update 24-Jun-2017: SOFIA Arrives in New Zealand to Observe Southern Skies There are plans to fly SOFIA through another predicted occultation path on July 17. SOFIA is a huge (2.5 meter dia.) infrared telescope (1 ~ 250 um) with various cryogenic focal plane arrays that is flown above most of the water in Earth's atmosphere (YouTube). It sound like they will just use the visible light guide camera (behind the Nasmyth mirror?), rather than the infrared capability, but the portability is certainly handy. This mission might be "An Airplane Hunting for Shadows from the Kuiper Belt".

update 14-Jun-2017: non-committal blurb: https://www.nasa.gov/feature/new-horizons-team-digs-into-new-data-on-next-flyby-target

update 08-Jun-2017: There is also this blurb in Sky and Telescope's June 8 2017 article Observers Track New Horizons’ Next Target:

The Results are In (Sort of)

According to early reports gleaned by Sky & Telescope, June 3rd's effort couldn't have gone much better. Buie says that every team collected usable data, though some might have been partially impacted by clouds. "That is quite remarkable," he says, "and it took some heroics on the part of the South African teams." (Bad weather forced many of them to relocate.)

The stellar "shadow" cast by 2014 MU69 took about 11 minutes to sweep across Earth, so from any given location the star would disappear for no more than about 2 seconds. Since the cameras were making ½-second-long exposures, at most four frames will show the star missing. But even with such beefy telescopes, the expected signal-to-noise ratio (even in optimal conditions) won't be high.

So did anyone see the star disappear? Anja Genade (SAAO) reports good data but no disappearance with the 74-inch Radcliffe reflector in Sutherland. As for all those mobile teams, Buie isn't saying — at least just yet. Look for him to announce those results early next week.

update 03-Jun-2017: There is a cool image in this tweet from (at)NASANewHorizons:

@NASANewHorizons Jun 3

Clear skies and successful occultation obs in ARG and SA; now to dig into all the data! Credit:J.Jewell #mu69occ http://go.nasa.gov/2rOdJ3x

which suggests an occultation was successful, but I'm not sure of the definition of success in the tweet yet. Still looking for more info on this amazing group effort. There are two more similar occultations predicted for early July in AsteroidOccultations.com's News & Announcements for 2014 MU69, I hope we'll hear something more about this one before then.

The predicted time of the first of three occultations of +12 to +14 magnitude stars by asteroid 2014 MU69 has come and passed.

People have fanned out over South America and South Africa with telescopes with cameras and GPS clocks and are going to try to watch the shadow of a roughly magnitude +13 star cast by a rock in the KUIPER BELT pass over the Earth!

This is of course weather permitting, and early Twitter reports are already showing clear skies and images of the Omega Centauri star cluster. There is a Twitter hash tag for these events, #mu69occ. Here is a 500 millisecond exposure from a few days ago. The short exposure time is necessary to resolve small scale debris from the main occultation.

enter image description here

above: Omega Centari Star Cluster, 500 millisecond exposure. Tweeted by Alex Partker.

The goal is actually to look for shadows cast by even smaller debris, orbiting around the rock in the Kuiper belt. This is for New Horizons mission planning.

When will we hear at least a little news? Did anyone see a dip in a light curve at all? Something?

enter image description here

above: From AsteroidOccultations.com's News & Announcements for 2014 MU69

  • 2
    $\begingroup$ 2014MU69 is in the Kuyper Belt, not the Oort cloud... $\endgroup$
    – Hobbes
    Commented Jun 3, 2017 at 11:16
  • 3
    $\begingroup$ Ah, I get them mixed up. Every since they decided Pluto wasn't a planet, my whole world is turned upside down. $\endgroup$
    – uhoh
    Commented Jun 3, 2017 at 11:18
  • 1
    $\begingroup$ Well, there is at least plenty of data... Each team collected 5,400 half-second images of the occultation star. That's a lot of images to process. twitter.com/Alex_Parker/status/870887753021624320 $\endgroup$
    – uhoh
    Commented Jun 3, 2017 at 13:22
  • 1
    $\begingroup$ @Uwe if the asteroid is 40km wide, then the path will be about 40km wide. However, the uncertainty may be much larger, so the observers have spread out over a wider region, spaced at 8 to 15 km apart in the North-South direction. For this geometry it's just geometrical optics with parallel rays from infinity. $\endgroup$
    – uhoh
    Commented Jun 4, 2017 at 14:47
  • 1
    $\begingroup$ @Uwe that's really an interesting question, but a good answer is too long for a string of comments here. If you are interested, why not ask it as a separate question? $\endgroup$
    – uhoh
    Commented Jun 4, 2017 at 15:25

1 Answer 1


One of the scientists involved wrote a blog post for the Planetary Society dated June 16, 2017:

“What about the results? Did you see the occultation?” you ask. Everyone asks this. Right now, we don’t know yet. This was an extremely challenging occultation to observe. MU69 occulted a very dim star, which always makes the observation tough. On top of that, we need to combine data from 24 deployed sites, plus some fixed sites, that cover a wide range of conditions, including seeing and illumination. Therefore, the data analysis will take awhile. It is likely that only a couple of the telescopes actually observed the occultation. All of the data, however, will be useful for the New Horizons mission. All of us—astronomers and the general public—just need to wait until the New Horizons team finishes the analysis and announces the results. I am not a New Horizons team member, so I am eagerly awaiting the results like everyone else.

MU69 has three stellar occultations this summer—June 3rd, July 10th, and July 17th.

Update July 6th:

On July 5th (so before the second stellar occultation opportunity), the New Horizons team has shared a first look at the results:

Combined, the pre-positioned mobile telescopes captured more than 100,000 images of the occultation star that can be used to assess the environment around this Kuiper Belt object (KBO). While MU69 itself eluded direct detection, the June 3 data provided valuable and unexpected insights that have already helped New Horizons.

“These data show that MU69 might not be as dark or as large as some expected,” said occultation team leader Marc Buie, a New Horizons science team member from Southwest Research Institute (SwRI) in Boulder, Colorado.

Initial estimates of MU69’s diameter, based primarily on data taken by the Hubble Space Telescope since the KBO’s discovery in 2014, fall in the 12-25-mile (20-40-kilometer) range – though data from this summer’s ground-based occultation observations might imply it’s at or even below the smallest sizes expected before the June 3 occultation.

Besides MU69’s size, the readings offer details on other aspects of the Kuiper Belt object.

“These results are telling us something really interesting,” said New Horizons Principal Investigator Alan Stern, of SwRI. “The fact that we accomplished the occultation observations from every planned observing site but didn’t detect the object itself likely means that either MU69 is highly reflective and smaller than some expected, or it may be a binary or even a swarm of smaller bodies left from the time when the planets in our solar system formed.”

Update July 20

At least 5 telescopes have captured the occultation during the July 17 observation campaign (animated GIF):

Analysis of the data is still ongoing.

  • $\begingroup$ Whew, OK this is 'good' news, thank you for the update and for keeping track. It sounds like the success is that they did not observe any occultation whatsoever, and this is an extremely important result because it means whatever New Horizons is approaching, it's not what was originally expected; either smaller in diameter (and brighter) so it was able to squeeze between two sites, or made of multiple smaller bodies which each 'squoze' between sites. Looking forward to the next observations! $\endgroup$
    – uhoh
    Commented Jul 9, 2017 at 7:57
  • $\begingroup$ fyi I've just asked NASA's flying telescope SOFIA — How to find flight plans and real time location? $\endgroup$
    – uhoh
    Commented Jul 9, 2017 at 10:10
  • $\begingroup$ Third time's a charm! They got it - take a look at NASA and Science News. The SN article has a GIF - can I ask you to include it - it's pretty spectacular! If not I'll post it as a supplemental answer. $\endgroup$
    – uhoh
    Commented Jul 21, 2017 at 11:42

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