“Everything we know about Pluto comes from studying it from billions of miles away,” said planetary scientist Alan Stern of the Southwest Research Institute, the mission’s principal investigator. “But the lesson of planetary science is that when we see things up close, our ideas from afar are often overturned.”
So what is the current state of Pluto science and how might things look different in one year?
Pluto is located far beyond all the outer planets, roughly 4.5 billion miles from Earth. Out there, sunlight is about 1,000 times fainter than on our own planet, and Pluto’s surface temperature is a chilly -380 degrees Fahrenheit. Like Uranus, Pluto rotates on its axis like a knocked over top, so that its north pole is at about the same place that other planets’ equators are. No one is sure exactly why this is, but some scientists suspect a major impact by a large space rock billions of years ago could have tipped the dwarf planet over.
Pluto has a radius of 733 miles, making it roughly two-thirds the size of our moon. It is the second-largest known object in the Kuiper belt, a collection of small frozen bodies beyond the orbit of Neptune. Its surface is almost entirely nitrogen ice and it has an extremely thin atmosphere of nitrogen, methane, and carbon dioxide. This faint envelope of gas has a pressure more than 10,000 times less than surface pressure on Earth.
Beyond these basic facts, there is still a great deal we don’t know about Pluto, including what it really looks like. Think about it: We have close-up shots of pretty much every other large body in the solar system but the best we’ve got for Pluto is a few blurry pixels from Hubble. Scientists have managed to map out general dark and light areas on Pluto’s surface but the finer details remain terra incognita.
Starting in January 2015, New Horizons will be passing what Stern calls the BTH (better than Hubble) line. The spacecraft will start returning images of the frozen dwarf planet that look better than anything we’ve ever seen before. This is when Stern suspects researchers might start getting surprises about the dwarf planet. Craters and mountains are some of the first things New Horizons could see, though it may also discover new moons.
Just prior to its Pluto encounter, New Horizons will be watching the dwarf planet rotate on its axis, spinning around every 6.4 Earth days. This will allow it to map most of the surface at high enough resolution to pick out features approximately 25 miles across, or roughly what you could see on the moon’s surface with a good pair of binoculars. The probe might see large impact craters or a network of geological fractures supporting the hypothesis that a large object hit Pluto in the past.
As the spacecraft swoops down over the surface at its closest approach, it will map one side of the planet down to a resolution of about 1,000 feet, with the best imagery reaching down to 230 feet. In image of New York City at 230-foot resolution, you’d be able to see streets, wharfs, buildings, and even count the ponds in Central Park. The motion of the probe as it passes over the surface will allow scientists to see features from slightly different angles, giving them the ability to create stereo 3-D images and infer heights.
The point of closest encounter is planned to take New Horizons over an area of Pluto with the widest variety of different features. Because of the regularity of orbital mechanics, the science team was able to choose this precise location extremely far in advance of arrival, maximizing their chance of seeing something interesting. As it flies over the dwarf planet, the probe will also take the temperature of the surface, sample the composition of Pluto’s atmosphere, and bounce radio waves off its surface, which will tell researchers about underground features.
What exactly will New Horizons find? Nobody can say for sure but one of the most interesting possibilities would be the discovery of a faint ring system around the dwarf planet. It’s the gas and ice giants such as Saturn and Neptune that are famous for their rings. But scientists speculate that an asteroid impact could kick up a spray of debris on Pluto, which would settle in orbit as a thin ring and eventually dissipate over millions of years. Such events could have happened many times over the course of the solar system’s history, and it’s possible that New Horizons’ visit will coincide with one of these intermittent ringed eras.
New Horizons will make detailed maps of Pluto’s main moon Charon, which orbits close to the dwarf planet. The probe won’t pass as close to Pluto’s other moons but should be able to photograph some of their features as well. As the probe zooms away from Pluto, it will turn and try to get a picture of the dwarf planet’s night side bathed in reflected light from Charon. Because Charon is far more reflective than our own moon, it provides about the same light at night as a full moon on Earth, even though the sunlight out there is so dim. Glare from the sun might make this maneuver tricky, but the team is hopeful that they will pull it off.
“If it works, it’ll be spectacular,” said Stern. In addition to providing a one-of-a-kind photograph, the maneuver will give scientists information about frost deposits on Pluto and the percentage of the atmosphere that freezes out at night.
New Horizon’s Pluto visit will transform the science of this small body in a matter of weeks, and it will likely take a long time before all of the data it provides will be unpacked. The only thing that would truly surprise the science team at this point would be if they find no surprises on Pluto, said Stern. It’s a safe bet to assume the probe probably won’t be definitively answering scientific questions so much as raising interesting new problems and providing researchers with many decades of mysteries.
In that sense, New Horizons harkens back to an earlier era of planetary exploration, when the first probes swung past Mercury, Venus, and Mars in the 1960s, giving scientists their first up-close encounters with other worlds. This process continued to the outer planets with the twin Voyager probes. Because New Horizons is the first probe to visit Pluto, it represents the “final bookend in the initial reconnaissance of our solar system,” said Stern.
As it leaves the Pluto system, New Horizons will burn its rockets and head toward a new destination. The team plans to send it to another Kuiper belt object, though exactly which one has not yet been decided. Hubble is right now searching for candidates, giving the mission a whole new world to observe and learn from.
source: wired.com By Adam Mann