Shortly after midnight on January 1, a NASA spacecraft will pass the farthest outer space rock ever seen in our solar system. This remote interplanetary flyby is over in an instant. If successful, however, the event could tell us a great deal about the objects that dominate the expanses of our cosmic neighborhood.
The robotic spacecraft that makes this bold visit is called New Horizons and has been flying through space for the last 13 years. You may remember this famous bot: it was the first man-made object that Pluto visited in the summer of 2015. Since this flyby, New Horizons continues to plunge into the solar system. Three years later, it's ready to hit another far-off destination, a rock called Ultima Thule, located one billion miles beyond Pluto. That's 4.1
This new rock is unlike anything we have visited before. It's a tiny cool New York City-sized object located in what's known as the Kuiper belt, the solar system. This space beyond Neptune's orbit is filled with millions of small frozen objects. It's a bit like a distant asteroid belt. It is believed that the bodies in the Kuiper belt are incredibly primitive – remnants of the birth of the solar system. When the planets were founded 4.5 billion years ago, materials in the region of the Kuiper Belt did not merge into new worlds but remained as tiny fragments. And since then they have mostly remained the same.
This is because they are so small and so far from the sun. Kuiper Belt objects are incredibly cold – only 35 degrees Kelvin above absolute zero. At this temperature, the objects on the surface do not change much. They were essentially frozen for billions of years. Moreover, they are so small that they do not develop much inside. Larger worlds such as Neptune or Uranus ultimately form internal engines in which materials that are deep in the objects are transformed under pressure and heat over millions of years. But the objects of the Kuiper Belt are simply not big enough. That is, they are like tiny time capsules and provide snapshots of what materials our first planetary system was. "We have never been to such a thing that has been frozen for so long," says Alan Stern, chief investigator of the New Horizons mission, The Verge . "Everything that was so perfectly preserved from the early days of the solar system."
Ultima Thule will pass by incredibly challenging Task. Since it is so small and so far away, it is difficult to see and track the object from Earth. And the New Horizons team only has one chance to get that fly by right. The spaceship is currently traveling through space at 32,000 miles per hour. If something is botched, there is no way to turn around New Horizons and try again. "Like Pluto, it's just a chance," says Stern. "A week later, no second spacecraft will arrive. And because it's a very complex business to make one of these flyaways, there are literally hundreds of variables that all need to choreograph perfectly. "
New guaranteed horizons was not always guaranteed to visit an object like Ultima Thule. The main task of the vehicle was to fly past Pluto, with the possibility of later passing through a second object of the Kuiper Belt. When the spacecraft was first launched from Earth in January 2006, astronomers did not even know if was an object near Pluto that could attack New Horizons. All the objects that we knew about were unreachable. As the New Horizons team prepared for Pluto, they also searched the sky for the spacecraft's second target. Finally, in 2014, they found a destination with NASA's Hubble Space Telescope: a Kuiper Belt object named 2014 MU69.
MU69, now called Ultima Thule, was ideally placed on the way from New Horizons out of the solar system. The spacecraft still had enough fuel to fire the engines and reach the object. In October and November 2015, before NASA officially approved New Horizons' new mission, the spacecraft crew made some course correction maneuvers and set the vehicle on course to hit Ultima Thule.
Since then, New Horizons has gradually closed on the rock, led by the team on Earth. It has also observed other distant objects in the Kuiper Belt and taken some of the farthest images ever taken by a robot. But New Horizons has been in hibernation for many months and has come out of it, a mode in which most of its instruments are off. To avoid unnecessary wear of the vehicle while driving. It's also a bit like an autopilot – a time when the spacecraft only travels and does not have to be overseen by the mission team on the ground.
In the meantime, the New Horizons team had the task to learn as much as possible about Ultima Thule. With a diameter of about 30 kilometers, it is too small and too weak to visualize with one of the telescopes available to us here on Earth. That's why the team had to get creative. In 2017, New Horizons scientists were able to observe Ultima Thule in front of a background star. It was a brief solar eclipse, known as occultation, in which Ultima Thule briefly blanked out the star's light. From this intersection in a fraction of a second, scientists were able to better understand the shape of the rock.
All data indicate that this stone is funny . In fact, it may not even be a single stone. The covering revealed that Ultima Thule is either shaped like a rubber duck and looks a bit like two compressed hills. Or it could be two separate rocks that move super close together. We will not know it until a day or two before reaching Ultima Thule. The tiny object is 100 times smaller than Pluto, so with New Horizons cameras on board it's harder to see it in advance. The best pictures will not come until New Horizons is more or less over the object. "This is a point in the distance to the last minute, and then you snap your fingers and you go from one point to a world within 48 hours," says Stern.
That's when everything goes according to plan, and Stern argues that this flyby is even more difficult than Pluto's, as New Horizons was located at a distance of 7500 kilometers from the surface of the dwarf planet At that time, the radio connection from Earth needed 4.5 hours to reach New Horizons, but now that the spacecraft is farther away, it takes even longer – Six hours – to send a signal to the vehicle, which, combined with the small size and weakness of Ultima Thule, presents an even more complex test to scientists and engineers.
And the smallest unforeseen detail can be at the last minute For example, just last month, the New Horizons team averted a potentially major problem when it discovered that the spacecraft was a little off course They finally realized that each time the vehicle had reoriented to observe a distant object in the Kuiper belt, the New Horizons movement easily got out of the track. Fortunately, the team captured this early enough to correct the spacecraft trajectory and decided to sacrifice some upcoming observations to be extra cautious. "That was a late start, but the guy who discovered it is my hero," says Stern.
But now there's nothing left to do. The last orders for the Flyby sequence were uploaded to the spacecraft on Christmas Day and can not be changed. New Horizons must do what it's meant to do: Complete a series of pre-planned tasks when Ultima Thule passes at 12:33 pm (ET) on January 1, and is within 2,200 miles (3,200 miles) of the surface of the rock , It creates images, captures the surface of the object, searches for moons and an atmosphere, and measures body temperature. Basically it will try to learn everything about Ultima Thule in a few seconds.
It will be a short while before we get these first enticing close-ups. Four hours after the flyby, New Horizons sends a signal back to Earth to let the mission team know if the encounter was successful. And since the radio needs six hours to reach our planet, we do not know for 10 hours whether the flyby was as planned. A few hours after this first signal, New Horizons begins to send back all data collected, including the first high-resolution images.
It will take up to two years for all the data to return to Earth. New Horizons collects about 50 gigabits of data. This is the storage capacity that you might find on a small flash drive. However, due to the spacecraft's low computational power, it takes up to 20 months to link everything to Earth. In 2019 and 2020, new surprises and pictures will appear again and again.
What we will find at Ultima Thule is reluctant to speculate on the mission team. The rock is really in a new category of solar system objects, and there is no precedent for what we could find. But Stern is optimistic that we will see something amazing. "I do not make predictions," says Stern. "The only prediction I made at Pluto is that we would find something wonderful. I think the fun is that we do not know what we're going to see. "