New Horizons probe to Pluto has scientists 'drooling'

NASA's New Horizons spacecraft is on track to become the first probe to visit distant Pluto, capping a reconnaissance of the solar system that began more than 50 years ago.

• Pluto-bound New Horizons spacecraft resumes operations after glitch

The spacecraft is "very healthy; it has just happily taken away all the commands necessary to carry out the observations," Mark Holdridge, Pluto mission encounter manager, said on Friday.

The five-billion-kilometre journey to Pluto, an unexpectedly peach-hued world with contrasting dark and light regions across its face, has taken more than nine years.

For most of the voyage the equivalent of flying 120,477 times around Earth the probe hibernated, saving wear-and-tear on its systems and trimming ground control costs to help the mission meet its $720 million US budget.

But now it's sending back photos with more clarity and definition.

"It's just juicier and juicier, it's amazing," Hall Weaver, a New Horizons project scientist, said in a mission update that NASA released on Friday.

• New Horizons spacecraft shedding light on mysterious Pluto
• Pluto, Charon images reveal dwarf planets' colours, strange dark spot
• NASA's New Horizons navigator Frdric Pelletier guides Pluto probe

"The science team is just drooling over these pictures. If you look at the new pictures now, it's already five to six times better resolution than what we've been able to get before," Weaver said.

Clipping along at 14 km/second, New Horizons awoke in January to begin observations of Pluto and its primary moon, Charon, located beyond Neptune in the Kuiper Belt region, which was discovered in 1992.

Before then, Pluto was considered an odd, outlier ninth planet of the solar system, smaller than Earth's moon and out of place among the gas giants that occupy what was previously considered the outer solar system.

Six months after New Horizons launched and with more than 40 Kuiper Belt objects on the books, the International Astronomical Union made a controversial call to reclassify Pluto as a "dwarf planet."

Astronomers have since discovered about 2,000 more Kuiper Belt residents out of a population estimated at hundreds of thousands.

• Meet Pluto's smallest moons,Kerberosand Styx
• New Horizons spacecraft spots possible ice cap on Pluto
• How Dawn, New Horizons cross huge distances

Ironically, it was the discovery of the Kuiper Belt that provided the scientific motivation and money for a mission to Pluto. Scientists believe the Kuiper Belt holds fossils from the formation of the solar system 4.6 billion years ago.

New Horizons will conduct its science on the fly, much like NASA's Pioneer, Mariner and Voyager missions of the 1960s to the 1980s, when exploration of the solar system began. Built lean, New Horizons does not carry propellant for a braking burn to slow down and slip into orbit around Pluto.

A computer program to orchestrate every aspect of the spacecraft's pass by Pluto began on Tuesday, following a nail-biting computer crash that suspended science operations for three days. But it was resolved.

"So far it is looking really good, looks like we are converging and we are happy with this results," said Holdridge.

New Horizons is expected to come as close as 12,500 kilometres from Pluto at 7:49 a.m. ET onTuesday.