The telescopes took more than 100,000 images of the star, waiting for MU69 to pass in front of it.
But the star never vanished. The scientists had completely missed the shadow.
“I was physically and emotionally exhausted, psychically damaged,” Dr. Buie said.
In late June and early July, Hubble made additional observations of MU69 that refined the orbit.
The July 10 occultation track mostly passed over the southern Pacific. This time, the New Horizons scientists took off from Christchurch, New Zealand, in Sofia, a NASA 747 equipped with an 8.2-foot-diameter telescope. They headed north, toward Fiji, to intercept the shadow and returned 10 hours later.
Again, the star never disappeared. They had missed the opportunity again.
They immediately headed back to Argentina for one more try.
S. Alan Stern, the principal investigator of New Horizons, said he was confident, with the additional Hubble measurements, that they would capture the vanishing of a star this time. But mission managers also always worry about the so-called unknown unknowns. Perhaps something unanticipated in the Hubble data was deceiving them about MU69’s position.
The July 17 shadow was predicted to pass over Comodoro Rivadavia, a city along the Atlantic coast of South America. Comodoro’s nickname is “the capital of wind.” In the middle of winter, the weather was also cold.
“It was a pretty intense event,” Dr. Stern said. “Your telescopes were shaking.”
At several observing sites, tractor-trailer trucks served as windbreaks, as did contraptions made of poles and canvas.
A highway was shut for a couple of hours so that the headlights of cars and trucks would not spoil the observations.
The skies were clear, and the time of the shadow, 12:50 a.m., passed.
A few hours later, Amanda M. Zangari, one of the Southwest Research Institute scientists on the New Horizons team, was staring blearily at her laptop analyzing the data from one of the telescopes.
In her exhaustion, the data was not making sense to her. Then it hit her. “I realized it didn’t make any sense, because the occultation star was missing,” she said.
This is what she saw:
Five telescopes, it turned out, had detected the star’s vanishing for up to about a second.
The success also confirmed that the Sofia observations a week earlier had barely missed the occultation and were close enough to the shadow to be useful. Preliminary analysis found no signs of dimming, indicating there are no clouds of debris in the neighborhood of MU69 that could imperil New Horizons.
The five blinks established the odd shape. If it is one skinny potato, MU69 is no more than 20 miles long. If it is two spheres circling each other, each is about nine to 12 miles wide.
Many Kuiper belt objects in this region are binaries, although most are considerably larger than MU69. If one this small can be a binary, that may change the understanding of how Kuiper belt objects formed.
Mission managers can still tweak the flyby time of the New Horizons spacecraft by a couple of hours. Ideally, they want to view the broad side of MU69 and optimize geometry of tracking stations on Earth during the flyby.
“We’re working through all those mathematical issues,” Dr. Stern said.
Another occultation is possible in August next year. The scientists have not decided whether they will chase the shadow one more time.