Supported by
New Horizons Approaches the Most Distant Object Ever Visited. ‘We Only Get One Shot.’
For people working on the flyby of Ultima Thule, it all comes down to a plan years in the making that must be executed some four billion miles away.
LAUREL, Md. — As NASA’s New Horizons spacecraft zips past a small, distant icy world early on New Year’s Day, at 12:33 a.m. Eastern time, there will still be a nagging question for people working on the mission: Did the spacecraft’s cameras get the shot?
New Horizons collected a wealth of fascinating pictures and data on Pluto when it flew by in 2015. Now it is set to speed past another object in the solar system’s mysterious Kuiper belt region, nicknamed Ultima Thule, which should yield clues about the early days of the solar system.
[How to follow the New Horizons flyby of Ultima Thule.]
Getting the flyby right at a speed of 31,500 miles per hour is a challenging task that has taken years of planning. Despite the best efforts, Ultima Thule remains almost a complete mystery to the New Horizons’ managers and everyone else less than a day before the flyby.
“We don’t know a thing about MU69,” said S. Alan Stern, the principal investigator for the mission, referring to 2014 MU69, Ultima Thule’s official designation here at the Johns Hopkins Applied Physics Laboratory, which is operating the mission. “We’ve never in the history of spaceflight gone to a target we knew less about. It’s remarkable that we are on the verge of learning a great deal about it.”
Getting the shot will require taking many pictures of empty space. That’s necessary to ensure that at least some of the photographs do include the target the scientists are aiming to study.
[Sign up to get reminders for space and astronomy events on your calendar.]
Imagine driving along the New Jersey Turnpike, hoping to take a picture of the Manhattan skyline. But you don’t get to look through the camera viewfinder. In fact, you have to decide days in advance when you’re going to press the shutter button. Worse, you’re not exactly sure where Manhattan is.
That essentially is the challenge faced by the New Horizons team. Except instead of Manhattan, New Horizons’ managers are trying to point their instruments at a 12- to 22-mile-wide world some four billion miles away.
At closest approach, New Horizons will take nearly 900 images at the highest resolution. Ultima Thule is expected to appear in a few.
In many ways, this flyby is more difficult than the one for Pluto. Ultima Thule is about one-100th the diameter of Pluto and far dimmer. The spacecraft is to come within 2,200 miles of Ultima Thule’s surface, less than a third of the distance of the spacecraft’s closest approach to Pluto.
While Pluto has been studied for decades, Ultima Thule was discovered only four and a half years ago by the Hubble Space Telescope, and none of the telescopes on Earth have been able to clearly spot it.
Still, the New Horizons team is confident that it has figured out where it will be.
“I think we're good,” said Marc W. Buie, an astronomer working to pin down Ultima Thule’s position. “I think we're better than good.”
In the last couple of years, there were several fortuitous times when Ultima Thule passed in front of a distant star, causing the starlight to vanish briefly, what astronomers call an occultation. That tells them that Ultima Thule was along the line of sight between Earth and the star.
Using the information from the occultations, the spacecraft navigators believe they have calculated the time of the nearest approach to Ultima Thule to within six or seven seconds, Dr. Buie said.
That is better than was possible for Pluto, even though astronomers have been studying Pluto for decades. “We had a lot of trouble with Pluto, believe it or not,” Dr. Buie said.
Those occultation observations also showed that the object is not a sphere, but rather elongated like a long potato or perhaps two bodies touching each other.
New Horizons itself was able to spot Ultima Thule beginning in August, although as no more than a speck of light until this weekend. As the spacecraft approached, scientists hoped to spot a rhythmic brightening and dimming of Ultima Thule, which would reveal how fast it is spinning. Instead, the brightness seems to have remained steady the whole time.
“It’s really puzzling, because we know the shape is irregular,” Dr. Stern said.
While the partial federal government shutdown has little direct effect on the flyby — it is considered an essential government activity, plus most of the people working on the mission are employees of the Johns Hopkins laboratory, not NASA — it has been a bureaucratic hassle.
The laboratory has to take over some communications responsibilities usually handled by NASA, and two members of the mission’s science team who work at the NASA Ames Research Center in California needed a special exemption to come to Maryland and take part.
Final tweaks to the instructions for the flyby choreography, adjusting the time of the closest approach by a couple of seconds, were sent on Sunday to New Horizons.
Now all anyone can do at this point is watch and wait.
Early on Monday, a science fair-like atmosphere prevailed as specialists from New Horizons presented overviews of the mission and science to friends and families who came to share in the excitement. They will celebrate the start of the new year at midnight and then the closest approach of the flyby 33 minutes later, but they will not know how New Horizons, which will be busy making its scientific observations, will be doing at that moment.
“We’re very confident in the spacecraft, and we’re very confident in the plan that we have for the exploration of Ultima,” said Dr. Stern, the principal investigator for the mission. “But I’d be kidding you if I didn’t tell you that we’re also on pins and needles to see out how this turns out. We only get one shot at it.”
Hours later, the spacecraft will turn back to Earth and send a 15-minute message that will confirm that the encounter occurred, but will not include any photographs or scientific data. If all goes well, that data — which takes six hours to reach Earth — will arrive at 10:28 a.m. on Tuesday.
Over the next couple of days, preliminary looks at the data, including what the scientists hope will be striking images of Ultima Thule, will be beamed back to Earth. Twenty months will pass before scientists have the full set of measurements. And they will be eagerly awaiting every bit of that stream.
“We are ready to science the heck out of Ultima Thule,” Dr. Stern said.
Kenneth Chang has been at The Times since 2000, writing about physics, geology, chemistry, and the planets. Before becoming a science writer, he was a graduate student whose research involved the control of chaos. @kchangnyt
Advertisement
Bagikan Berita Ini
0 Response to "New Horizons Approaches the Most Distant Object Ever Visited. ‘We Only Get One Shot.’ - The New York Times"
Post a Comment