New Horizons: Occultations in Preparation for MU69

by Paul Gilster

Our spacecraft have never encountered an object as far from Earth as 2014 MU69, but New Horizons will change all that when it races past the Kuiper Belt object on New Year’s Day of 2019. This summer is an interesting part of the project because planners will use it to gather as much information as possible about what they’ll find at the target. We have three occultations to work with, one of them just past, and they are as tricky as it gets.

But before I get to the occultations, let me offer condolences to the family and many New Horizons friends of Lisa Hardaway, who died in January at age 50. Hardaway helped to develop the LEISA (Linear Etalon Imaging Spectral Array) spectrometer that brought us such spectacular results during the Pluto/Charon flyby. She was program manager at Ball Aerospace for the Ralph instrument that contains LEISA. Mission scientists used data from the instrument package to make geological, colour and composition maps of Pluto and its moons. The mission team has now dedicated the spectrometer in her memory.

Tracking a Fleeting Shadow

The MU69 occultations should provide useful data as we learn more about the KBO encounter environment. The first event occurred on June 2-3, with observers in Argentina and South Africa — 54 telescope teams in all — trying to track the shadow of MU69, which had occulted a star. Alan Stern, principal investigator for New Horizons, explains the goal:

Predicting the narrow stripe of MU69’s shadow over the Earth called for data from the European Space Agency’s Gaia mission as well as the Hubble Space Telescope. Remember that it was only in 2014, after a determined search, that the Hubble instrument discovered the 45-kilometre object, which is only 1/10,000th the mass of Pluto, although ten times larger than the average comet. Just the kind of KBO we’d like to study, in other words, but one we’ve had to characterize quickly in preparation for the upcoming flyby.

As the data from the recent occultation are analysed, we can look forward to another on July 10 and a third on July 17. For the July 10 event, mission scientists will use the Stratospheric Observatory for Infrared Astronomy (SOFIA), a 2.5-meter airborne telescope mounted in a Boeing 747SP jet. SOFIA can work at 45,000 feet, well above intervening clouds and capable of providing better data than the army of small telescopes used in the June occultation.

For the July 17 occultation, two dozen 40-centimetre telescopes will be deployed to Patagonia, where observers hope to scan more deeply for any debris around MU69. The star being occulted will be the brightest of the three, offering the best prospect for such detections. To track all this, keep an eye on the New Horizons KBO Chasers page, but as we get close to the event check the project’s Facebook page and the Twitter hashtag #mu69occ.

As of this morning, we’re 689,472,210 km from MU69 with 553 days to go until flyby.