[meteorite-list] Planets continue being weird

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Tue, 13 Apr 2010 17:37:06 -0500
Message-ID: <pds9s59fojb3h0058sti952ch2dlennt53_at_4ax.com>

http://www.eso.org/public/news/eso1016/

Turning Planetary Theory Upside Down

13 April 2010

The discovery of nine new transiting exoplanets is announced today at the RAS
National Astronomy Meeting (NAM2010). 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. The new discoveries provide an unexpected and serious
challenge to current theories of planet formation. They also suggest that
systems with exoplanets of the type known as hot Jupiters are unlikely to
contain Earth-like planets.

?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.

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.

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.

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.
Notes

[1] The current count of known exoplanets is 454.

[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 Marseille).

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 hemisphere.

[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.
More information

ESO, the European Southern Observatory, is the foremost intergovernmental
astronomy organisation in Europe and the world?s most productive astronomical
observatory. It is supported by 14 countries: Austria, Belgium, the Czech
Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal,
Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious
programme focused on the design, construction and operation of powerful
ground-based observing facilities enabling astronomers to make important
scientific discoveries. ESO also plays a leading role in promoting and
organising cooperation in astronomical research. ESO operates three unique
world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At
Paranal, ESO operates the Very Large Telescope, the world?s most advanced
visible-light astronomical observatory and VISTA, the world?s largest survey
telescope. ESO is the European partner of a revolutionary astronomical telescope
ALMA, the largest astronomical project in existence. ESO is currently planning a
42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT,
which will become ?the world?s biggest eye on the sky?.
Received on Tue 13 Apr 2010 06:37:06 PM PDT