LAUREL, Maryland – A day before NASA's New Horizons spacecraft was closed at a outpost dubbed the Thule Ultima 4.1 billion miles (6.6 billion kilometers) from Earth, the basic facts about an object the size of the city continued to shy away from scientists on Sunday when the land team prepared to face a flood of data and imagery that should unmask the unexplored world on the border of the solar system.
Its length is no more than 20 miles (30 kilometers), Ultima Thule – officially named MU69 2014 – is one billion miles outside Pluto, the last world visited by New Horizons. The color is reddish, and scientists have determined its location with extraordinary precision for a newly discovered object in 2014.
In addition, Ultima Thule's appearance was revealed to the imagination of scientists and space enthusiasts. That will change in a hurry as images taken by black and white cameras and the colors of the New Horizons spacecraft begin to return to Earth on Tuesday and Wednesday.
"We know nothing about MU69," said Alan Stern, principal investigator of New Horizons of the Southwest Research Institute. "We have never, in the history of spaceflight, gone to targets we don't know enough, and it's amazing that we almost know a lot about this.
"Today, I can't tell you more than five facts about it," Stern said at a briefing with reporters on Sunday. "We know the orbit, we know the color, we know a little about its shape, and its reflectivity. We can't even get the rotation period. I think we will have it 10 weeks ago. "
While scientists know that Ultima Thule will only reveal her secrets in the last days – or hours – from flyby, questions that remain unanswered have prompted New Horizons team members to enter their creative side.
"Our team has made small clay numbers (guesses) here we think this looks like today based on the latest information we have," said Hal Weaver, New Horizons project scientist at Johns Hopkins University's Applied Physics Laboratory, where New Horizons built and home mission control center.
However, scientists think they are starting to see some details.
Ultima Thule has just begun to be completed by the LORRI New Horizons imaging camera, which so far has seen objects only as light points – one pixel in the field of view of the camera. That will change rapidly when the probe speed is in that direction at 32,000 mph (14 kilometers per second).
The target is now almost 2 pixels, but it's still not enough to complete the shape.
"How fast is it spinning? A few hours, tens of hours, or days? "Weaver said.
"There are several indications, some clues, that maybe this is a fast rotator," Weaver said. "Little can we tease that it might spin fast enough, but we've gone up and down on the team, whether we believe it or not."
If Ultima Thule rotates relatively quickly, it would be good news for researchers eagerly awaiting their first look at the primitive world. The fast rotator will show more of its surface to the new horizon during flyby.
One of the main mysteries so far in the approach to Ultima Thule is that the New Horizon has not observed light curves, or changes in brightness, from objects.
Scientists hope to see Ultima Thule dim and enlighten while playing, New Horizons has not detected a change.
"We thought when we entered and began to observe it systematically from mid-September until now that we would get something called a light curve, which allows us to see variations in the brightness of Ultima Thule that would tell us something about shapes," Weaver said.
"We systematically made these observations hoping to turn this observation into a Ultima Thule form model, but every time we came back and made the observation really flat.
"So, maybe the rotation might lead to us, which is a very unusual thing … It can be anywhere in space – rotational poles – but pointing towards us is an unusual situation," Weaver said.
"So it might be very elongated, which we think is due to the measurement of star occultation," he said, referring to observations made when Thule Ultima briefly blocked the background starlight seen from Earth, allowing scientists to limit its shape and size.
Cathy Olkin, deputy project scientist at Southwest Research Institute, agrees.
"I think, based on the occultation results, we see a clear signature that it is elongated or two lobes … I believe that we will not see anything round," Olkin said.
"I think what we will see is that we are looking for objects. That's one way to reconcile the fact that we don't see the light curve on this object. We don't see variations of light over and over again."
Scientists believe Ultima Thule is a relic of the early solar system 4.5 billion years ago, a type of object known as "cold classic" because it is in an orbit that is more or less the same as where it was formed. This discovery will open a new window on how all planetary systems are born and develop, said Jason Kalirai, executive for the area of civil space missions on APL.
"This is really the basis of breakthrough science," said Kalirai, an astrophysicist.
Weaver said the New Year meeting with Ultima Thule was a once-in-a-lifetime event for most people on the New Horizons team – because of the time needed to prepare for space missions and bring them from Earth to the Kuiper Belt.
New Horizons launched from Cape Canaveral on January 19, 2006, received gravitational assistance by Jupiter on February 28, 2007, then reached Pluto on July 14, 2015. Weaver called Pluto the gatekeeper to the Kuiper Belt, an ice-cold primordial ring that stretched beyond Neptune's orbit.
Pluto is the largest object known in the Kuiper Belt, where scientists think short-period comets originated.
"There is nothing else in the book to do things like this," Weaver said.
"I don't think I will live when the next cool classic Kuiper Belt Object is found, so we all look forward to this flyby. In that case, this is the border of planetary science … As civilizations, we step out into the third zone of the solar system that hasn't even discovered until the early 1990s. "
Scientists have brought sleeping bags, pillows, and even a tent to camp here at Johns Hopkins University's Applied Physics Laboratory in Laurel, Maryland, when New Horizons drove towards Ultima Thule – the next target after Pluto.
Alice Bowman, mission operations manager for New Horizons, said she started working at 3am. EST Sunday to get the latest navigation updates and help set up "knowledge updates" for uplinks to spacecraft.
The update changes the timing of the image and data to be collected during the flight in just 2 seconds, but that is enough to require some adjustments to ensure the camera and sensors get the best information during a one-shot meeting with Ultima Thule.
"This last day is probably the most intense for us," Bowman said.
"Whatever is needed, we are here for exploration and we like to spend the night if that is needed," he said.
New Horizons was right on track for its meeting with Ultima Thule, and Bowman tweeted late Sunday that "knowledge updates" were successfully received by the spacecraft after taking 6 hours and 8 minutes to cross the distance from Earth at 186,000 mph, or 300,000 kilometers per second.
In fact, the latest navigation updates from images of Ultima Thule captured by a LORRI camera on a spacecraft show that New Horizons is about 18 miles (30 kilometers) from its destination 2,200 miles (3,500 kilometers) from the object.
Not bad for a mission that was almost 13 years off the launch pad.
No further orders are expected to be sent to the spacecraft before flying.
Pure as a consequence of astrodynamics, New Horizons will reach its closest point with Ultima Thule at 12.33 am EST (0533 GMT) on Tuesday, New Year's Day. About four hours later, the spacecraft will temporarily stop its observations to change the antenna 6.9 feet (2.1 meters) to Earth to call home.
Parts of a 70-foot (70-meter) giant satellite dish from NASA's Deep Space Network near Madrid will receive signals more than six hours later at 10:29 EST (1529 GMT). But the best images – with Ultima Thule stretching hundreds of pixels – will not arrive on Earth until Tuesday night, and are expected to be released to the public Wednesday afternoon.
The black and white LORRI camera is programmed to take around 1,500 images during flyby. Other instruments above the new horizon will take color images, measure the composition of Ultima Thule, and retrieve infrared data.
The flyby command sequence has been run by a spacecraft. Because of the great distance between Earth and Ultima Thule, scientists and engineers faced off for the meeting.
New Horizons has instructions that have been loaded into the computer to handle last-minute interruptions and continue the sequence of data collection.
"At this point, the navigation effort was completed effectively," said Marc Buie, a member of the New Horizons team at the Southwest Research Institute. "From now on, it's time for a party."
The final driver's shot to completely change the New Horizons trajectory was completed on December 18, and there was no more chance to make a directional correction when flyby approached quickly.
Buie led a team that looked at Ultima Thule during a pair of stellar occultations when it passed between two stars and Earth in July 2017 and August 2018.
These observations gave scientists an idea of the shape of Ultima Thule, which Buie suggested might be a peanut shape, at least according to occult data. Some scientists believe Thule's Ultima could be a pair of binary objects, but Buie said he had ruled out that possibility, based on the latest occult measurements in August.
"We just have to be patient and wait for the image to come in, and we will see more pixels," Buie said.
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