Back to galleries

MU69 Occulation - South Africa - June 3 2017

New Horizons flew past Pluto two years ago, in July 2015. But the outer solar system has more things to see, so the spacecraft is now headed to fly past a Kuiper Belt Object (KBO) on January 1, 2019.

The KBO is a small chunk of ice named 2014 MU69, at a distance of around 44 AU. We know where to find it in the sky, but we don't know its orbit precisely enough to target the spacecraft's cameras as we fly past it. Taking more images -- even with Hubble or large ground-based telescopes -- won't do the job. But hope is not lost: there are several stellar occultations, where MU69 will pass in front of a distant star, that can be used to help measure the KBO's position and size. If you set up a telescope at the right place, and observe the right star at the right time, you'll see it briefly blink out. If you do this from even a couple of different places along the shadow path, you can get a good idea of the size and position of the body.

This is relatively common thing to do for a 'large' body like Pluto. MU69 is comparably tiny -- some 10,000 times fainter -- and this makes observing an occultation a real challenge. But, New Horizons has just one chance to fly past it, so in prep for the encounter, the mission and NASA decided to invest substantial effort into a large campaign to observe three occultations with MU69 during the summer of 2017.

I was lucky enough to be invited to join about 25 others in heading to South Africa to observe the occultation on the morning of June 3, 2017 (the first of three occultations). We brought 5000 pounds of telescopes with us, primarily a dozen 16-inch motorized Dobsonians, fitted with low-noise detectors. Our plan was to fly to Cape Town, get up to speed on the equipment, and then spread apart across the occultation path, in order to observe the event on the morning of the 3rd. Another group of 25 headed to Argentina to see the same event, essentially a backup in case of bad weather at one site.

Although I've analyzed a lot of occultation data from from the ground and New Horizons, this was my first* occultation-chasing trip. This trip had a combination of professional astronomers (students, postdocs, faculty, etc.) and some very advanced amateurs, and we all learned from each other. It's an amazing world where we get to do these sorts of projects while traipsing past sage brush and springbok, and see the effects several years later in our new knowledge of the Kuiper belt.

As of early July, the data taken in June were still being analyzed. This particular occultation is a lot more complex than a Pluto occultation: smaller target, many more chords, and low SNR. [Update: Check out the NASA press release on the occultation results!]

Many thanks to the organizers for bringing me on board, and for everyone else for putting up with me sticking a camera in their face!

* I attempted to observe a Pluto occultation from Sutherland with Amanda Sickafoose, but we were blizzarded out and were eating lamb shank in town by the time of the event. And, Trina Ruhland reminded me that I observed an asteroid occultation with her and her dad -- my thesis advisor, John Bally -- at their rooftop observatory in Colorado.

A few other pages worth reading: