From New Horizon’s position, 4.8bn kilometres from Earth, radio signals, travelling at the speed of light, take four and a half hours to reach the ground.
Not that the probe, which has been travelling toward Pluto for nine years, is spending much time relaying back pictures and data from its seven science instruments.
With its closest approach to Pluto slated for tomorrow afternoon, New Horizons is on auto-pilot, gathering as much scientific information as possible before its one-shot punch past Pluto and its entourage of five known moons. Data will be radioed back to Earth over the next 16 months.
“You have to really be into delayed gratification if you want to be on this mission,” said New Horizons lead scientist Alan Stern of the Southwest Research Institute in Boulder, Colorado.
The space craft, the size of a baby grand piano and weighing 454kg, does not carry the propellant needed to fire braking rockets so as to slow down and slip into orbit.
Nasa launched a fleet of initial reconnaissance missions between 1960 and 1977 to every planet in the solar system except Pluto.
However, after the 1992 discovery that the solar system had a heavily populated ‘backyard’ beyond Neptune, a region known as the Kuiper Belt, a band of scientists won their long crusade to send a probe to Pluto.
Just months after New Horizons launched, Pluto was formally removed from the solar system’s primary planets list and rebranded a dwarf planet. Pluto, and its icy Kuiper Belt, are believed to be relics of the formation of the solar system 4.6bn years ago.
The most recent image relayed from New Horizons, and released on Saturday, shows large, evenly spaced dark spots on the side of Pluto that permanently faces its primary moon, Charon. The spots are related to a dark belt that circles Pluto’s equatorial region.
“We’re seeing these crazy black-and-white patterns. We have no idea what those mean,” said New Horizons scientist John Spencer.
New Horizons will pass on the other side of Pluto, coming as close as 12,552km to the planet and traveling at 50,000kph.
From there, it will shoot deeper into the Kuiper Belt.