The Five Escapers, and Arrokoth

Watch out for the launch of a new publication: a poster of 2-by-3-foot size like the Map of the Starry Sky and Zodiac Wavy Charts. It depicts in three dimensions the journeys of the five spacecraft that are escaping from the solar system into the winder universe: Pioneers 10 and 11, Voyagers 1 and 2, and New Horizons.

There is much that could be said about them, and my present struggle is to squeeze the descriptive text down enough for the space left by the large illustrations. There are entertaining details that have to be left out. For instance, Arrokoth. So we’ll tell the Arrokoth story here. It’s a creature of many names.

When the New Horizons probe finished its main mission of observing Pluto in 2015, and continued outward, it had an “extended mission”: try to take a look at one of the thousands of small objects in the vast outer zone that is called the Kuiper Belt. The target had to be large enough,not too distant for radio communication, and close to the spacecraft’s direction of travel – within a cone of less than one degree outward from Pluto.

The “New Horizons Kuiper Belt Object Search” began in 2011, four years in advance. It used the world’s large telescopes, and “citizen science” help from the public in examining the images. 143 hopeful objects were discovered, but none were close enough to the right direction. It took the Hubble Space Telescope to find, in 2014, four candidates, all too small to be seen by ground-based telescopes. They were at first called PT1, PT2, PT3, and PT4 (“potential targets”). The PTs received provisional designations based on their discovery dates, in the style used for all asteroids: 2014 MU69, 2014 OS393, 2014 PN70, and 2014 MT69. PT3 was the brightest, probably largest, but PT1 was closer to the right direction, and it was chosen, 2015 August 28.

It had had a temporary designation 1110113Y on the Hubble Telescope’s website, but, becoming the target, it was nicknamed Ultima Thule, as the most remote place ever sailed to by a spacecraft. (Thule was ancient Greeks’ name for the most remote northern land, possibly Shetland or Norway or a land beyond the known world. Goethe wrote in 1774 a melancholy ballad that became popular and was set to music by Schubert, Es war ein König in Thule, “There was a king in Thule,” and the name was given in the 19th century to a mythical northern homeland of the “Aryan race,” and in 1910 to a settlement in far-northern Greenland.)

Finally, as is the custom when a minor planet’s orbit is well enough known that it will not be lost, the thing got a permanent number and name: 486958 Arrokoth.

The word is thought, rather uncertainly, to have meant “sky” or “cloud” in Powhatan, an extinct Algonquian language of eastern Virginia and Maryland, where are based the Hubble Space Telescope and the Johns Hopkins University Applied Physics Lab.

New Horizons used 35% of its remaining fuel to make course corrections, and flew past Arrokoth at a range of 3,500 km (2,200 miles) on 2019 Jan. 1.

It’s an extraordinary object, like two huge potatoes stuck together. It is a contact binary: two lobes, with diameters of 21 and 15 km (13 and 9 miles) that must have collided gently enough to stick together. They are planetesimals: the kind of early-solar-system objects that amalgamated to form planets. This is why observing the Kuiper Belt is of such interest to scientists.

As nicknamers would have it, the larger lobe is “Ultima,” the smaller “Thule.” But for the naming committee, searching among Powhatan words, they are “Wenu” and “Weeyo.” What these mean I don’t know.

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