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Eris en Dysnomia
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Eris and Dysnomia
(M. Brown (Caltech), C. Trujillo (Gemini), D. Rabinowitz (Yale), NSF, NASA, apod050731)
The largest known KBO (Kuiper Belt Object), 2003 UB313, as imaged at three
different times on October 21 of 2003, by the Palomar 48-inch Schmidt telescope.
Curently about 19th magnitude, the object is near aphelion, 97 AUs (about 9 billion
miles), or about twice as far as Pluto, from the Sun. Original estimates of its size,
based on its brightness and distance, suggested that it might be as much as 2000
miles in diameter, making it substantially larger than Pluto, which is only about 1420
miles in diameter; but recent observations with the Hubble Space Telescope (see
image below) indicate that an unusually high albedo (in the range of 85%) makes it
brighter than would be expected for an object of its size, and that it is at most 5%
larger than Pluto, or around 1490 miles in diameter, with an uncertainty about equal
to the difference in size between Pluto and 2003 UB313. In September 2006, the
object was officially named Eris (prior to that, anyone could call it anything they
wanted; its discoverer nicknamed it Xena, while I called it Dubi-Ubi, because of its
numerical appellation and uncertain status).
Initial reports in the news media suggested that since Eris was larger than Pluto, it
should be called a tenth planet; but it has been uncertain for years whether even
Pluto should be called a planet, and as a result of Eris' discovery, the International
Astronomical Union made a controversial decision to demote Pluto to "dwarf planet"
status, and to simultaneously elevate Eris and Ceres (the largest asteroid, or minor
planet) to the same status.
2003 UB313 (Eris) in December 2005 (M. Brown, Cal Tech, ESA, HST, NASA)
A point nearly indistinguishable from a star, implying a high albedo and small size.
Like many other objects, whether large or small, made of rocks, gases or ices, Eris
has a moon, which is seen to the right of the dwarf planet in this image taken by the
10-meter Keck Telescope. The distance and motion of Dysnomia (named after the
daughter of Eris, in Greek mythology) are very uncertain, but as better observations
are obtained, the application of Kepler's Third Law to the orbital motion should yield
accurate estimates of the mass of Eris, and its density. Pending those currently
unknown results, it is presumed, based on their distance from the Sun, that both Eris
and its moon are made of frozen compounds of carbon, nitrogen and oxygen with
each other and hydrogen -- that is, water ice, and other ices. (W. M. Keck Observatory,
apod060918)
Relative sizes of the largest known trans-Neptunian objects (Pluto and KBOs)
Dwergplaneten:
Eris: More Massive than Pluto
Credit & Copyright: Thierry Lombry
Explanation: Eris, a dwarf planet currently orbiting the Sun at about twice Pluto's distance,
has been measured to have about 27 percent more mass than Pluto. The mass was calculated
by timing the orbit of Eris' moon Dysnomia. Images taken with a ground-based Keck
telescope, when combined with existing images taken by Hubble Space Telescope, show that
Dysnomia has a nearly circular orbit lasting about 16 days. Cataloged as 2003 UB313 only a
year ago, infrared images also showed previously that Eris is actually larger in diameter than
Pluto. The plane of Eris' orbit is well out of the plane of the Solar System's planets. In the
above drawing, a scientific artist has imagined Eris and Dysnomia orbiting our distant Sun.
No space missions are currently planned to Eris, although the robotic New Horizons
spacecraft bound for Pluto has recently passed Jupiter.
Makemake of the Outer Solar System
Credit: R. Hurt (SSC-Caltech), JPL-Caltech, NASA
Explanation: Recently discovered Makemake is one of the largest objects known in the outer
Solar System. Pronounced MAH-kay MAH-kay, this Kuiper belt object is only slightly
smaller than Pluto, orbits the Sun only slightly further out than Pluto, and appears only
slightly dimmer than Pluto. Makemake, however, has an orbit much more tilted to the ecliptic
plane of the planets than Pluto. Designated 2005 FY9 soon after its discovery by a team led
by Mike Brown (Caltech) in 2005, the outer Solar System orb was recently renamed
Makemake for the creator of humanity in the Rapa Nui mythology of Easter Island.
Additionally, Makemake has been recently classified as a dwarf planet under the new
subcategory plutoid, making Makemake the third cataloged plutoid after Pluto and Eris.
Makemake is known to be a world somewhat red in appearance, with spectra indicating it is
likely covered with frozen methane. Since no images of Makemake's surface yet exist, an
artist's illustration originally meant to depict Sedna has been boldly co-opted above to now
illustrate Makemake. A hypothetical moon is visualized above nearly in the direction of our
distant Sun.
Haumea of the Outer Solar System
Illustration Credit: NASA
Explanation: One of the strangest objects in the outer Solar System was classified as a dwarf
planet last week and given the name Haumea. This designation makes Haumea the fifth
designated dwarf planet after Pluto, Ceres, Eris, and Makemake. Haumea's smooth but oblong
shape make it extremely unusual. Along one direction, Haumea is significantly longer than
Pluto, while in another direction Haumea has an extent very similar to Pluto, while in the third
direction is much smaller. Haumea's orbit sometimes brings it closer to the Sun than Pluto,
but usually Haumea is further away. Illustrated above, an artist visualizes Haumea as a nearly
featureless ellipsoid. Quite possibly, however, Haumea has interesting craters and surface
features that currently remain unknown. Originally discovered in 2003 and given the
temporary designation of 2003 EL61, Haumea was recently renamed by the IAU for a
Hawaiian goddess. Haumea has two small moons discovered in 2005, recently renamed
Hi'iaka and Namaka for daughters of the goddess.