New Horizons Just Hours Away From Closest Approach to "Enchanting" Pluto

NASA’s New Horizons spacecraft is closing in on Pluto and its five moons after a nine-and-a-half year journey.  Alan Stern, principal investigator (PI) for the mission, refers it as the “Pluto system,” an “enchanting” place. Closest approach to Pluto is at 7:50 am Eastern Daylight Time (EDT) tomorrow, July 14, but it will not be until 8:53 pm EDT that scientists will know that the encounter took place as planned.

NASA is holding a series of media briefings today, tomorrow and Wednesday covering the encounter.   At this morning’s briefing, Stern and deputy PI Cathy Olkin, both from the Southwest Research Institute (SwRI), discussed what they have learned about Pluto in recent days, though Stern cautioned that time is needed to fully analyze the data before making final conclusions:  “Science on the fly is often wrong,” he warned, and they will stick to the facts for now. 

Pluto and New Horizons are 3 billion miles (4.9 billion kilometers) from Earth and it takes a signal 4.5 hours to travel that far (meaning a 9-hour two-way signal travel time).   That plus limited data rates mean that it will take a long time to get back all the data the spacecraft is collecting — 16 months, Olkin said.  For now, the focus is high priority data, including imagery.  Right now, they are prioritizing black and white imagery from the LORRI instrument that requires many fewer bits than color imagery.  That is why so many of the images publicized in recent days have been in black and white, but Olkin promised new color images tomorrow.

That will be from data taken before the closest encounter, however.   The spacecraft’s instruments and antenna will be pointed toward Pluto and its moon Charon during the flyby tomorrow, which begins at 7:50 am EDT, so it cannot send data back to Earth.  Not until the data are collected and the spacecraft is past Pluto will it turn to face Earth so the antenna can transmit data home.  At that moment, it will be only an engineering signal, not scientific data.  

NASA will broadcast media briefings tomorrow from 7:30-8:00 am EDT, 8:00-9:00 am EDT, 8:30-9:15 pm EDT and 9:30-10:30 pm EDT to discuss the mission’s progress.  A key one will be the 8:30-9:15 pm briefing during which time the signal should be received that the spacecraft got through the encounter OK.

One concern is that there may be debris around Pluto that could interfere with the spacecraft as it flies past, but Stern downplayed that today.  He said the area of greatest concern is as the spacecraft crosses Pluto’s equatorial plane, but it is not a big worry.   Stern said there is only a 1 in 10,000th chance of loss of mission because of a debris interaction and he is not going to lose any sleep over it.

Stern called the data from New Horizons a “gift for the ages.”  Recent “mouth-watering” scientific findings are that:

• Pluto is bigger than expected, 1,185 kilometers in radius (plus or minus 10 kilometers), meaning that it is less dense than scientists thought;
• Pluto’s polar cap is, indeed, made of ice — methane ice and nitrogen ice; and
• Nitrogen escaping from Pluto’s atmosphere was detected 5 days out, much earlier than expected.

He and Olkin were reluctant to discuss the implications of these findings yet, but the data appear tantalizing.

Stern often calls New Horizons a lesson in delayed gratification because it took so long to reach Pluto.  Unlike other deep space missions, including ESA’s Rosetta mission that took even longer to reach its destination, there has been little for New Horizons to study along its journey.  It has not passed anything of scientific interest for the past 8 years.   Stern said he and the New Horizons team feel like they’ve been on an escalator for all that time and now have stepped onto a supersonic transport, exclaiming at one point: “Fasten your seatbelts, New Horizons has arrived at the Pluto system!”