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New horizons ready to fly. Ultima Thule

LAUREL, Md. – NASA's New Horizons spacecraft is ready to fly around the most distant object in the solar system, an event largely unaffected by the government’s ongoing shutdown.

New Horizons will approach the 2014 Kuiper Belt object, nicknamed Ultima Thule, at 12:33 pm Eastern January. 1st of January. The spacecraft will travel at a speed of 3,500 kilometers from a small body, 6.6 billion km from Earth, at a speed of 14 kilometers per second.

The controllers transmitted the “Knowledge Update” to New Horizons at the beginning of December 30, changing the time of events during the flight by two seconds to reflect improved knowledge of the Ultima Thule position regarding the spacecraft. Most likely, this will be the last update before the flight, said Alice Bowman, Operations Manager for the New Horizons mission, during a briefing at the Applied Physics Laboratory at Johns Hopkins University (APL) here on December 30.

New Horizons itself is in good condition, without any signs of any problems that may interfere with the overflight. “The spacecraft is healthy,” she said. When the spacecraft transmits confirmation that the update was successfully applied, "we are likely to breathe a sigh of relief." At the end of December 30, Bowman tweeted that the update was indeed successfully installed on the spacecraft,

Mission scientists were thrilled by the science they expect New Horizons to return, but they didn’t worry about the flight itself. “My peace of mind reflects the fact that the mission works as we expect. There is no indication that something is abnormal, ”said Jeff Moore, a planetologist from the Ames Research Center at NASA, who heads the New Horizons geological and geophysical research team. “The latest update of knowledge gives us very good opportunities to get really beautiful photos.”

The biggest problem in the days leading up to the flight was not technical, but bureaucratic. The partial closure of the government, which began on December 22, when funding for some government agencies, including NASA, ceased, led to the destruction of plans developed several months earlier for the publication of this event. NASA's closure plan states that the agency’s website and social networks will not be updated during closure and that NASA television will also be disabled.

Anyway, NASA Administrator Jim Bridenstein said December 27 that the NASA accounts on television and social networks will continue to operate during the flyby, because the contract to support this work was “financed” before closing. APL also planned to broadcast briefings about the flight on their accounts on social networks and on the website.

Alan Stern, chief investigator for New Horizons, said on December 30 that due to the closure, NASA officials who had previously planned to attend the flight could not do it in an official capacity, including speaking at events in the media or making statements. “In addition, we are virtually untouched,” he said, adding that these officials can participate in fly-by activities as private citizens.

Several members of the science team, who are NASA’s civil servants, were to receive exemptions from leave, which affects about 95 percent of the agency’s workforce, “because this is a critical operation,” said Stern.

Among them was Moore, who said that he and another Ames scientist, Dale Cruikshank, had to “deal with the bureaucracy” in order to free themselves from vacations and get permission to go to the APL to fly around. “We both spent the day filling out documents and working with the system,” he said.

Stern Ultima Thule circled
Alan Stern, principal investigator for New Horizons, discusses the upcoming overflight at a briefing on December 30 at the APL. Credit: SpaceNews / Jeff Faust

Scientific Wonderland

Moore and other scientists are eagerly awaiting the expected seven gigabytes of data that New Horizons will collect during the flight, including images, spectra and particle data about Ultima Thule. Although several images and other data will be returned a few days after the flight, the spacecraft will need about 20 months to transfer all the collected data due to its extreme distance from Earth.

New Horizons will be out of contact with the Earth during the span itself. It will transmit some data collected until December 31st. After convergence, it will transmit 15 minutes of telemetry, which Bowman described as the “health and safety data stream”, including the amount of data collected. He is expected to arrive on Earth at 10:29 am East of January 1. The spacecraft will begin to return data collected during the flight, later than January 1.

Ultima Thule is considered part of the Kuiper Belt family of objects, called “cold classics.” The “chill” in the title does not refer to their temperature, but to the fact that they have low-sloping and eccentric orbits, said Hal Weaver, project New Horizons scientist, suggesting that they were not disturbed or changed since the formation of the Solar System 4, 6 billion years ago.

“This is probably the most primitive object a spacecraft has ever encountered,” he said of Ultima Thule. "This is the best possible relic of the formation of the solar system at these distances."

“The Kuiper belt is just a scientific wonderland. This is the place where we have the best samples from the era of the formation of our solar system, ”said Stern. "From a scientific point of view, there is nothing like that."

Scientists are also excited about the flyby because so little is known about Ultima Thule, discovered only in 2014, when they were looking for potential targets for an expanded mission for New Horizons after its Pluto flyby in July 2015. An object not more than 30 kilometers wide was visible only by the Hubble Space Telescope and the New Horizons themselves.

“We don't know anything about MU69,” said Stern. "We never in the history of space flight went to a goal of which we knew less."

Among these uncertainties is the period of rotation of the object. Scientists hoped to determine how quickly Ultima Thule rotates around its axis, looking for patterns in the brightness of an object over time, known as the light curve. However, observations of the object have so far revealed a flat light curve, which makes it difficult to recognize the rotation period.

Weaver said that there is a “hint” in the light curve data that the spacecraft rotates quickly, in the order of several hours. “A little of what we were able to identify reveals that it can rotate rather quickly, but we constantly discuss whether we believe in it or not,” he said.

Weaver said that the most likely explanation for the lack of light curvature is that New Horizons is looking straight down the Ultima Thule's axis of rotation, so he constantly looks at the same part of the object.

However, there are alternative explanations. Mark Bui, who led the team that observed the star eclipses in July 2017 and August 2018, when Ultima Thule passed in front of the star, said that the unusual shape of the object could explain the flat light curve. Although these shadows indicate that an object can have two petals, an object with three petals can also create a flat light curve.

Given that he had plenty of time to develop models, he said that he could come up with a form for Ultima Thule that explains the light curve. But the spacecraft will soon give its answers, he added. “Why not just wait until we get the photos?”

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