An artist's illustration of NASA's Dawn spacecraft with its ion propulsion system approaching Ceres. Image: NASA/JPL-Caltech.
The Dawn spacecraft, NASA’s asteroid hopping probe, may not be going gently into that good night as planned. Dawn has visited Vesta and Ceres, and for now remains in orbit around Ceres. The Dawn mission was supposed to end after its rendezvous with Ceres, but now, reports say that the Dawn team has asked NASA to extend the mission to visit a third asteroid.
Dawn was launched in 2007, and in 2011 and 2012 spent 14 months at Vesta. After Vesta, it reached Ceres in March 2015, and is still in orbit there. The mission was supposed to end, but according to a report at New Scientist, the team would like to extend that mission.
Dawn is still is fully operational, and still has some xenon propellant remaining for its ion drive, so why not see what else can be achieved? There’s only a small amount of propellant left, so there’s only a limited selection of possible destinations for Dawn at this point. A journey to a far-flung destination is out of the question.
Chris Russell, of the University of California, Los Angeles, is the principal investigator for the Dawn mission. He told New Scientist, “As long as the mission extension has not been approved by NASA, I’m not going to tell you which asteroid we plan to visit,” he says. “I hope a decision won’t take months.”
If the Dawn mission is not extended, then its end won’t be very fitting for a mission that has accomplished so much. It will share the fate of some other spacecraft at the end of their lives; forever parked in a harmless orbit in an out of the way place, forgotten and left to its fate. The only other option is to crash it into a planet or other body to destroy it, like the Messenger spacecraft was crashed into Mercury at the end of its mission.
The crash and burn option isn’t available to Dawn though. The spacecraft hasn’t been sterilized. If it hasn’t been sterilized of all possible Earthly microbial life, then it is strictly forbidden to crash it into Ceres, or another body like it. Planetary protection rules are in place to avoid the possible contamination of other worlds with Earthly microbial life. It’s not likely that any microbes that may have hitched a ride aboard Dawn would have survived Dawn’s journey so far, nor is it likely that they would survive on the surface of Ceres, but rules are rules.
The secret of Dawn’s long-life and success is not only due to the excellent work by the teams responsible for the mission, it’s also due to Dawn’s ion-drive propulsion system. Ion drives, long dreamed of in science and science fiction, are making longer voyages into deep space possible.
Ion drives start very slow, but gain speed incrementally, continuing to generate thrust over long distances and long periods of time. They do all this with minimal propellant, and are ideal for long space voyages like Dawn’s.
The success of the Dawn mission is key to NASA’s plans for further deep space exploration. NASA continues to work on improving ion drives, and their latest project is the Advanced Electric Propulsion System (AEPS.) This project is meant to further develop the Hall Thruster, a type of ion-drive that NASA hopes will extend spacecraft mission capabilities, allow longer and deeper space exploration, and benefit commercial space activities as well.
The AEPS has the potential to double the thrust of current ion-drives like the one on Dawn. It’s a key component of NASA’s Journey to Mars. NASA also has plans for a robotic asteroid capture mission called Asteroid Redirect Mission, which will use the AEPS. That mission will visit an asteroid, retrieve a boulder- sized asteroid from the surface, and place it in orbit around the Moon. Eventually, astronauts will visit it and return samples to Earth for study. Very ambitious.
As far as the Dawn mission goes, it’s unclear what its next destination might be. Vesta and Ceres were chosen because they are thought be surviving protoplanets, formed at the same time as the other planets. But they stopped growing, and they remain largely undisturbed, so in that sense they are kind of locked in time, and are intriguing objects of study. There are other objects in the vicinity, but it would be pure guesswork to name any.
We are prone to looking at the past nostalgically, and thinking of prior decades as the golden age of space exploration. But as Dawn, and dozens of other current missions and scientific endeavours in space show us, we may well be in a golden age right now.
An artist's conception of 2007 OR10, nicknamed Snow White. Astronomers suspect that its rosy color is due to the presence of irradiated methane. [Credit: NASA]
Over the course of the past decade, more and more objects have been discovered within the Trans-Neptunian region. With every new find, we have learned more about the history of our Solar System and the mysteries it holds. At the same time, these finds have forced astronomers to reexamine astronomical conventions that have been in place for decades.
Consider 2007 OR10, a Trans-Neptunian Object (TNO) located within the scattered disc that at one time went by the nicknames of “the seventh dwarf” and “Snow White”. Approximately the same size as Haumea, it is believed to be a dwarf planet, and is currently the largest object in the Solar System that does not have a name.
Discovery and Naming:
2007 OR10 was discovered in 2007 by Meg Schwamb, a PhD candidate at Caltech and a graduate student of Michael Brown, while working out of the Palomar Observatory. The object was colloquially referred to as the “seventh dwarf” (from Snow White and the Seven Dwarfs) since it was the seventh object to be discovered by Brown’s team (after Quaoar in 2002, Sedna in 2003, Haumea and Orcus in 2004, and Makemake and Eris in 2005).
Comparison of Sedna with the other largest TNOs and with Earth (all to scale). Credit: NASA/Lexicon
At the time of its discovery, the object appeared to be very large and very white, which led to Brown giving it the other nickname of “Snow White”. However, subsequent observation has revealed that the planet is actually one of the reddest in the Kuiper Belt, comparable only to Haumea. As a result, the nickname was dropped and the object is still designated as 2007 OR10.
The discovery of 2007 OR10 would not be formally announced until January 7th, 2009.
Size, Mass and Orbit:
A study published in 2011 by Brown – in collaboration with A.J. Burgasser (University of California San Diego) and W.C. Fraser (MIT) – 2007 OR10’s diameter was estimated to be between 1000-1500 km. These estimates were based on photometry data obtained in 2010 using the Magellan Baade Telescope at the Las Campanas Observatory in Chile, and from spectral data obtained by the Hubble Space Telescope.
However, a survey conducted in 2012 by Pablo Santos Sanz et al. of the Trans-Neptunian region produced an estimate of 1280±210 km based on the object’s size, albedo, and thermal properties. Combined with its absolute magnitude and albedo, 2007 OR10 is the largest unnamed object and the fifth brightest TNO in the Solar System. No estimates of its mass have been made as of yet.
2007 OR10 also has a highly eccentric orbit (0.5058) with an inclination of 30.9376°. What this means is that at perihelion, it is roughly 33 AU (4.9 x 109 km/30.67 x 109 mi) from our Sun while at aphelion, it is as distant as 100.66 AU (1.5 x 1010 km/9.36 x 1010 mi). It also has an orbital period of 546.6 years, which means that the last time it was at perihelion was 1857 and it won’t reach aphelion until 2130. As such, it is currently the second-farthest known large body in the Solar System, and will be farther out than both Sedna and Eris by 2045.
Composition:
According to the spectral data obtained by Brown, Burgasser and Fraser, 2007 OR10 shows infrared signatures for both water ice and methane, which indicates that it is likely similar in composition to Quaoar. Concurrent with this, the reddish appearance of 2007 OR10 is believed to be due to presence of tholins in the surface ice, which are caused by the irradiation of methane by ultraviolet radiation.
The presence of red methane frost on the surfaces of both 2007 OR10 and Quaoar is also seen as an indication of the possible existence of a tenuous methane atmosphere, which would slowly evaporate into space when the objects are closer to the Sun. Although 2007 OR10 comes closer to the Sun than Quaoar, and is thus warm enough that a methane atmosphere should evaporate, its larger mass makes retention of an atmosphere just possible.
Also, the presence of water ice on the surface is believed to imply that the object underwent a brief period of cryovolcanism in its distant past. According to Brown, this period would have been responsible not only for water ice freezing on the surface, but for the creation of an atmosphere that included nitrogen and carbon monoxide. These would have been depleted rather quickly, and a tenuous atmosphere of methane would be all that remains today.
However, more data is required before astronomers can say for sure whether or not 2007 OR10 has an atmosphere, a history of cryovolcanism, and what its interior looks like. Like other KBOs, it is possible that it is differentiated between a mantle of ices and a rocky core. Assuming that there is sufficient antifreeze, or due to the decay of radioactive elements, there may even be a liquid-water ocean at the core-mantle boundary.
Classification:
Though it is too difficult to resolve 2007 OR10’s size based on direct observation, based on calculations of 2007 OR10’s albedo and absolute magnitude, many astronomers believe it to be of sufficient size to have achieved hydrostatic equilibrium. As Brown stated in 2011, 2007 OR10 “must be a dwarf planet even if predominantly rocky”, which is based on a minimum possible diameter of 552 km and what is believed to be the conditions under which hydrostatic equilibrium occurs in cold icy-rock bodies.
That same year, Scott S. Sheppard and his team (which included Chad Trujillo) conducted a survey of bright KBOs (including 2007 OR10) using the Palomar Observatory’s 48 inch Schmidt telescope. According to their findings, they determined that “[a]ssuming moderate albedos, several of the new discoveries from this survey could be in hydrostatic equilibrium and thus could be considered dwarf planets.”
Currently, nothing is known of 2007 OR10’s mass, which is a major factor when determining if a body has achieved hydrostatic equilibrium. This is due in part to there being no known satellite(s) in orbit of the object, which in turn is a major factor in determining the mass of a system. Meanwhile, the IAU has not addressed the possibility of accepting additional dwarf planets since before the discovery of 2007 OR10 was announced.
Alas, much remains to be learned about 2007 OR10. Much like it’s Trans-Neptunian neighbors and fellow KBOs, a lot will depend on future missions and observations being able to learn more about its size, mass, composition, and whether or not it has any satellites. However, given its extreme distance and fact that it is currently moving further and further away, opportunities to observe and explore it via flybys will be limited.
However, if all goes well, this potential dwarf planet could be joining the ranks of such bodies as Pluto, Eris, Ceres, Haumea and Makemake in the not-too-distant future. And with luck, it will be given a name that actually sticks!
The vast Kuiper Belt, which orbits at the outer edge of our Solar System, has been the site of many exciting discoveries in the past decade or so. Otherwise known as the Trans-Neptunian region, small bodies have been discovered here that have confounded our notions of what constitutes a planet and thrown our entire classification system for a loop. Of these, the most famous (and controversial) discovery was undoubtedly Eris.
First observed in 2005 by Mike Brown and his team, the discovery of Eris overturned decades of astronomical conventions. But both before and since then, many other “dwarf planets“, “plutoids” and “Trans-Neptunian Objects” (TNOs) have been found that further illustrated the need for reclassification. This includes the Kuiper Belt Object (KBO) 5000 Quaoar (or just Quaoar), which was actually discovered three years before Eris.
Discovery and Naming:
Quaoar was discovered on June 4th, 2002 by astronomers Chad Trujillo and Michael Brown of the California Institute of Technology, using images that were obtained with the Samuel Oschin Telescope at Palomar Observatory. The discovery was announced on October 7th, 2002, at a meeting of the American Astronomical Society. At the time, the object was designated as 2002 LM60, but would soon be renamed by Brown and Caltech his team.
Consistent with the IAU conventions for naming non-resonant Kuiper Belt Objects after creator deities, the object was given the name Quaoar after the Tongva creator god. The Tongva people (otherwise known as the Mission Indians) are native to the area around Los Angeles, where the discovery of Quaoar was made.
Images of Quaoar taken using the Oschin Telescope at the Palomar Observatory, California. Credit: Chad Trujillo & Michael Brown (Caltech)
Size, Mass and Orbit:
Given its distance, accurate measurements of Quaoar have been difficult to obtain. In 2004, Brown and Trujillo made direct measurements of the object with the Hubble Space Telescope and came up with an estimated diameter of 1260 ± 190 km.
However, these estimates were subsequently revised downward in 2013 by teams using a stellar occultation, and with data obtained with the Herschel Observatory’s PACS instrument and the Spectral and Photometric Imaging Receiver (SPIRE) at the University of Lethbridge, Alberta.
Combining this information, estimates of its diameter were then changed to between 1110 ± 5 km and 1074±38 km. By these estimates, Quaoar was the largest object to be discovered in the Solar System since the discovery of Pluto. However, it would later be supplanted by the discoveries of Eris, Haumea, and Makemake.
In addition, new techniques and a greater knowledge of KBOs led scientists to conclude that the 2004 HST size estimate for Quaoar was approximately 40% too large, and that a more proper estimate would be about 900 km. Using a weighted average of the SST and corrected HST estimates, Quaoar, as of 2010, is now believed to be about 890±70 km in diameter.
Given these dimensions, Quaoar is roughly one-twelfth the diameter of Earth, one third the diameter of the Moon, and half the size of Pluto. And with an estimated mass of 1.4 ± 0.1 × 1021 kg, Quaoar is about as massive as Pluto’s moon Charon, equivalent to 0.12 times the mass of Eris, and approximately 2.5 times as massive as Orcus.
Quaoar orbit around the Sun varies slightly, ranging from 45.114 AU (6.75 x 109 km / 4.19 x 109 mi) at aphelion to 41.695 AU (6.24 x 10 km9/3.88 x 109 mi) at perihelion. Quaoar has an orbital period of 284.5 years, and a sidereal rotation period of about 17.68 hours.
Its orbit is also nearly circular and moderately inclined at approximately 8°, which is typical for the population of small classical KBOs, but exceptional among the large KBO. Pluto, Makemake, Haumea, Orcus, Varuna, and Salacia are all on highly inclined, more eccentric orbits.
At 43 AU and with a near-circular orbit, Quaoar is not significantly perturbed by Neptune; unlike Pluto, which is in 2:3 orbital resonance with Neptune. As of 2008, Quaoar was only 14 AU from Pluto, which made it the closest large body to the Pluto–Charon system. By Kuiper Belt standards this is very close.
The orbit of Quaoar (yellow) and various other cubewanos compared to the orbit of Neptune (blue) and Pluto (pink). Credit: Wikipedia Commons/kheider
Composition:
At the time of its discovery, not much was known about Kuiper belt objects. However, subsequent findings about this region have led scientists to conclude that the surface of Quaoar is likely to be highly similar to those of the icy satellites of Uranus and Neptune. This includes a low albedo, which could be as low as 0.1, which may be an indication that fresh ice has disappeared from its surface.
The surface is also moderately red, meaning that Quaoar is relatively more reflective in the red and near-infrared than in the blue. A 2006 model of internal heating via radioactive decay suggested that, unlike Orcus, Quaoar may not be capable of sustaining an internal ocean of liquid water at the mantle-core boundary.
Observations of Quaoar in the near infrared spectrum have indicated the presence of a small quantities of methane and ethane ice (about 5%). Scientists have also been surprised to find signs of crystalline ice on Quaoar, which is caused by sublimation and refreezing of water. This would indicate that the temperature rose to at least -160 °C (110 K or -260 °F) sometime in the last ten million years.
Artist’s impression of the size difference between Quaoar, Pluto, Sedna, Earth and the Moon. Credit: NASA/JPL-Caltech
Speculation as to what could have caused Quaoar to heat up from its natural temperature of -220 °C (55 K or -360 °F) have led to theories ranging from a barrage of mini-meteors that could have raised the temperature, to the presence of cryovolcanism. The latter theory, which is the more widely accepted one, holds that cryovolcanism occurred as a result of the decay of radioactive elements within Quaoar’s core.
Some scientist believe that Quaoar was nearly twice its current size before an ancient collision with another object, possibly Pluto, stripped it of its outer mantle. If true, it would mean that Quaoar once had more ice on its surface, and possibly a liquid water ocean at the core-mantle boundary.
Moon:
Quaoar has one known satellite, which was discovered on February 22nd, 2007. It orbits its primary at a distance of 14,500 km and has an orbital eccentricity of 0.14. Based on the assumption that the moon has the same albedo and density as Quaoar, the apparent magnitude of the moon indicates that it is 74 km in diameter and has 1/2000 the mass of Quaoar.
In terms of where it came from, Brown has suggested that it may be a remnant from a collision, which lost most of its mantle ice in the process. The choice for naming the moon was deferred to the Tongva people themselves, who selected the sky god Weymot, who is the son of Quaoar in Tongva mythology. The name became official on October 4th, 2009, with the publication of the Minor Planet Center’s latest issue.
Artist’s impression of the moderately red Quaoar and its moon Weywot. Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)
Classification:
According to the IAU, a dwarf planet is any celestial body that orbits a star, is massive enough to have become spherical under the power of its own gravity, but has not cleared its path of planetesimals, and is not the satellite of another object. Also, it must have enough mass to overcome its own compression and be in hydrostatic equilibrium.
Because Quaoar is a binary object, the mass of the system can be calculated from the orbit of the secondary. From this, Quaoar’s estimated density of 2.2 g/cm³ and its estimated diameter of 820 – 960 km suggest that it is large enough to be a dwarf planet.
This is based in part on estimates made by Mike Brown, who has claimed that rocky bodies around 900 km in diameter are sufficient to relax into hydrostatic equilibrium, whereas icy bodies can reach this state with diameters somewhere between 200 and 400 km.
In addition, Quaoar’s mass (which is believed to be greater than 1.6×1021 kg) is also greater than what the 2006 IAU draft definition of a planet claims is “usually” required for being in hydrostatic equilibrium (5×1020 kg, 800 km). Light-curve-amplitude analysis shows only small deviations, suggesting that Quaoar is indeed a spheroid with small albedo spots.
Therefore, while it is not currently classified as a dwarf planet, it is considered a viable candidate. In the coming years, it may go on to join the ranks of Pluto, Eris, Haumea and Makemake as being officially recognized as such by the IAU and other astronomical bodies.
Exploration:
So far, no missions have been planned to Quaoar. While some have advocated sending the New Horizons mission to visit Quaoar and/or Sedna now that it’s flyby of Pluto is complete, NASA has declared this to be impossible. Much like Sedna, Quaoar is too far from the trajectory of the spacecraft, but also insists that both KBOs will be high on the list of candidate targets for future missions to the outer Solar System.
It has further been calculated that a flyby mission to Quaoar could take 13.57 years, using a Jupiter gravity assist and based on the launch dates of December 25th, 2016, November 22nd, 2027, December 22nd, 2028, January 22nd, 2030, or December 20thm, 2040. During any of these launch windows, Quaoar would be at a distance of 41 to 43 AU from the Sun by the time the spacecraft arrived.
In the meantime, all we can do is wait, and continue to observe Quaoar and its fellow Kuiper Belt Objects from afar. In the coming years, a decision is also likely to be made about whether or not it will be included on the list of the Solar System’s acknowledge dwarf planets.
We have written many articles about Quaoar for Universe Today. Here’s an article about the discovery of Quaoar, and here’s an article about the Kuiper Belt.
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.
The largest known trans-Neptunian objects (TNO), shown to scale. Credit: Larry McNish/M.Brown
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). 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.”
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.
This image of Ceres was taken by NASA's Dawn spacecraft on May 7, 2015, from a distance of 8,400 miles (13,600 kilometers). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Video caption: This new video animation of Ceres was created from images taken by NASA’s Dawn spacecraft at altitudes of 8,400 miles (13,600 kilometers) and 3,200 miles (5,100 kilometers) away. Vertical dimension has been exaggerated by a factor of two and a star field added. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Scientists leading NASA’s Dawn mission to dwarf planet Ceres have just released a brand new animated video showing a dramatic fly over of the heavily cratered world featuring its mysterious bright spots whose exact origin and nature remain elusive.
Meanwhile, the venerable probe has just successfully entered its new and lower mapping orbit on June 3 from which researchers hope to glean hordes of new data to unravel the secrets of the bright spots and unlock the nature of Ceres origin and evolution.
Pockmarked Ceres is an alien world unlike any other in our solar system.
“Dawn completed the maneuvering to reach its second mapping orbit and stopped ion-thrusting on schedule. Since May 9, the spacecraft has reduced its orbital altitude from 8,400 miles (13,600 kilometers) to 2,700 miles (4,400 kilometers),” reported Marc Rayman, Dawn Chief Engineer/ Mission Director of NASA’s Jet Propulsion Laboratory, Pasadena, California.
“As Dawn flew 2,700 miles (4,400 kilometers) over Ceres’ north pole on June 5 that marked the beginning of the new mapping phase, and Dawn began taking photos and making other measurements on schedule.”
Each orbit of Dawn around Ceres at this second science mapping orbit lasts 3.1 days.
The new video was created by the research team based on observations of Ceres that were taken from Dawn’s initial mapping orbit, at an altitude of 8,400 miles (13,600 kilometers), as well as the most recent navigational images taken from 3,200 miles (5,100 kilometers), according to NASA.
It is based on data from over 80 images captured by Dawn’s framing cameras which were provided The German Aerospace Center (DLR) and Max Planck Institute for Solar System Research in Göttingen, Germany.
The images were used to provide a three-dimensional video view. The vertical dimension is exaggerated by a factor of two in the video.
“We used a three-dimensional terrain model that we had produced based on the images acquired so far,” said Dawn team member Ralf Jaumann of the German Aerospace Center (DLR), in Berlin.
“They will become increasingly detailed as the mission progresses — with each additional orbit bringing us closer to the surface.”
Imagery of the mysterious bright spots show them to seemingly be sheets of many spots of water ice, and not just single huge patches. The famous duo of ice spots are located inside the middle of a 57 miles (92 kilometers) wide crater situated in Ceres northern hemisphere.
Dawn is an international science mission managed by NASA’s Jet Propulsion Laboratory, Pasadena, California. The trio of science instruments are from the US, Germany and Italy.
The framing camera was provided by the Max Planck Institute for Solar System Research, Göttingen, Germany and the German Aerospace Center (DLR).
This view of Ceres was taken by Dawn spacecraft on May 23 and shows finer detail becoming visible on the dwarf planet. The spacecraft snapped the image at a distance of 3,200 miles (5,100 kilometers) with a resolution of 1,600 feet (480 meters) per pixel. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Dawn will spend most if June at this second mapping orbit before firing up the ion engines and spiraling yet lower for a mission expected to last until at least June 2016.
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Dawn’s spiral descent from its first mapping orbit (RC3) to its second (survey). The two mapping orbits are shown in green. The color of Dawn’s trajectory progresses through the spectrum from blue, when it began ion-thrusting on May 9, to red, when ion-thrusting concludes on June 3. The red dashed sections show where Dawn is coasting, mostly for telecommunications. The first two coast periods include OpNav 8 and 9. Image credit: NASA/JPL-Caltech
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, 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 AtmosphericSciences (IAG) at the University of SãoPaulo.
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.
We’ve seen way too many science fiction episodes that show asteroid belts as dense fields of tumbling boulders. How dense is the asteroid belt, and how to spacecraft survive getting through them?
For the purposes of revenue, lazy storytelling, and whatever it is Zak Snyder tells himself to get out of bed in the morning, when it comes to asteroids, Science fiction and video games creators have done something of disservice to your perception of reality.
Take a fond trip down sci-fi memory lane, and think about the time someone, possibly you, has had to dogfight or navigate through yet another frakkin’ asteroid belt. Huge space rocks tumbling dangerously in space! Action! Adventure! Only the skilled pilot, with her trusty astromecha-doplis ship can maneuver through the dense cluster of space boulders, dodging this way and that, avoiding certain collision.
And then she shoots her pew pew laser breaking up larger asteroids up into smaller ones, possibly obliterating them entirely depending on the cg budget. Inevitably, there’s bobbing and weaving. Pursuit craft will clip their wings on asteroids, spinning off into nearby tango. Some will fly straight into a space boulder.
Finally you’ll thread the needle on a pair of asteroids and the last ship of the whatever they’re called clicky clacky mantis Zorak bug people will try and catch you, but he/it won’t be quite so lucky. Poetically getting squashed like… a… bug. Sackhoff for the win, pilot victorious.
Okay, you probably knew the laser part is totally fake. I mean, everybody knows you can’t hear sounds in space. Outside of Starbuck being awesome, is that at all realistic? And if so, how does NASA maneuver unmanned spacecraft through that boulder-strewn grand canyon death trap to reach the outer planets?
The asteroid belt is a vast region between the orbits of Mars and Jupiter. Our collection of space rocks starts around 300 million kilometers from the Sun and ends around 500 million kilometers. The first asteroid, the dwarf planet Ceres which measures 950 km across, was discovered in 1801, with a “That’s funny.”. Soon after astronomers turned up many more small objects orbiting in this region at the “Oooh neat!” stage.
Artist’s concept of Dawn in its survey orbit at dwarf planet Ceres. Credit: NASA/JPL-Caltech
They realized it was a vast belt of material orbiting the Sun, with I suspect a “We’re all gonna die.”. To date, almost half a million asteroids have been discovered, most of which are in the main belt.
As mentioned in a another video, gathering up all the material in the asteroid belt and gluing it together makes a mass around 4% of the Moon. So, in case one of your friends gets excited and suggests it was a failed planet, you can bust out that stat and publicly shame them for being so 1996, Goodwill Hunting style. You like asteroids? How about them asteroids?
There’s a few hundred larger than 100 km across, and tens of millions of rocks a hundred meters across. Any one of these could ruin a good day, or bring a bad day to a welcome firey close for either a depressed wayfaring spacecraft or a little bluegreen speck of a planet. Which sounds dangerous all the way around.
Fortunately, our asteroid belt is a vast region of space. Let’s wind up the perspective-o-meter. If you divide the total number of objects in the field by the volume of space that asteroid belt takes up, each space rock is separated by hundreds of thousands of kilometers. Think of it as gravity’s remarkably spacious zen rock garden.
Ceres compared to asteroids visited to date, including Vesta, Dawn’s mapping target in 2011. Image by NASA/ESA. Compiled by Paul Schenck.
As a result, when NASA engineers plot a spacecraft’s route through the asteroid belt, they don’t expect to make a close encounter with any asteroids – in fact, they’ll change its flight path to intercept asteroids en route. Because hey look, asteroid!
Even though Ceres was discovered in 1801, it’s never been observed up close, until now. NASA’s Dawn spacecraft already visited Asteroid Vesta, and by the time you’re watching this video, it will have captured close-up images of the surface of Ceres.
Once again, science fiction creatives sold us out to drama over hard science. If you’re passing through an asteroid belt, you won’t need to dodge and weave to avoid the space rocks. In fact, you probably wouldn’t even know you were passing through a belt at all. You’d have to go way the heck over there to even get a nearby look at one of the bloody things. So we’re safe, our speck is safe, and all the little spacecraft are safe…. for now.
Which dramatic version of “asteroids” are you most fond of? Tell us in the comments below.
Ceres compared to asteroids visited to date, including Vesta, Dawn's mapping target in 2011. Image by NASA/ESA. Compiled by Paul Schenck.
When the Dawn mission was in its planning stages, Ceres was considered an asteroid. But in 2006, a year before the mission launched, the International Astronomical Union formed a new class of solar system objects known as dwarf planets, and since by definition a dwarf planet is spherical and travels in an orbit around the Sun, Ceres fit that definition perfectly.
But since it’s located in the Asteroid Belt, we still tend to think of Ceres as an asteroid. So, how does Ceres compare to other asteroids?
Dr. Paul Schenk, who is a participating scientist on the Dawn mission, recently put together some graphics on his website and the one above compares Ceres to other asteroids that we’ve visited with spacecraft.
Of course, Ceres is bigger (it’s the biggest object in the Asteroid Belt) and more spherical than the other asteroids. When it comes right down to it, Ceres doesn’t look much like an asteroid at all!
“Ceres is most similar in size to several of Saturn’s icy moons and may be similar internally as well, being composed of 25% water ice by mass,” Schenk noted on his website.
Comparisons of Ceres with other prominent icy objects. Dione is Ceres’ closest twin in size and mass. Image credit: NASA/ESA. Compiled by Paul Schenk.
And water is one of the most interesting and mysterious aspects of Ceres. A year ago, the Herschel space telescope discovered water vapor around Ceres, and the vapor could be emanating from water plumes — much like those that are on Saturn’s moon Enceladus – or it could be from cryovolcanism from geysers or icy volcano.
“The water vapor question is one of the most interesting things we will look for,” Schenk told Universe Today. “What is its source, what does it indicate about the interior and activity level within Ceres? Is Ceres active, very ancient, or both? Does it go back to the earliest Solar System? Those are the questions we hope to answer with Dawn.”
Some scientists also think Ceres may have an ocean and possibly an atmosphere, which makes Dawn’s arrival at Ceres in March one of the most exciting planetary events of 2015, in addition to New Horizon’s arrival at Pluto.
“Since we don’t know why the water vapor venting has happened, or even if it continues, it’s hard to say much more than that,” Schenk said via email, “but it is theoretically possible that some liquid water still exists within Ceres. Dawn will try to determine if that is true.”
One of the possibilities that has been discussed is that if the water vapor is confirmed, Ceres could potentially host microbial life. I asked Schenk what other factors would have to be present in order for that to have occurred?
“The presence of carbon molecules is often regarded as necessary for life,” he replied, “and we think we see that on the surface spectroscopically in the form of carbonates and clays. So, I think the questions will be, whether there is actually liquid water of any kind, whether the carbon compounds are just a surface coating or in the interior, and whether Ceres has ever been warm. If those are true then some sort of prebiotic or biotic activity is in play.”
Since we do not know the answer to any of these questions yet, Schenk says Dawn’s visit to Ceres should be interesting!
On thing of note is that Dawn is now closing in on Ceres and just today, the team released the best image we have yet of Ceres, which you can see in our article here.
With the Dawn spacecraft now heading towards the dwarf planet/asteroid Ceres, the mission has suddenly gotten even more intriguing. The Herschel space observatory has discovered water vapor around Ceres, and the vapor could be emanating from water plumes — much like those that are on Saturn’s moon Enceladus – or it could be from cryovolcanism from geysers or icy volcano.
“This is the first time water vapor has been unequivocally detected on Ceres or any other object in the asteroid belt and provides proof that Ceres has an icy surface and an atmosphere,” said Michael Küppers of ESA in Spain, lead author of a paper in the journal Nature.
Ceres might be considered to have a bit of an identity crisis, and this new discovery might complicate things even more. When it was discovered in 1801, astronomers thought it was a planet orbiting between Mars and Jupiter. Later, other bodies with similar orbits were found, marking the discovery of our Solar System’s main belt of asteroids.
Ceres laid claim as the largest asteroid in our Solar System, but in 2006, the International Astronomical Union reclassified Ceres as a dwarf planet because of its large size.
But now, could Ceres also have comet-like attributes? Herschel scientists say the most straightforward explanation of the water vapor production is through sublimation, where ice is warmed and transformed directly into gas, dragging the surface dust with it, and exposing fresh ice underneath to sustain the process. This is how comets work.
Ceres is roughly 950 kilometers (590 miles) in diameter. The best guess on Ceres composition is that it is layered, perhaps with a rocky core and an icy outer mantle. Ice had been theorized to exist on Ceres but had not been detected conclusively, until now.
This graph shows variability in the intensity of the water absorption signal detected at Ceres by the Herschel space observatory on March 6, 2013. Credit: ESA.
Herschel used its far-infrared vision with the HIFI instrument to see a clear spectral signature of the water vapor. But, interestingly, Herschel did not see water vapor every time it looked. There were variations in the water signal during the dwarf planet’s 9-hour rotation period. The telescope spied water vapor four different times, on one occasion there was no signature. The astronomers deduced that almost all of the water vapor was seen to be coming from just two spots on the surface.
Although Herschel was not able to make a resolved image of Ceres, the team was able to derive the distribution of water sources on the surface.
“We estimate that approximately 6 kg of water vapour is being produced per second, requiring only a tiny fraction of Ceres to be covered by water ice, which links nicely to the two localised surface features we have observed,” says Laurence O’Rourke, Principal Investigator for the Herschel asteroid and comet observation programme called MACH-11, and second author on the paper.
The two emitting regions are about 5% darker than the average on Ceres. Since darker regions are able to absorb more sunlight, they are then likely the warmest regions, resulting in a more efficient sublimation of small reservoirs of water ice, the team said.
They added that this new finding could have significant implications for our understanding of the evolution of the Solar System.
“Herschel’s discovery of water vapour outgassing from Ceres gives us new information on how water is distributed in the Solar System,” said Göran Pilbratt, ESA’s Herschel Project Scientist. “Since Ceres constitutes about one fifth of the total mass of asteroid belt, this finding is important not only for the study of small Solar System bodies in general, but also for learning more about the origin of water on Earth.”
Dawn is scheduled to arrive at Ceres in the spring of 2015 after spending more than a year orbiting the large asteroid Vesta. Dawn will give us the closest look ever at Ceres surface and provide more insight into this latest finding.
“We’ve got a spacecraft on the way to Ceres, so we don’t have to wait long before getting more context on this intriguing result, right from the source itself,” said Carol Raymond, the deputy principal investigator for Dawn. “Dawn will map the geology and chemistry of the surface in high resolution, revealing the processes that drive the outgassing activity.”
Artist's rendering of the distant dwarf planet Eris. New suggests that Eris is almost exactly the same diameter as Pluto. Eris is very reflective - possibly due to the frozen remains of its atmosphere. Image Credit: ESO/L. Calçada
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Back a couple of weeks ago, I wrote an article highlighting the debate between scientists on which dwarf planet is bigger, Pluto or Eris. During a planetary science conference earlier this month in France, word “leaked” out that Eris was still more massive, but likely smaller in diameter.
Today, the latest findings were published in Nature, and as such are now “official”. There’s also some additional information, so I’d like to revisit this topic and include some new details which may help answer the question:
Bruno Sicardy of the Paris Observatory and his team calculated the diameter of Eris in 2010. The technique they used took advantage of an occultation between Eris and a faint background star. Sicardy’s results provided a diameter of 2,326 kilometers for Eris, slightly less than his 2009 estimate of Pluto’s diameter at 2,338 kilometers.
Combining the diameter estimate with mass estimates yielded a density estimate for Eris which suggests, and is supported by its extra mass, that its composition is far more rocky than Pluto, with Eris being only 10-15% ice by mass.
In this week’s announcement by the European Southern Observatory, additional information was presented which sheds new light on cold, distant Eris.
Regarding the new density estimates, Emmanuel Jehin, one of Sicardy’s team members mentions, “This density means that Eris is probably a large rocky body covered in a relatively thin mantle of ice”.
Further supporting Jehin’s assertion, The surface of Eris was found to be extremely reflective, (96% of the light that falls on Eris is reflected, making it nearly as reflective as a backyard telescope mirror). Based on the current estimate, Eris is more reflective than freshly fallen snow on Earth. Based on spectral analysis of Eris, its surface reflectivity is most likely due to a surface of nitrogen-rich ice and frozen methane. Some estimates place the thickness of this layer at less than one millimeter.
Jehin also added, “This layer of ice could result from the dwarf planet’s nitrogen or methane atmosphere condensing as frost onto its surface as it moves away from the Sun in its elongated orbit and into an increasingly cold environment. The ice could then turn back to gas as Eris approaches its closest point to the Sun, at a distance of about 5.7 billion kilometers.”
Based on the new information on surface composition and surface reflectivity, Sicardy and his team were able to make temperature estimates for Eris. The team estimates daytime temperatures on Eris of -238 C, and that temperatures on the night side of Eris would be much lower.
Sicardy concluded with, “It is extraordinary how much we can find out about a small and distant object such as Eris by watching it pass in front of a faint star, using relatively small telescopes. Five years after the creation of the new class of dwarf planets, we are finally really getting to know one of its founding members.”
