Back in June 2015 our member Jacquie Milner spoke to MBO about “An Introduction to Observing Occultations” and in that presentation mentioned that she was participating in a ground based campaign to observe the occultation of a star by Pluto to characterise its atmosphere. 7 months on from that and there is now a paper from that work published on which she is a co-author!

Jacquie writes:

There was an international campaign to observe an occultation of a star by Pluto two weeks before New Horizons flew past Pluto on 29 June 2015. This was important to see how Pluto’s atmosphere looked from Earth at more or less the same time that New Horizons would be seeing it for comparison, and also to get some idea what might be happening there just before the spacecraft arrived. The path of the occultation was over New Zealand and Tasmania, and professional astronomers from around the world came down to our region to record this event. Amateur astronomers who regularly observed occultations were also observing and their results were combined with professional efforts to provide the result in the paper recently published below. Basically Pluto’s atmosphere is not collapsing as some thought it might, from it moving away from the Sun in its orbit and cooling down, but the occultation result shows it is expanding. Here in Melbourne I just caught the top 15% of the atmosphere, and the lead astronomer on the paper told me that my resulting light curve, while not detailed due to my relative small 20cm telescope, still fits well within their model.

It’s been a big thrill to be part of the campaign and to be able to provide useful data that supports the final result. Astronomy is one of the few areas of science where amateurs can work closely with professionals and produce real science and I encourage anyone who thinks that sounds like a good idea to make the leap and get involved in the area of astronomy of their choice, be it variable stars, planet imaging, asteroid photometry or astrometry, supernova searching, comet searching, exoplanets, meteors or…whatever it is, just start! This was a 10 year journey for me and while it’s not the first occultation paper I’ve contributed to it’s the most important one so far. I hope there will be more in the future, too!

The preprint of the paper is available on the arxiv.org preprint server under the title “Pluto’s atmosphere from the 29 June 2015 ground-based stellar occultation at the time of the New Horizons flyby“.