The outer solar system is a secluded place. But for one small stone the size of a city on the New Year it will be a little less lonely for a while, since a spacecraft sent from Earth more than ten years ago is about to visit.
This lonely stone is called Ultima Thule, and it is the target of the Nasa New Horizons spacecraft, which flew past Pluto in July 2015. If everything goes according to plan, a historical overflight will take place on January 1, 2019. “This is the most distant exploration of the world in history,” says Alan Stern of the Southwestern Research Institute in Texas, a senior scientist at the mission. "It will be a truly record setting."
At a distance of 6.6 billion kilometers (4.1 billion miles) from the Sun, Ultima is in the region of the outer limits of the Sun, known as the Kuiper belt, a ring of objects that are essentially rocky and ice fragments left over from the formation of a planet in our solar system . Ultima, however, is special because we believe that he was formed there
Other objects in the Kuiper belt, which is 30-50 times the Earth-Sun distance (from 30 to 50 astronomical units, or AU), were formed near the giant planets, before migrating further. But, appearing right on the Belt, Ultima is probably part of the untouched material left over from the infancy of our Sun 4.6 billion years ago. However, it is shrouded in mystery because of the long distance and tiny size. We know very little about this, since most of our data comes from remote telescopes and stellar eclipses — moments when they passed in front of distant stars and cast a shadow on the Earth.
We know that the object is red. We know that its length is about 30 kilometers (19 miles), and we know that its reflectivity is about ten percent, like dirt in your garden. “It really is,” says Stern. "Compared to Pluto, this is an open book."
Ultima, located 1.6 billion kilometers (1 billion miles) from Pluto, was selected as the next target for the New Horizons in August 2015. Originally designated as MU69 2014, it was later given the nickname Ultima Thule, which means “outside the known world”. It is planned that New Horizons will fly past at a close distance of 3,500 kilometers (2,200 miles), which is more than three times closer than Pluto. However, this can be increased to 10,000 kilometers (6,000 miles) if the team detects potentially dangerous debris nearby when approaching a span.
Regardless of the distance, the spacecraft will use its own set of seven instruments and cameras to study the object according to a pre-configured procedure, including returning to images from the other side when it flies at a speed of 50,700 kilometers (31,500 miles). ) at one o'clock.
One of the most intriguing questions about Ultima Thule is its shape. We think this is a binary file — two objects, not one, but it is unclear whether the two objects rotate relative to each other or touch them. The latter is called a contact binary file, similar to the comet 67P, which was launched in orbit by the ESA Rosetta spacecraft in 2014, although Ultima is 1000 times more massive.
It will also be interesting how much Ultima we actually see. We do not know how fast it rotates, but this speed of rotation will determine how much the object is illuminated by the sun when the “New Horizons” are rushing past. In Pluto with a rotational speed of 6.4 days, we could only see half illuminated by the sun during the passage. “If it’s just a few hours, then we’ll have a pretty good idea of all this,” says Stern. “If it's a slow rotator, say, a day or more, we will only approach one side on the day we fly, and we will never know what the other side looks like.”
The closest approach of the spacecraft to the object is scheduled for 5:33 GMT on January 2. But the action will start a day earlier, on December 31, when we get a rough image of the object just six pixels across with half a million miles. This will be enough to reveal the shape of Ultima. On the night of January 1, we get an image with a resolution of 10,000 pixels. January 2 will be an image size of 40,000 pixels. And later, in 2019, after loading the primary data, we get a great high-resolution image, the width of which is one megapixel.
Thanks to the 12-hour communication time between Earth and the spacecraft, the group prioritized the data that will be sent first, in accordance with the mission’s main scientific objectives. It will return about 50 GB of data in total to the Earth in 20 months, which is comparable to the span of Pluto, and the latest data will arrive in September 2020.
These group 1, the most important, will be the first. This includes images of the Ultima Thule's surface, its composition of the surface and the search for tiny moons or rings revolving around it. Data from group 2, which includes measuring the temperature of the object and searching for any signs of the atmosphere, will be obtained later. Data group 3 will be the last.
Even after receiving this latest data, even more worries may appear. Because after September 2020, depending on how much fuel is left, the team will explore the possibility of visiting another facility in the Kuiper belt. New Horizons is not going to leave this region until 2028, and its capacity will be sufficient until 2038.
However, before this all attention is paid to Ultima Thule. And the team will hope that all their hard work will pay off. “We put all our heart and soul into trying to plan and test it,” says Stern. “But there is no backup. There is no turning back and make a U-turn. These are just new horizons. ”
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