Philosophical Society of Washington

Minutes of the 2371st Meeting

At the Cosmos Club, Washington, DC
January 6, 2017

President Larry Millstein called the 2371st meeting of the Society to order at 8:08 p.m.  He announced the order of business and welcomed new members.  President Millstein presented a summary of the 33rd meeting of the Society, held in 1872.  The minutes of the previous meeting were read and approved.  President Millstein then introduced the speaker for the evening, Scott Bolton, Principal Investigator on the JUNO Mission, Associate Vice President for Space Science and Engineering at the Southwestern Research Institute, and Senior Staff Scientist at the Jet Propulsion Laboratory.  His lecture was titled “Juno’s Exploration of Jupiter”.


Dr. Bolton began by explaining that Juno is the second mission under NASA’s New Frontiers program—the first was the New Horizon’s mission to Pluto, which Dr. Alan Stern presented to the Society in April of last year.  Dr. Bolton explained that the Juno mission is similarly ambitious: To use Jupiter as a window into the earliest period of the solar system to learn how the planets formed.

Dr. Bolton explained that stars form out of nebulae, spinning clouds of hydrogen and helium gas. In the nebula that would eventually become our solar system, the formation of our sun captured nearly all of this gas. The little material that was left over formed the gas giant Jupiter. All of the other planets, moons, and asteroids were formed from the “leftovers of the leftovers.” 

Dr. Bolton explained that this is why studying Jupiter is so important. Because it formed early and is so massive, Jupiter had sufficient gravity to hold on to the original hydrogen and helium present in the nebula  as planets were just forming. As the 1995 Galileo mission atmospheric probe showed, Jupiter is also enriched with heavy elements such as Argon, Krypton, Carbon, and Oxygen, but in a uniformly different ratio than those elements are present in the sun. These data invalidated every then-current theory of planet formation, and set the stage for a closer investigation of Jupiter in the Juno mission 20 years later.

The Juno instrumentation was chosen to examine Jupiter from two scientific angles. The first is gravity science, with the goal of answering questions such as whether Jupiter has a rocky core of heavy elements—meaning they were present in the early solar system. The second is water abundance, as measured by Juno’s microwave radiometer, which receives in different frequencies to pick up thermal radiation from as deep as 600 kilometers below the visible cloud layer.  This will help map water and ammonia abundances in the atmosphere around the planet, and provide clues as to how the planets got their heavy elements. Old theories of water on Earth suggested that it came from comets, but the water in comets we see is of different isotopic ratios, meaning that we need a new theory for Earth’s water. Observations about the abundance and isotopic ratios of oxygent in Jupiter can provide a piece of this puzzle. Juno’s science objectives also include characterizing Jupiter’s magnetic field, which is the strongest in the solar system.

Dr. Bolton then presented a summary of findings from the early Juno data. The microwave radiometer data showed that the color bands on Jupiter closely track temperature variations, even hundreds of kilometers into the atmosphere. The radiometer data also identified a vast high pressure “geyser” of ammonia emerging at the equator from deep in the planet, an unpredicted and as yet unexplained phenomenon.

Juno’s gravity science package has produced similarly unprecedented findings. The data do not yet indicate whether Jupiter has a solid core, but they have already shown that all existing models for Jupiter’s shape are wrong.

Juno’s electromagnetic field sensors similarly observed contradictory data about the magnetic field around Jupiter that was not fully consistent with any of the models. One potential explanation for the preliminary data may be that the magnetic field of Jupiter emanates from far closer to the surface than originally predicted. This could indicate that the layer of liquid metallic hydrogen, which acts as a dynamo to create the planet’s magnetic field, is actually closer to the surface than prior models predicted.

Juno’s visible light camera revealed that the poles of Jupiter have none of the familiar orderly color bands in shades of red that mark the rest of the planet. Instead, the poles are a mix of transient circular storms in shades of blue, including funnel clouds 80 kilometers tall and half the diameter of the Earth.

Dr. Bolton concluded by noting that 400 years ago, Galileo first discovered moons orbiting Jupiter, working alone with only a crude telescope. Today, the Juno mission is collecting a wealth of data about Jupiter, and it is being shared freely with the scientific community and amateur astronomers alike, opening the door to still greater discoveries.

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

One questioner asked about the Migration Theory, which suggests that Jupiter and other planets may have changed their orbits. Dr. Bolton explained that Juno will provide some insight into the distance from the sun at which Juno formed, but will not provide definitive evidence that any particular migration model is accurate.

After the question and answer period, President Millstein thanked the speaker, made the usual housekeeping announcements, and invited guests to join the Society.  At 10:12 p.m., President Millstein adjourned the 2371st meeting of the Society to the social hour.


Attendance: 161
The weather: Overcast
The temperature: -3°C

Respectfully submitted,

Preston Thomas
External Communications Director


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