Un piccolo telescopio analizza le atmosfere degli esopianeti [ita-eng]

Il NASA's Infrared Telescope Facility di Mauna Kea, (Hawaii) sembra aver compiuto un'impresa a dir poco sorprendente.

Nonostante le sue relativamente piccole dimensioni (3 metri di diametro) e la sua longevità (circa trentanni), è riuscito ad identificare la presenza di molecole organiche in un esopianeta distante dalla Terra ben 63 anni luce.
Mark Swain, un astronomo del Jet Propulsion Laboratory di Pasadena ha detto che a favorire la scoperta è stata una nuova tecnica, che potrebbe di molto accelerare la ricerca, senza dover per forza utilizzare i super telescopi di terra o in orbita, risparmiando tra l'altro sui costi di gestione. Ha aggiunto inoltre che utilizzando la stessa tecnica con i super telescopi sarà possibile analizzare gli esopianeti terrestri più piccoli che verrano presto scoperti.

Attualmente sono stati catalogati circa 400 esopianeti di cui la maggior parte sono di tipo gassoso come Giove, ma alcuni potrebbero essere delle "Super Terre" o pianeti rocciosi. Il telescopio Keplero ha il compito di scoprirli e ci si aspetta che entro il termine della sua missione venga anche identificato qualche pianeta delle stesse dimensioni della Terra.
Nell'agosto del 2007, Swain e il suo team osservarono l'esopianeta HD 189733b nella constellatione della Vulpe. Ogni 2.2 giorni, il pianeta ruota attorno alla sua stella, che è molto più fredda e piccola del nostro Sole.
Su HD 189733b sono stati già rilevati vapore acqueo, metano e carbone diossido grazie ausando i telescopi spaziali Spritzer e Hubble. Gli astronomi hanno utilizzato uno spettografo che divide la luce nei suoi componenti per rilevare i singoli spettri dei componenti chimici.
La chiave di volta è stato lo sviluppo di un nuovo metodo di calibrazione che rimuove gli errori causati dall'atmosfera terrestre e dal movimento terrestre del telescopio rispetto a quello dell'esopianeta.

Ora si aprono nuove interessanti prospettive per la ricerca di pianeti esotici.
Ma la scoperta del metano su HD 189733b dimostra che nella sua alta atmosfera devono avvenire delle attività particolari, forse dovute all'irradiamento ultravioletto della stella, ci dice Swain.

Uno dei possibili obiettivi che questa tecnica potrà raggiungere, sarà ricercare molecole organiche pre-biotiche sugli esopianeti, molecole che precedono la formazione stessa della vita, dice ancora Swann.
Se poi associamo la nuova tecnica al supporto fornitoci dai grandi telescopi come l'Hubble, lo Spitzer, e il prossimi James Webb Space Telescope, saranno fatte grosse scoperte nell'analisi delle super terre.

Adattamento per l'italiano a cura di Arthur McPaul

English

A little telescope goes a long way

A relatively small Earth-based telescope identified an organic molecule in the atmosphere of a Jupiter-size planet nearly 63 light-years away.

Provided by JPL, Pasadena, California

This artist concept shows the planetary system called HD 189733, located 63 light-years away in the constellation Vulpecula. NASA/JPL-Caltech

February 3, 2010
NASA astronomers have successfully demonstrated that a David of a telescope can tackle Goliath-size questions in the quest to study Earth-like planets around other stars. Their work provides a new tool for ground-based observatories, promising to accelerate the search for prebiotic, or life-related, molecules on planets orbiting stars beyond our solar system.

The scientists reported on a new technique used with a relatively small Earth-based telescope to identify an organic molecule in the atmosphere of a Jupiter-size planet nearly 63 light-years away. The measurement revealed details of the exoplanet's atmospheric composition and conditions, an unprecedented achievement from an Earth-based observatory.

The surprising new finding comes from a venerable 30-year-old, 10-foot (3-meter) diameter telescope that ranks 40th among ground-based telescopes — NASA's Infrared Telescope Facility atop Mauna Kea, Hawaii.

This new technique promises to speed the work of studying planet atmospheres by enabling studies from the ground that were possible previously only through a few high-performance space telescopes. "Given favorable observing conditions, this work suggests we may be able to detect organic molecules in the atmospheres of terrestrial planets with existing instruments," said Mark Swain, an astronomer at NASA's Jet Propulsion Laboratory in Pasadena, California. This can allow fast and economical advances in focused studies of exoplanet atmospheres, accelerating our understanding of the growing stable of exoplanets.

"The fact that we have used a relatively small, ground-based telescope is exciting because it implies that the largest telescopes on the ground using this technique may be able to characterize terrestrial exoplanet targets," Swain said.

Currently, more than 400 exoplanets are known. Most are gaseous like Jupiter, but some "super-Earths" are thought to be large terrestrial, or rocky, worlds. A true Earth-like planet, with the same size as our planet and distance from its star, has yet to be discovered. NASA's Kepler mission is searching from space now, and it is expected to find several of these earthly worlds by the end of its three-and-a-half-year prime mission.

On August 11, 2007, Swain and his team turned the infrared telescope to the hot, Jupiter-size planet HD 189733b in the constellation Vulpecula. Every 2.2 days, the planet orbits a K-type main sequence star slightly cooler and smaller than our Sun. HD 189733b had already yielded break-through advances in exoplanet science, including detections of water vapor, methane, and carbon dioxide, using space telescopes. Using the new technique, the astronomers successfully detected carbon dioxide and methane in the atmosphere of HD 189733b with a spectrograph that splits light into its components to reveal the distinctive spectral signatures of different chemicals. Their key work was development of a novel calibration method to remove systematic observation errors caused by the variability of Earth's atmosphere and instability due to the movement of the telescope system as it tracks its target.

"As a consequence of this work, we now have the exciting prospect that other suitably equipped yet relatively small ground-based telescopes should be capable of characterizing exoplanets," said John Rayner, the NASA Infrared Telescope Facility support scientist who built the SpeX spectrograph used for these measurements. "On some days we can't even see the Sun with the telescope, and the fact that on other days we can now obtain a spectrum of an exoplanet 63 light-years away is astonishing."

In the course of their observations, the team found unexpected bright infrared emission from methane that stands out on the dayside of HD 189733b, indicating some kind of activity in the planet's atmosphere. Swain said this puzzling feature could be related to the effect of ultraviolet radiation from the planet's parent star hitting the planet's upper atmosphere, but more detailed study is needed. "This feature indicates the surprises that await us as we study exoplanet atmospheres," he said.

"An immediate goal for using this technique is to more fully characterize the atmosphere of this and other exoplanets, including detection of organic and possibly prebiotic molecules" like those that preceded the evolution of life on Earth, said Swain. "We're ready to undertake that task." Some early targets will be the super-Earths. Used in synergy with observations from NASA's Hubble, Spitzer, and the future James Webb Space Telescope, the new technique "will give us an absolutely brilliant way to characterize super-Earths," Swain said.
Fonte: http://www.astronomy.com/asy/default.aspx?c=a&id=9120