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Mars polar cap mystery solved

...the Martian weather system and a giant impact crater could explain why the residual ice cap at the south pole of Mars is offset by several degrees...

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Hubble's ANGST reveals diversity of galaxies a survey of 14 million stars in 69 galaxies from the ACS Nearby Galaxy Survey Treasury (ANGST), Hubble reveals the true diversity of galaxies...

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Young galaxy's magnetism surprises astronomers

...the first direct measurement of the magnetic field in a young, distant galaxy, reveals it to be 10 times stronger than that of our own Milky Way...

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Video archive

STS-120 day 2 highlights

Flight Day 2 of Discovery's mission focused on heat shield inspections. This movie shows the day's highlights.


STS-120 day 1 highlights

The highlights from shuttle Discovery's launch day are packaged into this movie.


STS-118: Highlights

The STS-118 crew, including Barbara Morgan, narrates its mission highlights film and answers questions in this post-flight presentation.

 Full presentation
 Mission film

STS-120: Rollout to pad

Space shuttle Discovery rolls out of the Vehicle Assembly Building and travels to launch pad 39A for its STS-120 mission.


Dawn leaves Earth

NASA's Dawn space probe launches aboard a Delta 2-Heavy rocket from Cape Canaveral to explore two worlds in the asteroid belt.

 Full coverage

Dawn: Launch preview

These briefings preview the launch and science objectives of NASA's Dawn asteroid orbiter.

 Launch | Science

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COROT discovery stirs exoplanet classification rethink

Posted: October 06, 2008

COROT scientists have discovered the most massive planet-sized object closely orbiting its parent star yet, but there remains one question: is it really a planet or is it a failed star?

COROT-exo-3b is about the size of Jupiter but 20 times more massive and takes just 4 days and 6 hours to orbit its parent star, which is slightly larger than the Sun. The exotic body was detected by the COROT space telescope as the object transited in front of its parent star, forcing a drop in the star’s brightness.

"We were taken by surprise when we found this massive object orbiting so close to its parent star,” says Dr Magali Deleuil from the Laboratoire d'Astrophysique de Marseille and leader of the team that made the discovery. "COROT-exo-3b is really unique - we're still debating its nature."

An artist§s impression of the relative sizes of the Sun, Jupiter and COROT-exo-3b. Image: OAMP.

Planet-hunters have been searching for planets which closely orbit their parent stars with periods of less than 10 days for almost 15 years. During this time, scientists have encountered planets with masses 12 times that of Jupiter, and stars with 70 times as massive as Jupiter, but none in between, which adds to the surprise of discovering 20-Jupiter-mass COROT-exo-3b. And it is even more of a surprise since it does not fall into either conventional category of planets or brown dwarfs. A brown dwarf is a 'failed star', one that is not massive enough to maintain nuclear fusion at its core, but which still displays some stellar characteristics.

"COROT-exo-3b might turn out to be a rare object found by sheer luck,” says team member Dr Francois Bouchy. "But it might just be a member of a new-found family of very massive planets that encircle stars more massive than our Sun. We're now beginning to think that the more massive the star, the more massive the planet.”

The perplexing discovery could require a rethink as to where to draw the line between planets and brown dwarfs. As a planet, COROT-exo-3b would be the most massive and the densest found to date - more than twice as dense as lead. Further study of the system will help astronomers better understand how to categorise such objects, and to learn how such a massive object formed so close to its parent star.

In addition to the initial discovery by COROT, the observations were supported from the ground to further study the object's mass, orbit and stellar properties. The international network of telescopes included the telescope of Observatoire de Haute Provence in France, the European Southern Observatory telescopes at Paranal and La Silla in Chile, the Thuringia State Observatory in Tautenburg, Germany, the Canada-France-Hawaii Telescope on Mauna Kea, the Swiss Euler Telescope at La Silla, Chile, the Wise Observatory in Israel, the ESA telescope on Mt. Teide, Tenerife, and the telescope of the Astrophysical Institute of the Canary Islands.