NASA's New Horizons mission team has published the first profile of the most distant world ever explored, a planetary building block and a Kuiper Belt object called 2014 MU69.
Analyzing only the first sets of data gathered during MU69's New Horizons New Year's Flight of 2019 (nicknamed Ultima Thule), the mission team quickly discovered a much more complex object than expected. The team publishes the first scientific results and peer-reviewed interpretations – just four months after the fly-over – in the May 17 issue of Science.
In addition to being the most distant exploration of an object in history – four billion miles from Earth – Ultima Thule's overfly was also the first investigation of any space mission of a well preserved planetesimal, an ancient relic of the era of planetary formation.
The initial data summarized in Science reveal much about the development, geology, and composition of the object. It is a contact torque, with two distinctly different lobes. At about 22 miles (36 kilometers) in length, the Ultima Thule consists of a large and strangely flat lobe (nicknamed "Ultima") connected to a smaller, rounded lobe (dubbed "Thule") at a point called " neck". As the two wolves have acquired their unusual form it is an unforeseen mystery that probably relates to how they formed billions of years ago.
The wolves probably orbited one another, like many so-called binary worlds in the Kuiper Belt, until some process brought them together in what scientists have shown to be a "gentle" fusion. For that to happen, much of the orbital momentum of the binary must have dissipated for the objects to come together, but scientists still do not know whether this was due to the aerodynamic forces of the gas in the old solar nebula, or if Ultima and Thule have ejected other lobes who formed with them to dissipate energy and shrink their orbit. The alignment of the axes of Ultima and Thule indicates that before the merger the two lobes must have become locked in half, which means that the same sides always faced each other while orbiting around the same point.
"We are studying the well-preserved remnants of the past," said New Horizons chief researcher Alan Stern of the Southwest Research Institute in Boulder, Colorado. "There is no doubt that the findings on Ultima Thule will promote theories of solar system formation."
As the Science report reports, New Horizons researchers are also investigating a number of surface features at Ultima Thule, such as bright spots and spots, hills and valleys, and craters and holes at Ultima Thule. The largest depression is an 8-km-wide feature that the team dubbed Maryland's crater – which probably formed from an impact. Some smaller wells on the Kuiper Belt object, however, may have been created by the material falling into underground spaces, or due to exotic ice that goes from a solid to a gas (called a sublimation) and leaving holes in place.
In color and composition, Ultima Thule resembles many other objects found in its area of the Kuiper Belt. It is very red – more red than a width of 2,400 kilometers Pluto, which New Horizons explored on the inner edge of the Kuiper Belt in 2015 – and is, in fact, the object of the reddest solar system ever visited by spacecraft; It is believed that its reddish hue is caused by the modification of the organic materials on its surface. Scientists at New Horizons found evidence of methanol, water ice and organic molecules on the surface of Ultima Thule – a very different mix of most of the chilled objects previously explored by the spacecraft.
Overflight data transmission continues, and will continue until the end of the summer of 2020. Meanwhile, New Horizons continues to make further observations of additional Kuiper Belt objects passing in the distance. These additional KBOs are too far away to reveal discoveries like those of MU69, but the team can measure things like object brightness. New Horizons also continues to map the radiation and dust environment with charged particles in the Kuiper Belt.
The New Horizons spacecraft is 4.1 billion miles (6.6 billion kilometers) from Earth, operating normally and advancing deeper into the Kuiper Belt at nearly 33,000 miles (53,000 kilometers) per hour.
The Applied Physics Laboratory at Johns Hopkins University in Laurel, Maryland, designed, built and operates the New Horizons spacecraft and manages the mission to the NASA Science Mission Directory. The MSFC Planetary Management Office provides NASA supervision for New Horizons. The Sanwest-based Southwest Research Institute runs the mission through Stern Principal Investigator and leads the scientific team, payload operations and scientific planning. New Horizons is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama.
Publication: S. A. Stern, et al., "Initial results of the New Horizons exploration of 2014 MU69, a small object of the Kuiper Belt ", Science 17 May 2019: vol. 364, edition 6441, eaaw9771; DOI: 10.1126 / science.aaw9771