Members of the team at NASA's Jet Propulsion Laboratory overseeing the Dawn spacecraft orbiting the dwarf planet Ceres are dismayed by the agency's decision not to have Dawn explore the dark asteroid 145 Adeona.

NASA will instead support an extension for the New Horizons spacecraft mission now leaving Pluto to chase 2014 MU69, a massive and icy Kuiper Belt Object (KBO).

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NASA bosses said Dawn will remain in orbit around Ceres, which it began orbiting on March 6, 2015, instead of visiting 145 Adeona in 2019. This 150 kilometer-wide asteroid in the main asteroid belt between Mars and Jupiter is a C-type asteroid probably composed of primitive carbonaceous material.

NASA planetary division director Jim Green said the agency's decision to forego 145 Adeona was based on recommendations of a senior review panel that evaluated all the agency's ongoing planetary missions,

"The long-term monitoring of Ceres, particularly as it gets closer to perihelion -- the part of its orbit with the shortest distance to the sun -- has the potential to provide more significant science discoveries than a flyby of Adeona," said Green.

NASA JPL mission leaders supported the trek to 145 Adeona since it would be better to exhaust Dawn's remaining fuel in exploring another large asteroid. There were dismayed by the decision to let Dawn continue orbiting Ceres.

Chris Russell, the Dawn mission's principal investigator at the University of California, Los Angeles, said the decision not to go to 145 Adeona was disappointing.

"We thought that everyone we had talked to about this plan was enthusiastic about it. I had no negative vibes until this particular moment."

Russell said it's a mistake to think the science of staying outweighs the chance to visit a new asteroid. He said Ceres has already been mapped and there are few signs of scientifically interesting changes in Ceres.

The Dawn mission was designed to study Ceres and Vesta, two large bodies in the asteroid belt, to answer questions about the formation of the Solar System. It was also to test the performance of its ion drive in deep space. Dawn is the first spacecraft powered by ion propulsion.

TagsDawn Spacecraft, Ceres, 145 Adeona, NASA, Jet Propulsion Laboratory