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New Horizons Science Chat discusses Ultima Thule flyby

An illustration of NASA’s New Horizons spacecraft encountering the Kuiper Belt object nicknamed Ultima Thule on Jan. 1, 2019. Image and Caption Credit: NASA/JHUAPL/SWRI

An illustration of NASA’s New Horizons spacecraft encountering the Kuiper Belt object nicknamed Ultima Thule on Jan. 1, 2019. Image and Caption Credit: NASA/JHUAPL/SWRI

NASA’s New Horizons spacecraft is now closer to its second target, Ultima Thule, than the Earth is to the Sun, and with the flyby just over 100 days away, mission scientists are actively preparing for the encounter.

In a Science Chat livestreamed on Sept. 19, 2018, NASA chief scientist Jim Green, mission Principal Investigator Alan Stern of the Southwest Research Institute (SwRI) in Boulder, Colorado, and Mission Operations Manager Alice Bowman of the Johns Hopkins University Applied Physics Laboratory (JHUAPL) discussed the upcoming New Year’s Day flyby of the small Kuiper Belt Object four billion miles from Earth.

Traveling at a speed of 31,000 mph (50,000 kph), the spacecraft will make its closest approach to Ultima Thule at 12:33 a.m. EST (05:33 GMT) Jan. 1, 2019, when it will pass within just 2,175 miles (3,500 kilometers) of the KBO, closer than it flew by Pluto in July 2015.

Ultima Thule and KBOs like it are made up of pristine materials from the earliest days of the solar system that became the building blocks of the planets, moons, and other small bodies orbiting the Sun.

“We’re going four billion years into the past,” Stern said. “Nothing that we’ve ever explored in the entire history of space exploration has been kept in this kind of deep freeze the way Ultima has.”

Flying by the KBO, which is just one percent the size of Pluto, or approximately 30 miles (45 kilometers) across, will be more challenging than flying by Pluto for several reasons. Ultima Thule was discovered just four years ago with the Hubble Space Telescope, so its orbit is not fully known. It is significantly darker than Pluto, as it is one billion miles further from the Sun with a dark, reddish-brown surface that reflects very little sunlight.

At the same time, it is located in the direction of the Galactic Center, in a dense field of background stars.

“The orbit is not very well characterized. That’s why we’re doing optical navigation measurements, continuously looking to make sure we know the point in space we want to target,” Bowman said.

During the remaining time between now and the flyby, mission scientists will use optical navigation measurements to search for potential hazards to the spacecraft, such as dust and debris, as well as possible moons and rings around Ultima Thule.

Approximately 80 days before the encounter, sometime in October, New Horizons will begin sending back images of its second target.

The actual encounter will begin on Dec. 25 and run through Jan. 3. During closest approach, New Horizons will use its seven science instruments to collect data and images of Ultima Thule and will not be in contact with Earth. As was done at Pluto, images will be sent back by the spacecraft just prior to closest approach on Dec. 30 and 31 to assure the probe is on target and to enable mission scientists to make any last minute changes if they are needed.

Traveling at the universal speed of light, radio signals will take slightly over six hours each way between Earth and the spacecraft. They will be sent via NASA’s Deep Space Network.

Current plans call for the spacecraft to send a signal after closest approach indicating it successfully made it through the flyby, which is scheduled to arrive Jan. 1 around 10 a.m. EST (15:00 GMT). The first images from the flyby are expected to arrive the same day between 6 p.m. and 8 p.m. EST (23:00 GMT Jan. 1 and 01:00 GMT Jan. 2).

Because of New Horizons’ very slow transmission rate, it will take approximately 20 months to return all the flyby data.

A graphic of the flyby timeline. Image Credit: NASA

A graphic of the flyby timeline. Image Credit: NASA



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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