LAUREL, Maryland – The day before NASA’s New Horizons spacecraft approaches a frozen outpost nicknamed Ultima Thule 4.1 billion miles (6.6 billion kilometers) from Earth, the main facts about a city-sized object are: Scientists still eluded scientists on Sunday, when a ground group was preparing a stream of data and images that were supposed to expose the unknown world on the edge of the solar system.
Ultima Thule, officially called the 2014 MU69, no longer than 20 miles (30 kilometers) is a billion miles from Pluto, the last world visited by New Horizons. It is reddish in color, and scientists with surprising accuracy determined its location for an object discovered in 2014.
In addition, the appearance of Ultima Thule pushed to the imagination of scientists and space enthusiasts. This will change in a hurry, as soon as the photos taken with the black and white and color cameras of the spacecraft New Horizons begin to return to Earth on Tuesday and Wednesday.
“We don’t know anything about MU69,” said Alan Stern, principal investigator for the New Horizons at the Southwestern Research Institute. “In the history of space flight, we never came across a goal that we knew less about, and it's great that we are on the verge of learning a lot about it.
“Today I can’t tell you more than five facts about this,” Stern said at a press briefing on Sunday. “We know its orbit, we know its color, we know a little about its shape and its reflectivity. We can't even get a rotation period. I thought we would have it 10 weeks ago.
Although scientists knew that Ultima Thule would only reveal its secrets in the last few days — or hours — of flight, unanswered questions prompted members of the New Horizons team to tap into their creative abilities.
“Our team made small clay figures (guessing), this is how we think how it looks today, based on the information we have,” said Hal Weaver, a researcher at the New Horizons project at the Johns Hopkins Applied Physics Laboratory, where New Horizons was built and the home of the mission control center.
However, scientists believe that they are beginning to see some details.
Ultima Thule is just beginning to be recognized with the LORRI camera from New Horizons, which until now viewed the object as just a point of light – one pixel in the camera's field of view. This will change rapidly as the probe moves towards it at a speed of 32,000 miles per hour (14 kilometers per second).
The target width is now almost 2 pixels, but this is still not enough to determine its shape.
"How fast does it spin?" A few hours, tens of hours or days? said Weaver.
“There are some signs, some hints that maybe this is a fast rotator,” said Weaver. “The little that we were able to identify reveals that it can rotate rather quickly, but we are constantly discussing whether we believe in it or not.”
If Ultima Thule rotates relatively quickly, this will be good news for researchers who are looking forward to their first look at such a primitive world. The fast rotator will show most of its surface New Horizons during the flight.
Until now, one of the main mysteries in the approach to Ultima Thule was that New Horizons did not observe any light curve or brightness variation from the object.
Scientists expected to see how Ultima Tule dims and becomes brighter when he rotates, New Horizons did not detect any changes.
“When we entered and began to systematically observe it from mid-September to the present, we thought that we would get something called a light curve that allows us to see a change in the brightness of the Ultima Thule that tells us something about the form,” said Weaver.
“We systematically conducted these observations in the hope that we could transform these observations into a model of the Ultima Thule form, but each time we returned and made observations, they were completely flat.
“Thus, it is possible that the rotation can be directed at us, which is quite unusual … It can be anywhere in space — the pole of rotation — but pointing to us is an unusual circumstance,” says Weaver.
“So, perhaps, he is very elongated, that we think because of the stellar measurements of the eclipse,” he said, referring to the observations made when Ultima Thule briefly blocked the light of the background star, visible from Earth, which allowed scientists impose restrictions on its shape and size.
Kathy Olkin, deputy research associate at the Southwestern Research Institute, agreed.
“I think that, based on the results of the mixing, we saw a clear signature that it was either elongated or two lobes … I believe that we will not see something round,” said Olkin.
“I think we will see what we are looking at the object. This is one way to reconcile the fact that we do not see the light curve on this object. We do not see repeated changes in coverage. ”
Scientists believe that Ultima Thule is a relic of the early solar system 4.5 billion years ago, a type of object known as the “cold classic,” because it remained approximately in the same orbit where it was formed. The discoveries will open a new window on how all planetary systems are born and develop, said Jason Kalirai, head of the civilian space mission at APL.
“This is a fundamental breakthrough in science,” says Caliphay, an astrophysicist.
Weaver said that the New Year's meeting with Ultima Thule is an event that occurs once in a lifetime for most people in the New Horizons team because of the time it takes to prepare a space mission and move it from Earth to the Kuiper belt.
New horizons launched from Cape Canaveral on January 19, 2006, received gravitational assistance from Jupiter on February 28, 2007, and then reached Pluto on July 14, 2015. Weaver called Pluto the gatekeeper to the Kuiper belt, the ring of the ice of the primordial worlds, extending beyond the orbit of Neptune.
Pluto is the largest known object in the Kuiper belt, where scientists believe that short-period comets have arisen.
“There’s nothing more to do in books like this,” said Weaver.
“I don’t think I’ll survive when the next cold classic Kuiper Belt object meets, so we all look forward to this flight.” In this respect, this is the boundary of the science of the planet … As a civilization, we are entering this third zone of the solar system, which was not even open until the early 1990s. ”
Scientists brought sleeping bags, pillows, and even a tent to camp here at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, as New Horizons accelerates towards Ultima Thule, its next target after Pluto.
Alice Bowman, mission manager for the New Horizons, said she came to work at 3:00 am EST on Sunday to get the latest navigation update and help prepare a “knowledge update” to communicate with the spacecraft.
The update changed the synchronization of the sequence of images and data that will be collected during the flight, by just 2 seconds, but this is enough to require some adjustment to ensure that cameras and sensors get the best information during a single encounter with Ultima Thule,
“This last day was probably the busiest for us,” said Bowman.
"Anyway, we are here for research, and we will be happy to spend the night if this is what is needed," she said.
New Horizons is on its way with Ultima Thule, and on Sunday evening Bowman tweeted that the “knowledge update” was successfully received by the spacecraft after it took him 6 hours and 8 minutes to cross the distance from Earth at a speed of 186 000 miles per hour or 300,000 kilometers. per second.
In fact, the latest navigation updates from Ultima Thule photos taken with the LORRI camera aboard the spacecraft indicate that New Horizons is about 18 miles (30 kilometers) from the aiming point 2,200 miles (3,500 kilometers) from the object.
Not bad for a mission that has been on the launch pad for almost 13 years.
It is expected that no further space crew commands will arrive before the flight.
Purely as a result of astrodynamics, New Horizons will reach its closest point to Ultima Thule at 12:33 pm Eastern Time (0533 GMT) on Tuesday, New Year. Approximately four hours later, the spacecraft will suspend its observations in order to turn its 6.9-foot (2.1-meter) antenna to Earth to call home.
The giant 230-foot (70-meter) antenna part of the NASA Deep Space Network antenna near Madrid will receive signals in more than six hours at 10:29 EST (1529 GMT). But the best images — from Ultima Thule, spanning hundreds of pixels — will not appear on Earth until late Tuesday, and are expected to be published on Wednesday afternoon.
The black and white LORRI camera is programmed to take about 1500 shots during the flight. Other tools onboard New Horizons will receive color images, measure the composition of Ultima Thule and receive infrared data.
The flight command sequence is already being executed by the spacecraft. Because of the huge distance between Earth and Ultima Thule, scientists and engineers are ready for a meeting.
New Horizons already has instructions downloaded to his computer to cope with any last minute crashes and continue the data collection sequence.
“At this stage, navigation is almost complete,” said Mark Buie, a member of the New Horizons team at the Southwestern Research Institute. "From now on, it's party time."
The last shooting of the engine, in order to actually change the trajectory of the New Horizons, was completed on December 18, and it is no longer possible to make a course correction as fast flight approaches.
Bui led a team that watched Ultima Thule during a pair of star eclipses when the object passed between two stars and the Earth in July 2017 and August 2018.
These observations gave scientists an idea of the shape of Ultima Thule, which, as Bui suggested, was perhaps a form of peanuts, at least according to occlusion data. Some scientists believe that Ultima Thule may be a binary pair of objects, but Bui says that he ruled out this possibility based on the latest measurements of the eclipse in August.
“We just need to be patient and wait for the images to appear, and we will see more and more pixels,” said Bui.
Write to the author
Follow Steven Clark on Twitter: @ StephenClark1,