Very late at night (or tomorrow very early in the morning, if you want), the New Horizons spacecraft will fly farthest from the astronomical object that humanity has tried. At 5:33 p.m. UTC on January 1, New Year's Day, it will pass around 3,500 kilometers from 2014 MU69, clumps of ice and strange stones orbiting the Sun far past Neptune. If successful, the probe will return the first close-up image of the Kuiper Belt Object in situ, transmitting data from shock 6.6 billion kilometers from earth.
So yes, this is a big problem.
You might remember New Horizons as a spacecraft flying by Pluto in July 2015 and returning a lot of data from a tiny ice world, including beautiful images that change the way we see and think of the outer solar system.
But the solar system does not end with Neptune and Pluto. There is a volume of bagel-shaped space out there that is occupied by millions of objects, most of which consist of rock and ice. For historical reasons this is called the Kuiper Belt. Predicted to have existed for decades, the first Kuiper Belt Objects (or KBO) were not discovered until the 1990s … and now we know thousands. Some people (including me) consider Pluto the largest of the objects known so far.
Even before Pluto flyby in 2015, a search was underway to find a second potential target for the New Horizon in the Kuiper Belt. The story behind it was very cool – team member Alex Parker wrote a good blog post for NASA about it, too extraordinary Twitter thread – but to make a long story short, KBO was discovered by Hubble in 2014 which was quite close along the spacecraft track to make it the target with the remaining fuel. It was given the 2014 MU69 designation, although you might hear it referred to as Ultima Thule, an unofficial nickname given after a public contest was held by the New Horizons team.
We still don't know much about MU69. It's so far and so small that it's barely visible to telescopes that are bound to Earth, and even New Horizons doesn't see it until August 2018. The orbit is rather elliptical and makes it more than 6 billion kilometers from the Sun, far from a billion kilometers further than Pluto. Some intelligent observations show that MU69 are two objects that orbit each other very closely (making it a binary object) or double-hollow objects such as comet 67P / Churyumov-Gerasimenko. Both components are probably around 20 kilometers (and maybe smaller). We know the color is reddish, because many objects like that (ultraviolet light from the Sun breaks down carbon-based molecules that rearrange themselves into more complex molecules called tholin, and this tends to be red).
And that's all. But in a few days we will know a many more.
I am very, very urgent for you to read the description of my friend Emily Lakdawalla about this evening meeting she wrote for The Planetary Society. As always the article is clear, interesting, and has all the info you need to understand what it is.
There are some points that I want to convey too.
One of them is because MU69 was very small and fainted, and it was discovered recently, we don't know its position right. It is well known enough to plan flights, but when New Horizons draws near that uncertainty really looks bigger. Also remember, that MU69 is only 20-40 kilometers or around … and New Horizons will shout past KBO at relative speed 14 kilometers per second – more than 50,000 kilometers per hour. Therefore, MU69 will not be more than one or three pixels until almost the meeting itself.
Engineers played it safely, and had programmed the spacecraft to return some images from the start from quite a distance so they were sure MU69 would take part in the shoot, and once again some from nearby where it would be big enough to see some details. But the meeting was so fast that the spacecraft would carry out a series of programmed observations during the meeting itself, spending all their time examining MU69. Images will not be sent back until after they have passed … and that too requires radio waves, traveling at the speed of light (because they are light), six hours to return to Earth. Even then they will not be released to the public until scientists get the chance to see it and clean it up a bit (raw data from spacecraft generally needs to be processed to make it easier to check), so that maybe a day or more before we start seeing the actual picture.
And what will we see? That's a good question. There are already some interesting news that the brightness of MU69 from time to time (what astronomers call light curve) quite flat, which is strange. If it is elongated (or two objects are orbiting each other) then you would expect it to be brighter and dimmer over time. If the surface is uneven, you will expect brightness to change as it rotates too. But nothing like that is seen. Is this without features? Or do we see it straight down on one of the poles, so that when we spin we don't see a new feature visible. The last bit seems impossible, because we have seen it has two major components, and it is difficult to see how we can separate them but look down to the poles. So it's weird.
Are there smaller moons orbiting the main body? Could it ring? Is there a cloud of dust around it? Is the surface smooth or rough, hilly or flat, veined or smooth? All of these are important questions that will tell us a lot about this distant object, and everything, hopefully, will be answered by New Horizons.
And they will be answered in the next few days.
Therefore, I will add that for the next week I will be on Star Trek: The Cruise III, where the internet is not evenly distributed. I probably won't be able to write about any images that come down. So check the SYFY homepage for the views of other authors, follow Emily on Twitter, and also list of people covering it on Twitter. You can also follow New Horizons mission on Twitter, and hey: Give Alex Parker a follow too.
Let's see what's out there.