[meteorite-list] CoRoT-7b rocks!

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Wed, 16 Sep 2009 12:21:56 -0500
Message-ID: <oj72b51i6dad5uphbp0u10mtcej2ea357k_at_4ax.com>

http://spacefellowship.com/2009/09/16/smallest-exoplanet-is-shown-to-be-a-solid-rocky-world/

Smallest exoplanet is shown to be a solid, rocky world
Published By
Matt
On: 16 September 2009 11:26 AM CEST Source

The confirmation of the nature of CoRoT-7b as the first rocky planet outside our
Solar System marks a significant step forward in the search for Earth-like
exoplanets. The detection by CoRoT and follow-up radial velocity measurements
with HARPS suggest that this exoplanet, CoRoT-7b, has a density similar to that
of Mercury, Venus, Mars and Earth making it only the fifth known terrestrial
planet in the Universe.

The search for a habitable exoplanet is one of the holy grails in astronomy. One
of the first steps towards this goal is the detection of terrestrial planets
around solar-type stars. Dedicated programmes, using telescopes in space and on
ground, have yielded evidence for hundreds of planets outside of our Solar
System. The majority of these are giant, gaseous planets, but in recent years
small, almost Earth-mass planets have been detected demonstrating that the
discovery of Earth analogues ? exoplanets with one Earth mass or one Earth
radius orbiting a solar-type star at a distance of about 1 astronomical unit ?
is within reach.

Transit detections yield key physical properties

A number of techniques are routinely employed in the search for exoplanets:
spectroscopic radial velocity, astrometry, microlensing, photometric transits.
Of these, the search for transits ? the passage of the exoplanet in front of the
parent star ? provides unprecedented access to the planet?s physical properties.
In particular, the combination of transit photometry and radial velocity
measurements provides direct and very accurate estimates of the planetary mass
and radius, and hence mean density. These parameters in turn provide tight
constraints on the composition and physical structure of the planet and hence on
the likelihood of the exoplanet being a true Earth analogue.

The CoRoT space mission employs the transit strategy in the search for
exoplanets. Continuous observations, lasting about 150 days each, are made of
two large (4 square degrees) regions towards the centre and anti-centre of the
Galaxy. During the first of these observation periods towards the anti-centre
(October 2007 to March 2008), 46 stars exhibited evidence for transits, among
them CoRoT-7, a main-sequence, close-by (at a distance of 150 pc) solar-type
star.

The size is determined with photometry from CoRoT


Investigation of the data, as described by Alain L?ger and colleagues, provided
compelling evidence for the presence of an exoplanet. The discovery was
announced earlier this year at which time the analysis of CoRoT data had shown
that CoRoT-7b (as the planet is known) has a diameter less than twice that of
Earth making it the smallest exoplanet (to date) orbiting a main-sequence star.
The CoRoT data also demonstrated that the planet is about 2.5 million km from
its parent star and orbits once every 20.4 hours.


 and HARPS radial velocity measurements provide the mass

Further progress, and in particular the determination of the planet mass, could
only be made by obtaining accurate measurements of the variation in the velocity
of the star caused by the gravitational pull of the orbiting planet. The need
for ground-based support observations for CoRoT had always been envisaged and
time on the HARPS spectrograph (at the ESO 3.6-m telescope at La Silla in Chile)
had been secured as a result of an ESA call for European co-investigators for
CoRoT. Didier Queloz and colleagues describe how almost 70 hours of observations
of the CoRoT-7 system with HARPS finally provided the sought-after result:
CoRoT-7b is one of the lightest exoplanets detected to date with a mass five
times that of the Earth. This puts CoRoT-7b firmly in the category of
?super-Earth? ? an exoplanet with a mass between that of Earth and gas giants.

A terrestrial exoplanet orbiting a solar-type star

Although about a dozen super-Earths have been detected CoRoT-7b is the first for
which both mass and radius estimates are available. Combining the radius
estimates from CoRoT and the mass estimates from HARPS results in an exoplanet
mean density of 5.5 g/cm3. There are only three other known planets with
similar density: Earth, Mercury and Venus (Mars is less dense) which strongly
suggests that the planet is a solid, rocky planet.

?We are coming tantalising close to reaching the ultimate goal of detecting a
true Earth-like planet,? comments Malcolm Fridlund, ESA CoRoT Project Scientist
and member of the CoRoT Science Team. ?This bodes well for future exoplanet
search missions, such as the Cosmic Vision candidate, PLATO.?

About CoRoT

CoRoT is a mission led by the French national space agency, CNES. ESA has joined
the mission by providing the optics and baffle for the telescope and testing of
the payload. Through this collaboration a number of European scientists, from
Denmark, Switzerland, the United Kingdom and Portugal, have been selected as
Co-Investigators in open competition. As a result of ESA?s participation in
CoRoT, scientists from ESA?s Member States have access to the satellite?s data.

ESA?s Research and Scientific Support department (RSSD) at ESTEC is a full
partner in CoRoT by providing the on-board Data Processing Units (DPU?s). Other
partners in CoRoT are Austria, Spain, Germany, Belgium and Brazil.

The ESA PRODEX programme has supported the development of the CoRoT telescope
baffle, and the software development and data processing of CoRoT light curves.

The ground stations used for CoRoT are located in Kiruna (S), Aussaguel (F)
Hartebeesthoek (South Africa), Kourou (French Guyana), with mission-specific
ground stations in Alcantara (Brazil) and Vienna (A).
Received on Wed 16 Sep 2009 01:21:56 PM PDT