By Irene Klotz
LAUREL, Md. (Reuters) – Mysterious Pluto looms large & turns out to be larger than expected as NASAâ€™s New Horizons spacecraft wraps up a nearly decade-long journey, with a close flyby on track for Tuesday, scientists said on Monday.
The nuclear-powered probe was in position to pass dead center of a 60-by-90-mile (97-by-145 km) target zone between the orbits of Pluto & its primary moon, Charon, at 7:49 a.m. EDT on Tuesday, said managers at New Horizons mission control center, located at the Johns Hopkins University Applied Physics Laboratory outside of Baltimore.
p> After a journey of 3 billion miles (4.88 billion km), threading that needle is like golfer in New York hitting a hole-in-one in Los Angeles, project manager Glen Fountain told reporters.
During the 30-minute dash past Pluto & its entourage of five moons, New Horizons will perform a carefully choreographed series of maneuvers to position its cameras & science instruments for hundreds of observations.
Already, scientists have learned that Pluto, once considered the ninth & outermost planet of the solar system, is bigger than thought, with a diameter of approximately 1,473 miles (2,370 km), some 50 miles (80 km) wider than previous predictions. Pluto is now officially bigger than Eris, one of hundreds of thousands of mini-planets & comet-like objects circling beyond Neptune in a region called the Kuiper Belt. The discovery of this region in 1992 prompted the official reclassification of Pluto from planet to "dwarf planet."
Pluto is pictured in this July 7, 2015 handout image from New Horizons Long Range Reconnaissance Ima …
Size matters, even for dwarf planets. The notch up in girth means that Pluto consists of slightly more ice & a little less rock than predicted, an significant detail for scientists piecing together the story of how it & the rest of the solar system formed.
â€œThe Pluto system is a fossil remnant of the beginnings of our solar system,â€ said NASA chief scientist John Grunsfeld. "Weâ€™re going to learn more approximately that."
Plutoâ€™s diameter moreover affects the size of its atmosphere, which New Horizons has learned is bleeding off into space at a faster rate than expected.
Most of New Horizonsâ€™ data will be stored on the spacecraft & transmitted back to Earth after the probe passes beyond the Pluto system. Flight controllers expect to receive just a short message from New Horizons around 9 p.m. on Tuesday that it survived the Pluto encounter.
Lead scientist Alan Stern said there was a one-in-10,000 chance that a debris strike could destroy New Horizons as it nears Pluto.
â€œWeâ€™re flying into the unknown," Stern said. "I donâ€™t lose sleep over this, yet fact is, tomorrow evening is going to be a little bit of drama.â€
(Editing by Lisa Von Ahn)