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  • richardmitnick 10:21 am on October 29, 2017 Permalink | Reply
    Tags: , , , , Dwarf Planets, Dwarf Planets: Science & Facts About the Solar System’s Smaller Worlds,   

    From SPACE.com: “Dwarf Planets: Science & Facts About the Solar System’s Smaller Worlds” 

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    October 27, 2017
    SPACE.com Staff
    No writer credit found

    Dwarf planet Eris Credit: ESO/L. Calçada

    Dwarf planets are worlds that are too small to be considered full-fledged planets, but too large to fall into smaller categories.

    In recent years, there’s been a lot of hubbub about Pluto losing its status as one of the planets of the solar system. Pluto is no longer considered the ninth planet in the series of major planetary objects, but instead is now just one of the many so-called “dwarf planets.” The debate started anew after the New Horizons mission passed by Pluto in 2015, revealing a world of surprising geological complexity. As of 2017, delegates from the mission are trying to get Pluto’s planethood status back.

    Astronomers estimate that there could be as many as 200 dwarf planets in the solar system and the Kuiper Belt. But the differences between planets and dwarf planets may not be obvious at first.

    Kuiper Belt. Minor Planet Center

    Dwarf planets of the solar system

    The International Astronomical Union defines a planet as being in orbit around the sun, has enough gravity to pull its mass into a rounded shape (hydrostatic equilibrium), and has cleared its orbit of other, smaller objects. This last criterion is the point at which planets and dwarf planets differ. A planet’s gravity either attracts or pushes away the smaller bodies that would otherwise intersect its orbit; the gravity of a dwarf planet is not sufficient to make this happen.

    Meet the dwarf planets of our solar system, Pluto Eris, Haumea, Makemake and Ceres. Credit: Karl Tate, SPACE.com contributor.

    As of 2014, the IAU recognizes five named dwarf planets: Ceres, Pluto, Eris, Haumea, and Makemake. But those aren’t the only ones. Other solar system bodies that are possibly dwarf planets include Sedna and Quaoar, small worlds far beyond Pluto’s orbit, and 2012 VP113, an object that is thought to have one of the most distant orbits found beyond the known edge of our solar system. The object DeeDee could also be a dwarf planet, according to observations made in 2017. According to NASA, scientists think that there may be more than a hundred dwarf planets awaiting discovery.

    However, the debate over the status of dwarf planets, particularly Pluto, remains a hot topic. The primary concern stems from the requirement for a planet to clear out its local neighborhood.

    “In no other branch of science am I familiar with something that absurd,” New Horizons principle investigator Alan Stern told Space.com in 2011. “A river is a river, independent of whether there are other rivers nearby. In science, we call things what they are based on their attributes, not what they’re next to.”

    Is a dwarf planet a separate entity from a planet, or simply another classification? The question may not be settled in the near future.


    Ceres is the earliest known and smallest of the current category of dwarf planets. Sicilian astronomer Giuseppe Piazzi discovered Ceres in 1801 based on the prediction that the gap between Mars and Jupiter contained a missing planet. It is only 590 miles (950 km) in diameter and has a mass of just 0.015 percent that of Earth.

    In fact, Ceres is so small that it is classified as both a dwarf planet and an asteroid, and is often named in scientific literature as one of the largest asteroids in the solar system. Although it makes up approximately a fourth of the mass of the asteroid belt, it is still 14 less massive than Pluto.

    Unlike its asteroid neighbors, Ceres has a nearly round body. The rocky dwarf planet may have water ice beneath its crust. In 2014, the European Space Agency’s Herschel Space Observatory detected water vapor spewing from two regions on Ceres.

    NASA’s robotic Dawn mission arrived at Ceres in 2015. The mission has shown many interesting features on its surface, ranging from various bright spots to a 4-mile-high (6.5-kilometer-high) mountain. (Another mission, the European Space Agency’s Herschel Space Observatory, spotted evidence of water vapor in 2014.)

    NASA/Dawn Spacecraft

    ESA/Herschel spacecraft


    Pluto is the most well known of the dwarf planets. Since its discovery in 1930 and until 2006, it had been classified as the ninth planet from the sun. Pluto’s orbit was so erratic, however, that at times it was closer to the sun than the eighth planet, Neptune. In 2006, with the discovery of several other rocky bodies similar in size or larger than Pluto, the IAU decided to re-classify Pluto as a dwarf planet.

    This is the most detailed view to date of the entire surface of the dwarf planet Pluto, as constructed from multiple NASA Hubble Space Telescope photographs taken from 2002 to 2003.
    Credit: NASA, ESA, and M. Buie (Southwest Research Institute)

    NASA/ESA Hubble Telescope

    Despite its small size — 0.2 percent the mass of Earth and only 10 percent the mass of Earth’s moon — Pluto’s gravity is enough to capture five moons of its own. The pairing between Pluto and its largest moon, Charon, is known as a binary system, because both objects are orbiting around a central point that is not within the mass of Pluto.

    NASA’s New Horizons mission flew by Pluto in 2015 and revealed a wealth of surprises.

    NASA/New Horizons spacecraft

    This included zones that are bereft of craters (indicating the surface is relatively young), mountains that are likely as high as 11,000 feet (3,500 meters), and even haze above the dwarf planet’s surface.




    When it was first discovered, Eris was thought to be the largest of the dwarf planets, with a mass 27 percent larger than that of Pluto and a diameter of approximately 1,400 to 1,500 miles (2,300 to 2,400 km). It was the discovery of Eris that prompted the IAU to reconsider the definition of a planet. Further observation went on to suggest that the dwarf planet is slightly smaller than Pluto.

    The orbit of Eris is very erratic, crossing that of Pluto and nearly intersecting the orbit of Neptune, but is still more than three times larger than Pluto’s orbit. It takes 557 years for Eris to orbit the sun. At its farthest point from the sun, a point that is also called its aphelion, Eris and its satellite Dysmonia travel far beyond the Kuiper Belt. The surface of Eris is likely nitrogen and methane-rich, but in a thin (1 millimeter) layer across the surface. Some scientists suggest the surface is the condensed atmosphere of Eris, which expands into gas when the dwarf planet is closer to the sun.

    Haumea and Makemake

    Haumea. Wikipedia

    An early artist’s interpretation of the dwarf planet Makemake beyond Pluto. Credit: NASA

    Haumea and Makemake are the most recently named dwarf planets in the solar system.

    Haumea is unique because of its ellipsoid shape, only just meeting the hydrostatic equilibrium criteria for dwarf planet status. The elongated shape of the dwarf planet is due to its rapid rotational spin, not a lack of mass, which is about one-third that of Pluto. The cigar-shaped dwarf planet rotates on its axis every four hours, likely a result of a collision. The odd object also hosts a red spot and a layer of crystalline ice. Finally, Haumea is the only object in the Kuiper belt other than Pluto known to host more than one moon.

    A moon was discovered around Makemake in 2016, more than a decade after the dwarf planet itself was found. Its diameter is known to be about two-thirds that of Pluto, and the newly found moon will allow for measurements of its mass. Makemake is also of value to the astronomical community, as it is another reason for the reconsideration of the definition of a planet. Its comparable mass and diameter to Pluto would grant it planet status if Pluto wasn’t also stripped of that title.

    Dwarf planets as ‘plutoids’

    Pluto, Eris, Haumea and Makemake are all known as “plutoids,” unlike the asteroidal dwarf planetoid Ceres. A plutoid is a dwarf planet with an orbit outside that of Neptune. Plutoids are sometimes also referred to as “ice dwarfs” due to their diminutive size and cold surface temperatures.

    The outer planets show evidence of interaction with plutoids. Triton, the largest moon of Neptune, is likely a captured plutoid, and it is even possible that the odd tilt of Uranus on its axis is due to a collision with a plutoid. Similarly to dwarf planets, there are potentially hundreds of plutoid objects in the solar system that have yet to be given official status.

    Additional reporting by Elizabeth Howell and Nola Taylor Redd

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  • richardmitnick 12:17 pm on September 7, 2017 Permalink | Reply
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    From NASA New Horizons: “Pluto Features Given First Official Names” 

    NASA image


    NASA/New Horizons spacecraft

    New Horizons

    Editor: Bill Keeter

    It’s official: Pluto’s “heart” now bears the name of pioneering American astronomer Clyde Tombaugh, who discovered Pluto in 1930. And a crater on Pluto is now officially named after Venetia Burney, the British schoolgirl who in 1930 suggested the name “Pluto,” Roman god of the underworld, for Tombaugh’s newly-discovered planet.

    Tombaugh Regio and Burney crater are among the first set of official Pluto feature names approved by the International Astronomical Union (IAU), the internationally recognized authority for naming celestial bodies and their surface features.

    These and other names were proposed by NASA’s New Horizons team following the first reconnaissance of Pluto and its moons by the New Horizons spacecraft in 2015. The New Horizons science team had been using these and other place names informally to describe the many regions, mountain ranges, plains, valleys and craters discovered during the first close-up look at the surfaces of Pluto and its largest moon, Charon.

    A total of 14 Pluto place names have now been made official by the IAU; many more will soon be proposed to the IAU, both on Pluto and on its moons. “The approved designations honor many people and space missions who paved the way for the historic exploration of Pluto and the Kuiper Belt, the farthest worlds ever explored,” said Alan Stern, New Horizons principal investigator from Southwest Research Institute, Boulder, Colorado.

    Pluto’s first official surface-feature names are marked on this map, compiled from images and data gathered by NASA’s New Horizons spacecraft during its flight through the Pluto system in 2015. Credits: NASA/JHUAPL/SwRI/Ross Beyer

    “We’re very excited to approve names recognizing people of significance to Pluto and the pursuit of exploration as well as the mythology of the underworld. These names highlight the importance of pushing to the frontiers of discovery,” said Rita Schulz, chair of the IAU Working Group for Planetary System Nomenclature. “We appreciate the contribution of the general public in the form of their naming suggestions and the New Horizons team for proposing these names to us.”

    Stern applauded the work of the New Horizons Nomenclature Working Group, which along with Stern included science team members Mark Showalter — the group’s chairman and liaison to the IAU — Ross Beyer, Will Grundy, William McKinnon, Jeff Moore, Cathy Olkin, Paul Schenk and Amanda Zangari.

    The team gathered many ideas during the “Our Pluto” online naming campaign in 2015. Following on Venetia Burney’s original suggestion, several place names on Pluto come from underworld mythology. “I’m delighted that most of the approved names were originally recommended by members of the public,” said Showalter, of the SETI Institute, Mountain View, California.

    The approved Pluto surface feature names are listed below. The names pay homage to the underworld mythology, pioneering space missions, historic pioneers who crossed new horizons in exploration, and scientists and engineers associated with Pluto and the Kuiper Belt.

    Tombaugh Regio honors Clyde Tombaugh (1906–1997), the U.S. astronomer who discovered Pluto in 1930 from Lowell Observatory in Arizona.

    Burney crater honors Venetia Burney (1918-2009), who as an 11-year-old schoolgirl suggested the name “Pluto” for Clyde Tombaugh’s newly discovered planet. Later in life she taught mathematics and economics.

    Sputnik Planitia is a large plain named for Sputnik 1, the first space satellite, launched by the Soviet Union in 1957.

    Tenzing Montes and Hillary Montes are mountain ranges honoring Tenzing Norgay (1914–1986) and Sir Edmund Hillary (1919–2008), the Indian/Nepali Sherpa and New Zealand mountaineer were the first to reach the summit of Mount Everest and return safely.

    Al-Idrisi Montes honors Ash-Sharif al-Idrisi (1100–1165/66), a noted Arab mapmaker and geographer whose landmark work of medieval geography is sometimes translated as “The Pleasure of Him Who Longs to Cross the Horizons.”

    Djanggawul Fossae defines a network of long, narrow depressions named for the Djanggawuls, three ancestral beings in indigenous Australian mythology who traveled between the island of the dead and Australia, creating the landscape and filling it with vegetation.

    Sleipnir Fossa is named for the powerful, eight-legged horse of Norse mythology that carried the god Odin into the underworld.

    Virgil Fossae honors Virgil, one of the greatest Roman poets and Dante’s fictional guide through hell and purgatory in the Divine Comedy.

    Adlivun Cavus is a deep depression named for Adlivun, the underworld in Inuit mythology.

    Hayabusa Terra is a large land mass saluting the Japanese spacecraft and mission (2003-2010) that performed the first asteroid sample return.

    Voyager Terra honors the pair of NASA spacecraft, launched in 1977, that performed the first “grand tour” of all four giant planets. The Voyager spacecraft are now probing the boundary between the Sun and interstellar space.

    Tartarus Dorsa is a ridge named for Tartarus, the deepest, darkest pit of the underworld in Greek mythology.

    Elliot crater recognizes James Elliot (1943-2011), an MIT researcher who pioneered the use of stellar occultations to study the solar system – leading to discoveries such as the rings of Uranus and the first detection of Pluto’s thin atmosphere.

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    The New Horizons mission is helping us understand worlds at the edge of our solar system by making the first reconnaissance of the dwarf planet Pluto and by venturing deeper into the distant, mysterious Kuiper Belt – a relic of solar system formation.

    The Journey

    New Horizons launched on Jan. 19, 2006; it swung past Jupiter for a gravity boost and scientific studies in February 2007, and conducted a six-month-long reconnaissance flyby study of Pluto and its moons in summer 2015, culminating with Pluto closest approach on July 14, 2015. As part of an extended mission, pending NASA approval, the spacecraft is expected to head farther into the Kuiper Belt to examine another of the ancient, icy mini-worlds in that vast region, at least a billion miles beyond Neptune’s orbit.

    Sending a spacecraft on this long journey is helping us to answer basic questions about the surface properties, geology, interior makeup and atmospheres on these bodies.

    New Science

    The National Academy of Sciences has ranked the exploration of the Kuiper Belt – including Pluto – of the highest priority for solar system exploration. Generally, New Horizons seeks to understand where Pluto and its moons “fit in” with the other objects in the solar system, such as the inner rocky planets (Earth, Mars, Venus and Mercury) and the outer gas giants (Jupiter, Saturn, Uranus and Neptune).

    Pluto and its largest moon, Charon, belong to a third category known as “ice dwarfs.” They have solid surfaces but, unlike the terrestrial planets, a significant portion of their mass is icy material.

    Using Hubble Space Telescope images, New Horizons team members have discovered four previously unknown moons of Pluto: Nix, Hydra, Styx and Kerberos.

    A close-up look at these worlds from a spacecraft promises to tell an incredible story about the origins and outskirts of our solar system. New Horizons is exploring – for the first time – how ice dwarf planets like Pluto and Kuiper Belt bodies have evolved over time.

    The Need to Explore

    The United States has been the first nation to reach every planet from Mercury to Neptune with a space probe. New Horizons is allowing the U.S. to complete the initial reconnaissance of the solar system.

    A Team Approach

    The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, designed, built, and operates the New Horizons spacecraft and manages the mission for NASA’s Science Mission Directorate.
    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

  • richardmitnick 12:05 pm on August 17, 2016 Permalink | Reply
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    From Eos: “Six Things Dwarf Planets Have Taught Us About the Solar System” 

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    JoAnna Wendel

    On 14 July 2015, NASA’s New Horizons probe snapped the first ever close-up images of Pluto. Scientists continue to be stunned by its unexpectedly complex surface features. Credit: NASA/JHUAPL/SRI

    Classrooms across the world received some bad news on 24 August 2006. Pluto—the celestial body discovered in 1930 and named by an 11-year-old girl, the “pizzas” in the planet mnemonic “My very educated mother just served us nine pizzas”—had been officially stricken from the solar system’s family of planets and reclassified as a “dwarf planet.”

    The discovery of the slightly more massive object Eris inspired the International Astronomical Union’s (IAU) decision. Proponents of the change insisted that if Pluto got to keep the label “planet,” so too should similarly sized objects—like Ceres, for instance, which was then considered a large asteroid.

    A dwarf planet, by IAU’s new definition, must directly orbit the Sun. It must be massive enough for gravity to pull it into a roughly spherical shape. But unlike regular planets, dwarf planets haven’t cleared other smaller celestial debris out of its orbital path.

    As more objects got discovered, Pluto’s new label “dwarf planet” stuck. Then the jokes began.

    Facebook group pages popped up, with snarky titles of “When I was your age, Pluto was a planet!” Angry Pluto enthusiasts wrote hate mail to astronomer Mike “Pluto Killer” Brown, one of the scientists who found Eris. Astrophysicist Neil deGrasse Tyson, a strong proponent of the dwarf planet label, received his own stream of hate mail from crushed 6-year-olds; Twitter users still hurl insults at him occasionally.

    Although some consider the reclassification a “demotion,” Pluto and its cousins Ceres, Makemake, Eris, Haumea, and others continue to dazzle scientists with their strange features and surprising geology. But perhaps more critically, these dwarf planets also trace a trail of scientific breadcrumbs that scientists can follow back in time to understand the origins of the solar system.

    “I like to think of Pluto being the dwarf planet that showed us how the solar system’s architecture came to be,” said Renu Malhotra, a planetary scientist at University of Arizona’s Lunar and Planetary Laboratory.

    Here are six such revelations about the solar system that we gained from studying dwarf planets.

    1. Dwarf Planets Are as Complex as Regular Planets

    When the New Horizons probe passed by Pluto more than a year ago, scientists found a complex system with areas of geologically young surface and evidence of active geology.

    NASA/New Horizons spacecraft
    NASA/New Horizons spacecraft

    Pluto, the images revealed, wasn’t just a chunk of rock orbiting in space. “Even I underestimated what we would find,” said Alan Stern, principal investigator of the New Horizons mission.

    A mosaic of Pluto’s complex surface taken by the New Horizons probe from about 15,000 kilometers away as it approached Pluto on 14 July 2015. Scientists are working to understand the origins of these unexpectedly diverse features. Credit: NASA/JHUAPL/SwRI

    Pluto continues to stun scientists with its unexpected surface features, but its newly revealed complexity is just the beginning.

    Makemake has no atmosphere. Haumea spins faster than any other known large object in the solar system. Eris might have a thin, icy surface. Ceres hosts mysterious bright spots.

    “The fact that these objects can be every bit as complicated as terrestrial planets is a headline,” Stern said. “It should be written in as big a point size as we can write it, because it was completely unexpected.”

    2. Dwarf Planets Reveal Neptune’s Orbital Origins

    Scientists calculated that in the early solar system, Neptune migrated out to its current position and nudged Pluto into a resonance orbit. Although Pluto sometimes crosses Neptune’s orbital path, the resonance protects the two planets from colliding. Credit: NASA/JPL

    By studying the particular orbital relationship between Pluto and Neptune, scientists figured out how Neptune got to its current position in the solar system. The two bodies are inextricably locked in an orbital resonance: Every time Neptune orbits the Sun three times, Pluto orbits twice, which means that even though Pluto may occasionally cross Neptune’s orbital path, they will never meet.

    Scientists have always known about this resonance, but it was Malhotra who realized its significance. In a 1995 paper, Malhotra calculated that the only way Neptune and Pluto could have ended up in this resonance was if they both had formed closer to the Sun, then migrated out.

    Scientists theorize that in the early days of the solar system, the gas giants, Jupiter, Saturn, Neptune, and Uranus, migrated inward toward the Sun and knocked out leftover debris. This gravitational push on planetary debris ended up changing the planets’ orbits as well, sending Neptune farther out. Neptune’s gravitational force encountered Pluto’s, and the two bodies pushed and pulled at each other until they fell into a resonance orbit. Astronomers detected the same effect in other bodies, including a new dwarf planet announced to the world this year.

    3. Dwarf Planets Give Us a Peek into the Early Solar System

    Dwarf planets are handy guides to the ancient solar system. For instance, all the Kuiper belt dwarf planets—Pluto, Haumea, Makemake, and Eris—have moons that scientists suspect formed from high-impact collisions, said Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D. C. Haumea in particular is the only known Kuiper belt object to have a “family” that orbits along with Haumea and its moons, meaning that the debris kicked off by an impact long ago didn’t have enough energy to escape Haumea’s gravitational pull.

    The presence of such moons is further evidence of an early period of “late heavy bombardment” of objects in the solar system. Scientists think that during this time, about 3.8–4 billion years ago, gravitational interactions between Jupiter, Saturn, and Neptune sent comets and asteroids sprawling across the solar system to collide with planets.

    In the last 2 years, Ceres has also provided various windows into the past. In 2015, NASA’s Dawn probe headed to the dwarf planet after visiting the asteroid Vesta. There, scientists detected ammonia-rich clays in Ceres’s surface.

    Ammonia itself isn’t stable at the temperatures found on Ceres (130–200 kelvins), but it is plentiful in the outer solar system. So how did the molecule get there? Scientists have formulated different hypotheses, said Carol Raymond, deputy principal investigator for Dawn. Either Ceres formed in the outer solar system, during its early days, and got kicked inward by a chaotic migration of the gas giants, or Ceres formed in the asteroid belt, and somehow ammonia-rich material from the outer solar system made its way inward.

    Further study of Ceres will help clarify details of solar system formation, Raymond said.

    4. Dwarf Planet Candidates Helped Scientists “Find” Planet 9

    Thanks to a handful of debris orbiting farther away than Pluto, scientists this year found evidence that a rocky, Neptune-sized planet may lurk beyond the gaze of even our most powerful telescopes.

    The story began in 2003, when Brown and his team at the California Institute of Technology (Caltech) discovered Sedna, a dwarf planet candidate that orbits far beyond the Kuiper belt, Pluto’s neighborhood of large, icy bodies 30 astronomical units (AU) away.

    Kuiper Belt. Minor Planet Center
    Kuiper Belt. Minor Planet Center

    Sedna maintains a steady orbit and comes within only 76 AU of the Sun at its closest approach.

    The orbits of Planet 9 and the dwarf planets it supposedly influences. Scientists calculated that only a Neptune-sized planet could keep these objects in their peculiar, angled orbit. The diagram was created using WorldWide Telescope. Credit: Caltech/R. Hurt

    Since then, scientists have spotted several more objects near Sedna, including 2012 VP113, found by Sheppard and colleague Chad Trujillo of Hawaii’s Gemini Observatory.

    This orbit diagram shows the paths of Oort cloud objects 2012 VP113 (red) and Sedna (orange), which circle the Kuiper belt (blue) at the Solar System’s edge. Scott S. Sheppard/Carnegie Institution for Science

    Gemini/North telescope at Manua Kea, Hawaii, USA
    Gemini North Interior
    Gemini/North telescope at Manua Kea, Hawaii, USA

    The pair noticed that their new object and the rest of these far-away objects had similar, steady orbits.

    Back at Caltech, after reading Sheppard’s and Trujillo’s work, Brown and his colleagues set out to find the cause of such clustering, and after many hours of poring over models and simulations, they officially proposed that only a planet-sized body could exert enough gravitational pull to keep the far-away cluster of dwarf-planet-sized objects in steady orbits. This hypothesized planet was deemed Planet 9 (sometimes called Planet X).

    “Right now we’re doing surveys trying to find more dwarf planets,” Sheppard said. “If we find more and more of these, they can lead us to the much bigger, major Planet X.”

    5. Ceres (We Hope) Will Help Us Understand Icy Ocean Moons

    Kuiper belt dwarf planets aren’t the only thing keeping scientists busy. Dawn mission scientists recently discovered that regions of Ceres contain higher concentrations of carbonate minerals than anywhere outside of the Earth’s ocean floor. These minerals reveal that Ceres is like a “fossilized” ocean world, Raymond explained. They could be the remnants of a vast ocean that once existed on the dwarf planet.

    In Ceres’s geologically young Occator crater, scientists figured out that mysterious bright patches come from sodium carbonate, a highly reflective mineral found in hydrothermal environments under Earth’s oceans. This means that at some point in Ceres’s history, hydrothermal processes must have pushed this material to the surface, Raymond said.

    Scientists found evidence of carbonate minerals in the bright spots of dwarf planet Ceres’s Occator crater. Stripes on the inset represent where the spectrometer frames lie, whereas red signifies a high abundance of carbonates and gray indicates a low abundance. These carbonate minerals mean that Ceres may have been covered once by an ocean. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/ASI/INAF

    If hydrothermal processes are confirmed, Ceres’s surface may be analogous to the current seafloors underneath the solar system’s ice-covered moons. Astrobiologists yearn to peek below the icy shells of Jupiter’s and Saturn’s moons Europa and Enceladus because there are vast oceans underneath, and life needs water to proliferate.

    Ceres is similar to these moons because 25% of the dwarf planet is water ice. Plus, its seafloor-type conditions are “where all of the elements necessary for habitability occur together,” Raymond said.

    6. Dwarf Planets Are Prolific

    Pluto holds a special place in the Internet’s collective heart but may not be so special in the solar system. Currently, there are six dwarf planets officially designated by the IAU: Pluto, Ceres, Eris, Makemake, Haumea, and 2015 RR245, discovered in July. Since scientists started looking deeper into the Kuiper belt, they have found at least 20 more similarly sized objects, Sheppard said.

    There may be only six officially designated dwarf planets (missing from the image is 2015 RR245, announced this year), but many more dwarf-planet-sized objects exist. They may even be the dominant class of objects in the solar system. Credit: Konkoly Observatory/András Pál, Hungarian Astronomical Association/Iván Éder, NASA/JHUAPL/SwRI

    And there may be dozens more out there. “We discovered that dwarf planets are the most populous class in the solar system,” Stern said. Other galaxies may be like ours, too, he added.

    This population revelation, along with the surprising geological and atmospheric complexity found on dwarf planets, means that the field could be “at the very beginning of a paradigm shift and a revolution,” Stern said. Perhaps, he continued, it’s the classic large planets that are the “oddballs” of planetary formation.

    He wonders, “Who’s the misfit now?”

    See the full article here .

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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

  • richardmitnick 10:27 am on January 27, 2015 Permalink | Reply
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    From Space.com: “Eris: The Dwarf Planet That is Pluto’s Twin” 

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    January 27, 2015
    Nola Taylor Redd


    Eris with moon Dysmonia

    In addition to eight full-size planets, the solar system is home to a number of smaller “dwarf planets.” One of these, Eris, is almost the exact same size as the most well-known member of the collection, Pluto.


    When Eris was first discovered in 2005, it was thought to be significantly larger than Pluto. Originally, it was submitted as the tenth planet in the solar system. Ultimately, however, Eris’ discovery was a big reason astronomers demoted Pluto to dwarf planet status in 2006. That decision remains controversial to this day, making Eris’ name fitting.

    “Eris is the Greek goddess of discord and strife,” astronomer Mike Brown, a member of the discovery team, said via NASA. “She stirs up jealousy and envy to cause fighting and anger among men. At the wedding of Peleus and Thetis, all the gods were invited with the exception of Eris, and, enraged at her exclusion, she spitefully caused a quarrel among the goddesses that led to the Trojan War.”

    Like almost all of the known dwarf planets (with the exception of Ceres), Eris lies in the Kuiper Belt that rings the outer solar system. But Eris is even farther-flung than Pluto, circling our star from about three times farther away. It takes 561 years for the distant dwarf planet to make a single trip around the sun, though it rotates once every 25 hours, making the length of its day very similar to a day on Earth.

    Kuiper Belt

    Watching Eris

    Eris’ distance allowed astronomers to make precise measurements when it passed in front of a dim star in 2010, an event known as an occultation. In addition to measuring its size, researchers were also able to conclude its shape, size and mass.

    “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,” study lead author Bruno Sicardy, of the Pierre et Marie Curie University and Observatory of Paris, said in a statement. “Five years after the creation of the new class of dwarf planets, we are finally really getting to know one of its founding members.”

    The observations helped scientists determine that Eris’ diameter is 1,445 miles (2,326 kilometers), give or take 7 miles (12 km). That makes Eris’ size even more precisely known than Pluto’s. (Pluto is thought to be between 1,429 and 1,491 miles — or 2,300 to 2,400 km — across.)

    It also means that Pluto and Eris are, for all intents and purposes, the same size, researchers said.

    The researchers concluded that Eris is a spherical body. And, by studying the motion of Eris’ moon Dysnomia, they peg the dwarf planet to be about 27 percent heavier than Pluto, which means it’s considerably denser than Pluto as well.

    “This density means that Eris is probably a large rocky body covered in a relatively thin mantle of ice,” said co-author Emmanuel Jehin, of the Institut d’Astrophysique de I’Université de Liège in Belgium.

    Eris’ surface was also found to be extremely reflective, bouncing back 96 percent of the light that strikes it. That makes Eris one of the most reflective bodies in the solar system, roughly on par with Saturn’s icy moon Enceladus.

    Researchers believe Eris’ surface is probably composed of a nitrogen-rich ice mixed with frozen methane in a layer less than 1 millimeter thick. This ice layer could result from the dwarf planet’s atmosphere condensing as frost onto its surface periodically as it moves away from the sun, they said.

    The observations also allow researchers to make another estimate for the surface temperature of Eris. The side of the dwarf planet facing the sun likely gets no warmer than minus 396 degrees Fahrenheit (minus 238 Celsius), while temperatures on the night side would be even lower, researchers said.
    Dwarf planet’s companion

    Eris is one of the few dwarf planets to boast a moon. Named Dysnomia, after Eris’ daughter the demon goddess of lawlessness, the moon allowed astronomers to make more accurate measures of the planet than would have been otherwise possible, such as measurements of its density.
    Just the facts

    Semi-major axis of its orbit around the sun: 6.3 billion miles (10.2 billion kilometers)
    Perihelion (closest approach to sun): 3.6 billion miles (5.8 billion km)
    Aphelion (farthest distance from sun): 9.1 billion miles (14.6 billion km)
    Orbital period (length of year): 561.37 Earth years
    Orbit eccentricity: 0.434
    Orbit inclination: 46.87
    Sidereal rotation period (length of day): 25.9 hours, or 1.08 Earth days

    See the full article here.

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