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Sunday, July 28, 2013

Pluto's Geology and Surface-Atmosphere Interactions

A point frequently cited in support of Pluto’s planet status is that it is a complex world with geology and weather. On the fourth day of the conference, these subjects took center stage, as researchers described what is known about the surfaces of Pluto, Charon, and the four tiny moons and the interactions between these worlds’ surfaces and atmospheres.

Issues addressed regarding surface geology included predictions of whether Pluto and Charon have plate tectonics (processes in which a planet’s crust and upper mantle divide into plates which float and travel independently over the planet’s mantle), predictions on the overall geology of Pluto and Charon, impact craters and the dust particles they eject, and the effects of gravity on the surface processes of the system’s four tiny moons.

PhD student Marc Neveu presented a study questioning whether “exotic sodas” or gas exsolutions (the processes of separating or precipitating from a solid crystalline phase) could cause cryovolcanism on Pluto and Charon. His talk was followed by Dr. Lynnae Quick, who presented her predictions for cryovolcanic flows on Pluto’s surface.

Also discussed in depth were landforms and surface processes on Pluto and Charon, using the seasonal caps on Mars as an analogue for Pluto regarding jets, fans, and cold trapping, mapping coordinate systems used for Pluto, the use of geologic mapping to investigate the geologic history of Pluto and its moons, and speculation about what Pluto will look like.

I felt very grateful to Swinburne for their insistence that students use at least some scholarly journals in our research, in order to familiarize ourselves with the level and format of articles by professionals in the field. Even if one has difficulty following all the equations and theories presented in these studies, the key is to understand the major points being made, the conclusions the researchers reached and how and why they arrived at those conclusions.

Both Pluto and Charon are likely to have impact craters on their surfaces. Such craters are ubiquitous throughout the solar system, and researchers can use the wide variety of craters to learn about the impacting bodies that caused them.

Because Pluto has an icy surface, craters there will appear like those on other icy bodies. The craters will likely be small and shallow since the impacting bodies likely traveled at low velocities.

Pluto’s smaller moons are likely to have surfaces akin to those of asteroids and other small solar system bodies.

Pluto and Charon are tidally locked to one another, meaning they rotate synchronously, with the same side of Pluto always facing the same side of Charon and vice versa. This tidal locking provides unique constraints on the bodies’ interior structure, thermal history, and likely patterns of tectonic deformation.

Cryovolcanism is possible on Pluto, Charon, and other large Kuiper Belt Objects if there is liquid below their surfaces and there are cracks in ice on these objects’ surfaces. The gases able to exert enough pressure to get to their surfaces are hydrogen, nitrogen, argon, methane, and carbon dioxide.

Other places in the solar system where cryovolcanism occurs include Jupiter’s moon Europa, Saturn’s moons Titan and Enceladus, and Neptune’s moon Triton. Many speakers emphasized the similarities likely between Triton and Pluto. This is useful because we have data on Triton from the Voyager 2 flyby of Neptune in 1989. Triton likely originated in the Kuiper Belt and may have been a planet with its own orbit around the Sun before being captured by Neptune.

Pluto and Triton have similar densities, surfaces, and atmospheric compositions, so Pluto’s surface is likely to look a lot like Triton’s. However, albedo contrast is very different for the two bodies. Triton has only modest contrast in the brightness of its surface areas while Pluto shows enormous contrast, with some areas very bright and others dark.

Almost all presenters at the conference made reference to computer models used to determine the outcomes of the processes they are studying. Some described computer models they created either individually or through a team.

Three possibilities were discussed for Pluto’s surface. The first is that Pluto is geologically differentiated with a floating ice shell and a subsurface ocean. The second also has Pluto geologically differentiated, but frozen down to its core, with no ocean present. The third is that Pluto has uniform density globally with a viscous (thick, sticky consistency between that of a solid and that of a liquid) interior and a rigid outer shell.

Scarps, or cliff lines caused by erosion, are also ubiquitous in the solar system; they can be found on Earth, Mars, Titan, and Triton and are also expected on Pluto and Charon, where surface material is moved via condensation (change of physical matter from gas to liquid) and sublimation (change of physical matter from solid to gas without passing through a liquid phase). Another process that likely occurs on Pluto and Charon is sedimentation, or the transportation of eroded particles over long distances in thin atmospheres via plumes.

Geologic mapping is a tool in which scientists take data from many different observations and use it to understand an object as a whole. It was first used on Earth to map geologic features and their ages and characteristics, but has since been used for other solar system bodies and will be an ideal tool for astronomers to use New Horizons data for the purpose of defining and characterizing the brightness, texture, color, and morphology (form and structure) of Pluto and its moons and teasing out their natural history.

The next series of talks centered on surface-atmosphere interactions, addressing issues such as seasonal variations on Pluto’s surface, seasonal transport of volatile organic compounds and the use of computer models to illustrate these phenomena, seasonal light curves, computer modeling of Pluto’s climate, processes driving sublimation and deposition on Pluto, global surface-atmosphere interaction on the planet, chemistry in Pluto’s atmosphere, a comparison of Pluto’s photochemistry (the study of chemical reactions that proceed with the absorption of light by atoms or molecules) with that of Titan and Triton, and three dimensional modeling of the methane cycle on Pluto.

It may come as a surprise to some that Pluto does have seasons! Pluto’s seasons are affected by its highly eccentric orbit, which results in seasons of different lengths for its northern and southern hemispheres.

A good research project for students involves examining the history of Pluto’s light curves, then taking new ones, and comparing the information from all of them to determine whether volatiles have been or are being transported across the planet’s surface. Triton’s light curve has changed significantly since the Voyager 2 flyby. Past light curves of Pluto show no volatile transport; however, in recent years, it has been difficult to obtain accurate data since Pluto has been passing through the plane of the Milky Way. Starting in 2014, Pluto will move away from that plane and data collection will become easier.

Many scientists believe Pluto does experience significant seasonal transport of volatiles. If this is the case, light curve measurements will best confirm these processes, as these measurements are good at detecting changes in albedo (brightness) patterns.
Photometry is a technique that measures the intensity of an astronomical object’s electromagnetic radiation; it has been used to monitor Pluto’s brightest regions. The planet’s color appeared constant until 1992, but after that it changed significantly. Pluto’s south pole has become brighter, and its surface has become more red. The only explanation for these changes is that there have been actual changes on Pluto’s surface.

Three factors control Pluto’s climate. These are its obliquity (axial tilt) of 58 degrees, resulting in its poles receiving more sunlight than its equatorial regions; the eccentricity of its orbit, and the fact that the nitrogen in its atmosphere is in vapor pressure equilibrium with its surface ices (meaning the pressure of atmospheric nitrogen in gaseous form and surface nitrogen in ice form are the same).

In discussing Pluto’s atmosphere, Dr. Kevin Baines compared it to Titan and Triton, describing Pluto as “a really alive planet—really a small Titan.” Dr. Vladimir Krasnopolsky noted that the chemistries on Titan and Triton are very different from one another. Triton is a far better analogue for Pluto. Titan is much closer to the Sun than Pluto; its surface temperature is 94 Kelvin. If it were moved to Pluto’s orbit, Titan would be much more similar to both Pluto and Triton.

A computer model known as the LMD Pluto Climate Model has been used to simulate Pluto’s atmosphere, surface, and subsurface temperatures between 1988 and 2015. The model is being used to determine whether methane that never sublimated will disappear from the surface of Pluto’s poles by 2015. On most areas of Pluto, the atmosphere is much colder than the surface; however, this is not true in the areas where sublimating materials are carried by wind.

This model will be a useful tool to the New Horizons community and to researchers investigating climates on other planets.

Thursday, July 25, 2013

Rings, Interiors, Surface Composition--and One Man's Personal Agenda

Who would have imagined there is SO much to discuss about one small planet?

This five-day conference is truly a gathering of great minds, the most knowledgeable people in the world regarding Pluto. With every aspect of the Pluto system under intense analysis and discussion, those of us present are witnesses to the frontier of all we know about these worlds, at the same time knowing that in two years, that knowledge and understanding will dramatically change.

Today, discussion moved from satellites to rings, addressing the possibility of rings around Pluto and their potential sources. Most dust ejected by the small moons is thrown out of the Pluto system altogether while some lands on Pluto and Charon.

Naturally, computer simulations were conducted to determine potential hazards to New Horizons, as the dust particles present in planetary rings could destroy the spacecraft in the event of an impact.

Alternative flyby routes, known as Safe Haven Bail Out Trajectories, or SHBOTS, have been designed by the New Horizons team in the event such hazards are discovered. One such alternative, the Deep Inner SHBOT, actually presents opportunities not afforded on the original trajectory. This path goes through the best locations for higher density particles, meaning it potentially yields the best opportunity for discovery of moons and/or rings. But are potential hazards worth it?

There was much discussion on the process that drives the formation of rings, including the influx of material from the Kuiper Belt. Additionally, as Pluto passes the ecliptic plane twice during each of its orbits, it passes through a thick patch of dust.

The remote search for rings is done in two ways—by direct imaging and by measurements made when Pluto occults (passes in front of) a star. So far, no rings have been found. On its original path, New Horizons faces a reduced risk but is not entirely out of the danger zone.

From dust and rings, discussion moved to the composition of the surfaces of Pluto and its four moons. There is evidence for methane frost on Pluto; various researchers described spectroscopic studies in wavelengths ranging from the infrared to the ultraviolet in the quest to discover the makeup of these objects.

We know methane exists in a pure state and in a diluted state on Pluto; some of it is dissolved in nitrogen. It is distributed uniformly across the surface, as are nitrogen and carbon monoxide. Neptune’s moon Triton contains carbon dioxide, and there is clear evidence it also harbors water ice. Evidence has not been found for carbon dioxide on Pluto though the James Webb Space Telescope, once in operation, should be able to do a more thorough search for it.

What do we know so far? For one thing, ultraviolet light does not make it to Pluto’s surface due to the shielding effects of methane in its atmosphere. Methane is present in Pluto’s atmosphere and on its surface.

The surface of Charon is different from that of Pluto. Pluto’s surface is colored, meaning it has more material than pure ice, which is white. Charon does not appear to have carbon monoxide, carbon dioxide, or methane; it does have water ice and a hybrid form of ammonia. Pluto’s coloring is likely due to organic residue resulting from solar irradiation of its surface. Other hydrocarbons must be present, but we don’t have access to all parts of the electromagnetic spectrum to distinguish them.

Observations with IRAC/Spitzer confirm that Pluto’s surface is heterogeneous. Participants learned about the many methods used to identify what is on that surface through measurements of Pluto’s thermal lightcurve and observations at long wavelengths.

In general, the physical properties of Trans-Neptunian Objects (TNOs) are not well known. Spectroscopy shows that Quaoar, which is probably large enough to be spherical, has a surface dominated by water ice. A current goal of Earth-based observations with ALMA is to obtain accurate information on the size and densities of medium-sized TNOs. Measuring in long wavelengths is important in determining these objects’ characteristics and surfaces.

Makemake, a small Kuiper Belt planet, is known to contain large slabs of methane. Quaoar and Eris also have methane on their surfaces. A total of 56 hydrocarbons have been identified on the surfaces of TNOs.

Pluto has also been measured in the mid-ultraviolet portion of the electromagnetic spectrum. Laboratory studies have been used to simulate conditions on Charon. In some ways, Charon’s surface resembles that of Saturn’s moon Tethys. No variation in Charon’s color or lightcurve has been seen since 1992. Charon is believed to have a reasonably cratered surface, and very subtle albedo and color features. The side facing Pluto looks different than the side facing away from Pluto. Cryovolcanism is possible; the presence of nitrogen is uncertain.

Speakers presented studies on the spectra and chemistry of Pluto’s ices, the formation of high mass hydrocarbons on Kuiper Belt Objects, and radiation chemistry on Pluto. A long-term goal is to obtain optical data for nitrogen, methane, and methane ices on Pluto.

A huge question explored is the possibility that Pluto harbors a subsurface ocean. The presence of an ocean depends on the presence of minor compounds and on whether the processes of convection and dehydration have occurred. Studies of the interiors of both Pluto and Charon play a crucial role in determining whether either body could have such an ocean.

To that end, researchers discussed constraints on the interior structures of both Pluto and Charon, mass determination for both objects by New Horizons’ REX instrument, the process involved through which Pluto’s interior structure evolved, and distinguishing formation scenarios for both objects based on the question of whether the impactor that created them was partially differentiated.

If Pluto and/or Charon have subsurface oceans, how did they evolve and cool?

One way that could help determine whether either body has a subsurface ocean is a look at the objects’ shape, which New Horizons will make possible. If Pluto and/or Charon show fossil bulges on either side, chances are no ocean is present. But if they don’t show these fossil bulges, there is a good chance an ocean exists. The formation of subsurface oceans depends on heat production and heat removal.

One of the most interesting subjects raised was presented as background information by Dr. Marc Buie, whose talk was titled “The Surface of Charon.” Buie revealed an interesting factoid. While Charon was discovered in July 1978, the late Brian Marsden, head of the IAU Minor Planet Center, did not officially recognize it as a satellite of Pluto until February 1985! Buie displayed copies of several IAU circulars issued between July 1978 and February 1985 that referred to Charon as an “unconfirmed” satellite of Pluto. During this time period, astronomers, despite IAU reluctance to recognize Pluto's moon, all recognized its existence and even referred to it by the name Charon—long before that name became “official.”

The display drew repeatedly drew laughter and recognition by those in attendance.

Did Marsden have a personal agenda? This is the same man who told the late Clyde Tombaugh that he “will torpedo your planet” and see that Pluto gets a minor planet number, even if Tombaugh did not live to see that. For decades, Marsden wanted Pluto under his auspices at the Minor Planet Center. And in 2006, it was Marsden who pushed hard for demoting Pluto.

It took seven years for an established astronomer to be certain that Pluto has a large moon, well beyond the time this was accepted as common knowledge, not just by astronomers, but by the general public?

More likely, Marsden didn't want to know that the object he was so determined to downgrade was actually half of a binary system.

Personal agendas should not come into scientific discussions. This is just one more reason that the minor planet numbers assigned to Pluto and the other dwarf planets should be removed—in spite of the fact that Marsden will not see it.

Wednesday, July 24, 2013

Atmospheres, Origins, and Moons Get Spotlight on Conference's Second Day

The second day of the Pluto Science Conference, July 23, brought more detailed and exciting discussion of Pluto, now focusing on the atmospheres of both Pluto and Charon and then proceeding to the subject of Pluto’s satellites—all five of them. In the evening, Alan Stern gave a public talk, “New Horizons to Planet Pluto: Exploring the Frontier of Our Solar System,” which can be viewed here: .

Between staying late for Alan’s talk and having problems of my laptop constantly freezing on me, this post is actually a day late.

My friends and family find it hard to believe I found a five-day conference entirely about Pluto. Sure enough, participants continue talking about Pluto in between the sessions! If only this could be a regular thing, preferably closer to home!

Being here is an amazing, exciting opportunity. I am actually meeting people whose works I have read and whom I have watched online giving talks about Pluto and other areas of planetary science. Everyone here is incredibly friendly—while many don’t know me, not a single person has been negative, cold, or insulting. The conference is thankfully free of ego issues, a place where many people share the same interest, and a tremendous learning opportunity for all.

At times there is disagreement, but it is always friendly and respectful.

The discussion on atmospheres reviewed current knowledge, noting Pluto has a nitrogen-dominated atmosphere and also contains methane and carbon monoxide. Until 1985, no one knew this small planet has an atmosphere. This was revealed first when Pluto occulted a star in 1985. Three years later, mutual eclipses by Pluto and Charon of one another, enabling astronomers to obtained improved spectral measurements and observe ongoing changes, such as increasing pressure.

Talks addressed the interaction between surface methane and atmospheric methane on Pluto and the question of whether haze is present in its atmosphere. The size of that atmosphere has increased significantly between 1988 and 2012. And there is a difference between the planet’s upper and lower atmospheres.

Researchers presented their work and that of others in the form of spectral lightcurves (graphs of light intensity, plotted for celestial objects or regions as a function of time), data learned from occultations by Pluto of stars, and through observations using the world’s largest telescopes, including Hubble.

While we know little about Pluto just two short years before the New Horizons flyby, the information we have shows that Pluto’s atmosphere is fully formed and global.

Speakers addressed the issue of whether Pluto’s atmosphere will at some point collapse as it recedes from the Sun. Collapsing in this case means the nitrogen gets so cold that it falls back onto the surface.

The planet has volatile organic compounds (organic chemicals that have a high vapor pressure at ordinary, room temperature conditions) in its atmosphere, and these can condense and evaporate when clouds are present.

New Horizons will make map the distribution of volatile organic compounds in Pluto’s atmosphere through the REX (Radio Science Experiment) thermal imaging instrument. It will also the source of any hazes on Pluto and whether they come from condensates or from sources higher in the atmosphere.

Various researchers presented the findings learned from different occultations of stars by Pluto. A study this year used global circulation models to predict that the atmosphere would have much more cold methane than warm methane in localized regions.

The atmospheres of Pluto and Charon have been studied in the infrared and near-infrared portions of the electro-magnetic spectrum. Stern pointed out that comet impacts could cause a temporary, transient atmosphere on Charon. The large moon has no permanent atmosphere since it lost its volatile organic compounds long ago.

With Pluto’s moon count now up to five, there was no shortage of areas to discuss regarding Pluto’s origins and satellites. Pluto likely did not form where it currently is located. A model of the evolution of the solar system, known as the Nice model, proposes that the four giant planets, Jupiter, Saturn, Uranus, and Neptune, migrated to their current positions, having initially formed between 15 and 20 astronomical units or AU (one AU equals the distance from the Sun to the Earth, about 93 million miles). Jupiter likely formed closer to the Sun and moved outward, leading Uranus and Neptune to go unstable and scatter into the proto-planetary disk around the early Sun.

Where did Pluto come from? Dr. Hal Levison stated that Pluto was already in that disk, at least according to this model, when the giant planets migrated. Yet the model has flaws. The only way it works without resulting in total destruction of Earth and the terrestrial planets is if a third ice giant is added, a planet that subsequently was scattered out of the solar system altogether by Jupiter.

Pluto’s Kuiper Belt neighborhood should have more mass than it does. If all Kuiper Belt Objects are put together, they result in a mass less than 0.1 Earth masses. Far more mass is needed to have formed what is there now. Where did it go?

There are “cold classical Kuiper Belt Objects (KBOs) that have orbits of low eccentricity and inclination as well as plutinos, objects in various resonances with Neptune, and “hot” or highly eccentric KBOs with high inclinations, such as those in the Scattered Disk.

Astronomers presented different theories of planet formation to explain how these KBOs accreted. But do processes work the same at 20 AU from the Sun as they do at Earth’s distance (one AU)?

Notice how many talks end up with more questions than answers. That is part of the fascination of Pluto. We know a lot about this very cold, distant world, yet that knowledge is the tip of the iceberg, showing us how much we don’t yet know.

The New Horizons mission initially motivated the search for additional moons of Pluto. From 1978-2005, only Charon was known. Nix and Hydra were discovered through a deep exposure using Hubble. Pluto’s fourth moon, Kerberos, was found during an intense search for rings around Pluto in 2011, and Hydra was found a year later, its fifth, Styx, was discovered through use of a broader filter that allowed astronomers to probe even more deeply.

All five moons orbit roughly in the same plane as Pluto and Charon, and all are very close to being in mean motion resonances with Charon. Nix and Hydra are estimated to be about 50 kilometers in diameter while Kerberos and Styx are smaller, about 10-15 kilometers in diameter.

The position of these moons was discussed in the context of New Horizons and possible alternate trajectories in the event there is debris present that could destroy the small spacecraft on impact. New Horizons will measure the surface temperatures of Nix and Hydra and obtain high resolution images of all four small moons.

Also addressed were the origins of Pluto’s satellites, likely through an impact by another planetary body with “proto-Pluto,” similar to the impact believed to have formed Earth’s moon. It is unlikely that the small moons were captured rather than formed this way. Charon is thought to be composed of material from the impacting object.

That impact may have heated Pluto to temperatures between 50 and 100 Kelvin, causing Pluto to lose ice.

The orbits, physical properties, and chaotic rotations of Pluto’s moons were subjects of extensive discussion. Just about every speaker tied his or her talk to New Horizons, outlining how the mission will answer the many unresolved questions.

Current plans call for New Horizons to fly through an area interior to Charon known as the Charon Instability Strip (CIS), an area of about 2500 kilometers where no satellites are expected. Hubble will allow further constraining of that region, to less than 25 kilometers in one small area. The LORRI instrument will look for hazards upon approach seven days before the flyby. LORRI will continue to search for satellites, down to much more narrow areas.

From the flyby, there will be a “final answer” to the question of whether or not there are more moons of Pluto out there, Alan Stern said.

His talk that evening on the New Horizons mission was well attended and broadcast live online. One proud Pluto fan from India noted he got up at 5 AM (his time) to hear the talk live. During the question and answer section, a boy asked about planet definition and whether objects have to clear their orbits to be planets. Dr. Stern responded by confirming this is an ongoing debate, adding his view that the solar system now has a third region of planets where prior to 20 years ago, it consisted of four terrestrials, four gas giants, and one misfit, Pluto.

Tuesday, July 23, 2013

The Pluto Science Conference Day 1: New Horizons and the Kuiper Belt

Today was the first of a five-day Pluto Science Conference being held at the Johns Hopkins University Applied Physics Lab, the same site where the Great Planet Debate was held five years ago. I feel very lucky to be back here, in a town named Laurel in Maryland for five days of All Pluto, All the Time!

The conference is being held in anticipation of the New Horizons flyby of Pluto, now just five years away. Most though not all attendees are professional astronomers and/or members of the New Horizons team.

Day one focused on New Horizons itself, with separate presentations on each of the instruments on board the spacecraft. This comes only about a week after a successful nine-day rehearsal for the encounter held earlier this month.

We learned that New Horizons will be able to take images better than those taken by the Hubble Space Telescope starting in May 2015.

Dr. Alan Stern and several other speakers discussed the effort to get a mission to Pluto off the ground, an effort that goes back 20 years, conceived after mutual eclipses by Pluto and Charon of one another revealed that Pluto has an atmosphere.

“Pluto has received worldwide attention because it is a solar system body worthy of intense study,” Stern noted.

Dr. Tom Krimigis outlined the science objectives of New Horizons, divided into three groups: measurements required for the mission to be a success, known as group 1; highly desired measurements, group 2; and bonus/desired measurements, group 3.

Seven phases of the Pluto encounter were outlined. These include Approach 1, January 6-April 4, 2015; Approach 2, April 4-June 23, 2015; Approach 3, June 23-July 13, 2015; Near Encounter Period, July 13-15, 2015; Departure Phase 1, July 15-August 4, 2015; Departure Phase 2, August 5-October 22, 2015; and Departure Phase 2, October 22, 2015-January 1, 2016.

During the flyby, observations from Earth-based telescopes will be done to complement the data from the encounter. This means there will be two simultaneous studies of the same objects—one “in situ,” meaning at the site (Pluto), and the other from Earth.

While the most important data will be sent back first, it will take an entire year to downlink all the data from the flyby. Pluto will still be surprising us well into 2016.

The second part of the day focused on the context of the Kuiper Belt, including plans to fly by one or two small KBOs after Pluto. Because of fuel concerns, these KBOs must be in a narrow cone along the spacecraft's trajectory. Astronomers have been searching for such objects but have not yet chosen any specific ones although they expect to find two or three. This was also a goal of the citizen science Ice Hunters and Ice Investigators projects though both those projects have completed going through the data they had been given.

There was much discussion of the different parts of the Kuiper Belt—the area of objects in resonances with Neptune, the classical Kuiper Belt, and the Scattered Disk. The latter is the location of Eris and other KBOs with highly eccentric orbits.

Where did Pluto form—in its location, or somewhere else. Various theories attempt to answer this question. One theory, discussed by Dr. Renu Malhotra at the Great Planet Debate, and also discussed extensively in Malhotra's research publications, is that Neptune formed closer to the Sun and then migrated outwards, sweeping objects located closer to the Sun, including Pluto, with it.

The hope is that data from the flyby will answer questions such as what Pluto and Charon are made of, how both accreted, and what their internal structure is. What is known so far is that Pluto and Charon are dense, rock-rich worlds that accreted very rapidly. They probably formed closer to the Sun than their present location.

As I have noted many times in this blog, Pluto is believed to be about 70 percent rock and very likely differentiated into core, mantle, and crust just like Earth. The possibility of Pluto having a subsurface ocean was discussed as well.

Ceres is also estimated to be 70 percent rock and may contain materials brought from the Kuiper Belt region. The small planet is actually more like objects in the Kuiper Belt than like inner solar system bodies, to the point that some astronomers theorize Ceres actually came from the region beyond Neptune.

Also noted was a search for a system of small moons around Haumea, a small, football-shaped planet beyond Pluto in the Kuiper Belt. Haumea is known to have two moons, but as Dr. Luke Burkhart, who conducted a search for additional satellites, noted, no such objects were found.

“Haumea doesn't have a cohort of satellites; Pluto remains unique,” Burkhart said.

These are just the highlights of presentations that were far more intense, detailed, and at times technical.

Kimberly Ennico, New Horizons Deputy Project Scientist, is blogging from the conference, and her posts can be found at . You can also follow the discussion on Twitter here, and by following the hashtag #PlutoSci.

The conference has brought together an amazing group of scientists and others who share a fascination with distant Pluto. I personally recognized some from other conferences and many names from scholarly publications I have downloaded and read.

Little mention was made of the IAU. At the same time, debates and disagreements among scholars, such as the question of Ceres' place of origin, were noted genially and recognized as positives that are part and parcel of such discussions. Ideas rise and fall based on data from missions like New Horizons and from studies like those discussed by the speakers. They are not imposed by fiat.

This conference represents the kind of discussion astronomers and others interested in Pluto should be having, a healthy back and forth exchange of ideas. Those who reject such an exchange for simpler but largely unscientific “decrees from on high” will likely be left behind and consigned to irrelevance.

Two important notes: Tomorrow, July 23, Dr. Alan Stern will give a public lecture, “New Horizons to Planet Pluto: Exploring the Frontier of Our Solar System.” The talk will take place at 7:30 PM EDT in the Kossiakoff Center at APL. It will be webcast live at mms://

Second, there is a public campaign to get LEGO to make and sell a LEGO model of New Horizons. They have already done this for the Mars Curiosity Rover and for the Japanese Hyabusa cometary mission. We all can help make this happen! The LEGO program is called CUUSOO. A model is created, shared on the CUUSOO web site, and then must get 10,000 individual votes. At that point, it will be reviewed by LEGO and then possibly chosen for production as one of their products, meaning it will be sold online and in stores.

Cast a vote for LEGO New Horizons at .