Testing the atmosphere of an exoplanet

Astronomers have managed for the first time to measure the atmosphere surrounding a "super-Earth" extrasolar planet.

Planet, GJ 1214b, which is 40 light years away, is three times larger than Earth and about seven times heavier, and is the first planet of its kind known to have an atmosphere.

According to the BBC researchers have found that it appears to have either a dense atmosphere of water steam, or is wrapped in thick clouds like Venus.

More experiments measuring more colours of light will bear out which it is.

The method used could be used on many ground-based telescopes to yield atmospheric data on other exoplanets. It works by canceling out the disruptive effects of the Earth's atmosphere while that of far-flung worlds is measured from the ground.

"'Super-Earths' are really interesting, they're at the forefront of what's going on in exoplanet research," said Jacob Bean, the Harvard-Smithsonian University Center for Astrophysics scientist who led the research. "They're an interesting regime because they're defined as being the transition from terrestrial planets like Earth, Venus and Mars, up to the ice giants like Uranus and Neptune."
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From what is known about GJ 1214b, three theories of its composition and atmosphere dominated. It could either be covered in a dense layer of steam, or it could be an icy, rocky world with a hydrogen or helium atmosphere, or perhaps a large rocky planet with a mixture of volcanic gases.


Drake Deming, of Nasa's Planetary Systems Laboratory said the work "opens the door to characterisng these kinds of super-Earth atmospheres".

"We've been seduced by the abundance of exoplanet results into thinking that these are routine measurements, but they're actually extraordinarily difficult," he told BBC News.

"This is certainly the most significant atmospheric exoplanet result in the last year - and a year is a long time in this field."

The next step is to carry out the same measurement using different colours of light, further into the infrared where the distinction can be made; .

I may be an utter ignoramus where physics is concerned but this is truly fascinating stuff. I daresay in a few years time such results will be routine

The first pictures of exoplanets

HR8799 and its consorts

This is one of the first picture taken of planets outside our solar system. It shows an exoplanetary system comprising three planets, has been directly imaged, circling a star called HR8799 in the constellation Pegasus. What may look like a few fuzzy blobs is something truly amazing in my view.

In addition the http://news.bbc.co.uk/1/hi/technology/7725584.stm BBC reports that both visible and infrared images have been snapped of a planet orbiting a star 25 light-years away. The planet is believed to be the coolest, lowest-mass object ever seen outside our own solar neighbourhood. Being able to directly detect the light from these planets will allow astronomers to study their composition and atmospheres in detail. Advances in optics and image processing have allowed astronomers to effectively subtract the bright light from stars, leaving behind light from the planets. That light can either come in the infrared, caused by the planets' heat, or be reflected starlight.

Fomalhaut and Farmalhaut b

Paul Kalas of the University of California led an international group that used the Hubble Space Telescope to image the region around a star called Fomalhaut. The star has a massive ring of dust surrounding it that appears to have a cleanly groomed inner edge. That is in keeping with what is known as accretion theory - that young planets gather up dust and matter as they orbit - and prompted the team to begin looking for the suspected planet in 2005.

The team estimates that the planet, dubbed Fomalhaut b, is 11bn miles away from its star, about as massive as Jupiter and completes an orbit in about 870 years. It may also have a ring around it. "I nearly had a heart attack at the end of May when I confirmed that Fomalhaut b orbits its parent star," Dr Kalas said. "It's a profound and overwhelming experience to lay eyes on a planet never before seen."

Christian Marois of the Herzberg Institute for Astrophysics and his team used the Keck and Gemini telescopes in Hawaii to look near HR 8799. The team looked for light in the infrared part of the spectrum, hoping to spot planets that were still hot from their formation. What they found in 2004, and confirmed again this year, are three planets circling the star.

According to a theoretical model that accounts for the light coming from the planets, they range in size from five to 13 times the mass of Jupiter and are probably only about 60 million years old. The trio have similarities with our own solar system. Their orbits are comparable in size to those of the outer planets, and the smaller planets are those closest to the sun - again suggesting a system that formed through accretion.

Dr Marois pointed out that the current methods used in the exoplanet hunt are sensitive primarily to Jupiter-sized planets and larger. "We thus do not have a full picture. The detection of the three planets around HR 8799 does not mean that no planets are orbiting at smaller separations. Other gas giant or even rocky planets could reside there."

The study of the light directly from the planets will yield information about their atmospheres and surfaces that is impossible to collect from planets discovered indirectly.

The youngest planet?

A team of astronomers has detected an embryonic planet detected around the star HL Tau. What makes this discovery interesting is that it could be less than 2,000 years old. Research leader Dr Jane Greaves said the planet's growth may have been kick started when another young star passed the system 1,600 years ago.

The scientists studied a disc of gas and rocky particles around HL Tau, which is 520 light-years away and thought to be less than 100,000 years old. The disc is unusually massive and bright, making it an excellent place to search for signs of planets in the process of formation. Dr Greaves, from the University of St Andrews, Scotland, said the discovery of a forming planet around such a young star was a major surprise. "It wasn't really what we were looking for. And we were amazed when we found it," she told BBC News. The next youngest planet confirmed is 10 million years old."

Dr Ken Rice, from the Institute of Astronomy in Edinburgh, said the discovery shed new light on theories of planet formation. According to one model, planets form from the bottom up. Under this scenario, particles of rocky material collide and "stick" to one another, forming a bigger and bigger object. But he thinks the proto-planet in HL Tau formed relatively quickly when a region of the disc collapsed to form a self-contained structure. This could occur because of gravitational instability in the disc itself.

Intriguingly, another young star in the same region called XZ Tau may have made a close pass of HL Tau about 1,600 years ago. Although not required for planet formation, it is possible that this flyby perturbed the disc, making it unstable. This would be a very recent event in astronomical terms. "It's possible it gave a 'yank' to one side of the disc around HL Tau, making it unstable, and that this was a 'trigger' for the planet to form," Dr Greaves explained. "If the planet formed in the last 1,600 years, that would be incredibly recent."

Methane and water discovered on extrasolar planet

Astronomers have discovered methane in the atmosphere of planet HD 189733b which is 63 light years away. This is the first time that an organic molecule has been detected on a planet outside our Solar System. Water has also been discovered but the planet is far too hot to support life.

The discovery, unveiled in the journal Nature, is an important step towards exploring new worlds that might be more hospitable to life. Under certain circumstances, methane can play a key role in prebiotic chemistry. Co-author Giovanna Tinetti from University College, London, said "This planet is a gas giant very similar to our own Jupiter, but orbiting very close to its star. The methane here, although we can call it an organic constituent, is not produced by life - it is way too hot there for life."

Dr Tinetti, and co-authors Mark Swain and Gautam Vasisht, from NASA’s Jet Propulsion Laboratory in Pasadena, California, found the tell-tale signature of methane in the planet's atmosphere using the Hubble Space Telescope. The observations were made as the planet passed in front of its parent star, as viewed from Earth. As the star's light passed briefly through the planet's atmosphere, the gases imprinted their chemical signatures on the transmitted light Spectroscopy revealed the chemical "fingerprint" of methane.

It shows that Hubble, Spitzer and a new generation of space telescopes yet to be launched can detect organic molecules on other extrasolar planets using spectroscopy, they say. Dr Swain said: "This is a crucial stepping stone to eventually characterising prebiotic molecules on planets where life could exist." Dr Tinetti said the technique could eventually be applied to extrasolar planets that appear more suitable for life than HD 189733b. "I definitely think that life is out there. My personal view is it is way too arrogant to think that we are the only ones living in the Universe." She said

Adam Showman of the Department of Planetary Sciences at the University of Arizona, US, said scientists were finally starting to move beyond simply discovering extrasolar planets to truly characterising them as worlds. Dr Showman, who was not part of the study, said: "The discovery does not by itself have any direct implications for life except that it proves a technique which might potentially be useful for characterising the atmosphere of rocky planets when we finally start discovering them."

It gets worse for poor old Pluto

Last year we saw Pluto (left with its satellite Charon) booted out of the first division of planets, relegated to “dwarf planet” status. Now it has been confirmed it doesn’t even top the “tiddlers league”

A http://news.bbc.co.uk/1/hi/sci/tech/6751975.stm study has confirmed that the dwarf planet Eris - whose discovery prompted Pluto's relegation from planet to dwarf - outranks it in mass.

The discovery of Eris, formerly known as 2003 UB313, marked the beginning of the end for Pluto as a planet. Previous measurements from the Hubble Space Telescope confirmed that Eris was larger in diameter than Pluto, leading the International Astronomical Union (IAU) to rule in 2006 that Pluto could no longer be classed as a planet. A new category of dwarf planets was adopted, into which Pluto, Eris and another body called Ceres, which is located in the asteroid belt, were placed.

Eris (left) lies 14.5 billion km from Earth in the Kuiper Belt. It has a moon, Dysnomia, and scientists used this satellite, to calculate its mass. The researchers, led by Eris' discoverer Mike Brown from the California Institute of Technology, discovered that the more distant world has 27% more mass than Pluto. So in addition to being the largest, Eris is also the most massive known dwarf planet.

Poor Pluto stares into the abyss and the abyss gazes also... over its planetary shoulder at something more interesting - in this case a few pixels!

Earth 2?

Perhaps not but Astronomers have found the most Earth-like exoplanet so far. And one that could have water running on its surface. The planet, Gliese 581c, orbits the red dwarf star Gliese 581, which is 20.5 light-years away.

"We have estimated that the mean temperature of this 'super-Earth' lies between 0 and 40 degrees Celsius, and water would thus be liquid," explained Stephane Udry of the Geneva Observatory "Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky - like our Earth - or covered with oceans."

Gliese 581c is the smallest exoplanet found so far, and completes a full orbit of its parent star in just 13 days. It is 14 times closer to its star than the Earth is to our Sun. However, Giese 581 is smaller and colder than the Sun - and thus less luminous - the planet lies in the star’s "habitable zone". The “super earth” is one of three exoplanete discovered in the Gliese 581 system.

Commenting on the discovery, Alison Boyle, the curator of astronomy at London's Science Museum, said: "Of all the planets we've found around other stars, this is the one that looks as though it might have the right ingredients for life.”