New Horizons scientists successfully observe second target during stellar occultation
New Horizons‘ scientists successfully observed Ultima Thule, the spacecraft’s second target, from Senegal on Aug. 4, 2018, when the Kuiper Belt Object (KBO) passed in front of an occulted star.
In spite of weather-related hardships, such as the occultation taking place at the start of Senegal’s rainy season, the observation was even more successful than three occultation observations during the summer of 2017, yielding information about Ultima Thule’s shape and size as well as possible hazards near it, such as rings or debris, according to a mission statement.
NASA’s Hubble Space Telescope (HST) observed the occultation from space, as it did for all three last year, specifically to search for rings and other potential hazards to the spacecraft. The telescope was better positioned this time around and was able to observe as close as 1,000 miles (1,600 kilometers) from Ultima Thule.
Last year, the closest Hubble could see was about 12,400 miles (20,000 kilometers) because it was positioned on the opposite side of the Earth during the middle of the occultations.
No evidence of rings around Ultima Thule was obtained this year or last, said observation team member Josh Kammer, of the Southwest Research Institute (SwRI) in Boulder, Colorado.
“There were no detectable ring signatures for either event, so using the Hubble data, we were able to set important constraints on the presence of any rings or dust that could jeopardize a safe flyby,” Kammer said.
Marc Buie also of SwRI Boulder, led the observation team, which received international support, including assistance from Senegal, Colombia, Mexico, and France.
“We owe the success of these observations in large part to this amazing multinational collaboration,” Buie said. “This work is in preparation for our next New Horizons flyby, coming up on Jan. 1, during which we expect to learn much more about Ultima Thule by examining it up close.”
New Horizons assistant project scientist Anne Verbiscer of the University of Virginia praised the team’s Senegalese colleagues, whose efforts made the project a success.
Data from the occultation, along with navigation tracking, is helping the New Horizons team formulate commands that will be uploaded to the spacecraft in preparation for the flyby. Science instruments and subsystems will be checked in anticipation of the event, and a course correction toward Ultima Thule will be conducted in early October.
Located more than a billion miles beyond Pluto, Ultima Thule and small KBOs like it are made of pristine materials from the solar system’s earliest days and can provide scientists with insight into planet formation in general and evolution of the solar system’s third zone specifically.
Data from last year’s occultations indicate Ultima Thule is either a double-lobed object or a binary system composed of two objects orbiting each other. It could also be a contact binary, in which the two orbiting objects actually touch one another. There is also some evidence Ultima Thule might have a moon.
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.