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Chasing a Stellar Occultation in Colombia, August 2018

Also see my images from the 2017 occultation trip to South Africa!

NASA's New Horizons mission launched in 2006, and flew plast Pluto in 2015. Now with Pluto in the rear-view mirror, the science team is planning a flyby with an even smaller, even more distant body: the Kuiper belt object 2014 MU69 (aka Ultima Thule).

MU69 is the furthest solar system object discovered. But even with Hubble, it's extraordinarily difficult to get a good handle on its size, shape, or even position. With the flyby coming up in 5 months, we really need more data to plan the encounter.

Although Hubble isn't capable of doing the job itself, there is one way that we can do this study which is to watch an eclipse of a distant star. When MU69 moves in front of the star, the starlight gets blocked out, just like the solar eclipse that went acros the US in 2017. By measuring the time at which the star blinks out and then back on, you can measure the size and position of the asteroid. By doing this from a bunch of different places on Earth, you can actually map out the shape of MU69, as its shadow passes across the earth -- kind of like how the Moon's shadow moved across the US during the solar eclipse.

The New Horizons mission used this technique -- a stellar occulation -- to study MU69 during the summer of 2017. During the summer of 2018, there was one final occultation predicted to occur, on the night of August 3, 2018.

The path for this event passed roughly over Senegal and Colombia. With NASA's support, the mission sent a group of about 25 US-based astronomers to Senegal, and six to Colombia. Both countries have some clouds during the summer season, but the idea was to increase the odds by spreading ourselves geographically. I was assigned to the Colombia team.

The six of us flew to Bogota, meeting up on July 29, 2018. That gave us a week on the ground to set up for a 1.5-second long observation. Here are some photos from our trip. Many thanks to the organizers for inviting me to come along!

As of late August the results are still being analyzed, but some preliminary info is in a press release: New Horizons Team Reports Initial Success in Observing Ultima Thule.