Eris Archives

August 19, 2015August 11, 2016 by Matt Williams

The Dwarf Planet (and Plutoid) Makemake

Discovered in 2005, Makemake, a Kuiper Belt Object (KBO) has . Credit: NASA

In 2003, astronomer Mike Brown and his team from Caltech began a discovery process which would change the way we think of our Solar System. Initially, it was the discovery of a body with a comparable mass to Pluto (Eris) that challenged the definition of the word “planet”. But in the months and years that followed, more discoveries would be made that further underlined the need for a new system of classification.

This included the discovery of Haumea, Orcus and Salacia in 2004, and Makemake in 2005. Like many other Trans-Neptunian Objects (TNOs) and Kuiper Belt Objects (KBOs) discovered in the past decade, this planet’s status is the subject of some debate. However, the IAU was quick to designate it as the fourth dwarf planet in our Solar System, and the third “Plutoid“.

Discovery and Naming:

Makemake was discovered on March 31st, 2005, at the Palomar Observatory by a team consisting of Mike Brown, Chad Trujillo and David Rainowitz. The discovery was announced to the public on July 29th, 2005, coincident with the announcement of the discovery of Eris. Originally, Brown and his team had been intent on waiting for further confirmation, but chose to proceed after a different team in Spain announced the discovery of Haumea on July 27th.

The provisional designation of 2005 FY₉ was given to Makemake when the discovery was first made public. Before that, the discovery team used the codename “Easterbunny” for the object, because it was observed shortly after Easter. In July of 2008, in accordance with IAU rules for classical Kuiper Belt Objects, 2005 FY₉ was given the name of a creator deity.

*Photograph of Makemake taken by the Hubble Space Telescope. Credit: NASA/Mike Brown*

In order to preserve the object’s connection with Easter, the object was given a name derived from the mythos of the Rapa Nui (the native people of Easter Island) to whom Makemake is the creator God. It was officially classified as a dwarf planet and a plutoid by the International Astronomical Union (IAU) on July 19th, 2008.

Size, Mass and Orbit:

Based on infrared observations conducted by Brown and his team using the Spitzer Space Telescope, which were compared to similar observations made by the Herschel Space Telescope, an estimated diameter of 1,360 – 1,480 km was made. Subsequent observations made during the 2011 stellar occulation by Makemake produced estimated dimensions of 1502 ± 45 × 1430 ± 9 km.

Estimates of its mass place it in the vicinity of 4 x 10²¹ kg (4,000,000,000 trillion kg), which is the equivalent of 0.00067 Earths. This makes Makemake the third largest known Trans-Neptunian Object (TNOs) – smaller than Pluto and Eris, and slightly larger than Haumea.

Makemake has a slightly eccentric orbit (of 0.159), which ranges from 38.590 AU (5.76 billion km/3.58 billion mi) at perihelion to 52.840 AU ( 7.94 billion km or 4.934 billion miles) at aphelion. It has an orbital period of 309.09 Earth years, and takes about 7.77 Earth hours to complete a single sidereal rotation. This means that a single day on Makemake is less than 8 hours and a single year last as long as 112,897 days.

*A selection of dwarf planets, sometimes considered trans-Neptunian objects depending on their interactions with the planet Neptune. Credit: NASA/STSci*

As a classical Kuiper Belt Object, Makemake’s orbit lies far enough from Neptune to remain stable over the age of the Solar System. Unlike plutinos, which can cross Neptune’s orbit, classical KBOs are free from Neptune’s perturbation. Such objects have relatively low eccentricities (below 0.2) and orbit the Sun in much the same way the planets do. Makemake, however, is a member of the “dynamically hot” class of classical KBOs, meaning that it has a high inclination compared to others in its population.

Composition and Surface:

With an estimated mean density of 1.4–3.2 g/cm³, Makemake is believed to be differentiated between an icy surface and a rocky core. Like Pluto and Eris, the surface ice is believed to be composed largely of frozen methane (CH4) and ethane (C2H6). Though evidence exists for traces of nitrogen ice as well, it is nowhere near as prevalent as with Pluto or Triton.

Javier Licandro and his colleagues at the Instituto de Astrofisica de Canarias performed examinations of Makemake using the William Herschel Telescope and Telescopio Nazionale Galileo. According to their findings, Makemake has a very bright surface (with a surface albedo of 0.81) which means it closely resembles that of Pluto.

In essence, it appears reddish in color (significantly more so than Eris), which also indicates strong concentrations of tholins in the surface ice. This is consistent with the presence of methane ice, which would have turned red due to exposure to solar radiation over time.

Atmosphere:

During it’s 2011 occultation with an 18th-magnitutde star, Makemake abruptly blocked all of its light. These results showed that Makemake lacks a substantial atmosphere, which contradicted earlier assumptions about it having an atmosphere comparable to that of Pluto. However, the presence of methane and possibly nitrogen suggests that Makemake could have a transient atmosphere similar to that of Pluto when it reaches perihelion.

*Artist’s impression of the surface of Makemake. Credit: NASA*

Essentially, when Makemake is closest to the Sun, nitrogen and other ices would sublimate, forming a tenuous atmosphere composed of nitrogen gas and hydrocarbons. The existence of an atmosphere would also provide a natural explanation for the nitrogen depletion, which could have been lost over time through the process of atmospheric escape.

Moon:

In April of 2016, observations using the Hubble Space Telescope‘s Wide Field Camera 3 revealed that Makemake had a natural satellite – which was designated S/2015 (136472) 1 (nicknamed MK 2 by the discovery team). It is estimated to be 175 km (110 mi) km in diameter and has a semi-major axis at least 21,000 km (13,000 mi) from Makemake.

Exploration:

Currently, no missions have been planned to the Kuiper Belt for the purpose of conducting a survey of Makemake. However, it has been calculated that – based on a launch date of August 21st, 2024, and August 24th, 2036 – a flyby mission to Makemake could take just over 16 years, using a Jupiter gravity assist. On either occasion, Makemake would be approximately 52 AU from the Sun when the spacecraft arrives.

Makemake is now the fourth designated dwarf planet in the solar system, and the third Plutoid. In the coming years, it is likely to be joined several more objects in the Trans-Neptunian region that are similar in size, mass, and orbit. And assuming we mount a flyby to the region, we may discover many similar objects, and learn a great deal more about this one.

We have many interesting articles on Makemake and the Kuiper Belt here at Universe Today. Here’s How Many Planets are in the Solar System, and Makemake’s Mysterious Atmosphere.

Sources:

August 17, 2015April 8, 2018 by Matt Williams

What Is A Dwarf Planet?

An artist's concept showing the size of the best known dwarf planets compared to Earth and its moon (top). Eris is left center; Ceres is the small body to its right and Pluto and its moon Charon are at the bottom. Credit: NASA

The term dwarf planet has been tossed around a lot in recent years. As part of a three-way categorization of bodies orbiting the Sun, the term was adopted in 2006 due to the discovery of objects beyond the orbit of Neptune that were comparable in size to Pluto. Since then, it has come to be used to describe many objects in our Solar System, upending the old classification system that claimed there were nine planets.

The term has also led to its fair share of confusion and controversy, with many questioning its accuracy and applicability to bodies like Pluto. Nevertheless, the IAU currently recognizes five bodies within our Solar System as dwarf planets, six more could be recognized in the coming years, and as many as 200 or more could exist within the expanse of the Kuiper Belt.

Definition:

According to the definition adopted by the IAU in 2006, a dwarf planet is, “a celestial body orbiting a star that is massive enough to be rounded by its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite. More explicitly, it has to have sufficient mass to overcome its compressive strength and achieve hydrostatic equilibrium.”

In essence, the term is meant to designate any planetary-mass object that is neither a planet nor a natural satellite that fits two basic criteria. For one, it must be in direct orbit of the Sun and not be a moon around another body. Second, it must be massive enough for it to have become spherical in shape under its own gravity. And, unlike a planet, it must have not cleared the neighborhood around its orbit.

Size and Mass:

In order for a body to be become rounded, it must be sufficiently massive, to the point that its own gravity is the dominant force effecting it. Here, the internal pressure created by this mass would cause a surface to achieve plasticity, allowing high elevations to sink and hollows to fill in. This does not occur with smaller bodies that are less than a few km in diameter (such as asteroids), which are dominated by forces outside of their own gravity forces and tend to maintain irregular shapes.

Meanwhile, bodies that measure a few kilometers across – where their gravity is more significant but not dominant – tend to be spheroid or “potato-shaped”. The bigger the body is, the higher its internal pressure, until the pressure is sufficient to overcome its internal compressive strength and it achieves hydrostatic equilibrium. At this point, a body is as round as it can possibly be, given its rotation and tidal effects. This is the defining limit of a dwarf planet.

However, rotation can also affect the shape of a dwarf planet. If the body does not rotate, it will be a sphere. But the faster it does rotate, the more oblate or even scalene it becomes. The extreme example of this is Haumea, which is twice as long along its major axis as it is at the poles. Tidal forces also cause a body’s rotation to gradually become tidally locked, such that it always presents the same face to its companion. An extreme example of this is the Pluto-Charon system, where both bodies are tidally locked to each other.

The upper and lower size and mass limits of dwarf planets have not been specified by the IAU. And while the lower limit is defined as the achievement of a hydrostatic equilibrium shape, the size or mass at which an object attains this shape depends on its composition and thermal history.

For example, bodies made of rigid silicates (such as rocky asteroids) should achieve hydrostatic equilibrium at a diameter of approx. 600 km and a mass of 3.4×10²⁰ kg. For a body made of less rigid water ice, the limit would closer to 320 km and 10¹⁹ kg. As a result, no specific standard currently exists for defining a dwarf planet based on either its size or mass, but is instead more generally defined based on its shape.

Orbital Dominance:

In addition to hydrostatic equilibrium, many astronomers have insisted that a distinction between planets and dwarf planets be made based on the inability of the latter to “clear the neighborhood around their orbits”. In short, planets are able to remove smaller bodies near their orbits by collision, capture, or gravitational disturbance (or establish orbital resonances that prevent collisions), whereas dwarf planets do not have the requisite mass to do this.

To calculate the likelihood of a planet clearing its orbit, planetary scientists Alan Stern and Harold F. Levison (the former of whom is the principal investigator of the New Horizons mission to Pluto and the Chief Scientist at Moon Express) introduced a parameter they designated as ? (lambda).

This parameter expresses the likelihood of an encounter resulting in a given deflection of an object’s orbit. The value of this parameter in Stern’s model is proportional to the square of the mass and inversely proportional to the period, and can be used to estimate the capacity of a body to clear the neighborhood of its orbit.

Astronomers like Steven Soter, the scientist-in-residence for NYU and a Research Associate at the American Museum of Natural History, have advocated using this parameter to differentiate between planets and dwarf planets. Soter has also proposed a parameter he refers to as the planetary discriminant – designated as µ (mu) – which is calculated by dividing the mass of the body by the total mass of the other objects that share its orbit.

Recognized and Possible Dwarf Planets:

There are currently five dwarf planets: Pluto, Eris, Makemake, Haumea, and Ceres. Only Ceres and Pluto have been observed enough to indisputably fit into the category. The IAU decided that unnamed Trans-Neptunian Objects (TNOs) with an absolute magnitude brighter than +1 (and a mathematically delimited minimum diameter of 838 km) are to be named as dwarf planets.

Possible candidates that are currently under consideration include Orcus, 2002 MS₄, Salacia, Quaoar, 2007 OR₁₀, and Sedna. All of these objects are located in the Kuiper Belt or the Scattered Disc; with the exception of Sedna, which is a detached object – a special class that applies to dynamic TNOs in the outer Solar System.

It is possible that there are another 40 known objects in the solar system that could be rightly classified as dwarf planets. Estimates are that up to 200 dwarf planets may be found when the entire region known as the Kuiper belt is explored, and that the number may exceed 10,000 when objects scattered outside the Kuiper belt are considered.

Pluto and moons Charon, Hydra and Nix (left) compared to the dwarf planet Eris and its moon Dysmonia (right). This picture was taken before Kerberos and Styx were discovered in 2011 and 2012, respectively. Credit: International Astronomical Union — *Pluto and moons Charon, Hydra and Nix (left) compared to the dwarf planet Eris and its moon Dysmonia (right). Credit: International Astronomical Union*

Contention:

In the immediate aftermath of the IAU decision regarding the definition of a planet, a number of scientists expressed their disagreement with the IAU resolution. Mike Brown (the leader of the Caltech team that discovered Eris) agrees with the reduction of the number of planets to eight. However, astronomers like Alan Stern have voiced criticism over the IAUs definition.

Stern has contended that much like Pluto, Earth, Mars, Jupiter, and Neptune have not fully cleared their orbital zones. Earth orbits the Sun with 10,000 near-Earth asteroids, which in Stern’s estimation contradicts the notion that it has cleared its orbit. Jupiter, meanwhile, is accompanied by a whopping 100,000 Trojan asteroids on its orbital path.

Thus, in 2011, Stern still referred to Pluto as a planet and accepted other dwarf planets such as Ceres and Eris, as well as the larger moons, as additional planets. However, other astronomers have countered this opinion by saying that, far from not having cleared their orbits, the major planets completely control the orbits of the other bodies within their orbital zone.

Another point of contention is the application of this new definition to planets outside of the Solar System. Techniques for identifying extrasolar objects generally cannot determine whether an object has “cleared its orbit”, except indirectly. As a result, a separate “working” definition for extrasolar planets was established by the IAU in 2001 and includes the criterion that, “The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in the Solar System.”

Credit: The Habitable Exoplanets Catalog, Planetary Habitability Laboratory @ UPR Arecibo (phl.upl.edu) — *How the current IAU definition applies to exoplanets is a source of controversy for many astronomers. Credit: phl.upl.edu*

Beyond the content of the IAU’s decision, there is also the controversy surrounding the decision process itself. Essentially, the final vote involved a relatively small percentage of the IAU General Assembly – 425 out of 9000, or less than 5%. This was due in part to the timing of the vote, which happened on the final day of the ten-day event when many members had already left.

However, supporters of the decision emphasize that a sampling of 400 representative out of a population of 9,000 statistically yields a result with good accuracy. Ergo, even if only 4-5% of the members voted in favor of reclassifying Pluto, the fact that the majority of said members agreed could be taken as a sampling of IAU opinion as a whole.

There is also the issue of the many astronomers who were unable to attend to the conference or who chose not to make the trip to Prague. Astronomer Marla Geha has also clarified that not all members of the Union were needed to vote on the classification issue, and that only those whose work is directly related to planetary studies needed to be involved.

Lastly, NASA has announced that it will use the new guidelines established by the IAU, which constitutes an endorsement or at least acceptance of the IAUs position. Nevertheless, the controversy surrounding the 2006 decision is by no means over, and we can expect further developments on this front as more “dwarf planets” are found and designated.

Understanding what is a dwarf planet according to the IAU is easy enough, but making the solar system fit into a three tiered classification system will prove increasingly difficult as our understanding of the universe increases and we are able to see farther and farther into space.

We have written many articles about dwarf planets for Universe Today. Here’s one about Dwarf Planets, and here’s one on Why Pluto is no longer a planet.

Astronomy Cast also has an episode all about Dwarf Planets. Listen here, Episode 194: Dwarf Planets.

For more information, check out NASA’s Solar System Overview: Dwarf Planets, the Solar System Exploration Guide on Dwarf Planets, and Mike Brown’s Dwarf Planet page.

Here is the list of all the known Dwarf Planets and their moons. We hope you find what you are looking for:

Recognized Dwarf Planets:

Possible Dwarf Planets:

August 10, 2015August 26, 2017 by Matt Williams

The Dwarf Planet Sedna

An artist's conception of Sedna. this assumes that Sedna has a tiny as yet undiscovered moon. Image credit; NASA/JPl-Caltech

There has been quite a bit of buzz about dwarf planets lately. Ever since the discovery of Eris in 2005, and the debate that followed over the proper definition of the word “planet”, this term has been adopted to refer to planets beyond Neptune that rival Pluto in size. Needless to say, it has been a controversial subject, and one which is not likely to be resolved anytime soon.

In the meantime, the category has been used tentatively to describe many Trans-Neptunian objects that were discovered before or since the discovery of Eris. Sedna, which was discovered in the outer reaches of the Solar System in 2003, is most likely a dwarf planet. And as the furthest known object from the Sun, and located within the hypothetical Oort Cloud, it is quite the fascinating find.

Discovery and Naming:

Much like Eris, Haumea and Makemake, Sedna was co-discovered by Mike Brown of Caltech, with assistance from Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale University on November 14th, 2003. Initially designated as 2003 VB12, the discovery was part of a survey that commenced in 2001 using the Samuel Oschin Telescope at the Palomar Observatory near San Diego, California.

Observations at the time indicated the presence of an object at a distance of approximately 100 AU from the Sun. Follow-up observations made in November and December of 2003 by the Cerro Tololo Inter-American Observatory in Chile and the W. M. Keck Observatory in Hawaii revealed that the object was moving along a distant highly eccentric orbit.

*Comparison of Sedna with the other largest TNOs and with Earth (all to scale). Credit: NASA/Lexicon*

It was later learned that the object had been previously observed by the Samual Oschin telescope as well as the Jet Propulsion Laboratory’s Near Earth Asteroid Tracking (NEAT) consortium. Comparisons with these previous observations have since allowed for a more precise calculation of Sedna’s orbit and orbital arc.

According to Mike Brown’s website, the planet was named Sedna after the Inuit Goddess of the sea. According to legend, Sedna was once mortal but became immortal after drowning in the Arctic Ocean, where she now resides and protects all the creatures of the sea. This name seemed appropriate to Brown and his team because Sedna is currently the farthest (and hence coldest) object from the Sun.

The team made the name public before the object had been officially numbered; and while this represented a breach in IAU protocol, no objections were raised. In 2004, the IAU’s Committee on Small Body Nomenclature formally accepted the name.

Classification:

Astronomers remain somewhat divided when it comes to Sedna’s proper classification. On the one hand, its discovery resurrected the question of which astronomical objects should be considered planets and which ones could not. Under the IAU’s definition of a planet, which was adopted on August 24th, 2006 (in response to the discovery of Eris), a planet needs to have cleared its orbit. Hence, Sedna does not qualify.

However, to be a dwarf planet, a celestial body must be in hydrostatic equilibrium – meaning that it is symmetrically rounded into a spheroid or ellipsoid shape. With a surface albedo of 0.32 ± 0.06 – and an estimated diameter of between 915 and 1800 km (compared to Pluto’s 1186 km) – Sedna is bright enough, and also large enough, to be spheroid in shape.

Therefore, Sedna is believed by many astronomers to be a dwarf planet, and is often referred to confidently as such. One reason why astronomers are reluctant to definitively place it in that category is because it is so far away that it is difficult to observe.

Size, Mass and Orbit:

In 2004, Mike Brown and his team placed an upper limit of 1,800 km on its diameter, but by 2007 this was revised downward to less than 1,600 km after observations were made by the Spitzer Space Telescope. In 2012, measurements from the Herschel Space Observatory suggested that Sedna’s diameter was between 915 and 1075 km, which would make it smaller than Pluto’s moon Charon.

Because Sedna has no known moons, determining its mass is currently impossible without sending a space probe. Nevertheless, many astronomers think that Sedna is the fifth largest trans-Neptunian object (TNO) and dwarf planet – after Eris, Pluto, Makemake, and Haumea, respectively.

Sedna has a highly elliptical orbit around the Sun, which means it ranges in distance from 76 astronomical units (AU) at perihelion (114 billion km/71 billion mi) to 936 AU (140 billion km/87 billion mi) at aphelion.

Sedna's orbit, compared to other bodies in the Solar System and the Kuiper Belt. Credit: web.gps.caltech.edu — *Sedna’s orbit, compared to other bodies in the Solar System, the Kuiper Belt and the Oort Cloud. Credit: web.gps.caltech.edu*

Estimations on how long it takes Sedna to orbit the Sun vary, although it is known to be more than 10,000 years. Some astronomers calculate the orbital period could be as long as 12,000 years. Although astronomers believed at first that Sedna had a satellite, they have not been able to prove it.

Composition:

At the time of its discovery, Sedna was the intrinsically brightest object found in the Solar System since Pluto in 1930. In terms of color, Sedna appears to be almost as red as Mars, which some astronomers believe is caused by hydrocarbon or tholin. Its surface is also rather homogeneous in terms of color and spectrum, which may the result of Sedna’s distance from the Sun.

Unlike planets in the Inner Solar System, Sedna experiences very few surface impacts from meteors or stray objects. As a result, it does not have as many exposed bright patches of fresh icy material. Sedna, and the entire Oort Cloud, is freezing at temperatures below 33 Kelvin (-240.2°C).

Models have been constructed of Sedna that place an upper limit of 60% for methane ice and 70% for water ice. This is consistent with the existence of tholins on it’s surface, since they are produced by the irradiation of methane. Meanwhile, M. Antonietta Barucci and colleagues compared Sedna’s spectrum to that of Triton and came up with a model that included 24% Triton-type tholins, 7% amorphous carbon, 10% nitrogen, 26% methanol and 33% methane.

Planetoid Sedna — *Artist’s concept of the surface of Sedna. Credit: NASA/ESA/Adolf Schaller*

The presence of nitrogen on the surface suggests the possibility that, at least for a short time, Sedna may have a tenuous atmosphere. During a 200-year period near perihelion, the maximum temperature on Sedna would likely exceed 35.6 K (-237.6 °C), which would be just warm enough for some of the nitrogen ice to sublimate. Models of internal heating via radioactive decay suggest that, like many bodies in the Outer Solar System, Sedna might be capable of supporting a subsurface ocean of liquid water.

Origin:

When he and his colleagues first observed Sedna, they claimed that it was part of the Oort Cloud – the hypothetical cloud of comets believed to exist a light-year’s distance from the Sun. This was based on the fact that Sedna’s perihelion (76 AUs) made it too distant to be scattered by the gravitational influence of Neptune.

Because it was also closer to the Sun than was expected from on Oort cloud object, and has an inclination in line with the planets and Kuiper Belt, they described it as being an “inner Oort Cloud object”. Brown and his colleagues have proposed that Sedna’s orbit is best explained by the Sun having formed in an open cluster of several stars that gradually disassociated over time.

In this scenario, Sedna was lifted into its current orbit by a star that was part of this cluster rather than it having been formed in its current location. This hypothesis has also been confirmed by computer simulations that suggest that multiple close passes by young stars in such a cluster would pull many objects into Sedna-like orbits.

The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA

On the other hand, if Sedna formed in its current location, then it would mean that the Sun’s original protoplanetary disc would have extended farther than previously expected – approximately 75 AUs into space. Also, Sedna’s initial orbit would have been approximately circular, otherwise its formation by the accretion of smaller bodies into a whole would not have been possible.

Therefore, it must have been tugged into its current eccentric orbit by a gravitational interaction with another body – which could have been another planet in the Kuiper Belt, a passing star, or one of the young stars embedded with the Sun in the stellar cluster in which it formed.

Another possibility is the Sedna’s orbit is the result of influence by a large binary companion thousands of AU distant from our Sun. One such hypothetical companion is Nemesis, a dim companion to the Sun. However, to date no direct evidence of Nemesis has been found, and many lines of evidence have thrown its existence into doubt.

More recently, it has also been suggested that Sedna did not originate in the Solar System, but was captured by the Sun from a passing extrasolar planetary system.

Astronomers believe that they will find more objects in the Oort Cloud in years to come, especially as ground-based and space telescopes become more advanced and sensitive. Most likely, we will also see Sedna officially christened a “dwarf planet” by the IAU. As with other astronomical bodies that have been designated as such, we can expect some controversy to follow!

Universe Today has many interesting articles on Sedna, including Sedna probably doesn’t have a moon and Dwarf Planets.

For more information, check out the story of Sedna and Sedna.

Astronomy Cast has an episode on Pluto and the icy outer Solar System, and The Oort Cloud.

Sources:

July 28, 2015August 11, 2016 by Matt Williams

Eris’ Moon Dysnomia

Tenth planet? Artists concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. Credit: Robert Hurt (IPAC)

Ask a person what Dysnomia refers to, and they might venture that it’s a medical condition. In truth, they would be correct. But in addition to being a condition that affects the memory (where people have a hard time remembering words and names), it is also the only known moon of the distant dwarf planet Eris.

In fact, the same team that discovered Eris a decade ago – a discovery that threw our entire notion of what constitutes a planet into question – also discovered a moon circling it shortly thereafter. As the only satellite that circles one of the most distant objects in our Solar System, much of what we know about this ball of ice is still subject to debate.

Discovery and Naming:

In January of 2005, astronomer Mike Brown and his team discovered Eris using the new laser guide star adaptive optics system at the W. M. Keck Observatory in Hawaii. By September, Brown and his team were conducting observations of the four brightest Kuiper Belt Objects – which at that point included Pluto, Makemake, Haumea, and Eris – and found indications of an object orbiting Eris.

Provisionally, this body was designated S/2005 1 (2003 UB³¹³). However, in keeping with the Xena nickname that his team was already using for Eris, Brown and his colleagues nicknamed the moon “Gabrielle” after Xena’s sidekick. Later, Brown selected the official name of Dysnomia for the moon, which seemed appropriate for a number of reasons.

For one, this name is derived from the daughter of the Greek god Eris – a daemon who represented the spirit of lawlessness – which was in keeping with the tradition of naming moons after lesser gods associated with the primary god. It also seemed appropriate since the “lawless” aspect called to mind actress Lucy Lawless, who portrayed Xena on television. However, it was not until the IAU’s resolution on what defined a planet – passed in August of 2006 – that the planet was officially designated as Dysnomia.

Size, Mass and Orbit:

The actual size of Dysnomia is subject to dispute, and estimates are based largely on the planet’s albedo relative to Eris. For example, the IAU and Johnston’s Asteroids with Satellites Database estimate that it is 4.43 magnitudes fainter than Eris and has an approximate diameter of between 350 and 490 km (217 – 304 miles)

However, Brown and his colleagues have stated that their observations indicate it to be 500 times fainter and between 100 and 250 km (62 – 155 miles) in diameter. Using the Herschel Space Observatory in 2012, Spanish astronomer Pablo Santo Sanz and his team determined that, provided Dysnomia has an albedo five times that of Eris, it is likely to be 685±50 km in diameter.

Forget about Pluto for a moment. Should Eris be our tenth Planet? Like Pluto it has a prominent moon- Dysnomia. Human perception and conceptions of the Universe have shaped our view of the Solar System. The Ptolemaic system (Earth centered), Kepler's Harmonic Spheres, even the fact that ten digits reside on our hands impact our impression of the Solar System (Photo Credits:NASA/ESA and M. Brown / Caltech) — *Eris and its moon, Dysnomia, as imaged by the W.M. Keck Observatory in Hawaii. Credits:NASA/ESA and M. Brown/Caltech*

In 2007, Brown and his team also combined Keck and Hubble observations to determine the mass of Eris, and estimate the orbital parameters of the system. From their calculations, they determined that Dysnomia’s orbital period is approximately 15.77 days. These observations also indicated that Dysnomia has a circular orbit around Eris, with a radius of 37350±140 km. In addition to being a satellite of a dwarf planet, Dysnomia is also a Kuiper Belt Object (KBO) like Eris.

Composition and Origin:

Currently, there is no direct evidence to indicate what Dysnomia is made of. However, based on observations made of other Kuiper Belt Objects, it is widely believed that Dysnomia is composed primarily of ice. This is based largely on infrared observations made of Haumea (2003 EL61), the fourth largest object in the Kuiper Belt (after Eris, Pluto and Makemake) which appears to be made entirely of frozen water.

Astronomers now know that three of the four brightest KBOs – Pluto, Eris and Haumea – have one or more satellites. Meanwhile, of the fainter members, only about 10% are known to have satellites. This is believed to imply that collisions between large KBOs have been frequent in the past. Impacts between bodies of the order of 1000 km across would throw off large amounts of material that would coalesce into a moon.

This is an artist's concept of Kuiper Belt object Eris and its tiny satellite Dysnomia. Eris is the large object at the bottom of the illustration. A portion of its surface is lit by the Sun, located in the upper left corner of the image. Eris's moon, Dysnomia, is located just above and to the left of Eris. The Hubble Space Telescope and Keck Observatory took images of Dysnomia's movement from which astronomer Mike Brown (Caltech) precisely calculated Eris to be 27 percent more massive than Pluto. Artwork Credit: NASA, ESA, Adolph Schaller (for STScI) — Artist’s concept of Kuiper Belt Object Eris and its tiny satellite Dysnomia. The Hubble Space Telescope and Keck Observatory took images of Dysnomia’s movement from which astronomer Mike Brown (Caltech) precisely calculated Eris to be 27 percent more massive than Pluto. Credit: NASA/ESA/Adolph Schaller (for STScI)

This could mean that Dysnomia was the result of a collision between Eris and a large KBO. After the impact, the icy material and other trace elements that made up the object would have evaporated and been ejected into orbit around Eris, where it then re-accumulated to form Dysnomia. A similar mechanism is believed to have led to the formation of the Moon when Earth was struck by a giant impactor early in the history of the Solar System.

Since its discovery, Eris has lived up to its namesake by stirring things up. However, it has also helped astronomers to learn many things about this distant region of the Solar System. As already mentioned, astronomers have used Dysnomia to estimate the mass of Eris, which in turn helped them to compare it to Pluto.

While astronomers already knew that Eris was bigger than Pluto, but they did not know whether it was more massive. This they did by measuring the distance between Dysnomia and how long it takes to orbit Eris. Using this method, astronomers were able to discover that Eris is 27% more massive than Pluto is.

With this knowledge in hand, the IAU then realized that either Eris needed to be classified as a planet, or that the term “planet” itself needed to be refined. Ergo, one could make that case that it was the discovery of Dysnomia more than Eris that led to Pluto no longer being designated a planet.

Universe Today has articles on Xena named Eris and The Dwarf Planet Eris. For more information, check out Dysnomia and dwarf planet outweighs Pluto.

Astronomy Cast has an episode on Pluto’s planetary identity crisis.

Sources:

July 13, 2015December 23, 2015 by Ken Kremer

Big Discovery from NASA’s New Horizons; Pluto is Biggest Kuiper Belt Body

A portrait from the final approach. Pluto and Charon display striking color and brightness contrast in this composite image from July 11, showing high-resolution black-and-white LORRI images colorized with Ralph data collected from the last rotation of Pluto. Color data being returned by the spacecraft now will update these images, bringing color contrast into sharper focus. Credits: NASA-JHUAPL-SWRI

Plutophiles everywhere rejoice. On the eve of history’s first ever up close flyby of mysterious Pluto on Tuesday morning July 14 making the first detailed scientific observations, NASA’s New Horizons has made a big discovery about one of the most basic questions regarding distant Pluto. How big is it?

Measurements by New Horizons gathered just in the past few days as the spacecraft barrels towards the Pluto planetary system now confirm that Pluto is indeed the biggest object in the vast region beyond the orbit of Neptune known as the Kuiper Belt.

Pluto is thus the undisputed King of the Kuiper Belt!

Pluto measures 1,473 miles (2,370 kilometers) in diameter, which is at the higher end of the range of previous estimates.

The big news was announced today, by New Horizons principal investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado, during a live media briefing at Pluto mission control at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland.

“This settles the debate about the largest object in the Kuiper Belt,” Stern noted.

New Horizons will swoop to within about 12,500 kilometers (nearly 7,750 miles) of Pluto’s surface and about 17,900 miles (28,800 kilometers) from Charon during closest approach at approximately 7:49 a.m. EDT (11:49 UTC) on July 14.

The new and definitive measurement of Pluto’s size is based on images taken by the high resolution Long Range Reconnaissance Imager (LORRI) to make this determination.

“The size of Pluto has been debated since its discovery in 1930. We are excited to finally lay this question to rest,” said mission scientist Bill McKinnon, Washington University, St. Louis.

Pluto was the first planet discovered by an American, Clyde Tombaugh.

Pluto’s “Heart” is seen in this new image from New Horizons’ Long Range Reconnaissance Imager (LORRI) received on July 8, 2015 after normal science operations resumed following the scary July 4 safe mode anomaly that briefing shut down all science operations. The LORRI image has been combined with lower-resolution color information from the Ralph instrument. Credits: NASA-JHUAPL-SWRI

Pluto is bigger than Eris, another big Kuiper Belt object discovered in 2005 by Mike Brown of Caltech, which is much further out from the Sun than Pluto. The discovery of Eris further fueled the controversial debate about the status of Pluto’s planethood.

Eris comes in second in size in the Kuiper Belt at only 1,445 miles (2,326 km) in diameter.

On July 11, 2015, New Horizons captured a world that is growing more fascinating by the day. For the first time on Pluto, this view reveals linear features that may be cliffs, as well as a circular feature that could be an impact crater. Rotating into view is the bright heart-shaped feature that will be seen in more detail during New Horizons’ closest approach on July 14. The annotated version includes a diagram indicating Pluto’s north pole, equator, and central meridian. Credits: NASA/JHUAPL/SWRI — On July 11, 2015, New Horizons captured a world that is growing more fascinating by the day. For the first time on Pluto, this view reveals linear features that may be cliffs, as well as a circular feature that could be an impact crater. Rotating into view is the bright heart-shaped feature that will be seen in more detail during New Horizons’ closest approach on July 14. The annotated version includes a diagram indicating Pluto’s north pole, equator, and central meridian.
Credits: NASA/JHUAPL/SWRI

Stern also noted that because Pluto is slight bigger than the average of previous estimates, its density is slightly lower than previously thought. Therefore the fraction of ice in its interior is slightly higher and the fraction of rock is slightly lower. But further data is required to pin the density down more precisely.

The uncertainty in Pluto’s size has persisted for decades and was due to the fact that Pluto has a very tenuous atmosphere composed of nitrogen.

Furthermore Pluto’s lowest atmospheric layer called the troposphere, is shallower than previously believed.

On the other hand, its largest moon Charon with which it forms a double planet, lacks a substantial atmosphere and its size was known with near certainty based on ground-based telescopic observation.

New Horizons LORRI imagery has confirmed that Charon measures 751 miles (1208 km) kilometers) across.

Stern also confirmed that frigid Pluto also has a polar cap composed of methane and nitrogen ices based on measurements from the Alice instrument.

LORRI has also zoomed in on two of Pluto’s smaller moons, Nix and Hydra.

“We knew from the time we designed our flyby that we would only be able to study the small moons in detail for just a few days before closest approach,” said Stern. “Now, deep inside Pluto’s sphere of influence, that time has come.”

The approximate sizes of Pluto’s moons Nix and Hydra compared to Denver, Colorado. While Nix and Hydra are illustrated as circles in this diagram, mission scientists anticipate that future observations by New Horizons will show that they are irregular in shape. Credits: JHUAPL/Google

But because they are so small, accurate measurement with LORRI could only be made in the final week prior to the July 14 flyby.

Nix is estimated to be about 20 miles (about 35 kilometers) across, while Hydra is roughly 30 miles (roughly 45 kilometers) across. These sizes lead mission scientists to conclude that their surfaces are quite bright, possibly due to the presence of ice.

Determinations about Pluto’s two smallest moons, Kerberos and Styx, will be made later at some point during the 16-month long playback of data after the July 14 encounter.

It has been three decades since we last visited planetary bodies at the outer reaches of our solar system when Voyager 2 flew past Uranus and Neptune in 1986 and 1989.

New Horizons' last look at Pluto's Charon-facing hemisphere reveals the highest resolution view of four intriguing darks spots for decades to come. This image, taken early the morning of July 11, 2015, shows newly-resolved linear features above the equatorial region that intersect, suggestive of polygonal shapes. This image was captured when the spacecraft was 2.5 million miles (4 million kilometers) from Pluto. Credit: NASA/JHUAPL/SWRI — New Horizons’ last look at Pluto’s Charon-facing hemisphere reveals the highest resolution view of four intriguing darks spots for decades to come. This image, taken early the morning of July 11, 2015, shows newly-resolved linear features above the equatorial region that intersect, suggestive of polygonal shapes. This image was captured when the spacecraft was 2.5 million miles (4 million kilometers) from Pluto. Credit: NASA/JHUAPL/SWRI

New Horizons is closing in fast on its quarry at a whopping 31,000 mph (49,600 kph) after a nine year interplanetary voyage and is now less than half a million miles away, in the final hours before closest approach.

The New Frontiers spacecraft was built by a team led by Stern and included researchers from SwRI and the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. APL also operates the New Horizons spacecraft and manages the mission.

Watch for Ken’s continuing onsite coverage of the Pluto flyby on July 14 from the Johns Hopkins University Applied Physics Laboratory (APL).

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer

July 9, 2015February 27, 2017 by Fraser Cain

Why Don’t We Send Probes “Up” In The Solar System?

Wouldn’t it be easier to see what’s outside the solar system if we just send out probes straight up?

Dammit, science people! Why are you always firing probes “outwards”? Then they have to go past all this stuff, like planets and asteroids and crap to escape the solar system. Don’t you realize that if we want to see what’s outside the solar system we just need to shoot them straight up?

Then we don’t have to go past all that junk, and we can finally see what’s between us and the next star system over! Is it thick goo? Is it thin goo? Is it the aether?!

What the heck is wrong with you! It’s so easy. Just go up! Why are we always going out?

Whenever we talk Solar System, we’re always using flat objects for reference. Plates, flying disks, pancakes and pizzas, as it’s arranged in a flat disk known as the plane of the ecliptic.

Formed from a blob of hydrogen gas and dust in the solar nebula. Gravity pulled everything together, and the conservation of angular momentum set the whole thing spinning, faster and faster. The spinning pulled the whole Solar System into the disk we see today, with our star at the center and the planets embedded in the surrounding disk. As a result, the Sun, Moon, planets and their moons all move through a relatively small region in the sky.

This definitely makes things easier to send spacecraft from world to world. NASA’s Voyager 2 was able to visit Jupiter, Saturn, Uranus and Neptune because they were all lined up like dominoes.

When Willie Sutton was asked why he robbed banks, he answered, “that’s where the money is,” and we explore along the plane of the ecliptic because that’s where the science is. Everything in our Solar System is arranged along this flat area, so it makes sense to look along this region.

But wait! As you know, the Solar System isn’t actually flat. Some objects rise a little above or below the plane of the ecliptic. This is known as a planet’s orbital inclination.

Of all the planets, Mercury has the greatest with 7-percent. It’s even crazier for the the dwarf planets, Pluto is 17-percent off the plane of the ecliptic, and Eris is 44-percent.

One of the reasons Eris went undiscovered for so long is because it orbits so far outside the planet of the ecliptic. It wasn’t until Mike Brown and his team from Caltech looked far enough outside the usual hiding spaces that they found these additional dwarf planets.

There really isn’t much outside the flat plane of the ecliptic, it’s also much more difficult to get spacecraft to travel above or below. When spacecraft launch, they already have tremendous velocity just from the rotation of the Earth and the speed of the Earth orbiting the Sun.

I realize this is just more “outwardist” propaganda for you. So why no “up”? If you did want to go that way, you need a powerful rocket capable of creating velocity in this direction, or that direction.

If you wanted to escape the Earth’s gravity and explore the Solar System in the regular old way, you’d need to add about 10 km/s in velocity to your spacecraft. But for straight up, you’d need about 30 km/s, meaning more fuel, and compromises to your payload.

It still sounds like I’m making excuses. Here’s the deal, you might be amazed to learn that spacecraft actually have been sent “up”.

Artist impression of the Ulysses spacecraft. Credit: NASA/ESA

The European Space Agency’s Ulysses spacecraft, launched in 1990 had the goal of looking down on the Sun from above. It wasn’t possible to do this just with a rocket, but engineers were able to use a gravitational assist from Jupiter to kick Ulysses into an orbital inclination of 80-degrees, and for the first time, we were able to see the Sun from above and below.

A new European mission is in the works called the Solar Orbiter, and it’ll get into an orbital inclination of 90-degrees to be able to see the Sun’s poles directly for the first time. If all goes well, it’ll launch in 2018.

So, why don’t we go up? Actually, we do. We’re going “up” again very soon. It’s good to go up. It’s always good to get outside of our regular stomping grounds and see our Solar System from new angles and perspectives.

If you could send a probe anywhere in our Solar System, where would you choose?

July 6, 2015December 21, 2015 by Matt Williams

Newest Planet: Is it Pluto, Eris or Extrasolar?

With astronomers discovering new planets and other celestial objects all the time, you may be wondering what the newest planet to be discovered is. Well, that depends on your frame of reference. If we are talking about our Solar System, then the answer used to be Pluto, which was discovered by the American astronomer Clyde William Tombaugh in 1930.

Unfortunately, Pluto lost its status as a planet in 2006 when it was reclassified as a dwarf planet. Since then, another contender has emerged for the title of “newest planet in the Solar System” – a celestial body that goes by the name of Eris – while beyond our Solar System, thousands of new planets are being discovered.

But then, the newest planet might be the most recently discovered extrasolar planet. And these are being discovered all the time.

Continue reading “Newest Planet: Is it Pluto, Eris or Extrasolar?”

June 16, 2015March 11, 2016 by Matt Williams

What Is The Kuiper Belt?

Hubble Finds Smallest Kuiper Belt Object. Credit: NASA

Dr. Mike Brown is a professor of planetary astronomy at Caltech. He’s best known as the man who killed Pluto, thanks to his team’s discovery of Eris and other Kuiper Belt Objects. We asked him to help us explain this unusual region of our solar system.

Soon after Pluto was discovered by Clyde Tombaugh on February 18th, 1930, astronomers began to theorize that Pluto was not alone in the outer Solar System. In time, they began to postulate the existence of other objects in the region, which they would discover by 1992. In short, the existence of the Kuiper Belt – a large debris field at the edge of the Solar System – was theorized before it was ever discovered.

Definition:

The Kuiper Belt (also known as the Edgeworth–Kuiper belt) is a region of the Solar System that exists beyond the eight major planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, in that it contains many small bodies, all remnants from the Solar System’s formation.

But unlike the Asteroid Belt, it is much larger – 20 times as wide and 20 to 200 times as massive. As Mike Brown explains:

The Kuiper Belt is a collection of bodies outside the orbit of Neptune that, if nothing else had happened, if Neptune hadn’t formed or if things had gone a little bit better, maybe they could have gotten together themselves and formed the next planet out beyond Neptune. But instead, in the history of the solar system, when Neptune formed it led to these objects not being able to get together, so it’s just this belt of material out beyond Neptune.

Discovery and Naming:

Shortly after Tombaugh’s discovery of Pluto, astronomers began to ponder the existence of a Trans-Neptunian population of objects in the outer Solar System. The first to suggest this was Freckrick C. Leonard, who began suggesting the existence of “ultra-Neptunian bodies” beyond Pluto that had simply not been discovered yet.

That same year, astronomer Armin O. Leuschner suggested that Pluto “may be one of many long-period planetary objects yet to be discovered.” In 1943, in the Journal of the British Astronomical Association, Kenneth Edgeworth further expounded on the subject. According to Edgeworth, the material within the primordial solar nebula beyond Neptune was too widely spaced to condense into planets, and so rather condensed into a myriad of smaller bodies.

In 1951, in an article for the journal Astrophysics, that Dutch astronomer Gerard Kuiper speculated on a similar disc having formed early in the Solar System’s evolution. Occasionally one of these objects would wander into the inner Solar System and become a comet. The idea of this “Kuiper Belt” made sense to astronomers. Not only did it help to explain why there were no large planets further out in the Solar System, it also conveniently wrapped up the mystery of where comets came from.

In 1980, in the Monthly Notices of the Royal Astronomical Society, Uruguayan astronomer Julio Fernández speculated that a comet belt that lay between 35 and 50 AU would be required to account for the observed number of comets.

Following up on Fernández’s work, in 1988 a Canadian team of astronomers (team of Martin Duncan, Tom Quinn and Scott Tremaine) ran a number of computer simulations and determined that the Oort cloud could not account for all short-period comets. With a “belt”, as Fernández described it, added to the formulations, the simulations matched observations.

*The bodies in the Kuiper Belt. Credit: Don Dixon*

In 1987, astronomer David Jewitt (then at MIT) and then-graduate student Jane Luu began using the telescopes at the Kitt Peak National Observatory in Arizona and the Cerro Tololo Inter-American Observatory in Chile to search the outer Solar System. In 1988, Jewitt moved to the Institute of Astronomy at the University of Hawaii, and Luu later joined him to work at the University’s Mauna Kea observatory.

After five years of searching, on August 30th, 1992, Jewitt and Luu announced the “Discovery of the candidate Kuiper belt object” (15760) 1992 QB1. Six months later, they discovered a second object in the region, (181708) 1993 FW. Many, many more would follow…

In their 1988 paper, Tremaine and his colleagues referred to the hypothetical region beyond Neptune as the “Kuiper Belt”, apparently due to the fact that Fernández used the words “Kuiper” and “comet belt” in the opening sentence of his paper. While this has remained the official name, astronomers sometimes use the alternative name Edgeworth-Kuiper belt to credit Edgeworth for his earlier theoretical work.

However, some astronomers have gone so far as to claim that neither of these names are correct. For example, Brian G. Marsden – a British astronomer and the longtime director of the Minor Planet Center (MPC) at the Harvard-Smithsonian Center for Astrophysics – claimed that “Neither Edgeworth nor Kuiper wrote about anything remotely like what we are now seeing, but Fred Whipple (the American astronomer who came up with the “dirty snowball” comet hypothesis) did”.

Furthermore, David Jewitt commented that, “If anything … Fernández most nearly deserves the credit for predicting the Kuiper Belt.” Because of the controversy associated with its name, the term trans-Neptunian object (TNO) is recommended for objects in the belt by several scientific groups. However, this is considered insufficient by others, since this can mean any object beyond the orbit of Neptune, and not just objects in the Kuiper Belt.

Composition:

There have been more than a thousand objects discovered in the Kuiper Belt, and it’s theorized that there are as many as 100,000 objects larger than 100 km in diameter. Given to their small size and extreme distance from Earth, the chemical makeup of KBOs is very difficult to determine.

However, spectrographic studies conducted of the region since its discovery have generally indicated that its members are primarily composed of ices: a mixture of light hydrocarbons (such as methane), ammonia, and water ice – a composition they share with comets. Initial studies also confirmed a broad range of colors among KBOs, ranging from neutral grey to deep red.

This suggests that their surfaces are composed of a wide range of compounds, from dirty ices to hydrocarbons. In 1996, Robert H. Brown et al. obtained spectroscopic data on the KBO 1993 SC, revealing its surface composition to be markedly similar to that of Pluto, as well as Neptune’s moon Triton, possessing large amounts of methane ice.

8 largest Kuiper Belt Objects — *Artist’s comparison of the eight largest Kuiper Belt Objects. Credit: Lexicon/NASA Images*

Water ice has been detected in several KBOs, including 1996 TO₆₆, 38628 Huya and 20000 Varuna. In 2004, Mike Brown et al. determined the existence of crystalline water ice and ammonia hydrate on one of the largest known KBOs, 50000 Quaoar. Both of these substances would have been destroyed over the age of the Solar System, suggesting that Quaoar had been recently resurfaced, either by internal tectonic activity or by meteorite impacts.

Keeping Pluto company out in the Kuiper belt, are many other objects worthy of mention. Quaoar, Makemake, Haumea, Orcus and Eris are all large icy bodies in the Belt. Several of them even have moons of their own. These are all tremendously far away, and yet, very much within reach.

Exploration:

On January 19th, 2006, NASA launched the New Horizons space probe for the sake of studying Pluto, its moons and one or two other Kuiper Belt objects. As of January 15th, 2015, the spacecraft began its approach to the dwarf planet, and is expected to make a flyby by July 14th, 2015. When it reaches the area, astronomers are expecting several interesting photographs of the Kuiper Belt as well.

Even more exciting is the fact that surveys of other solar systems indicate that our Solar System isn’t unique. Since 2006, there have been other “Kuiper Belts” (i.e. icy debris belts) discovered around nine other star systems. These appear to fall into two categories: wide belts, with radii of over 50 AU, and narrow belts (like our own Kuiper Belt) with radii of between 20 and 30 AU and relatively sharp boundaries.

According to infrared surveys, an estimated 15-20% of solar-type stars are believed to have massive Kuiper-Belt-like structures. Most of these appear to be fairly young, but two star systems – HD 139664 and HD 53143, which were observed by the Hubble Space Telescope in 2006 – are estimated to be 300 million years old.

Vast and unexplored, the Kuiper Belt is the source of many comets, and is believed to be the point of origin for all periodic or short-period comet (i.e. ones with an orbit lasting 200 years or less). The most famous of these is Halley’s Comet, which has been active for the past 16,000–200,000 years.

Future of the Kuiper Belt:

When he initially speculated about the existence of a belt of objects beyond Neptune, Kuiper indicated that such a belt probably did not exist anymore. Of course, subsequent discoveries have proven this to be wrong. But one thing that Kuiper was definitely right about was the idea that these Trans-Neptunian Objects won’t last forever. As Mike Brown explains:

We call it a belt, but it’s a very wide belt. It’s something like 45 degrees in extent across the sky – this big swath of material that’s just been churned and churned by Neptune. And these days, instead of making a bigger and bigger body, they’re just colliding and slowly grinding down into dust. If we come back in another hundred million years, there’ll be no Kuiper Belt left.

Given the potential for discovery, and what up-close examination could teach us about the early history of our Solar System, many scientists and astronomers look forward to the day when we can examine the Kuiper Belt in more detail. Here’s hoping that the New Horizons mission is just the beginning of future decades of research into this mysterious region!

We have many interesting articles here at Universe Today on the subject on the Outer Solar System and Trans-Neptunion Objects (TNOs).

And be sure to check out this article on the planet Eris, the latest dwarf planet and the largest TNO to be discovered.

And astronomers are expecting to discover two more large planets in our Solar System.

Universe Today also has a full-length interview with Mike Brown from Caltech.

May 30, 2015August 11, 2016 by Matt Williams

The Dwarf Planet Eris

Artist illustration of Eris. Image credit: NASA

Eris is the largest dwarf planet in the Solar System, and the ninth largest body orbiting our Sun. Sometimes referred to as the “tenth planet”, it’s discovery is responsible for upsetting the traditional count of nine planets in our Solar System, as well as leading the way to the creation of a whole new astronomical category.

Located beyond the orbit of Pluto, this “dwarf planet” is both a trans-Neptunian object (TNO), which refers to any planetary object that orbits the Sun at a greater distance than Neptune – or 30 astronomical units (AU). Because of this distance, and the eccentricity of its orbit, it is also a member of a the population of objects (mostly comets) known as the “scattered disk”.

The discovery of Eris was so important because it was a celestial body larger than Pluto, which forced astronomers to consider, for the first time in history, what the definition of a planet truly is.

Discovery:

Eris, which has the full title of 136199 Eris, was first observed in 2003 during a Palomar Observatory survey of the outer solar system by a team led by Mike Brown, a professor of planetary astronomy at the California Institute of Technology. The discovery was confirmed in January 2005 after the team examined the pictures obtained from the survey in detail.

Classification:

At the time of it’s discovery, Brown and his colleagues believed that they had located the 10th planet of our solar system, since it was the first object in the Kuiper Belt found to be bigger than Pluto. Some astronomers agreed and liked the designation, but others objected since they claimed that Eris was not a true planet. At the time, the definition of “planet” was not a clear-cut since there had never been an official definition issued by the International Astronomical Union (IAU).

The matter was settled by the IAU in the summer of 2006. They defined a planet as an object that orbits the Sun, which is large enough to make itself roughly spherical. Additionally, it would have to be able to clear its neighborhood – meaning it has enough gravity to force any objects of similar size or that are not under its gravitational control out of its orbit.

In addition to finally defining what a planet is, the IAU also created a new category of “dwarf planets“. The only difference between a planet and a dwarf planet is that a dwarf planet has not cleared its neighborhood. Eris was assigned to this new category, and Pluto lost its status as a planet. Other celestial bodies, including Haumea, Ceres, and Makemake, have been classified as dwarf planets.

artist's impression shows the distant dwarf planet Eris. New observations have shown that Eris is smaller than previously thought and almost exactly the same size as Pluto. Eris is extremely reflective and its surface is probably covered in frost formed from the frozen remains of its atmosphere. Credit: ESO — *Artist’s impression shows the distant dwarf planet Eris, highlighting its bright surface. Credit: ESO*

Naming:

Eris is named after the Greek goddess of strife and discord. The name was assigned on September 13th, 2006, following an unusually long consideration period that arose over the issue of classification. During this time, the object became known to the wider public as Xena, which was the name given to it by the discovery team.

The team had been saving this name, which was inspired by the title character of the television series Xena: Warrior Princess, for the first body they discovered that was larger than Pluto. They also chose it because it started with the letter X, a reference to Percival Lowell’s hunt for a planet he believed to exist the edge of the Solar System (which he referred to as “Planet X“).

According to fellow astronomer and science writer Govert Schilling, Brown initially wanted to call the object “Lila”. This name was inspired by a concept in Hindu mythology that described the cosmos as the outcome of a game played by Brahma, and also because it was similar to “Lilah” – the name of Brown’s newborn daughter.

Size and Orbit:

The actual size and mass of Eris has been the subject of debate, as official estimates have changed with time and subsequent viewing. In 2005, using images from the Hubble Space Telescope. the diameter of Eris was measured to be 2397 ± 100 km (1,489 miles). In 2007, a series of observations of the largest trans-Neptunian objects with the Spitzer Space Telescope estimated Eris’s diameter at 2600 (+400/-200) km (1616 miles).

*A diagram showing solar system orbits. The highly tilted orbit of Eris is in red. Credit: NASA*

The most recent observation took place in November of 2010, when Eris was the subject of one of the most distant stellar occultations yet achieved from Earth. The teams findings were announced on October 2011, and contradicted previous findings with an estimated diameter of 2326 ± 12 km (1445 miles).

Because of these differences, astronomers have been hard-pressed to maintain that Eris is more massive than Pluto. According to the latest estimates, the Solar System’s “ninth planet” has a diameter of 2368 km (1471 miles), placing it on par with Eris. Part of the difficulty in accurately assessing the planet’s size comes from interference from Pluto’s atmosphere. Astronomers expect a more accurate appraisal when the New Horizons space probe arrives at Pluto in July 2015.

Eris has an orbital period of 558 years. Its maximum possible distance from the Sun (aphelion) is 97.65 AU, and its closest (perihelion) is 37.91 AU. This means that Eris and its moon are currently the most distant known objects in the Solar System, apart from long-period comets and space probes.

Eris’s orbit is highly eccentric, and brings Eris to within 37.9 AU of the Sun, a typical perihelion for scattered objects. This is within the orbit of Pluto, but still safe from direct interaction with Neptune (29.8-30.4 AU). Unlike the eight planets, whose orbits all lie roughly in the same plane as the Earth’s, Eris’s orbit is highly inclined – the planet is tilted at an angle of about 44° to the ecliptic.

Moons:

Eris has one moon called Dysnomia, which is named after the daughter of Eris in Greek mythology, which was first observed on September 10th, 2005 – a few months after the discovery of Eris. The moon was spotted by a team using the Keck telescopes in Hawaii, who were busy carrying out observations of the four brightest TNOs (Pluto, Makemake, Haumea, and Eris) at the time.

*Eris (center) and its moon of Dysnomia (left of center), taken by the Hubble Space Telescope. Credit: NASA/ESA/Mike Brown*

Interesting Facts:

The dwarf planet is rather bright and can be detected using something as simple as a small telescope. Models of internal heating via radioactive decay suggest that Eris may be capable of sustaining an internal ocean of liquid water at the mantle-core boundary. These studies were conducted by Hauke Hussmann and colleagues from the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG) at the University of São Paulo.

Brown and the discovery team followed up their initial identification of Eris with spectroscopic observations of the planet, which were made on January 25th, 2005. Infrared light from the object revealed the presence of methane ice, indicating that the surface may be similar to that of Pluto and of Neptune’s moon Triton.

Due to Eris’s distant eccentric orbit, its surface temperature is estimated to vary between about 30 and 56 K (?243.2 and ?217.2 °C). This places it on par with Pluto’s surface temperature, which ranges from 33 to 55 K (-240.15 and -218.15 °C).

We have many interesting articles on planets here at Universe Today, including this article on What is the newest planet and the 10th planet.

If you are looking for more information, try Eris and NASA’s Solar System Exploration entry.

Astronomy Cast has an episode on Pluto’s planetary identity crisis.

Source:

January 12, 2015December 23, 2015 by Tim Reyes

It Looks Like These Are All the Bright Kuiper Belt Objects We’ll Ever Find

The presently known largest trans-Neptunian objects (TNO) - are likely to be surpassed by future discoveries. Which of these trans-Neptunian objects (TNO) would you call planets and which "dwarf planets"? (Illustration Credit: Larry McNish, Data: M.Brown)

The self-professed “Pluto Killer” is at it again. Dr. Michael Brown is now reminiscing about the good old days when one could scour through sky survey data and discover big bright objects in the Kuiper Belt. In his latest research paper, Brown and his team have concluded that those days are over.

Ten years ago, Brown discovered what is now known as the biggest Kuiper Belt object – Eris. Brown’s team found others that rivaled Pluto in size and altogether, these discoveries led to the demotion of Pluto to dwarf planet. Now, using yet another sky survey data set but with new computer software, Brown says that its time to move on.

Instigators of the big heist - David Rabinowitz, Brown and Chad Trujillo, left to right. The researchers discovered dozens of Kuiper Belt objects (KBO) including six of the eight largest KBOs including the largest, Eris. — Instigators of the big heist – Rabinowitz, Brown and Trujillo, left to right. The researchers co-discovered dozens of Kuiper Belt objects (KBO) including nine of the ten largest KBOs including the largest, Eris.

Like the famous Bugs Bunny cartoon, its no longer Rabbit Season or Duck Season and as Bugs exclaims to Elmer Fudd, there is no more bullets. Analyzing seven years worth of data, Brown and his team has concluded we are fresh out of Pluto or Charon-sized objects to be discovered in the Kuiper Belt. But for Dr. Brown, perhaps it now might be Oort Cloud season.

His latest paper, A Serendipitous All Sky Survey For Bright Objects In The Outer Solar System, in pre-print, describes the completion of analysis of two past sky surveys covering the northern and southern hemisphere down to 20 degrees in Galactic latitude. Using revised computer software, his team scoured through the data sets from the Catalina Sky Survey (CSS) and the Siding Spring Survey (SSS). The surveys are called “fast cadence surveys” and they primarily search for asteroids near Earth and out to the asteroid belt. Instead Brown’s team used the data to look at image frames spaced days and months apart.

Update: In a Twitter communique, Dr. Brown stated, “I would say we’re out of BRIGHT ones, not big ones. Could be big ones lurking far away!” His latest work involved a southern sky survey (SSS) to about magnitude 19 and the northern survey (CSS) to 21. Low albedo (dark) and more distant KBOs might be lurking beyond the detectability of these surveys that are in the range of Charon to Pluto in size.

Animation showing the movement of Eris on the images used to discover it. Eris is indicated by the arrow. The three frames were taken over a period of three hours. (Credit: Brown, et al.) — Animation showing the movement of Eris on the images used to discover it. Eris is indicated by the arrow. The three frames were taken over a period of three hours. More images over several weeks were necessary to determine its orbit.(Credit: Brown, et al.)

Objects at Kuiper Belt distances move very slowly. For example, Pluto orbits the Sun at about 17,000 km/hr (11,000 mph), taking 250 years to complete one orbit. These are speeds that are insufficient to maintain ven a low-Earth orbit. Comparing two image frames spaced just hours apart will find nearby asteroids moving relative to the star fields but not Kuiper belt objects. So using image frames spaced days, weeks or even months apart, they searched again. Their conclusion is that all the big Kuiper belt objects have been found.

The only possibility of finding another large KBO lies in a search of the galactic plane which is difficult due to the density of Milky Way’s stars in the field of view. The vast number of small bodies in the Kuiper belt and Oort Cloud lends itself readily to statistical analysis. Brown states that there is a 32% chance of finding another Pluto-sized object hiding among the stars of the Milky Way.

Artists concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. Credit: Robert Hurt (IPAC)

Dr. Brown also released a blog story in celebration of the discovery of the largest of the Kuiper Belt objects, Eris, ten years ago last week. Ten years of Eris, reminisces about the great slew of small body discoveries by Dr. Brown, Dr. Chad Trujillo of Gemini Observatory and Dr. David Rabinowitz of Yale Observatory.

Brown encourages others to take up this final search right in the galactic plane but apparently his own intentions are to move on. What remains to be seen — that is, to be discovered — are hundreds of large “small” bodies residing in the much larger region of the Oort Cloud. These objects are distributed more uniformly throughout the whole spherical region that the Cloud defines around the Sun.

Furthermore, Dr. Brown maintains that there is a good likelihood that a Mars or Earth-sized object exists in the Oort Cloud.

Small bodies within our Solar System along with exo-planets are perhaps the hottest topics and focuses of study in Planetary Science at the moment. Many graduate students and seasoned researchers alike are gravitating to their study. There are certainly many smaller Kuiper belt objects remaining to be found but more importantly, a better understanding of their makeup and origin are yet to be revealed.

Artist's concept of the Dawn spacecraft at the protoplanet Ceres Illustration of Dawn's approach phase and RC3 orbit This artist’s concept of NASA’s Dawn spacecraft shows the craft orbiting high above Ceres, where the craft will arrive in early 2015 to begin science investigations. (Image credit: NASA/JPL-Caltech) — Artist’s concept of the Dawn spacecraft at the protoplanet Ceres Illustration of Dawn’s approach phase and RC3 orbit This artist’s concept of NASA’s Dawn spacecraft shows the craft orbiting high above Ceres, where the craft will arrive in early 2015 to begin science investigations. (Image credit: NASA/JPL-Caltech)

Presently, the Dawn spacecraft is making final approach to the dwarf planet Ceres in the Asteroid belt. The first close up images of Ceres are only a few days away as Dawn is now just a couple of 100 thousand miles away approaching at a modest speed. And much farther from our home planet, scientists led by Dr. Alan Stern of SWRI are on final approach to the dwarf planet Pluto with their space probe, New Horizons. The Pluto system is now touted as a binary dwarf planet. Pluto and its moon Charon orbit a common point (barycenter) in space that lies between Pluto and Charon.

So Dr. Brown and team exits stage left. No more dwarf planets – at least not soon and not in the Kuiper belt. Will that upstage what is being called the year of the Dwarf Planet?

But next up for close inspection for the first time are Ceres, Pluto and Charon. It should be a great year.

The relative sizes of the inner Solar System, Kuiper Belt and the Oort Cloud. (Credit: NASA, William Crochot)

References:

A Serendipitous All Sky Survey For Bright Objects In The Outer Solar System

Ten Years of Eris

2015, NASA’s Year of the Dwarf Planet, Universe Today

What is the Kuiper Belt?, Universe Today