Dwarf Planet 2007 OR10
The combined power of three space observatories, including NASA's
Hubble Space Telescope, has helped astronomers uncover a moon orbiting
the third largest dwarf planet, catalogued as 2007 OR10. The
pair resides in the frigid outskirts of our solar system called the
Kuiper Belt, a realm of icy debris left over from our solar system's
formation 4.6 billion years ago.
With this discovery, most of the known dwarf planets in the Kuiper
Belt larger than 600 miles across have companions. These bodies provide
insight into how moons formed in the young solar system.
"The discovery of satellites around all of the known large dwarf
planets — except for Sedna — means that at the time these bodies formed
billions of years ago, collisions must have been more frequent, and
that's a constraint on the formation models," said Csaba Kiss of the
Konkoly Observatory in Budapest, Hungary. He is the lead author of the
science paper announcing the moon's discovery. "If there were frequent
collisions, then it was quite easy to form these satellites."
The objects most likely slammed into each other more often because
they inhabited a crowded region. "There must have been a fairly high
density of objects, and some of them were massive bodies that were
perturbing the orbits of smaller bodies," said team member John
Stansberry of the Space Telescope Science Institute in Baltimore,
Maryland. "This gravitational stirring may have nudged the bodies out of
their orbits and increased their relative velocities, which may have
resulted in collisions."
But the speed of the colliding objects could not have been too fast
or too slow, according to the astronomers. If the impact velocity was
too fast, the smash-up would have created lots of debris that could have
escaped from the system; too slow and the collision would have produced
only an impact crater.
Collisions in the asteroid belt, for example, are destructive because
objects are traveling fast when they smash together. The asteroid belt
is a region of rocky debris between the orbits of Mars and the gas giant
Jupiter. Jupiter's powerful gravity speeds up the orbits of asteroids,
generating violent impacts.
The team uncovered the moon in archival images of 2007 OR10
taken by Hubble's Wide Field Camera 3. Observations taken of the dwarf
planet by NASA's Kepler Space Telescope first tipped off the astronomers
of the possibility of a moon circling it. Kepler revealed that 2007 OR10
has a slow rotation period of 45 hours. "Typical rotation periods for
Kuiper Belt Objects are under 24 hours," Kiss said. "We looked in the
Hubble archive because the slower rotation period could have been caused
by the gravitational tug of a moon. The initial investigator missed the
moon in the Hubble images because it is very faint."
The astronomers spotted the moon in two separate Hubble observations
spaced a year apart. The images show that the moon is gravitationally
bound to 2007 OR10 because it moves with the dwarf planet, as
seen against a background of stars. However, the two observations did
not provide enough information for the astronomers to determine an
orbit.
"Ironically, because we don't know the orbit, the link between the
satellite and the slow rotation rate is unclear," Stansberry said.
The astronomers calculated the diameters of both objects based on
observations in far-infrared light by the Herschel Space Observatory,
which measured the thermal emission of the distant worlds. The dwarf
planet is about 950 miles across, and the moon is estimated to be 150
miles to 250 miles in diameter. 2007 OR10, like Pluto, follows an eccentric orbit, but it is currently three times farther than Pluto is from the sun.
2007 OR10 is a member of an exclusive club of nine dwarf planets. Of those bodies, only Pluto and Eris are larger than 2007 OR10.
It was discovered in 2007 by astronomers Meg Schwamb, Mike Brown, and
David Rabinowitz as part of a survey to search for distant solar system
bodies using the Samuel Oschin Telescope at the Palomar Observatory in
California.
The team's results appeared in The Astrophysical Journal Letters.
The Hubble Space Telescope is a project of international cooperation
between NASA and ESA (European Space Agency). NASA's Goddard Space
Flight Center in Greenbelt, Maryland, manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore conducts Hubble science
operations. STScI is operated for NASA by the Association of
Universities for Research in Astronomy, Inc., in Washington, D.C.
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Contacts
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Csaba Kiss
Konkoly Observatory, Budapest, Hungary
011-36-1-391-9341
kiss.csaba@csfk.mta.hu
John Stansberry
Space Telescope Science Institute, Baltimore, Maryland
410-338-2442
jstans@stsci.edu
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Csaba Kiss
Konkoly Observatory, Budapest, Hungary
011-36-1-391-9341
kiss.csaba@csfk.mta.hu
John Stansberry
Space Telescope Science Institute, Baltimore, Maryland
410-338-2442
jstans@stsci.edu
Source: HubbleSite
