Wednesday, August 7, 2013

Pluto Conference Wrap-Up: Atmospheres, Magnetospheres, Predictions, and Resources--and Lollipops!

The last day of the Pluto Science Conference was only a half day, but speakers managed to get in a lot of discussion on the possible interaction of Pluto’s atmosphere with the solar wind, computer simulations of this interaction, X-ray emissions that might be seen from Pluto’s plasma (a state of matter containing charged particles, both positive and/or negative) environment, X-ray observations of Pluto by the Chandra Space Telescope (an X-ray telescope launched by NASA in 1999), predictions regarding Pluto’s wind structure, Pluto’s ultraviolet glow, and more, all connecting back to the New Horizons flyby in just two years.

Fran Bagenal, a huge Pluto supporter with whom I had fun comparing Pluto T-shirts, reported that Pluto interacts with the solar wind like a comet does, given its large atmospheric escape rate. The solar wind is a stream of charged particles released from the Sun’s upper atmosphere that varies in temperature, density, and speed with time and distance. Voyager 2 actually measured solar wind conditions at 30 AU, roughly Pluto’s distance from the Sun, even though it did not fly past Pluto, and found large variations in it.

Pluto has an extended, puffed up atmosphere, speaker Peter Delamere noted. This atmosphere presents an obstacle to the flow of the solar wind. New Horizons’ SWAP (Solar Wind at Pluto) instrument will look into the solar wind as it comes toward Pluto. Interestingly, the solar wind is currently a lot weaker than it was when Voyager 2 measured it.

On the day of its closest approach, SWAP will begin seeing ions from Pluto. As New Horizons departs, the instrument will likely get a good view of the long tail of ions coming from the planet.

Interstellar ions may also play a role in influencing just how the solar wind interacts with Pluto.

John Cooper questioned why some Kuiper Belt Objects appear red while others appear bright and still others dark. The cold classical KBOs are usually red. Objects created in cryogenic (very low temperature) material tend to be very bright.

Computer models have been utilized to study whether Pluto’s interaction with the solar wind is similar to that of a comet, as Bagenal stated, or whether that interaction is more like that between the solar wind and Venus. The solar wind can undergo many types of interactions with other objects. Four instruments on New Horizons—PEPPSI, REX, ALICE, and SWAP will provide data that could help answer this question.

X-ray observations will also assist in revealing the nature of the interactions between Pluto and the solar wind. This is because X-rays are very effective atmospheric probes and can tell us a lot about the escape rate of Pluto’s atmosphere. Such measurements have successfully been made of the interaction between comets and the solar wind. We can expect to see X-ray emissions from Pluto. During the New Horizons flyby, astronomers will seek observing time on the Chandra telescope, which can encompass Pluto and Charon with one pixel! This will enable very useful comparisons between New Horizons’ up close observations and ground-based observations from Earth.

With only two years until the flyby, excitement is building, and predictions abound. Angela Zalucha presented a computer model she created based on a Global Climate Model (GCM) used to study Earth’s climate. Her “Pluto GCM” assumes the planet has a dynamical core. The REX instrument on New Horizons will send radio waves through Pluto’s atmosphere while ALICE will measure the Sun’s light at Pluto as well as light from a background star shining through Pluto’s atmosphere. She emphasized that Triton is a very good analogue for Pluto.

Researcher Melanie Vangvichith also made use of a computer model, with the goal of creating a complete simulated 3D GCM of Pluto’s atmosphere for the years 1988-2016. Special focus was given to results for the years 2007, 2010, and 2015. Her model shows no troposphere (lowest atmospheric layer), unlike Triton; this is attributed to the abundance of methane on Pluto, which warms its atmosphere. Weather occurs when particles sublimate on the planet’s summer hemisphere and are then transported by wind to its winter hemisphere, where they subsequently condense.

While Vangvichith’s model produces results in agreement with Earth-based observations for this short period of time, it is uncertain whether it can produce the same accuracy when addressing changes over hundreds of years. This is largely due to difficulty in initializing Pluto’s surface and subsurface temperatures over such long periods, especially given its elliptical orbit.

A GCM model also based on Earth climate models created by Anthony Toigo produced its best results when its simulations of Pluto’s current climate assumed the existence of a relatively thick atmosphere. He noted that future studies of Pluto’s climate should focus on tides, general circulation, and surface winds.

To understand the evolution of a planet’s atmosphere, one needs to track the processes in that atmosphere. Nitrogen is the primary gas in the atmospheres of Pluto, Triton, Titan, and various large Kuiper Belt Objects. The ALICE instrument on New Horizons will analyze the composition and structure of Pluto’s atmosphere. It will also show the structure of Pluto’s darker regions against the interplanetary background.

The Cassini mission to Saturn observed ultraviolet airglow on Titan using a model known as AURIC, or Atmospheric Ultraviolet Radiance Integrated Code; New Horizons will use this model to measure ultraviolet airglow on Pluto. ALICE will make this possible by collecting atmospheric data in ultraviolet wavelengths. Interestingly, the AURIC model was initially created for Earth, then modified for Mars, Titan, and now Pluto.

ALICE’s observations are expected to show emissions of argon and nitrogen. Focusing on a profile of the planet’s limb (the outer edge of the planet’s disk) will reveal where the emissions are taking place.

New Horizons will encounter Pluto at a distance of 32.91 AU from the Sun (that is 32 times the Earth-Sun distance).

Stern closed the conference by reminding those present that this meeting was a follow up to a conference held 20 years ago at Lowell Observatory. That conference focused on turning the idea of a robotic mission to Pluto into a reality. Quite a few attendees at this year’s conference had attended that one, and to emphasize this, a picture of the 1993 group was displayed onscreen.

Papers presented at this conference will be published in a special edition of the journal Icarus.

The Pluto Science Conference featured more than just lectures. Two poster sessions were held, one on Tuesday and the other on Thursday, where attendees had the opportunity to view 30 posters and discuss them with the scientists who put them together. On Wednesday during lunch, a special “Triton Half Time Show” was presented, illustrating Voyager 2’s 1989 findings at Triton, which is believed to be a captured Kuiper Belt planet similar in composition to Pluto.

Looking ahead, Stern announced his goal of holding another conference in the summer of 2017 to digest and make sense of the findings of New Horizons, which will take approximately a year to be downlinked. The 2017 conference will lead to the compilation of a Pluto system book.
Abstracts of talks at this year’s conference are posted on . More detailed discussions of each speaker’s presentation can be found at Kimberly Ennico’s blog at . A summary of the conference and how it exceeded organizers’ expectations can be found here:

Only time will tell how accurate the predictions at this conference are in matching what is actually going on. It is worth remembering that prior to the discovery of planets orbiting stars other than the Sun, astronomers generally assumed other solar systems would look like ours. That turned out to be incorrect, to the point of sending scientists back to the drawing board in determining how planetary systems form. Whether models and predictions for Pluto are accurate or way off base will not be known until we actually see the planet and its moons up close.

Finally, to reward readers who hung in there and stayed with me to the end of these conference discussions, here is something on the lighter—and sweeter—side. I always urge supporters of Pluto’s planet status to vote with our dollars. Thanks to Kate McKinnon, wife of astronomer Bill McKinnon, who took part in the conference, I learned that one can buy solar system lollipops that DO include Pluto! Kate highlights these lollipops in a blog post titled, “Take That, Mike Brown!” That post can be found here:

To purchase these lollipops, visit the Colossal Shop, which is selling them as Solar System Lollipops, at , for $22 a set. Choose from a variety of flavors, including cherry, guava, marshmallow, strawberry, blackberry, and cotton candy.

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