Dwarf Planet Mysteries Beckon To New Horizons
September 4, 2011

Dwarf Planet Mysteries Beckon To New Horizons


At this very moment one of the fastest spacecraft ever launched -- NASA's New Horizons -- is hurtling through the void at nearly one million miles per day.  Launched in 2006, it has been in flight longer than some missions last, and still has four more years of travel to go.

New Horizons headed for the lonely world of Pluto on the outer edge of the solar system.

Although astronomers now call Pluto a dwarf planet, "it's actually a large place, about 5,000 miles around at the equator," says Alan Stern, principal investigator for the mission. "And it's never been explored."

Indeed, no spacecraft has ever visited Pluto or any dwarf planet(1).

"This is a whole new class of worlds," says Stern. "To understand the solar system, we need to understand worlds like Pluto."

Pluto is a resident of the Kuiper Belt, a vast region beyond the orbit of Neptune.  Stern believes "the Kuiper Belt contains a thousand dwarf planets or more — a whole zoo of them! Dwarf planets are, in fact, the most numerous class of planets in the solar system, and probably in the whole universe."

Pluto is a world of mysteries. For one thing, Stern wonders, what are the molasses-colored patches on Pluto´s surface seen by the Hubble Space Telescope? Some scientists think they could be deposits of primordial organic matter.  "New Horizon's spectrometers will help us identify the kinds of organic molecules on Pluto. We expect to find something pretty interesting."

Hubble recently contributed more intrigue by spotting a new moon circling Pluto -- bringing the total to four.  Composite Hubble images of Pluto now resemble a miniature planetary system.  New Horizons will hunt for even more moons as it approaches the dwarf planet.

The probe is primed for detective work -- equipped with instruments capable of "knocking the socks off anything Voyager carried." In addition to state of the art spectrometers, New Horizons wields one of the largest and highest resolution interplanetary telescopes ever flown. It's called LORRI, short for Long-Range Reconnaissance Imager.

"At closest approach to Pluto — about 10,000 km up — LORRI can resolve details almost as well as a spy camera. The view will be incredible. If we flew this instrument over Earth at that altitude, we could see individual buildings and their shapes."

What will we see on Pluto? Some researchers say we could spot icy geysers(2). Some say we could see those surface deposits of organic material. Stern says simply, "There could be all kinds of surprises! It's a first exploration of a new kind of planet."

Heading far from home, "New Horizons is like Noah's Ark — our ship has two of everything, for backup," says Stern. "Two heaters, two computer systems, two of everything except the scientific instruments. And even those have capabilities to back each other up."

When New Horizons reaches Pluto it will have traveled 9 ½ years — longer than any spacecraft has ever flown to reach its main target. To save power and reduce wear and tear, it hibernates(3) much of the time. But all systems will be ready to spring into action upon arrival in 2015.

Mark your calendar.

Another strange thing about Pluto: Its sky collapses once a year. Around the start of winter each Pluto year (248 Earth-years), it gets so cold on Pluto that the atmosphere freezes. The molecules crystallize when the temperature drops to around 32 K (-240 C), and the atmosphere falls to the ground as snow.

"This should occur again sometime in the next 30 years," says Stern. "Pluto is headed away from the sun and winter is coming. We're hoping to reach Pluto while the atmosphere is still thick."

New Horizons is primed to study the ice dwarf's atmosphere, if there still is one. Stern isn't really worried: "The most recent observations show no evidence of collapse. In fact the atmosphere seems to be getting thicker. Pluto's summer heat is lingering."


1. New Horizons is the just the fifth probe to travel interplanetary space so far from the sun. Voyager 1, Pioneer 10, and Pioneer 11 traveled this way as they exited the solar system after Jupiter and Saturn flybys. But only Voyager 2 visited Uranus and Neptune. And no spacecraft has ever visited Pluto. NASA's Dawn spacecraft is due to reach Ceres, a dwarf planet in the asteroid belt, in February 2015, so it could become the first spacecraft to visit a dwarf planet, if Dawn reaches Ceres before New Horizons reaches Pluto.

2. Geysers would be evidence for cryo-volcanism (i.e., volcanoes that spew icy cold material rather than hot magma) on Pluto's surface. During a 1989 Neptune flyby, Voyager 2 spotted dark streaks on Neptune's moon Triton that are thought to have been produced by geysers spewing dirty, frozen nitrogen particles. Pluto may exhibit something similar.

3. The spacecraft will "sleep" in electronic hibernation for much of the cruise to Pluto. Operators will turn off all but the most critical electronic systems and check in with the spacecraft once a year to check out the critical systems, calibrate the instruments and perform course corrections, if necessary. Between the in-depth checkouts, New Horizons will send back a beacon signal each week to give operators an instant read on spacecraft health. The entire spacecraft, drawing electricity from a single radioisotope thermoelectric generator, operates on less power than a pair of 100-watt household light bulbs.


Image Caption: Artist's concept of the New Horizons spacecraft as it approaches Pluto and its three moons in summer 2015. The craft's miniature cameras, radio science experiment, ultraviolet and infrared spectrometers and space plasma experiments would characterize the global geology and geomorphology of Pluto and large moon Charon, map their surface compositions and temperatures, and examine Pluto's atmosphere in detail. The spacecraft's most prominent design feature is a nearly 7-foot (2.1-meter) dish antenna, through which it will communicate with Earth from as far as 4.7 billion miles (7.5 billion kilometers) away. Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)


On the Net: