Philosophical Society of Washington

Minutes of the 2362nd Meeting

At the Cosmos Club, Washington, DC
April 15, 2016

President Larry Millstein called the 2362nd meeting of the Society to order at 8:04 p.m.  He announced the order of business and welcomed new members.  The minutes of the previous meeting were read and approved.  President Millstein summarized the proceedings of the 26th meeting of the Society in 1872.  President Millstein then introduced the speaker for the evening, Alan Stern, Principal Scientist for the New Horizons Mission, Vice President for Research at the Southwest Research Institute, and CEO of Uwingu and The Golden Spike Company.  His lecture was titled “The Exploration of Pluto”.


Dr. Stern began by explaining that New Horizons was the fastest spacecraft ever launched, flown 3 billion miles and 3000 days to the farthest world humans have ever explored.  The United States has been first to every planet in our solar system, beginning with the flyby of Venus by Mariner 2 in 1962.  The surveying of Pluto by New Horizons in 2015 completed this 53 year project and began a new phase in our exploration of the solar system.

New Horizons cost approximately 700 million dollars over its 15 year initial mission.  Dr. Stern observed that such an enormous investment requires demonstrating to the scientific community that the program is a funding priority.  The New Horizons team made their case using various observations, including infrared reflectivity surveys identifying molecules such as carbon dioxide, methane, and nitrogen moving on the surface—a richer surface environment than Mars. Atmospheric refraction indicated that Pluto had an atmosphere.  The team also showed that Pluto’s moon Charon was formed through a collision, closely analogous to the formation of Earth’s moon.

Perhaps the principal factor in finally elevating New Horizons to the top of the funding priority list was a paradigm shift in the 1990s.  The previous conventional wisdom was that the solar system consisted of four small rocky inner planets close to the sun, with four gas giants beyond them.  Pluto did not fit this pattern.  Advances in technology, however, began to identify further objects beyond Pluto.  Instead of being a misfit, Pluto was simply the first of a new trend, the Kuiper Belt objects.  The Kuiper Belt is now the single largest structure in the solar system, and its “dwarf planets” became a third class of planets—and by far the most numerous. Thus, the Pluto mission became a voyage toward truly new horizons.

The spacecraft designed for the mission was small, powered, appropriately enough, by Plutonium, because it would be too far away from the sun to use solar panels.  It carries seven scientific instruments that are so miniaturized that all of them together weigh less than the camera aboard the Cassini mission that imaged Saturn in 2004.

The other advance of New Horizons was its massive launch vehicle, the Atlas rocket.  Loaded with only the compact New Horizons probe, the rocket was launched essentially empty, providing maximum speed.  The rocket broke the sound barrier going vertically, reaching 18,000 MPH in Earth orbit, and ultimately 50,000 MPH, resulting in 14 Gs of acceleration.  The Apollo mission, at 25,000 MPH, required three days to reach the moon.  New Horizons passed the moon in nine hours.

The Pluto flyby was completed successfully in 2015, but the it will take 16 months to download all 15 gigabits of data back to Earth.  The data we have received thus far is already changing the way we see Pluto.  Images from the far side of Pluto show layers of haze, as the atmosphere is forced over mountains.  Pluto’s sky is blue like Earth’s because tiny particles in the atmosphere scatter the sun.  New Horizons also observed 1000 foot tall crystals of methane, and “cryovolcanoes” erupting ice.  One of the biggest mysteries to be investigated using these new data is why Pluto is still geologically active.  Even as the Pluto data is slowly transmitted back to Earth, the New Horizons mission continues toward the Kuiper Belt to image several large objects already identified for surveying.  Dr. Stern concluded by observing that a small robot millions of miles away captivated and inspired people all over the world, and he urged us to keep exploring.

After the conclusion of the talk, President Millstein invited questions from the audience.

One questioner asked about the difficulty of hitting such a small target.  Dr. Stern admitted that when New Horizons launched, Pluto’s orbit was not known well enough to complete the mission. Scientists pooled all available data to fine tune the knowledge of Pluto’s location and speed, going as far as re-analyzing the original Clyde Tombaugh images from the 1930s using modern data analysis tools to get the longest possible timespan.

Another questioner asked what would happen if New Horizons hit any debris, given its tremendous speed. Dr. Stern explained that the Pioneer 10 and 11 and Voyager 1 and 2 missions provided an opportunity to characterized the interplanetary dust environment. Based on these findings, multilayer insulation with Kevlar was added to mitigate the risk from dust, but a participle the size of a grain of rice would still shred the spacecraft.  Thus, the team actively imaged the route looking for rings and dust sheets, prepared to divert the probe at the first sign of such hazards.  Ultimately, Dr. Stern explained, exploring requires taking risks.

After the question and answer period, President Millstein thanked the speaker, made the usual housekeeping announcements, and invited guests to join the Society.  At 10:09 p.m., President Millstein adjourned the 2362nd meeting of the Society to the social hour.


Attendance: 143
The weather: Clear
The temperature: 11°C

Respectfully submitted,

Preston Thomas
External Communications Director


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