A dwarf
planet in our solar system, called Haumea, is known for its unusual shape and
fast spin. Now astronomers have discovered another distinguishing feature: a
dark red spot which appears to be richer in minerals and organic compounds than
the surrounding icy surface.
Haumea, discovered
in 2004, orbits the Sun beyond Neptune, in a region known as the Kuiper
Belt. It is classified as a dwarf planet
— a celestial body that is big enough to have been rounded by its own gravity,
but has not cleared its neighboring region of similar objects. There are four
other dwarf planets: Ceres, Pluto, Eris and
Makemake. Haumea is the fourth largest dwarf planet.
Haumea is
also the fastest spinning large object in the solar system – one day on Haumea
is equal to about 3.9 hours on Earth. This rapid rotation distorts Haumea,
elongating it into a football-like shape.
Most of
what we know about this object was determined from studying variations in its
brightness, called a "light curve." And it is through examination of
this light curve that scientists have found the dark spot.
"The
two brightness maxima and the two minima of the light curve are not exactly
equal, as would be expected from a uniform surface," said Pedro Lacerda of
Queen's University Belfast in the United Kingdom. "This indicates the
presence of a dark spot on the otherwise bright surface."
Additionally
the light curve is not exactly the same shape in all wavelengths. Small but
persistent differences indicate that the dark spot is slightly redder in
visible light and slightly bluer at infrared wavelengths.
"Our very
first measurements of Haumea already told us there was a spot on the surface,
but it was only when we got the infrared data that we were able to begin to
understand what the spot might be," Lacerda said.
While the
origin of the spot is unknown, possible interpretations of these measurements
are that the spot is richer in minerals and organic compounds, or that it
contains a higher fraction of crystalline ice. If the spot is a scar of a
recent impact, then the spot material might resemble the composition of the
impactor, perhaps mixed with material from the inner layers of Haumea.
Lacerda
will present the discovery Wednesday at the European Planetary Science Congress
in Potsdam, Germany.
New
observations of this spot are planned for early 2010 using the ESO
Very Large Telescope. "Now we will get detailed spectroscopy of the
spot to hopefully identify its chemical composition and solve the puzzle of its
origin" Lacerda concluded.
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