Pluto’s status as a non-planet may be coming to an end. Professor Mike Brown of Caltech ended Pluto’s planetary status in 2006. But now, Kirby Runyon, a doctoral student at Johns Hopkins University, thinks it’s time to cancel that demotion and restore it as our Solar System’s ninth planet.
Pluto’s rebirth as a planet is not just all about Pluto, though. A newer, more accurate definition of what is and what is not a planet is needed. And if Runyon and the other people on the team he leads are successful, our Solar System would have more than 100 planets, including many bodies we currently call moons. (Sorry elementary school students.)
In 2006, the International Astronomical Union (IAU) changed the definition of what a planet is. Pluto’s demotion stemmed from discoveries in the 1990’s showing that it is actually a Kuiper Belt Object (KBO). It was just the first KBO that we discovered. When Pluto was discovered by Clyde Tombaugh in 1930, and included as the ninth planet in our Solar System, we didn’t know much about the Kuiper Belt.
But in 2005, the dwarf planet Eris was discovered. It was like Pluto, but 27% more massive. This begged the question, Why Pluto and not Eris? The IAU struck a committee to look into how planets should be defined.
In 2006, the IAU had a decision to make. Either expand the definition of what is and what is not a planet to include Eris and other bodies like Ceres, or shrink the definition to omit Pluto. Pluto was demoted, and that’s the way it’s been for a decade. Just enough time to re-write text books.
But a lot has happened since then. The change to the definition of planet was hotly debated, and for some, the change should never have happened. Since the New Horizons mission arrived at Pluto, that debate has been re-opened.
“A planet is a sub-stellar mass body that has never undergone nuclear fusion…” – part of the new planetary definition proposed by Runyon and his team.
The group behind the drive to re-instate Pluto have a broader goal in mind. If the issue of whether Pluto is or is not a planet sounds a little pedantic, it’s not. As Runyon’s group says on their poster to be displayed at the upcoming conference, “Nomenclature is important as it affects how we compare, think, and communicate about objects in nature.”
Runyon’s team proposes a new definition of what is a planet, focused on the geophysics of the object: “A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has enough gravitation to be round due to hydrostatic equilibrium regardless of its orbital parameters.”
The poster highlights some key points around their new planetary definition:
Emphasizes intrinsic as opposed to extrinsic properties.
Can be paraphrased for younger students: “Round objects in space that are smaller than stars.”
The geophysical definition is already in use, taught, and included in planetological glossaries.
There’s no need to memorize all 110 planets. Teach the Solar Systems zones and why different planet types formed at different distances from the Sun.
Their proposal makes a lot of sense, but there will be people opposed to it. 110 planets is quite a change, and the new definition is a real mouthful.
“They want Pluto to be a planet because they want to be flying to a planet.” – Prof. Mike Brown, from a BBC interview, July 2015.
Mike Brown, the scientist behind Pluto’s demotion, saw this all coming when New Horizons reached the Pluto system in the Summer of 2015. In an interview with the BBC, he said “The people you hear most talking about reinstatement are those involved in the (New Horizons) mission. It is emotionally difficult for them.”
Saying that the team behind New Horizons find Pluto’s status emotionally difficult seems pretty in-scientific. In fact, their proposed new definition seems very scientific.
There may be an answer to all of this. The term “classical planets” might be of some use. That term could include our 9 familiar planets, the knowledge of which guided much of our understanding and exploration of the Solar System. But it’s a fact of science that as our understanding of something grows more detailed, our language around it has to evolve to accommodate. Look at the term planetary nebula—still in use long after we know they have nothing to do with planets—and how much confusion it causes.
“It is official without IAU approval, partly via usage.” – Runyon and team, on their new definition.
In the end, it may not matter whether the IAU is convinced by Runyon’s proposed new definition. As their poster states, “As a geophysical definition, this does not fall under the domain of the IAU, and is an alternate and parallel definition that can be used by different scientists. It is “official” without IAU approval, partly via usage.”
It may seem pointless to flip-flop back and forth about Pluto’s status as a planet. But there are sound reasons for updating definitions based on our growing knowledge. We’ll have to wait and see if the IAU agrees with that, and whether or not they adopt this new definition, and the >100 planet Solar System.
You can view Runyon and team’s poster here.
You can view Emily Lakdawalla’s image of round objects in our Solar System here.
You can read the IAU’s definition of a planet here.
Humanity’s understanding of what constitutes a planet has changed over time. Whereas our most notable magi and scholars once believed that the world was a flat disc (or ziggurat, or cube), they gradually learned that it was in fact spherical. And by the modern era, they came to understand that the Earth was merely one of several planets in the known Universe.
And yet, our notions of what constitutes a planet are still evolving. To put it simply, our definition of planet has historically been dependent upon our frame of reference. In addition to discovering extra-solar planets that have pushed the boundaries of what we consider to be normal, astronomers have also discovered new bodies in our own backyard that have forced us to come up with new classification schemes.
History of the Term:
To ancient philosophers and scholars, the Solar Planets represented something entirely different than what they do today. Without the aid of telescopes, the planets looked like particularly bright stars that moved relative to the background stars. The earliest records on the motions of the known planets date back to the 2nd-millennium BCE, where Babylonian astronomers laid the groundwork for western astronomy and astrology.
These include the Venus tablet of Ammisaduqa, which catalogued the motions of Venus. Meanwhile, the 7th-century BCE MUL.APIN tablets laid out the motions of the Sun, the Moon, and the then-known planets over the course of the year (Mercury, Venus, Mars, Jupiter and Saturn). The Enuma anu enlil tablets, also dated to the 7th-century BCE, were a collection of all the omens assigned to celestial phenomena and the motions of the planets.
By classical antiquity, astronomers adopted a new concept of planets as bodies that orbited the Earth. Whereas some advocated a heliocentric system – such as 3rd-century BCE astronomer Aristarchus of Samos and 1st-century BCE astronomer Seleucus of Seleucia – the geocentric view of the Universe remained the most widely-accepted one. Astronomers also began creating mathematical models to predict their movements during this time.
This culminated in the 2nd century CE with Ptolemy’s (Claudius Ptolemaeus) publication of the Almagest, which became the astronomical and astrological canon in Europe and the Middle East for over a thousand years. Within this system, the known planets and bodies (even the Sun) all revolved around the Earth. In the centuries that followed, Indian and Islamic astronomers would added to this system based on their observations of the heavens.
By the time of the Scientific Revolution (ca. 15th – 18th centuries), the definition of planet began to change again. Thanks to Nicolaus Copernicus, Galileo Galilei, and Johannes Kepler, who proposed and advanced the heliocentric model of the Solar System, planets became defined as objects that orbited the Sun and not Earth. The invention of the telescope also led to an improved understanding of the planets, and their similarities with Earth.
Between the 18th and 20th centuries, countless new objects, moons and planets were discovered. This included Ceres, Vesta, Pallas (and the Main Asteroid Belt), the planets Uranus and Neptune, and the moons of Mars and the gas giants. And then in 1930, Pluto was discovered by Clyde Tombaugh, which was designated as the 9th planet of the Solar System.
Throughout this period, no formal definition of planet existed. But an accepted convention existed where a planet was used to described any “large” body that orbited the Sun. This, and the convention of a nine-planet Solar System, would remain in place until the 21st century. By this time, numerous discoveries within the Solar System and beyond would lead to demands that a formal definition be adopted.
Working Group on Extrasolar Planets:
While astronomers have long held that other star systems would have their own system of planets, the first reported discovery of a planet outside the Solar System (aka. extrasolar planet or exoplanet) did not take place until 1992. At this time, two radio astronomers working out of the Arecibo Observatory (Aleksander Wolszczan and Dale Frail) announced the discovery of two planets orbiting the pulsar PSR 1257+12.
The first confirmed discovery took place in 1995, when astronomers from the University of Geneva (Michel Mayor and Didier Queloz) announced the detection of 51 Pegasi. Between the mid-90s and the deployment of the Kepler space telescope in 2009, the majority of extrasolar planets were gas giants that were either comparable in size and mass to Jupiter or significantly larger (i.e. “Super-Jupiters”).
These new discoveries led the International Astronomical Union (IAU) to create the Working Group of Extrasolar Planets (WGESP) in 1999. The stated purpose of the WGESP was to “act as a focal point for international research on extrasolar planets.” As a result of this ongoing research, and the detection of numerous extra-solar bodies, attempts were made to clarify the nomenclature.
As of February 2003, the WGESP indicated that it had modified its position and adopted the following “working definition” of a planet:
1) Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are “planets” (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.
2) Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are “brown dwarfs”, no matter how they formed nor where they are located.
3) Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not “planets”, but are “sub-brown dwarfs” (or whatever name is most appropriate).
As of January 22nd, 2017, more than 2000 exoplanet discoveries have been confirmed, with 3,565 exoplanet candidates being detected in 2,675 planetary systems (including 602 multiple planetary systems).
2006 IAU Resolution:
During the early-to-mid 2000s, numerous discoveries were made in the Kuiper Belt that also stimulated the planet debate. This began with the discovery of Sedna in 2003 by a team of astronomers (Michael Brown, Chad Trujillo and David Rabinowitz) working at the Palomar Observatory in San Diego. Ongoing observations confirmed that it was approx 1000 km in diameter, and large enough to undergo hydrostatic equilibrium.
This was followed by the discovery of Eris – an even larger object (over 2000 km in diameter) – in 2005, again by a team consisting of Brown, Trujillo, and Rabinowitz. This was followed by the discovery of Makemake on the same day, and Haumea a few days later. Other discoveries made during this period include Quaoar in 2002, Orcus in 2004, and 2007 OR10 in 2007.
The discovery of a several objects beyond Pluto’s orbit that were large enough to be spherical led to efforts on behalf of the IAU to adopt a formal definition of a planet. By October 2005, a group of 19 IAU members narrowed their choices to a shortlist of three characteristics. These included:
A planet is any object in orbit around the Sun with a diameter greater than 2000 km. (eleven votes in favour)
A planet is any object in orbit around the Sun whose shape is stable due to its own gravity. (eight votes in favour)
A planet is any object in orbit around the Sun that is dominant in its immediate neighbourhood. (six votes in favour)
After failing to reach a consensus, the committee decided to put these three definitions to a wider vote. This took place in August of 2006 at the 26th IAU General Assembly Meeting in Prague. On August 24th, the issue was put to a final draft vote, which resulted in the adoption of a new classification scheme designed to distinguish between planets and smaller bodies. These included:
(1) A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.
(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.
In accordance with this resolution, the IAU designated Pluto, Eris, and Ceres into the category of “dwarf planet”, while other Trans-Neptunian Objects (TNOs) were left undeclared at the time. This new classification scheme spawned a great deal of controversy and some outcries from the astronomical community, many of whom challenged the criteria as being vague and debatable in their applicability.
For instance, many have challenged the idea of a planet clearing its neighborhood, citing the existence of near-Earth Objects (NEOs), Jupiter’s Trojan Asteroids, and other instances where large planets share their orbit with other objects. However, these have been countered by the argument that these large bodies do not share their orbits with smaller objects, but dominate them and carry them along in their orbits.
Another sticking point was the issue of hydrostatic equilibrium, which is the point where a planet has sufficient mass that it will collapse under the force of its own gravity and become spherical. The point at which this takes place remains entirely unclear thought, and some astronomers therefore challenge it being included as a criterion.
In addition, some astronomers claim that these newly-adopted criteria are only useful insofar as Solar planets are concerned. But as exoplanet research has shown, planets in other star star systems can be significantly different. In particular, the discovery of numerous “Super Jupiters” and “Super Earths” has confounded conventional notions of what is considered normal for a planetary system.
In June 2008, the IAU executive committee announced the establishment of a subclass of dwarf planets in the hopes of clarifying the definitions further. Comprising the recently-discovered TNOs, they established the term “plutoids”, which would thenceforth include Pluto, Eris and any other future trans-Neptunian dwarf planets (but excluded Ceres). In time, Haumea, Makemake, and other TNOs were added to the list.
Despite these efforts and changes in nomenclature, for many, the issue remains far from resolved. What’s more, the possible existence of Planet 9 in the outer Solar System has added more weight to the discussion. And as our research into exoplanets continues – and uncrewed (and even crewed) mission are made to other star systems – we can expect the debate to enter into a whole new phase!
On July 14th, 2015, the New Horizons mission made history by conducting the first flyby of Pluto. This represented the culmination of a nine year journey, which began on January 19th, 2006 – when the spacecraft was launched from the Cape Canaveral Air Force Station. And before the mission is complete, NASA hopes to send the spacecraft to investigate objects in the Kuiper Belt as well.
To mark the 11th anniversary of the spacecraft’s launch, members of the New Horizons team took part in panel a discussion hosted by the Johns Hopkins University Applied Physics Laboratory (JHUAPL) located in Laurel, Maryland. The event was broadcasted on Facebook Live, and consisted of team members speaking about the highlights of the mission and what lies ahead for the NASA spacecraft.
The live panel discussion took place on Thursday, Sept. 19th at 4 p.m. EST, and included Jim Green and Alan Stern – the director the Planetary Science Division at NASA and the principle investigator (PI) of the New Horizons mission, respectively. Also in attendance was Glen Fountain and Helene Winters, New Horizons‘ project managers; and Kelsi Singer, the New Horizons co-investigator.
In the course of the event, the panel members responded to questions and shared stories about the mission’s greatest accomplishments. Among them were the many, many high-resolution photographs taken by the spacecraft’s Ralph and Long Range Reconnaissance Imager (LORRI) cameras. In addition to providing detailing images of Pluto’s surface features, they also allowed for the creation of the very first detailed map of Pluto.
Though Pluto is not officially designated as a planet anymore – ever since the XXVIth General Assembly of the International Astronomical Union, where Pluto was designated as a “dwarf planet” – many members of the team still consider it to be the ninth planet of the Solar System. Because of this, New Horizons‘ historic flyby was of particular significance.
As Principle Investigator Alan Stern – from the Southwestern Research Institute (SwRI) – explained in an interview with Inverse, the first phase of humanity’s investigation of the Solar System is now complete. “What we did was we provided the capstone to the initial exploration of the planets,” he said. “All nine have been explored with New Horizons finishing that task.”
Other significant discoveries made by the New Horizons mission include Pluto’s famous heart-shaped terrain – aka. Sputnik Planum. This region turned out to be a young, icy plain that contains water ice flows adrift on a “sea” of frozen nitrogen. And then there was the discovery of the large mountain and possible cryovolcano located at the tip of the plain – named Tombaugh Regio, (in honor of Pluto’s discovered, Clyde Tombaugh).
The mission also revealed further evidence of geological activity and cryovolcanism, the presence of hyrdocarbon clouds on Pluto, and conducted the very first measurements of how Pluto interacts with solar wind. All told, over 50 gigabits of data were collected by New Horizons during its encounter and flyby with Pluto. And the detailed map which resulted from it did a good job of capturing all this complexity and diversity. As Stern explained:
“That really blew away our expectations. We did not think that a planet the size of North America could be as complex as Mars or even Earth. It’s just tons of eye candy. This color map is the highest resolution we will see until another spacecraft goes back to Pluto.”
After making its historic flyby of Pluto, the New Horizons team requested that the mission receive an extension to 2021 so that it could explore Kuiper Belt Objects (KBOs). This extension was granted, and for the first part of the Kuiper Belt Extended Mission (KEM), the spacecraft will perform a close flyby of the object known as 2014 MU69.
This remote KBO – which is estimated to be between 25 – 45 km (16-28 mi) in diameter – was one of two objects identified as potential targets for research, and the one recommended by the New Horizons team. The flyby, which is expected to take place in January of 2019, will involve the spacecraft taking a series of photographs on approach, as well as some pictures of the object’s surface once it gets closer.
Before the extension ends in 2021, it will continue to send back information on the gas, dust and plasma conditions in the Kuiper Belt. Clearly, we are not finished with the New Horizons mission, and it is not finished with us!
Many of the rocket and space flight enthusiasts I know are also car buffs. If you fit into that category, here’s an opportunity you won’t want to miss: a chance to own the car that New Horizons principal investigator Alan Stern drove all the way to Pluto.
Well, technically, he drove his shiny red Nissan 350Z the entire time the New Horizons’ spacecraft was making a beeline for the icy dwarf planet. But Stern has now donated this car to the Lowell Observatory, the facility where Pluto was discovered. The car is being auctioned off on eBay, with proceeds going to support “Lowell’s mission of scientific research and education.” You can make your bid now, as bids are being accepted from December 15-24, and the winner will not only have the privilege of owning the car, but also enjoy a dinner with Stern.
Stern bought the car in 2006, the year New Horizons launched (it has a bumper sticker that says “My other vehicle is on its way to Pluto”) and he continued driving it until earlier this year, well past the spacecraft’s flyby of Pluto in July 2015.
It is a two-door model with red exterior and carbon interior, and has just over 77,000 miles on it, which, as Stern points out, is almost 10 times fewer miles than New Horizons clocked on its first day of flight. A November 9, 2016 appraisal states the vehicle is in excellent shape and has a life expectancy of 300,000 miles.
“It was Percival Lowell’s perseverance and dedication that resulted in the discovery of Pluto and, ultimately, resulted in the flight of New Horizons to explore this distant, small planet,” Stern said in a press release from the Lowell Observatory. “New Horizons was, and is, the best aspect of my career so far, so I wanted to donate this car to Lowell Observatory as a fundraising vehicle to recognize the fact that New Horizons could not have happened without the historic and pioneering work that took place at Lowell Observatory early in the last century.”
Stern was the impetus behind New Horizons, billed as the fastest spacecraft ever launched, so he calls the Nissan 350Z his “second fastest vehicle.” He still oversees the New Horizons mission, as the spacecraft continues on its journey through the Kuiper Belt. It will fly past another object, named 2014 MU69, which Stern said is an ancient KBO that formed where it orbits now.
“It’s the type of object scientists have been hoping to study for decades, and this will be the most distant world we’ve ever been able to see up close,” Stern told me during an interview for my upcoming book, “Incredible Stories From Space.” Chapter 1 tells the stories of the New Horizons mission, including many stories from Stern.
With a penchant for both creating and driving state-of-the-art vehicles, Stern revealed earlier this year that his new car is a Tesla.
Lowell director Jeff Hall said, “It’s been a real pleasure working with Alan over the past few years leading up to and past the Pluto flyby. He’s been tremendously supportive of Lowell, and his donation of his car for us to auction is a sterling example of this. We’re thrilled by this gesture, and we look forward to meeting the lucky winner.”
The Lowell Observatory was founded in 1894 by Percival Lowell and has been home to many important discoveries including the detection of the large recessional velocities (redshift) of galaxies by Vesto Slipher in 1912-1914 (a result that led to the realization the universe is expanding), and the discovery of Pluto by Clyde Tombaugh in 1930. Today, Lowell’s 14 astronomers use ground-based telescopes around the world, telescopes in space, and NASA planetary spacecraft to conduct research in astronomy and planetary science. Lowell is a private, non-profit research institution and is located near Flagstaff, Arizona.
Okay, so this article is Colonizing the Outer Solar System, and is actually part 2 of our team up with Fraser Cain of Universe Today, who looked at colonizing the inner solar system. You might want jump over there now and watch that part first, if you are coming in from having seen part 1, welcome, it is great having you here.
Without further ado let us get started. There is no official demarcation between the inner and outer solar system but for today we will be beginning the outer solar system at the Asteroid Belt.
The Asteroid Belt is always of interest to us for colonization. We have talked about mining them before if you want the details on that but for today I’ll just remind everyone that there are very rich in metals, including precious metals like gold and platinum, and that provides all the motivation we need to colonize them. We have a lot of places to cover so we won’t repeat the details on that today.
You cannot terraform asteroids the way you could Venus or Mars so that you could walk around on them like Earth, but in every respect they have a lot going for them as a candidate. They’ve got plenty for rock and metal for construction, they have lots of the basic organic elements, and they even have some water. They also get a decent amount of sunlight, less than Mars let alone Earth, but still enough for use as a power source and to grow plants.
But they don’t have much gravity, which – pardon the pun – has its ups and downs. There just isn’t much mass in the Belt. The entire thing has only a small fraction of the mass of our moon, and over half of that is in the four biggest asteroids, essentially dwarf planets in their own right. The remainder is scattered over millions of asteroids. Even the biggest, Ceres, is only about 1% of 1% of Earth’s mass, has a surface gravity of 3% Earth-normal, and an escape velocity low enough most model rockets could get into orbit. And again, it is the biggest, most you could get away from by jumping hard and if you dropped an object on one it might take a few minutes to land.
You can still terraform one though, by definition too. The gentleman who coined the term, science fiction author Jack Williamson, who also coined the term genetic engineering, used it for a smaller asteroid just a few kilometers across, so any definition of terraforming has to include tiny asteroids too.
Of course in that story it’s like a small planet because they had artificial gravity, we don’t, if we want to fake gravity without having mass we need to spin stuff around. So if we want to terraform an asteroid we need to hollow it out and fill it with air and spin it around.
Of course you do not actually hollow out the asteroid and spin it, asteroids are loose balls of gravel and most would fly apart given any noticeable spin. Instead you would hollow it out and set a cylinder spinning inside it. Sort of like how a good thermos has an outside container and inside one with a layer of vacuum in between, we would spin the inner cylinder.
You wouldn’t have to work hard to hollow out an asteroid either, most aren’t big enough to have sufficient gravity and pressure to crush an empty beer can even at their center. So you can pull matter out from them very easily and shore up the sides with very thin metal walls or even ice. Or just have your cylinder set inside a second non-spinning outer skin or superstructure, like your washer or dryer.
You can then conduct your mining from the inside, shielded from space. You could ever pressurize that hollowed out area if your spinning living area was inside its own superstructure. No gravity, but warmth and air, and you could get away with just a little spin without tearing it apart, maybe enough for plants to grow to normally.
It should be noted that you can potentially colonize even the gas giants themselves, even though our focus today is mostly on their moons. That requires a lot more effort and technology then the sorts of colonies we are discussing today, Fraser and I decided to keep things near-future and fairly low tech, though he actually did an article on colonizing Jupiter itself last year that was my main source material back before got to talking and decided to do a video together.
Hydrogen is plentiful on Jupiter itself and floating refineries or ships that fly down to scoop it up might be quite useful, but again today we are more interested in its moons. The biggest problem with colonizing the moons of Jupiter is all the radiation the planet gives off.
Europa is best known as a place where the surface is covered with ice but beneath it is thought to be a vast subsurface ocean. It is the sixth largest moon coming right behind our own at number five and is one of the original four moons Galileo discovered back in 1610, almost two centuries before we even discovered Uranus, so it has always been a source of interest. However as we have discovered more planets and moons we have come to believe quite a few of them might also have subsurface oceans too.
Now what is neat about them is that water, liquid water, always leaves the door open to the possibility of life already existing there. We still know so little about how life originally evolved and what conditions permit that to occur that we cannot rule out places like Europa already having their own plants and animals swimming around under that ice.
They probably do not and obviously we wouldn’t want to colonize them, beyond research bases, if they did, but if they do not they become excellent places to colonize. You could have submarine cities in such places floating around in the sea or those buried in the surface ice layer, well shielded from radiation and debris. The water also geysers up to the surface in some places so you can start off near those, you don’t have to drill down through kilometers of ice on day one.
Water, and hydrogen, are also quite uncommon in the inner solar system so having access to a place like Europa where the escape velocity is only about a fifth of our own is quite handy for export. Now as we move on to talk about moons a lot it is important to note that when I say something has a fifth of the escape velocity of Earth that doesn’t mean it is fives time easier to get off of. Energy rises with the square of velocity so if you need to go five times faster you need to spend 5-squared or 25 times more energy, and even more if that place has tons of air creating friction and drag, atmospheres are hard to claw your way up through though they make landing easier too. But even ignoring air friction you can move 25 liters of water off of Europa for every liter you could export from Earth and even it is a very high in gravity compared to most moons and comets. Plus we probably don’t want to export lots of water, or anything else, off of Earth anyway.
We should start by noting two things. First, the Asteroid Belt is not the only place you find asteroids, Jupiter’s Trojan Asteroids are nearly as numerous, and every planet, including Earth, has an equivalent to Jupiter’s Trojan Asteroids at its own Lagrange Points with the Sun. Though just as Jupiter dwarfs all the other planets so to does its collection of Lagrangian objects. They can quite big too, the largest 624 Hektor, is 400 km across, and has a size and shape similar to Pennsylvania.
And as these asteroids are at stable Lagrange Points, they orbit with Jupiter but always ahead and behind it, making transit to and from Jupiter much easier and making good waypoints.
Before we go out any further in the solar system we should probably address how you get the energy to stay alive. Mars is already quite cold compared to Earth, and the Asteroids and Jupiter even more so, but with thick insulation and some mirrors to bounce light in you can do fairly decently. Indeed, sunlight out by Jupiter is already down to just 4% of what Earth gets, meaning at Jovian distances it is about 50 W/m²
That might not sound like much but it is actually almost a third of what average illumination is on Earth, when you factor in atmospheric reflection, cloudy days, nighttime, and higher, colder latitudes. It is also a good deal brighter than the inside of most well-lit buildings, and is enough for decently robust photosynthesis to grow food. Especially with supplemental light from mirrors or LED growth lamps.
But once you get out to Saturn and further that becomes increasingly impractical and a serious issue, because while food growth does not show up on your electric bill it is what we use virtually all our energy for. Closer in to the sun we can use solar panels for power and we do not need any power to grow food. As we get further out we cannot use solar and we need to heat or cold habitats and supply lighting for food, so we need a lot more power even as our main source dries up.
So what are our options? Well the first is simple, build bigger mirrors. A mirror can be quite large and paper thin after all. Alternatively we can build those mirrors far away, closer to the sun, and and either focus them on the place we want illuminated or send an energy beam, microwaves perhaps or lasers, out to the destination to supply energy.
We also have the option of using fission, if we can find enough Uranium or Thorium. There is not a lot of either in the solar system, in the area of about one part per billion, but that does amount to hundreds of trillions of tons, and it should only take a few thousand tons a year to supply Earth’s entire electric grid. So we would be looking at millions of years worth of energy supply.
Of course fusion is even better, particularly since hydrogen becomes much more abundant as you get further from the Sun. We do not have fusion yet, but it is a technology we can plan around probably having inside our lifetimes, and while uranium and thorium might be counted in parts per billion, hydrogen is more plentiful than every other element combines, especially once you get far from the Sun and Inner Solar System.
So it is much better power source, an effectively unlimited one except on time scales of billions and trillion of years. Still, if we do not have it, we still have other options. Bigger mirrors, beaming energy outwards from closer to the Sun, and classic fission of Uranium and Thorium. Access to fusion is not absolutely necessary but if you have it you can unlock the outer solar system because you have your energy supply, a cheap and abundant fuel supply, and much faster and cheaper spaceships.
Of course hydrogen, plain old vanilla hydrogen with one proton, like the sun uses for fusion, is harder to fuse than deuterium and may be a lot longer developing, we also have fusion using Helium-3 which has some advantages over hydrogen, so that is worth keeping in mind as well as we proceed outward.
Okay, let’s move on to Saturn, and again our focus is on its moons more than the planet itself. The biggest of those an the most interesting for colonization is Titan.
Titan is aptly named, this titanic moon contains more mass than than all of Saturn’s sixty or so other moons and by an entire order of magnitude at that. It is massive enough to hold an atmosphere, and one where the surface pressure is 45% higher than here on Earth. Even though Titan is much smaller than Earth, its atmosphere is about 20% more massive than our own. It’s almost all nitrogen too, even more than our own atmosphere, so while you would need a breather mask to supply oxygen and it is also super-cold, so you’d need a thick insulated suit, it doesn’t have to be a pressure suit like it would on Mars or almost anyplace else.
There’s no oxygen in the atmosphere, what little isn’t nitrogen is mostly methane and hydrogen, but there is plenty of oxygen in the ice on Titan which is quite abundant. So it has everything we need for life except energy and gravity. At 14% of earth normal it is probably too low for people to comfortably and safely adapt to, but we’ve already discussed ways of dealing with that. It is low enough that you could probably flap your arms and fly, if you had wing attached.
It needs some source of energy though, and we discussed that. Obviously if you’ve got fusion you have all the hydrogen you need, but Titan is one of those places we would probably want to colonize early on if we could, it is something you need a lot of to terraform other places, and is also rich in a lot of the others things we want. So we often think of it as a low-tech colony since it is one we would want early on.
In an scenario like that it is very easy to imagine a lot of local transit between Titan and its smaller neighboring moons, which are more rocky and might be easier to dig fissile materials like Uranium and Thorium out of. You might have a dozen or so small outposts on neighboring moons mining fissile materials and other metals and a big central hub on Titan they delivered that too which also exported Nitrogen to other colonies in the solar system.
Moving back and forth between moons is pretty easy, especially since things landing on Titan can aerobrake quite easily, whereas Titan itself has a pretty strong gravity well and thick atmosphere to climb out of but is a good candidate for a space elevator, since it requires nothing more sophisticated than a Lunar Elevator on our own moon and has an abundant supply of the materials needed to make Zylon for instance, a material strong enough to make an elevator there and which we can mass manufacture right now.
Titan might be the largest and most useful of Saturn’s moons, but again it isn’t the only one and not all of the other are just rocks for mining. At last count it has over sixty and many of them quite large. One of those, Enceladus, Saturn’s sixth largest moon, is a lot like Jupiter’s Moon Europa, in that we believe it has a large and thick subsurface ocean. So just like Europa it is an interesting candidate for Colonization. So Titan might be the hub for Saturn but it wouldn’t be the only significant place to colonize.
While Saturn is best known for its amazing rings, they tend to be overlooked in colonization. Now those rings are almost all ice and in total mass about a quarter as much as Enceladus, which again is Saturn’s Sixth largest moon, which is itself not even a thousandth of the Mass of Titan.
In spite of that the rings are not a bad place to set up shop. Being mostly water, they are abundant in hydrogen for fusion fuel and have little mass individually makes them as easy to approach or leave as an asteroid. Just big icebergs in space really, and there are many moonlets in the rings that can be as large as half a kilometer across. So you can burrow down inside one for protection from radiation and impacts and possibly mine smaller ones for their ice to be brought to places where water is not abundant.
In total those rings, which are all frozen water, only mass about 2% of Earth’s oceans, and about as much as the entire Antarctic sheet. So it is a lot of fresh water that is very easy to access and move elsewhere, and ice mines in the rings of Saturn might be quite useful and make good homes. Living inside an iceball might not sound appealing but it is better than it sounds like and we will discuss that more when we reach the Kupier Belt.
But first we still have two more planets to look at, Uranus and Neptune.
Uranus, and Neptune, are sometimes known as Ice Giants instead of Gas Giants because it has a lot more water. It also has more ammonia and methane and all three get called ices in this context because they make up most of the solid matter when you get this far out in the solar system.
While Jupiter is over a thousand times the mass of Earth, Uranus weighs in at about 15 times the Earth and has only about double the escape velocity of Earth itself, the least of any of the gas giants, and it’s strange rotation, and its strange tilt contributes to it having much less wind than other giants. Additionally the gravity is just a little less than Earth’s in the atmosphere so we have the option for floating habitats again, though it would be a lot more like a submarine than a hot air balloon.
Like Venus, Uranus has very long days, at least in terms of places receiving continual sunlight, the poles get 42 years of perpetual sunlight then 42 of darkness. Sunlight being a relative term, the light is quite minimal especially inside the atmosphere. The low wind in many places makes it a good spot for gas extraction, such as Helium-3, and it’s a good planet to try to scoop gas from or even have permanent installations.
Now Uranus has a large collection of moons as well, useful and colonizable like the other moons we have looked at, but otherwise unremarkable beyond being named for characters from Shakespeare, rather than the more common mythological names. None have atmospheres though there is a possibility Oberon or Titania might have subsurface oceans.
Neptune makes for a brief entry, it is very similar to Uranus except it has the characteristically high winds of gas giants that Uranus’s skewed poles mitigate, meaning it has no advantages over Uranus and the disadvantages of high wind speeds everywhere and being even further from the Sun. It too has moons and one of them, Triton, is thought to have subsurface oceans as well. Triton also presumably has a good amount of nitrogen inside it since it often erupts geysers of nitrogen from its surface.
Triton is one of the largest moons in the solar system, coming in seventh just after our Moon, number 5, and Europa at number 6. Meaning that were it not a moon it would probably qualify as a Dwarf Planet and it is often thought Pluto might be an escaped moon Neptune. So Triton might be one that didn’t escape, or didn’t avoid getting captured. In fact there are an awful lot of bodies in this general size range and composition wandering about in the outer regions of our solar system as we get out into the Kuiper Belt.
The Kuiper Belt is one of those things that has a claim on the somewhat arbitrary and hazy boundary marking the edge of the Solar System. It extends from out past Neptune to beyond Pluto and contains a good deal more mass than the asteroid Belt. It is where a lot of our comets come from and while there is plenty of rocks out there they tend to be covered in ice. In other words it is like our asteroid belt only there’s more of it and the one thing the belt is not very abundant in, water and hydrogen in general, is quite abundant out there. So if you have a power source life fusion they can be easily terraformed and are just as attractive as a source of minerals as the various asteroids and moons closer in.
We mentioned the idea of living inside hollowed out asteroids earlier and you can use the same trick for comets. Indeed you could shape them to be much bigger if you like, since they would be hollow and ice isn’t hard to move and shape especially in zero gravity. Same trick as before, you place a spinning cylinder inside it. Not all the objects entirely ice and indeed your average comet is more a frozen ball of mud then ice with rocky cores. We think a lot of near Earth Asteroids are just leftover comets. So they are probably pretty good homes if you have fusion, lots of fuel and raw materials for both life and construction.
This is probably your cheapest interstellar spacecraft too, in terms of effort anyway. People often talk about re-directing comets to Mars to bring it air and water, but you can just as easily re-direct it out of the solar system entirely. Comets tend to have highly eccentric orbits, so if you capture one when it is near the Sun you can accelerate it then, actually benefiting from the Oberth Effect, and drive it out of the solar system into deep space. If you have a fusion power source to live inside one then you also have an interstellar spaceship drive, so you just carve yourself a small colony inside the comet and head out into deep space.
You’ve got supplies that will last you many centuries at least, even if it were home to tens of thousand of people, and while we think of smaller asteroids and comets as tiny, that’s just in comparison to planets. These things tend to be the size of mountain so there is plenty of living space and a kilometer of dirty ice between you and space makes a great shield against even the kinds of radiation and collisions you can experience at relativistic speeds.
Now the Oort Cloud is much like the Kupier Belt but begins even further out and extends out probably an entire light year or more. We don’t have a firm idea of its exact dimensions or mass, but the current notion is that it has at least several Earth’s worth of mass, mostly in various icy bodies. These will be quite numerous, estimates usually assumes at least trillion icy bodies a kilometer across or bigger, and even more smaller ones. However the volume of space is so large that those kilometer wide bodies might each be a around a billion kilometers distant from neighbors, or about a light hour. So it is spread out quite thinly, and even the inner edge is about 10 light days away.
That means that from a practical standpoint there is no source of power out there, the sun is simply too diffuse for even massive collections of mirrors and solar panels to be of use. It also means light-speed messages home or to neighbors are quite delayed. So in terms of communication it is a lot more like pre-modern times in sparsely settled lands where talking with your nearest neighbors might require an hour long walk over to their farm, and any news from the big cities might take months to percolate out to you.
There’s probably uranium and thorium out there to be found, maybe a decent amount of it, so fission as a power source is not ruled out. If you have fusion instead though each of these kilometer wide icy bodies is like a giant tank of gasoline, and as with the Kupier Belt, ice makes a nice shield against impacts and radiation.
And while there might be trillions of kilometer wide chunks of ice out there, and many more smaller bodies, you would have quite a few larger ones too. There are almost certainly tons of planets in the Pluto size-range out these, and maybe even larger ones. Even after the Oort cloud you would still have a lot of these deep space rogue planets which could bridge the gap to another solar system’s Oort Cloud. So if you have fusion you have no shortage of energy, and could colonize trillions of these bodies. There probably is a decent amount of rock and metal out there too, but that could be your major import/export option shipping home ice and shipping out metals.
That’s the edge of the Solar System so that’s the end of this article. If you haven’t already read the other half, colonizing the inner Solar System, head on over now.
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The evidence keeps growing for a large subsurface ocean at Pluto, which also provides clues how the iconic ‘heart’ of Pluto was formed.
We reported in early October that thermal models of Pluto’s interior and tectonic evidence suggest an ocean may exist beneath Pluto’s heart-shaped Sputnik Planitia. Now, new research on data from the New Horizons mission shows more indications of an ocean just below Pluto’s surface that consists of a slushy, viscous liquid, kept warm from Pluto’s interior and a hint of anti-freeze.
“As far as we can tell, there’s no tidal heating helping to keep the ocean liquid,” Francis Nimmo from UC Santa Cruz told Universe Today. He is the first author of a paper on the new findings published today in Nature. “The main heat source keeping the ocean liquid is radioactive decay in Pluto’s rocky interior, although it certainly helps if there is an ‘antifreeze’ present.”
Nimmo said he suspects the ocean is mostly water with ammonia acting as an antifreeze. This subsurface ocean is also bulging, similar to the ‘mascons’ on the Moon, putting stress on Pluto’s icy outer shell, causing fractures consistent with features seen in the New Horizons images.
Sputnik Planitia forms one side of the prominent heart-shaped feature seen in some of the first close-up images from New Horizons July 2015 flyby. It was likely created by the impact of a giant meteorite, which would have blasted away a huge amount of Pluto’s icy crust.
But a deep basin is just a “big, elliptical hole in the ground,” Nimmo said, that would not provide the extra mass needed to cause that kind of reorientation. “So, the extra weight must be hiding somewhere beneath the surface. And an ocean is a natural way to get that.”
But Pluto is cold, with temperatures ranging from -387 to -369 Fahrenheit (-233 to -223 Celsius). How could there be an ocean?
“Pluto is small enough that it’s just about almost cooled off but still has a little heat, and it’s about 2 percent the heat budget of the Earth, in terms of how much energy is coming out,” said co-author Richard Binzel, from MIT. “So we calculated Pluto’s size with its interior heat flow, and found that underneath Sputnik Planitia, at those temperatures and pressures, you could have a zone of water-ice that could be at least viscous. It’s not a liquid, flowing ocean, but maybe slushy. And we found this explanation was the only way to put the puzzle together that seems to make any sense.”
The massive basin also appears extremely bright relative to the rest of the planet, and the data from New Horizons suggest it is filled with frozen nitrogen ice.
Previous research from the the mission showed evidence that the liquid nitrogen may be constantly refreshing, or convecting, as a result of a weak spot at the bottom of the basin, and this weak spot may let heat rise through Pluto’s interior to continuously refresh the ice.
Additionally, the extra weight of an underground ocean could help explain the longstanding question of why Pluto’s heart aligns almost exactly opposite from Charon. Nimmo said this alignment is “suspicious” and that the likelihood of this being just a coincidence is only 5 percent. Therefore, the alignment suggests that extra mass in that location interacted with tidal forces between Pluto and Charon to reorient Pluto, putting Sputnik Planitia directly opposite the side facing Charon.
A thick, heavy ocean, the new data suggest, may have served as a “gravitational anomaly,” which would factor heavily in Pluto and Charon’s gravitational tug-of-war, the researchers said. Over millions of years, the planet would have spun around, aligning its subsurface ocean and the heart-shaped region above it, almost exactly opposite along the line connecting Pluto and Charon.
While scientists are still studying the data from New Horizons, it is safe to say that Pluto keeps surprising everyone, even the scientists who know it best.
“Pluto is hard to fathom on so many different levels,” said Binzel.
Finally, the New Horizons team has their entire “pot of gold.” 15 months after the mission’s flyby of the Pluto system, the final bits of science data from the historic July 2015 event has been safely transmitted to Earth.
“The New Horizons mission has required patience for many years, but we knew the results would be well worth the wait,” New Horizons project scientists Hal Weaver told me earlier this year.
Because of New Horizons’ great distance from Earth and the spacecraft’s low power output (the spacecraft runs on just 2-10 watts of electricity), it has a relatively low ‘downlink’ rate at which data can be transmitted to Earth, just 1-4 kilobits per second. That’s why it has taken so long to get all the science data back to Earth.
“This is what we came for – these images, spectra and other data types that are going to help us understand the origin and the evolution of the Pluto system for the first time,” New Horizons principal investigator Alan Stern said a few months ago during an interview. “We’re seeing that Pluto is a scientific wonderland. The images have been just magical. It’s breathtaking.”
Because it was a flyby, and the spacecraft had just one chance at gathering data from Pluto, New Horizons was designed to gather as much data as it could, as quickly as it could – taking about 100 times more data on close approach to Pluto and its moons than it could have sent home before flying onward. The spacecraft was programmed to send select, high-priority datasets home in the days just before and after close approach, and began returning the vast amount of remaining stored data in September 2015.
New Horizons is now over 3.1 billion miles (5 billion km) away from Earth as it continues its journey through the Kuiper Belt. That translates to a current radio signal delay time of five hours, eight minutes at light speed.
The science team created special software to keep track of all the data sets and schedule when they would be returned to Earth.
The final item that was received was a portion of a Pluto-Charon observation sequence taken by the Ralph/LEISA imager. It arrived at New Horizons’ mission operations at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, at 5:48 a.m. EDT on Oct. 25. The downlink came via NASA’s Deep Space Network station in Canberra, Australia. It was the last of the 50-plus total gigabits of Pluto system data transmitted to Earth by New Horizons over the past 15 months.
“We have our pot of gold,” said Mission Operations Manager Alice Bowman, of APL.
Bowman also said the team will conduct a final data-verification review of New Horizons two onboard recorders before sending commands to erase all the data on the spacecraft. New Horizons has more work to do, so erasing the “old” data will clear space for new data to be taken during its Kuiper Belt Extended Mission (KEM). The spacecraft will do a series of distant Kuiper Belt object observations as well as perform a close encounter flyby with with a small Kuiper Belt object, 2014 MU69, on Jan. 1, 2019.
“There’s a great deal of work ahead for us to understand the 400-plus scientific observations that have all been sent to Earth,” said Stern. “And that’s exactly what we’re going to do—after all, who knows when the next data from a spacecraft visiting Pluto will be sent?”
By the end of this week, all the data gathered by the New Horizons spacecraft during its July 2015 flyby of the Pluto system will have finished downloading to Earth and be in the hands of the science team. Bonnie Buratti, a science team co-investigator said they have gone from being able to look at the pretty pictures to doing the hard work required to study the data. During today’s press briefing from the Division of Planetary Sciences conference, the New Horizons team shared a few interesting and curious findings they’ve found in the data so far.
While the famous global view of Pluto appears to show a cloud-free dwarf planet, Principal investigator Alan Stern said the team has now take a closer look and found handful of potential clouds in images taken with New Horizons’ cameras.
“Clouds are common in the atmospheres of the solar system,” Stern said during the briefing, “ and a natural question was whether Pluto, with a nitrogen atmosphere, has any clouds.”
Stern said they’ve known since flyby that Pluto has haze layers, as seen in the backlit lead image above, as New Horizons flew away from Pluto. “They stretch more than 200 km into the sky, and we’ve counted over two dozen concentric layers,” he said.
While hazes are not clouds, Stern said they have identified candidates for clouds in high-phase images from the Long Range Reconnaissance Imager and the Multispectral Visible Imaging Camera.
“The seven candidates are all similar in that they are very low altitude,” Stern said, and they are all low-lying, isolated small features, so no broad cloud decks or fields. When we map them over the surface, they all lie near the terminator, so they occur near dawn or dusk. This is all suggestive they are clouds because low-lying regions and dawn or dusk provide cooler conditions where clouds may occur.”
Stern told Universe Today that these possible, rare condensation clouds could be made of ethane, acetylene, hydrogen cyanide or methane under the right conditions. Stern added these clouds are probably short-lived phenomena – again, likely occurring only at dawn or dusk. A day on Pluto is 6.4 days on Earth.
“But if there are clouds, it would mean the weather on Pluto is even more complex than we imagined,” Stern said.
Disappointingly, the New Horizons team has no way of confirming if these are clouds or not. “None of them can be confirmed as clouds because they are very low lying and we don’t have stereo images to tell us more,” Stern said, adding that the only way to confirm if there are condensation clouds on Pluto would be to return with an orbiter mission.
Landslides on Charon
While Pluto shows many kinds of activity, one surface process scientists haven’t seen on the dwarf planet is landslides. Surprisingly, though, they have been spotted on Pluto’s largest moon, Charon.
“We’ve seen similar landslides on other rocky and icy planets, such as Mars and Saturn’s moon Iapetus, but these are the first landslides we’ve seen this far from the sun, in the Kuiper Belt,” said Ross Beyer, a science team researcher from Sagan Center at the SETI Institute and NASA Ames Research Center, California. “The big question is will they be detected elsewhere in the Kuiper Belt?”
Long runout landslides seen on Charon’s Serenity Chasm shows a 200-meter thick lobate landslide that runs up against a 6 km high ridge.
“With our images, we can just resolve a smooth apron and the deposit as a whole,” said Beyer, “we can’t see individual grains. But given the cold conditions on Charon, the deposit likely made of boulders of ice and rock.”
Beyer said earthquakes or an impact could have jump started the landslide on regions that were ready to slide. “The boulders may have melted and the edges and got slippery enough to begin to slide down the slope,” he said.
The images of Serenity Chasma were taken by New Horizons’ Long Range Reconnaissance Imager (LORRI) on July 14, 2015, from a distance of 48,912 miles (78,717 kilometers).
Beyer added that while Pluto doesn’t have landslides, it does have material that appears to be moving downhill as rock falls and glacier-like flows.
Bright and active
New Horizons data shows that portions of Pluto’s large heart-shaped region, Sputnik Planitia, are among the most reflective in the solar system. “That brightness indicates surface activity,” said Buratti, “similar to how Saturn’s moon Enceladus is very reflective, about 100% reflective, and is very active with plumes and geysers. Because we see a pattern of high surface reflectivity equating to activity, we can infer that the dwarf planet Eris, which is known to be highly reflective, is also likely to be active.”
New Horizons is now making a beeline for its next target, KBO 2014 MU69. Cameras on the New Horizons spacecraft have been taking long range images and MU69 is the smallest KBO to have its color measured: it has a reddish tint. Scientists have used that data to confirm this object is part of the so-called cold classical region of the Kuiper Belt, which is believed to contain some of the oldest, most prehistoric material in the solar system.
“The reddish color tells us the type of Kuiper Belt object 2014 MU69 is,” said Amanda Zangari, a New Horizons post-doctoral researcher from Southwest Research Institute. “The data confirms that on New Year’s Day 2019, New Horizons will be looking at one of the ancient building blocks of the planets.”
Zangari added that they will be using the Hubble Space Telescope to better understand MU69.
“We would like to use Hubble to its find rotation rate and better understand its shape, as far as planning,” she said. “We would like to know ahead of time, if it is oblong, we would like to fly when the longest point is facing the telescope.”
Several times during the briefing, Stern indicated how having a future mission that orbited Pluto would answer so many outstanding questions the team has. He outlined one potential mission that is in the very earliest stages of study where a spacecraft could be launched on NASA’s upcoming Space Launch System (SLS) and the spacecraft could have an RTG-powered ion engine that would allow a fast-moving spacecraft the ability to slow down and go into orbit (unlike New Horizons). This type of architecture would allow for a flight time of 7.5 years to Pluto, quicker than New Horizons’ nearly 9.5 years.
The Kuiper Belt has been an endless source of discoveries over the course of the past decade. Starting with the dwarf planet Eris, which was first observed by a Palomar Observatory survey led by Mike Brown in 2003, many interesting Kuiper Belt Objects (KBOs) have been discovered, some of which are comparable in size to Pluto.
And according to a new report from the IAU Minor Planet Center, yet another body has been discovered beyond the orbit of Pluto. Officially designated as 2014 UZ224, this body is located about 14 billion km (90 AUs, or 8.5 billion miles) from the Sun. This dwarf planet is not only the latest member of the our Solar family, it is also the second-farthest body from our Sun with a stable orbit.
The discovery was made by David Gerdes, a professor of astrophysics at the University of Michigan, and various colleagues associated with at the Dark Energy Survey (DES) – a project which relies on the Cerro Tololo Inter-American Observatory in Chile. In the past, Gerdes’ research has focused on the detection of dark energy and the expansion of the Universe.
Towards this end, DES has spent the past five years surveying roughly one-eighth of the sky using the Dark Energy Camera (DECam), a 570-Megapixel camera mounted on the Victor M. Blanco telescope at Cerro Tololo. This instrument was commissioned by the US. Dept of Energy to conduct surveys of distant galaxies, and Dr. Gerdes had a hand in creating.
Not surprisingly, this same technology has also allowed for discoveries to be made at the edge of the Solar System. Two years ago, this is precisely what Gerdes challenged a group of undergraduate students to do (as part of a summer project). These students examined images taken by DES between 2013-2016 for indications of moving objects. Since that time, the analysis team has grown to include senior scientists, postdocs, graduate and undergraduate students.
Whereas distant stars and galaxies would appear stationary in these images, distant TNOs showed up in different places over time – hence why are called “transients”. As Dr. Gerdes explains in his 2014 UZ224 Fact Sheet, which is available through his University of Michigan homepage:
“To identify transients, we used a technique known as “difference imaging”. When we take a new image, we subtract from it an image of the same area of the sky taken on a different night. Objects that don’t change disappear in this subtraction, and we’re left with only the transients… This process yields millions of transients, but only about 0.1% of them turn out to be distant minor planets. To find them, we must “connect the dots” and determine which transients are actually the same thing in different positions on different nights. There are many dots and MANY more possible ways to connect them.”
This was a difficult process. In addition to needing thousands of computers at Fermilab to process the hundreds of terabytes of data, the team had to write special programs to do it. Gerdes and his colleagues also relied on help from Professors Masao Sako and Gary Bernstein of the University of Pennsylvania, who contributed the key breakthroughs that allowed them to perform difference imaging over the entire survey area.
In the end, dozens of new Trans-Neptunian Objects (TNOs) were discovered, one of which was 2014 UZ224. According to their observations, its diameter could be anywhere from 350 to 1200 km, and it takes 1,136 years to complete a single orbit of our Sun. For the sake of perspective, Pluto is 2370 km in diameter, and has an orbital period of 248 years.
Stephanie Hamilton, a graduate student at the University of Michigan, was personally involved with the project. Her role was to determine the size of 2014 UZ224, which was difficult from initial observations alone. As she told Universe Today via email:
“The object’s brightness in visible light alone depends both on its size and how reflective it is, so you can’t uniquely determine one of those properties without assuming a value for the other. Fortunately there’s a solution to that problem – the heat the object emits is also proportional to its size, so obtaining a thermal measurement in addition to the optical measurements means we would then be able to calculate the object’s size and albedo (reflectance) without having to assume one or the other.
“We were able to obtain an image of our object at a thermal wavelength using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. I am working on combining all of our data together to determine the size and albedo, and we expect to submit a paper on our results around mid-November or so.”
But as with all things related to “dwarf planets”, there has been some disagreement over this discovery. Given the dimensions of the object, there are some who question whether or not the label applies. But as Gerdes indicates on the Fact Sheet, this body fits most of the prerequisites:
“According to the official IAU guidelines, a dwarf planet must satisfy four criteria. It must a) orbit the sun (check!), b) not be a satellite (check!) c) not have cleared the neighborhood around its orbit (check!) and d) have enough mass to be round. It’s this last item that’s uncertain, and the only way for sure is to get a picture that’s detailed enough to actually see its shape. Nevertheless, an object over 400 km in diameter is likely to be round.”
Gerdes and his team expect to be busy, authoring the paper that will detail their findings, using the ALMA array to get more assessments of 2014 UZ224 size, and sifting through the data to look for more objects in the Kuiper Belt. This includes the fabled Planet 9, which astronomers have been seeking out for years.
Given its distance from the Sun, 2014 UZ224’s orbit would not be influenced by the presence of Planet 9, and is therefore of no help. However, Gerdes is optimistic that the evidence of this massive body is there in the data. Given time, and a lot of data-processing, they just might find it! In the meantime, this newly discovered object is likely to be the focal point of a lot of fascinating research.
“It’s an interesting object in its own right – distant objects like this are ‘cosmic leftovers’ from the primordial disk that gave birth to the solar system,” writes Gerdes. “By studying them and learning more about their distribution, orbital characteristics, sizes, and surface properties, we can learn more about the processes that gave birth to the solar system and ultimately to us.”