On July 14, NASA’s New Horizons probe will fly by Pluto on its way to the Kuiper Belt in the outer solar system, giving scientists the first up-close look at the dwarf planet. Charles Gammie, a University of Illinois professor of astronomy and physics, talked with News Bureau physical sciences editor Liz Ahlberg about Pluto’s close encounter.
Why all the excitement over seeing Pluto close up? What unanswered questions about Pluto or the solar system could New Horizons answer?
Pluto is the last of the original nine planets to be explored by NASA. It's small, cold and far away – about 40 times further from the sun than the Earth – so it's hard to study from the ground. Even in the mighty Hubble Space Telescope, Pluto is just a tiny blob a couple of pixels across.
We know that Pluto is about two-thirds the size of the Earth's moon. We know that it has at least five moons of its own, one of them not much smaller than Pluto itself. We know it's really, really cold – much colder than Antarctica in the dead of winter. We also know that Pluto has a low density, and thus is likely made from a combination of rock and ice. But other than that, we don't know much. It's completely unexplored territory. Does Pluto have more moons? Does it have rings? Volcanoes? Craters? Dunes? What sort of atmosphere does Pluto have? What is its surface like?
Pluto is also the gateway to a region of the outer solar system called the Kuiper Belt. Pluto and its sibling Kuiper Belt objects are solid, icy bodies, unlike anything in the inner solar system. Kuiper Belt objects are likely to be relatively pristine planetary building blocks left over from the formation of the solar system. So if we can understand more about them, then we can understand more about how our solar system formed and how other planetary systems formed.
With so much to learn, why can’t the probe slow down and study Pluto more? Must it be a passing look?
New Horizons is one of the fastest spacecraft ever launched, moving at about 10 miles per second. It would have had to carry a lot of rocket fuel to slow it down, and that would have made the mission impossibly expensive.
What kinds of information can we get from such a short encounter?
The flyby will produce all kinds of data from the mission's seven instruments.
To the general public, the most interesting results will come from the camera, which will take high-resolution images of a portion of Pluto's surface. Those images will be stored onboard the spacecraft and transmitted back to Earth after the encounter. That will take a long time, because the available bandwidth is much less than an old dial-up modem.
Some of the other instruments will give us information about how Pluto looks in light that is invisible to the human eye, but which carries information about the composition of the atmosphere and the surface of Pluto and its moons. Others will measure the properties of particles that hit the spacecraft, including tiny grains of dust produced by collisions between objects in the outer solar system.
Are there any plans to focus a future mission on Pluto and its moons?
I'm not aware of any planned missions to Pluto. If New Horizons finds something really interesting, then you can bet that there will be proposals. NASA has quite a few other interesting missions coming up, though. Next year, for example, NASA will launch a mission to sample material from an asteroid and return it to Earth. And next summer, the Juno spacecraft will begin investigating Jupiter's atmosphere.
Even though it’s been downgraded to a dwarf planet, why do you think there is such fascination surrounding Pluto?
We're reaching the beginning of the end of the exploration of the solar system.
So it's natural that the few completely unmapped places that are left hold special fascination, just as the north and south poles did for explorers in the 19th and early 20th centuries.