The New Horizons spacecraft has a new target.
New Horizons spacecraft. The large white radio dish is for communication with Earth. The black finned cylinder to the right is the power source, radioactive plutonium whose heat of decay is converted to electrical current.
Launched in 2006, its initial velocity was the fastest ever for an interplanetary probe, and a gravity assist maneuver at Jupiter gave it an additional boost. Even so, it did not arrive at its primary target of Pluto until more than nine years later in July 2015.
Regardless of its planetary status or lack of it, Pluto is a fascinating world. Every new object we see up close, every planet, moon, comet, asteroid, dwarf planet—every one has a unique history and clues to unravel.
The color differences have been exaggerated in this image to emphasize different landscape types.
This is Pluto in natural color.
There were good reasons to believe that there would be another object accessible to New Horizons after it had flown by Pluto. The area is known as the Kuiper Belt, and many bodies (Kuiper Belt Objects; KBOs) have been found, most of them smaller than Pluto. None were in the direct flight path, but mission planners argued that one would surely be found.
It turned out to be harder than expected. Years of telescope searching didn’t turn anything up. In something very near desperation, scientists requested time on the Hubble Space Telescope. After an initial rejection, the request was eventually granted, and a suitable target was found. 2014 MU69 is in New Horizons’ cross hairs.
But to aim the spacecraft precisely, and to know the size, shape, and reflectivity of the target in order to plan the images taken in the all-too-brief flyby, the scientists needed more information. The very thing that made it hard to find a target—the fact that the spacecraft is positioned before a rich background of stars—allowed for the gathering of this information.
An orbit for 2014 MU69 had been determined from the Hubble observations. This should have placed it directly in front of three faint stars in the summer of 2017. Well-placed observers on Earth could watch each star blink out for a few seconds, thereby revealing the KBO’s size and shape. These events are called occultations.
Predicted occultation #1 positioned observers in Argentina and South Africa last June 3rd with no results. A month later a dedicated flight over a remote area of the Pacific by an airborne observatory also gave no results for the second predicted event. The good news from these observations was that there was no cloud of debris surrounding the object that could have knocked out the spacecraft.
Finally on July 17th, five teams strung out along the ground path of the occultation got excellent data. The orbit was not only refined, the shape of 2014 MU69 was revealed to be quite strange, either highly elongated and up to 19 miles (30 km) long, or a binary body whose halves are each about 9 to 12 miles (15 to 20 km) across. Subsequent observations with the Hubble telescope seem to favor the latter option.
On New Year’s Day 2019, the New Horizons spacecraft will zoom by 2014 MU69, 43.4 astronomical units from the sun (the Earth is, by definition, one astronomical unit from the sun), with a one way communication travel time of a little more than six hours. The images and other data will tell the tale of yet another solar system object, the farthest yet visited by human-made machines, almost exactly 13 years after New Horizons left the launch pad in Florida.
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