Pluto and Charon Geophysics and Climate: Notes from the Conference

“Progress in Understanding thePluto System: Ten Years after Flyby” was a focused, informative conference in which scientists spent four-and-a-half days discussing Pluto in detail, comparing it with other, similar solar system bodies, and celebrating the milestone 10^th anniversary of the 2015 New Horizons flyby.

Alan Stern, New Horizons principal investigator, opened the conference by describing its goal as “bringing together everything we’ve learned about the Pluto system since the flyby.”

Because so much ground was covered during the weeklong, conference, it would be impossible to discuss everything in one entry, which is why I plan to write several for this site.

In the first session, “Pluto after Ten Years: A Holistic View,” discussion centered on Pluto’s climate, geological history, atmosphere, and chemistry. A second session focused on the geology and composition of Pluto’s largest moon and binary companion, Charon.

Throughout the conference, Pluto and its system of moons were compared and contrasted with Ceres, Haumea, Eris, Arrokoth, other Trans-Neptunian Objects and small planets, Neptune’s moon Triton, Saturn’s moons Titan and Enceladus, and Jupiter’s moon Europa.

While little is known about Haumea and Eris, every other one of these worlds is either an ocean world or a world suspected of having a subsurface ocean. This class of objects was relatively unknown just decades ago, but today, these worlds are front and center in the search for microbial life in the solar system.

In the lead up to the flyby, some scientists expected Pluto to be revealed as a geologically dead world, like our moon. Instead, many were surprised to find it, in the words of presenter Oliver White, “a geological wonderland at the edge of the solar system.”

Much focus was placed on Sputnik Planitia, the floating glacier that comprises the left side of Pluto’s “heart” feature, and the repository of the planet’s nitrogen ice. We know Sputnik Planitia is geologically young, has nitrogen ice flowing on its surface, and has no craters.

The flow of ice on Sputnik Planitia is similar to processes on Earth, but with nitrogen ice instead of water.

Pluto’s annual cycle is driven by the planet’s high obliquity or tilt toward the plane in which most but not all of the solar system’s planets orbit. Its north-facing slopes all have small deposits of methane ice. Over thousands of Pluto years, its equatorial regions have received less sunlight than its polar regions.

Pluto’s diverse geology, including bladed terrains, dunes, pitted regions, and even likely cryovolcanoes are the result of both endogenic, or internal, processes, and exogenic, or external ones.

The New Horizons team did not even know that Sputnik Planitia was there when the flyby was planned. Since this region controls almost everything that occurs on the planet, the opportunity to image it in high resolution was extremely fortuitous.

Not being a satellite of a giant planet, Pluto experiences no tidal heating. Its biggest source of energy is radioactive decay of rock.

The ancient impact that formed Charon melted ice, fractured terrain, and created Sputnik Planitia.

While the presence of a subsurface ocean on Pluto remains hypothetical, it is supported by a lot of evidence. Presenter James Tuttle Keane noted that a structure like Sputnik Planitia cannot have been created without an ocean.

Computer models are frequently used in studies to simulate conditions on remote objects like Pluto. Keane noted that “New Horizons triggered a wave of new theoretical models reshaping our understanding of Pluto and worlds beyond.”

Its axial tilt and eccentric orbit give Pluto extreme summers and winters. Its lower latitudes get at least some sunlight every day while its higher latitudes can go for long durations with no sunlight at all. These differing climates produce a variety of landscapes on Pluto’s surface.

But sunlight is not the only energy source on Pluto, which obtains a higher fraction of its energy from internal sources than the Earth does.

New Horizons found that Pluto’s atmosphere is escaping into space at a much lower rate than expected.

Much discussion centered on early migration of solar system planets. Neptune is believed to have formed closer to the Sun only to subsequently migrate outward. Now located at 39 AU (astronomical units, with one AU equal to 93 million miles or the average Earth-Sun distance), Pluto may have formed at 25 AU and then been pushed outward by Neptune.

Data obtained when various small planets occulted (passed in front of) a star indicate that Pluto, Charon, Haumea, Triton, and Quaoar all have similar densities.

“These objects are not iceballs,” emphasized presenter Bill McKinnon, a point that supports their classification as small planets. This is significant in light of the fact that the media often erroneously lump dwarf planets and tiny Kuiper Belt Objects (KBOs) in one broad category.

And KBOs, even those too small to be round, are not just giant comets—they are far more active than comets are.

Pluto’s atmosphere is similar to that of Saturn’s moon Titan, which itself is sometimes viewed as an analogue of early Earth. Its surface ices are methane, nitrogen, and carbon monoxide. Photochemical organic aerosols in Pluto’s atmosphere create its layered hazes, which extend to an altitude of more than 217 miles.

 Both Pluto and Triton, Neptune’s large moon that is believed to have once orbited the Sun on its own only to be captured by Neptune, look very different from comets. Rather than being frozen relics, both have interior energy sources. Because Triton orbits Neptune, a giant planet, it experiences far more tidal heating than Pluto.

Pluto and Triton have low levels of carbon monoxide in their surface ices. Data collected by the James Webb Space Telescope (JWST) show Eris and Makemake also lack surface carbon monoxide. As neither orbit a giant planet, their surfaces may be more like that of Pluto than that of Triton.

Since Triton is believed to have originated in the Kuiper Belt, all of this is evidence that supports classing these objects as a new subclass of planets, similar to one another but different from comets.

The distribution of ices on Pluto’s surface varies with its terrains. Nitrogen frost is found at the bottom of craters. Bright and dark regions on Pluto have different ice compositions.

Data collected by New Horizons’ MVIC and LEISA instruments was used in 2023 to create spectral maps of Sputnik Planitia, Cthulhu Macula, and Lowell Regio, regions on Pluto’s surface.

A global topography map of Pluto created in 2018 used data from New Horizons and stellar occultations to depict the distribution of volatiles, chemical elements and compounds that can be easily vaporized.

Three regions on Pluto—Kiladze, Viking Terra, and Virgil Fossae—could be cryovolcanoes. These resemble structures on Mars known to be cryogenic caldera, or depressions formed by cryovolcanism.

While Pluto’s topography is current, Charon’s is ancient. Charon may have experienced tectonics, processes that shape and create a planet’s crust, early in its history. While it may have once had a subsurface ocean, that has long since frozen solid.

Progress in Understanding the Pluto System: Ten Years After Flyby

 

It is almost impossible to believe, but tomorrow marks the 10^th anniversary of New Horizons’ historic Pluto flyby. To commemorate the anniversary and reflect on what has been learned about Pluto in the decade that has passed, the Universities Space Research Association’s (USRA) Lunar and Planetary Institute (LPI) is holding a weeklong conference titled “Progress in Understanding the Pluto System: Ten Years Since Flyby” from July 14-18 at the Johns Hopkins University Applied Physics Laboratory (JHUAPL), mission headquarters, in Laurel, Maryland.

The four-and-a-half-day conference offers an option to attend virtually, which I will be doing this week, and reporting here on the talks. Topics to be addressed include Pluto’s volatile ices, its geology and geophysics, its climate history, its atmosphere, Charon’s geology and craters; the comparative planetology of dwarf planets and Kuiper Belt Objects; history of the New Horizons mission; future exploration of Pluto and the Kuiper Belt; the origin of Pluto and its moons, and more.

On the afternoon of Thursday, July 17, presentations will address possible return missions to Pluto, including Persephone, a proposed Pluto orbiter and Kuiper Belt explorer, and the Gold Standard Mission, also a Pluto orbiter proposal and extended Kuiper Belt exploration mission.

While these are currently only in the concept stages, they matter because the New Horizons flyby raised more questions than answers, leading scientists to recognize the need for a follow up orbiter mission.

A Pluto day, one rotation of the planet on its axis, takes 6.4 Earth days. As a flyby mission, New Horizons did not have the time to study Pluto for a full rotation, as the spacecraft could not brake and slow down to observe the planet. Therefore, only one hemisphere of Pluto was imaged and studied in high resolution. The other hemisphere was imaged only on approach in low resolution, meaning less is known about it. An orbiter would reveal the secrets of that hemisphere as well as provide additional data about the side of Pluto that was explored in high resolution.

While the current political climate may not be conducive to spending money on new planetary missions, this could very well change with a different administration, so it is important to develop and study possible plans for a follow up mission.

Here, you can find a program of the conference talks along with links to the abstracts of those talks.

Oppose cuts to NASA missions: Call your representatives and senators now

 

                                           This image shows NASA missions that are cancelled in this bill

The proposed US budget reconciliation bill, which many of us refer to as the Big Ugly Bill, is a huge disaster for NASA and its space programs, including New Horizons, and anyone who values our space program must do everything in our power to make sure it does not pass.

Well known for its disastrous proposed cuts to Medicaid, , SNAP, social safety net programs, and environmental protection, this bill proposes huge cuts to NASA, including cancellation of the New Horizons mission, the Mars Sample Return mission, Juno, OSIRIS-Rex, MAVEN, various Earth science projects, the Chandra X-ray Observatory, the Nancy Grace Roman Space Telescope, the Lunar Gateway program, the Space Launch System, the Orion spacecraft after the Artemis 3 mission, and many others, for a total reduction of agency funding by 25%.

No reasons are given for the proposed termination of these programs, but presumably, the cuts would be done to fund yet another tax break for the wealthy and large corporations—the last thing this country needs.

Personally, I am a Democrat and a progressive, though I have tried to keep these views out of this blog and focus on Pluto’s planethood, planetary science, and our space program.

However, one does not need to be a Democrat or progressive to recognize how disastrous these cuts to NASA would be for our country and for science.

It is fair to say that the US space program has been a key player in American greatness since the 1960s. To this day, the US is the only country that has ever landed astronauts on the Moon, and it is the only country to have robotically explored all of the solar system’s planets, with the exception of newly-discovered remote dwarf planets such as Haumea, Makemake, Eris, Sedna, Orcus, etc.

In 2019, New Horizons conducted the most distant flyby of any solar system object when it visited KBO Arrokoth, located four billion miles (6.4 billion km) from Earth. Mission team members are still searching for a third, even more distant KBO flyby target.

Today, New Horizons is studying the solar wind, studying the Kuiper Belt far beyond Pluto, and even contributing to heliophysics, and the study of structures and processes in the Milky Way galaxy.

Every one of the NASA missions targeted for cancellation has contributed to our understanding of the origins and formation of the solar system, the study of astrophysics and cosmology, and the workings of Earth’s climate.

These missions have made the US a worldwide leader in science and have even led innovations in technology and robotics with far ranging implications, including new ways of assisting people with disabilities.

It is inconceivable that an administration whose stated goal is to make America “great” would propose to cancel so much of exactly that which makes us great.

Needless to say, cancellation of these missions will result in many scientists losing their jobs and thereby will increase our country’s unemployment rate. We are already experiencing a “brain drain” of scientists in other fields leaving the country due to other cuts being enacted to government programs in science, technology, and health.

I urge everyone, regardless of party affiliation, to contact your Senators and Congress members and urge them to vote against this bill and against these cuts. They amount to a giant step backwards, the exact opposite of the direction toward which we should be moving. If anything, NASA’s budget should be increased to the levels it was during the Apollo missions.

To contact your U.S. Senators and Representatives, you can visit the official websites of the House of Representatives and the U.S. Senate (.gov). You can find their contact information, including website links and online contact forms, by searching for your representatives based on your zip code or by browsing the directory of members.

This bill may be voted on within the next few days, so please call now to save these crucial missions and our space program!

Scientists Make Groundbreaking Discovery about Pluto's Formation

 This sounds similar to the formation theory for Arrokoth.

https://www.msn.com/en-us/news/technology/scientists-make-groundbreaking-discovery-about-pluto-s-formation/ar-AA1Em10J?ocid=nl_article_link

Pluto at 95

 

Happy International Pluto Day! Ninety-five years ago today, on February 18, 1930, 24-year-old Clyde Tombaugh discovered Planet Pluto while blinking between photographic plates of the sky taken on two separate nights in January of that year.

The goal was to find anything that moved against the background stars between nights. That object would not be a star but a planet within our solar system.

The announcement of Pluto’s discovery was not made until a month later, on March 13, 1930 by the Lowell Observatory, which chose this date because it was the birthday of its late founder Percival Lowell as well as the anniversary of the discovery of Uranus in 1781.

Incredibly, Tombaugh was not even credited in initial announcements of the discovery. He was described as a “junior astronomer” and not named, as the observatory wanted to focus the credit on Percival Lowell, who had predicted the existence of a planet beyond Neptune but had not actually found it.

Ironically, given that Lowell died despairing about never having discovered the planet, Pluto does appear on what are called “precovery” images he took around 1905 and 1906. It is not unusual for scientists to search earlier images after the discovery of a celestial object to determine whether that object appeared in a photo but remained unrecognized.

That was the case with Lowell and Pluto. He had photographed Pluto, but he didn’t recognize it for what it was, likely because he was looking for a giant planet like Uranus or Neptune rather than a small one, which Pluto turned out to be.

Celebrated annually at the Lowell Observatory to this day with an I Heart Pluto festival, Pluto’s discovery remains in many ways a triumph of underdogs. Tombaugh had only a high school diploma when he made the discovery. While searching for the planet, he was told by a professional astronomer that he was wasting his time, that if there were any more planets to be found, they would already have been found.

When Lowell Observatory director Vesto Slipher published an article about the discovery in Science News-Letter, he credited Lowell without even mentioning Tombaugh. Similarly, in the same publication, Harvard astronomer Harlow Shapley and Yale astronomer Frank Schlesinger wrote, “to Professor Lowell…belongs the credit.”

A certain elitism among astronomers of the time led them to have trouble accepting that a “kid” without an advanced degree had discovered a planet. Citizen science was not yet a “thing,” and the notion that an ordinary person could make the type of discovery for which those with PhDs worked hard for many years appeared to make those scholars uncomfortable.

After falling into obscurity for decades as the planet the least was known about, Pluto began to regain popularity during the 1960s and 1970s. Its largest moon, Charon, really a binary partner, was found in 1978.

Tombaugh himself described feeling like an outsider, someone who did not quite measure up to others in his field. This is evident from his sense of genuine surprise at his burgeoning popularity following the 50th anniversary celebrations of Pluto’s discovery, in 1980.  Biographer David Levy quotes Tombaugh’s ironic reaction. “I misjudged the attitude of astronomers. I thought I was a nobody. I thought they had contempt for me”

For almost a century, Pluto and its discoverer have shared this underdog quality, from some, a sense that they weren’t good enough and didn’t measure up, but from others, the sense of being a folk hero and a rock star.  Both were seriously underestimated—Tombaugh as a professional astronomer and Pluto as a planet.

Pluto may be smaller than most solar system planets and have an eccentric orbit, but those things do not preclude it from being a planet. They just make it a different type of planet. In the last 30 years, exoplanets have been found with orbits around their stars that are far more eccentric than Pluto’s path around the Sun. Some of these exoplanets are giant, Jupiter-like worlds.

New Horizons surprised scientists and ordinary people worldwide, who had expected to see a dead world but instead were treated to images of one that is geologically active and has some planetary processes seen elsewhere in the solar system only on Earth and Mars.

Yet even now, misinformation about Pluto is rampant. An article about the I Heart Pluto celebration stated that Pluto’s “reclassification” was done because objects larger than Pluto were discovered in the outer solar system. This is not true and is based on information that was proven wrong close to 15 years ago.

Eris was initially thought to be larger than Pluto, but a team of astronomers led by Bruno Sicardy observed it occult (pass in front of) a star in 2010 and found Eris to be marginally smaller than Pluto yet slightly more massive. It is disappointing that so many years later, the initial error about Eris being larger is still being spread in the mainstream media.

With time, Tombaugh has been recognized and fully credited for his discovery. Similarly, as time passes, I believe Pluto will be recognized for and credited as the planet it is. It may be different from the solar system’s four terrestrials and four jovians, but it is far from the only planet of its kind. And it is only a matter of time before similar small planets are discovered orbiting other stars.

Meanwhile, the same persistence and perseverance that led to Pluto’s discovery will motivate those of us who fight for its rightful recognition as a planet. Dwarf planets are planets too!

I Heart Pluto Festival at Lowell Observatory This Weekend

 

Lowell Observatory’s annual I Heart Pluto festival is back, celebrating the 95^th anniversary of Pluto’s discovery on February 18, 1930.

This year’s celebration, held in Flagstaff, Arizona, features a Pluto Pub Crawl with Pluto-themed drinks and talks with Lowell astronomers; various science talks including a keynote Night of Discovery featuring Alan Stern, David Levy, and Adam Nimoy, son of Star Trek actor Leonard Nimoy; various festival activities, and a children’s choir performance of “Ode to Pluto,” the song by Mark Burrows that I sing at my annual birthday party.

There will even be a “Shakespeare on Pluto” performance, a comedy with music celebrating both Shakespeare and space exploration.

For more on these events, which take place tonight and this weekend, visit Lowell’s I Heart Pluto page.

Even if you can’t make it to Flagstaff, this is the time to celebrate Pluto’s discovery 95 years ago and learn more about this small but amazing planet.

I hope some of the talks will be recorded and put online and will keep everyone informed if and when this happens.