails that were taken just as New Horizons was approaching it. Those
images had to be low resolution because at six and a half billion kilometres
from Earth, New Horizons’ download rate was less than
one kilobit per second. But now the closest images have been taken and they
are at full resolution and they are spectacular. This image was taken when
New Horizons was just 5358 kilometers from Ultima Thule. This image isn’t just
our closest look at Ultima Thule, it’s a window into the formation of our solar
system four and a half billion years ago. Welcome back to Launch Pad, I’m Christian
Ready, your friendly neighborhood astronomer. And here it is, the best image
ever taken of Ultima Thule. In fact, this image made the front cover of the May 17
issue of Science magazine, The image is actually a composite of two different
camera systems onboard the New Horizons spacecraft – the Multispectral Visible
Imaging Camera, or MVIC is responsible for capturing the color information of
Ultima Thule, while the Long-Range Reconnaissance Imager or LORRI is a
monochromatic camera but it has very high resolution. So by combining them we
get the color and details necessary to really understand what’s going on on
this Kuiper belt object. Ultima Thule is 43 astronomical units from the Sun –
that’s 43 times farther away from the Sun than Earth. It rotates once every 16
hours but its axis is tilted by 98 degrees and that means it’s currently
rotating almost face on to the Sun like a propeller. The daytime side spends 149
years in sunlight while the nighttime side spends the equal amount of time and
darkness. But at this distance the daytime side barely rises above 60
Kelvin – that’s -352 degrees Fahrenheit or -213 degrees Celsius.
Either way you cut it it’s cold. The night side is even
colder, reaching all the way down to just 30 Kelvin. Not only is its temperature
cold, it’s also dynamically cold. In other words, it follows a circular orbit around
the Sun in roughly the same plane as the rest of the planets. For this reason, it’s
considered dynamically cold because nothing ever happened to it that would
fling it into a higher, more eccentric orbit. That makes Ultima Thule a Cold
Classical Kuiper Belt Object (CCKBO) because it never experienced any perturbation from
Neptune or anything else that would fling it into a higher, more eccentric
orbit around the Sun. There are hundreds of thousands of Kuiper belt objects but
they occupy a volume of space beginning at Neptune’s orbit at 30 astronomical
units extending all the way out to 55 astronomical units so that’s a lot of
space and therefore the chances of there being an impact between any two
classical Kuiper belt objects is effectively zero. This means Ultima Thule
formed in its current orbit four-and-a-half billion years ago and
has remained undisturbed ever since. Ultima Thule is a contact binary with
the large and small lobes dubbed “Ultima” and “Thule”, respectively. There’s no
evidence of compression fractures or other features that are typical as a
result of high-speed collisions, so it seems that these two objects merged
together in a slow, gentle collision at just maybe a couple of meters per second.
Such environments were common in the early solar nebula. Overall, the nebula
was mostly gas and dust with the protosun forming at the center. But
throughout the nebula were pockets of denser particles called “pebble clouds”.
Objects coalescing in these clouds would have moved really slow relative to one
another, so low-speed collisions were easily
possible. Ultima and Thule likely merged together in such a low-speed environment
four-and-a-half billion years ago. But its overall shape turned out to be much
stranger than it first seemed. Rather than a snowman, Ultima Thule looks more
like a walnut stuck to a giant space pancake. This really started to become
apparent as additional images were downloaded and compared to each other.
The best overall fitting shape model has Ultima Thule at a roughly thirty
kilometers in length 20 kilometers in width and about ten kilometers in
thickness. The thickness measurement is the least
certain because only a small fraction of the nighttime side could be imaged. So
the big question is ‘how did Ultima Thule end up like this?’
Well one clue comes from its color, which is red. But it’s really more of a very
dark red. Ultima Thule only reflects a few percent of the sunlight that falls
on it, so think more along lines of potting soil except with a slight tint
of red if you shine a bright light on it. But both lobes are the same shade of
dark red, and that’s consistent with the idea that they formed in the same cloud
of material. The red color comes from complex organic compounds called “tholins.”
Tholins are produced when smaller, simpler organic compounds are broken
apart due to exposure to sunlight. They then recombine and form these larger,
more complex macromolecules that have a red color. Organic compounds are found on
asteroids, moons, and even comets everywhere we look in the solar system.
But the process of tholin creation is usually interrupted by some thermal
event, such as when a comet approaches the Sun and it really warms up. However,
in the outer Kuiper belt, Ultima Thule and other KBO’s never really experienced
any dramatic temperature fluctuations so the red tholin goo just emerges and
spreads all over the surface. In fact, tholins may be the reason we don’t see a
lot of water in Ultima Thule’s spectrum. It could be that these complex molecules
are are masking the water signature somehow or maybe the water is simply
underneath a layer of tholin goo. But apart from water and tholins, the only
other compound detected is methanol. No carbon monoxide, no ammonia, no acetylene
none of the high volatiles that are common throughout the outer solar system
are present. These molecules are abundant on Neptune’s moon Triton and on Pluto.
But Ultima Thule is about a thousand times smaller than those two other objects, so
any volatiles that were there probably have long since escaped to
space. There was however one absorption feature present in the spectra that has
yet to be identified, so I’m going with vibranium. Wakanda
forever! Ultima Thule has an extreme really complex geology with rolling
hills, troughs, and some craters. The largest is the Maryland crater on the
Thule lobe. It measures seven kilometers wide and two kilometers deep. Maryland is
probably the result of an impact, albeit a relatively gentle one. But the other
craters are a lot smaller – no more than a kilometer across. This suggests that
while they could be impact craters, it’s also equally likely that they were
formed by some other mechanism. For example, there could have been a drainage
or a collapse of the interior that would have just opened up a crater, or maybe
there were pockets of volatile ices that sublimated once they were first exposed
to sunlight. The larger Ultima lobe is made up of eight separate units that
appear to be smooshed together like monkey bread. Each unit is five
kilometers across. It’s possible that they each formed independently and then
later merged somehow to become the Ultima lobe. Such assembly models have
been proposed to explain the structures of comets like 67P Churyumov-Gerasimenko
and 9p Tempel 1. But the individual units making up these comets all have very
different sizes. It’s really not clear why Ultima’s units all seem to be roughly
the same size. Meanwhile, the Thule lobe doesn’t have any evidence of clumping or
assembly. It’s possible that when the Maryland crater formed, that event
may have resurfaced the rest of the Thule lobe, filling in and erasing any
seams or gaps in between the pieces. The brightest region is in the neck this may
be due to fine particles that roll downhill after the merger, or maybe they
are larger chunks of ice that were bashed up when the two objects merged
together. But then again, why would they merge together in the first place? Why
wouldn’t they just continue to orbit each other? We’re going to investigate
that in a moment, but first I want to thank my Patreon
supporters for helping to make this video possible.
And I want to offer a special shout out to my newest patron, Rock Howard. Thank
you so much for your support and if you would like to help keep this channel
going for the price of a cup of coffee every month, please make sure to head on
over to my Patreon page. So far we’ve uncovered a lot about the true nature of
Ultima Thule, but the big question is why would they
merge together, and why would their long axes be aligned the way they are? That’s
a very specific alignment, and it’s not something that would occur by random
chance. But it is exactly what should occur if the two objects were tidally
locked to one another and merged very slowly. Otherwise, the two lobes could
merge into any random orientation. But if they’re allowed to approach each other
slowly enough, then over time tidal forces will line the two objects up
along their long axes. Still, the Ultima lobe remains unusually flat, and we’ve
never seen anything quite like that elsewhere in the solar system. But there
are two small moons of Saturn that might offer a clue. Atlas and Pan orbit very
close to Saturn’s rings and they’ve acquired these really large skirts of
icy particles from the rings that make them kind of look like flying ravioli.
These two moons are small and they really don’t have very strong
gravitational fields so they’re able to build up these really tall walls of snow
which turn out to be really effective defenses against white walkers. Perhaps
the individual pieces of the Ultima lobe formed in the same manner, accreting snow
and ice from the surrounding pebble cloud and then later merging to become
Ultima. So now we have a workable model as to how Ultima could have formed and
we also understand how tidal forces can keep their long axes aligned together,
but why are they actually a contact binary? Why aren’t they just tidally
locked to each other orbiting a common center of mass like other Kuiper belt
objects? Well one of the big surprises from the flyby was that no satellites
were detected. That’s really strange because you would think that if there is
a pebble cloud that collapses, there should still be some pebbles around
acting as satellites. Well maybe there were satellites in the early days, but
they escaped. As they did so, they would carry away angular momentum and Ultima
and Thule would slow down and lose orbital energy until they eventually
merged. Or maybe the lobes lost angular momentum due to drag in the surrounding
gas of the solar nebula. As the Sun emerged, it blew out a powerful solar
wind and later swept away that gas. It’s also possible that there were impacts
that occurred on the leading edges of both
lobes, blunting their forward angular momentum and allowing them to merge. It was probably a combination of some or maybe all of these mechanisms
that overtime dumped angular momentum away from the two lobes allowing the
tidal forces to take hold and bring the two axes together in alignment as they
gently merged at two meters per second. In fact, you can model a two meter per
second collision yourself by taking a brisk walk into a wall. Or you could just
do a computer simulation. This is a simulation of about two hundred thousand
particles which includes both gravity and sliding friction. Blue particles
experience no acceleration and red particles experience the strongest. It
turns out that the neck region experiences the strongest acceleration
and this may help explain why the neck is so bright. Although these results were
published in the May issue of Science magazine, the manuscript was submitted at
the end of February. At the time the New Horizons team had only downloaded about
10% of the 50 gigabits of data collected during the flyby. Since then the download
total has risen to about 25% and that includes the closest approached
high-resolution images. There’s also some wide-field search data in the hopes of
maybe finding some distant satellites of Ultima Thule. If such satellites are
found then that would be a game-changer because it would allow the densities of
the Ultima and Thule lobes to be measured. That in turn would really help to answer
a lot of open questions. Meanwhile, the New Horizons spacecraft is in great
health it has plenty of fuel on board and a full set of working scientific
instruments. It’s speeding deeper into the Kuiper belt, so when it’s not
transmitting data back to Earth, it takes more images with its LORRI camera, hoping
to find a possible target to fly past next. Ultima Thule is telling us so much
about the conditions of the early solar nebula and how it formed. But its
formation story is not unique. In fact, most other planetesimals
probably formed exactly the same way. Some of those planetesimals are still
around today as asteroids, comets, and even small moons. But other
planetesimals combined with yet more planetesimals to become proto-planets,
which in turn went on to become the planets that we have today, including the
one that you and I are on right at the moment. You know, the day of the flyby I
got to interview Dr. Alan Stern and some other project scientists from the New
Horizons team. It’s really cool to go back and watch those videos and see how
much of what they initially thought held up and how much of it has changed since.
I’m gonna have a playlist of those videos right here and I’ll see you over
there when we’re done here. And please make sure to subscribe and ring that
notification bell so that you don’t miss out on any new videos. I’ll see you guys
next time and until then, stay curious my friends.

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