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Anónimo disse...

Turning Planetary Theory Upside Down: Nine New Exoplanets Found, Some
With Retrograde Orbits

ScienceDaily (Apr. 13, 2010) — The discovery of nine new transiting
exoplanets has been announced at the RAS National Astronomy Meeting.
When these new results were combined with earlier observations of
transiting exoplanets astronomers were surprised to find that six out
of a larger sample of 27 were found to be orbiting in the opposite
direction to the rotation of their host star -- the exact reverse of
what is seen in our own solar system.

"This is a real bomb we are dropping into the field of exoplanets,"
says Amaury Triaud, a PhD student at the Geneva Observatory who, with
Andrew Cameron and Didier Queloz, leads a major part of the
observational campaign.

Planets are thought to form in the disc of gas and dust encircling a
young star. This proto-planetary disc rotates in the same direction as
the star itself, and up to now it was expected that planets that form
from the disc would all orbit in more or less the same plane, and that
they would move along their orbits in the same direction as the star's
rotation. This is the case for the planets in the Solar System.

Anónimo disse...

After the initial detection of the nine new exoplanets [1] with the
Wide Angle Search for Planets (WASP, [2]), the team of astronomers
used the HARPS spectrograph on the 3.6-metre ESO telescope at the La
Silla observatory in Chile, along with data from the Swiss Euler
telescope, also at La Silla, and data from other telescopes to confirm
the discoveries and characterise the transiting exoplanets [3] found
in both the new and older surveys.

Surprisingly, when the team combined the new data with older
observations they found that more than half of all the hot Jupiters
[4] studied have orbits that are misaligned with the rotation axis of
their parent stars. They even found that six exoplanets in this
extended study (of which two are new discoveries) have retrograde
motion: they orbit their star in the "wrong" direction.

"The new results really challenge the conventional wisdom that planets
should always orbit in the same direction as their stars spin," says
Andrew Cameron of the University of St Andrews, who presented the new
results at the RAS National Astronomy Meeting (NAM2010) in Glasgow
this week.

Anónimo disse...

In the 15 years since the first hot Jupiters were discovered, their
origin has been a puzzle. These are planets with masses similar to or
greater than that of Jupiter, but that orbit very close to their suns.
The cores of giant planets are thought to form from a mix of rock and
ice particles found only in the cold outer reaches of planetary
systems. Hot Jupiters must therefore form far from their star and
subsequently migrate inwards to orbits much closer to the parent star.
Many astronomers believed this was due to gravitational interactions
with the disc of dust from which they formed. This scenario takes
place over a few million years and results in an orbit aligned with
the rotation axis of the parent star. It would also allow Earth-like
rocky planets to form subsequently, but unfortunately it cannot
account for the new observations.

To account for the new retrograde exoplanets an alternative migration
theory suggests that the proximity of hot Jupiters to their stars is
not due to interactions with the dust disc at all, but to a slower
evolution process involving a gravitational tug-of-war with more
distant planetary or stellar companions over hundreds of millions of
years. After these disturbances have bounced a giant exoplanet into a
tilted and elongated orbit it would suffer tidal friction, losing
energy every time it swung close to the star. It would eventually
become parked in a near circular, but randomly tilted, orbit close to
the star. "A dramatic side-effect of this process is that it would
wipe out any other smaller Earth-like planet in these systems," says
Didier Queloz of Geneva Observatory.

Two of the newly discovered retrograde planets have already been found
to have more distant, massive companions that could potentially be the
cause of the upset. These new results will trigger an intensive search
for additional bodies in other planetary systems.

Anónimo disse...

This research was presented at the Royal Astronomical Society National
Astronomy Meeting (NAM2010) that is taking place this week in Glasgow,
Scotland. Nine publications submitted to international journals will
be released on this occasion, four of them using data from ESO
facilities. On the same occasion, the WASP consortium was awarded the
2010 Royal Astronomical Society Group Achievement Award.


[1] The current count of known exoplanets is 452.

[2] The nine newly found exoplanets were discovered by the Wide Angle
Search for Planets (WASP). WASP comprises two robotic observatories,
each consisting of eight wide-angle cameras that simultaneously
monitor the sky continuously for planetary transit events. A transit
occurs when a planet passes in front of its parent star, temporarily
blocking some of the light from it. The eight wide-angle cameras allow
millions of stars to be monitored simultaneously to detect these rare
transit events. The WASP cameras are operated by a consortium
including Queen's University Belfast, the Universities of Keele,
Leicester and St Andrews, the Open University, the Isaac Newton Group
on La Palma and the Instituto Astrofisica Canarias.

[3] To confirm the discovery and characterise a new transiting planet,
it is necessary to do radial velocity follow-up to detect the wobble
of the host star around its common centre of mass with the planet.
This is done with a worldwide network of telescopes equipped with
sensitive spectrometers. In the northern hemisphere, the Nordic
Optical Telescope in the Canary Islands and the SOPHIE instrument on
the 1.93-metre telescope at Haute-Provence in France lead the search.
In the south, the HARPS exoplanet hunter attached to the 3.6-metre ESO
telescope and the CORALIE spectrometer on the Euler Swiss telescope,
both at La Silla, were used to confirm the new planets and measure the
angle through which each planet's orbit is tilted relative to its
star's equator. The robotic Faulkes Telescopes of the Las Cumbres
Observatory, located in Hawaii and Australia, provided the brightness
measurements that determined the sizes of the planets. Follow-up
observations of WASP exoplanet candidates are obtained at the Swiss
Euler Telescope at La Silla, Chile (in collaboration with colleagues
at Geneva Observatory), at the Nordic Optical Telescope on La Palma,
and at the 1.93-metre telescope of the Observatoire de Haute-Provence
in France (in collaboration with colleagues at the Institut
d'Astrophysique de Paris and the Laboratoire d'Astrophysique de

The studies of the orbital tilt angles of the WASP planets were made
with the HARPS instrument on the ESO 3.6-metre telescope and with the
CORALIE instrument on the Euler Swiss telescope, both at La Silla in
the southern hemisphere, and at Tautenburg Observatory, McDonald
Observatory and the Nordic Optical Telescope in the northern

[4] Hot Jupiters are planets orbiting other stars that have masses
similar to, or greater than, that of Jupiter, but that orbit their
parent stars much more closely than any of the planets in our own
Solar System. Because they are both large and close they are easier to
detect from their gravitational effect on their stars and also more
likely to transit the disc of the star. Most of the first exoplanets
to be found were of this class.

Story Source:
Adapted from materials provided by ESO.