|Update (March 27, 2018): A new analysis shows that the suspected moon isn't actually there. Marc Buie (Southwest Research Institute) had used Gaia data to pin down the positions of stars in images of the 2014 MU69 occultation. Turns out that some subtle bugs in the analysis had tweaked the stars' positions just enough to make it look like a background star had briefly been blocked by a moon of 2014 MU69, when instead it was actually 2014 MU69 itself that had done the blocking. Read more details from Emily Lakdawalla at The Planetary Society.|
New analysis from the New Horizons team suggests that the spacecraft’s next target, a Kuiper Belt object known as 2014 MU69, might have a moon. The object was already thought to be a binary, so this brings the party members to three. The preliminary results were presented at the meeting of the American Geophysical Union in New Orleans.
New Horizons will fly 3,500 kilometers from this little rock in the outer solar system on January 1, 2019. Although it’ll catch the first, better-than-Hubble glimpse in early September 2018, the initial views won’t resolve the object — we’ll see it as a steadily brightening pixel via the spacecraft’s long-range camera. It isn’t until after the flyby that we’ll begin to see stunning, high-resolution images depicting its surface. (The immense distance — 6.5 billion kilometers from Earth — means that the data will keep trickling in through 2019 and most of 2020, but the first views will come in about a week after the flyby.)
In preparation for the flyby, the team deployed observers across the globe to monitor occultations on June 3rd, July 10th, and July 17th. On these three dates, 2014 MU69 passed in front of three different stars. Although the object itself was invisible, the stars, and their disappearance, was observable — as long as the observers were in the right location.
The team had no luck on the first occultation. The second event resulted in a small blip, but the team wasn’t sure what it signified — the star’s short blink-out didn’t occur where it was predicted to be. The third event was where the team struck gold: five of 24 observers caught the star blinking off and on again. Subsequent analysis showed that the shape of the object was definitely not spherical. It could be potato-shaped, but Marc Buie (Southwest Research Institute) prefers a binary scenario, where two large objects, 15-20 kilometeres in diameter, orbit each other so closely they might even be touching.
But now the plot thickens: that blip that the team recorded on June 10th might not be nothing after all. The team conducted new analysis that includes observations of 2014 MU69’s orbit using data from the sharp-eyed Gaia mission. It turns out that the Kuiper Belt object might have a third member of its party: a much smaller moon.
“This is probably a sign that the object itself was not a collisional fragment. We think it was made like this,” Buie said in a press conference. “We really are going to see something that dates back to the birth of the solar system.”
However, Buie cautioned that the three-body explanation isn’t yet a final result.
“The story could change next week . . . we’ve been changing the story a lot since July 17th,” Buie added. “But today, right here, right now, we think this is our best explanation for everything we’ve seen.”
If you’ve ever wondered why we’re sending a spacecraft to study diminutive rocks in the frigid, outer reaches of the solar system, this is why: to explore objects nearly untouched by time. MU69 2014, however many pieces it may consist of, will shed light on the accretionary, planet-forming environment of our system’s early years.
The mission won't end with MU69 and its potential companions: In addition to sending back data, New Horizons will continue observing about 30 other Kuiper Belt objects from a larger distance throughout its extended mission, which goes through 2021. The mission could even be extended again, as its fuel could last until the mid-2030s.
For now, here's what we have to look forward to in the coming months: