Astronomy Picture of the Day |
APOD: 2006 September 18 - Eris: The Largest Known Dwarf Planet
Explanation:
Is Pluto the largest dwarf planet? No!
Currently, the largest known dwarf planet is
(136199) Eris,
renamed last week from 2003 UB313.
Eris is just slightly larger than Pluto, but orbits as far as twice
Pluto's distance from the Sun.
Eris is shown above in an image taken by a 10-meter
Keck Telescope from
Hawaii,
USA.
Like Pluto, Eris has a moon, which has been
officially named by the
International Astronomical Union
as (136199) Eris I (Dysnomia).
Dysnomia is visible above just to the right of Eris.
Dwarf planets
Pluto and Eris are
trans-Neptunian objects that orbit in the
Kuiper belt
of objects past Neptune.
Eris was discovered in 2003, and is likely composed of
frozen water-ice and
methane.
Since Pluto's recent demotion by the
IAU from planet to dwarf planet status,
Pluto
has recently also been given a new numeric designation: (134340) Pluto.
Currently, the only other officially designated "dwarf planet" is (1)
Ceres.
APOD: 2006 August 28 - Eight Planets and New Solar System Designations
Explanation:
How many planets are in the Solar System?
This popular question now has a new formal answer according the
International Astronomical Union (IAU): eight.
Last week, the IAU voted on a
new definition for planet and
Pluto did not make the cut.
Rather, Pluto was re-classified as a
dwarf planet and is considered as a prototype for a new category of
trans-Neptunian objects.
The eight planets now recognized by the IAU are:
Mercury,
Venus,
Earth,
Mars,
Jupiter,
Saturn,
Uranus, and
Neptune.
Solar System objects now classified as dwarf planets are:
Ceres,
Pluto, and the currently unnamed
2003 UB313.
Planets, by the new IAU definition, must be in orbit around the sun, be nearly spherical,
and must have cleared the neighborhood around their orbits.
The demotion of
Pluto to dwarf planet
status is a source of continuing
dissent and controversy in the astronomical community.
APOD: 2006 February 7 - UB313: Larger than Pluto
Explanation:
What do you call an outer Solar System object that is larger than Pluto?
Nobody is yet sure.
The question arose recently when
2003 UB313,
an object currently twice as far out as Pluto and not in the
plane with the rest of the planets, was
verified recently
to be 30 percent wider than
Pluto.
UB313's size was measured by a noting its distance from the
Sun and how much
infrared light it emits.
Previous size estimates were based only on visible light and greatly
affected by how reflective the object is.
Whether 2003 UB313
is officially declared a planet will be answered shortly by the
International Astronomical Union.
In the above picture, a scientific artist has imagined
UB313 in its
distant orbit around the Sun coupled with a hypothetical moon.