Exoplanet's Atmosphere Unveiled Through New Observing Technique
June 27, 2012

Exoplanet’s Atmosphere Unveiled Through New Observing Technique

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Lee Rannals for redOrbit.com

Astronomers have uncovered a clever new way of studying the atmosphere of an exoplanet in more detail.

An international team of astronomers used the European Space Observatory's Very Large Telescope to see the faint glow from the planet Tau Boötis b.

For the first time, the team reported that it has been able to study the planet's atmosphere, and was able to measure its orbit and mass precisely.

They wrote in the journal Nature study that Tau Boötis b's atmosphere seems to be cooler higher up, which is the opposite of what some astronomers had predicted.

Tau Boötis b was one of the first exoplanets to be discovered back in 1996, and is one of the closest exoplanets known.

The planet, unlike its star, is not visible to the naked eye, and up until now, it could only be detected by its gravitational effects on the star.

After 15 years of attempting to study the planet, astronomers have successfully been able to inspect the atmosphere of Tau Boötis b and measure its mass for the first time.

By combining a high quality infrared observatory with a clever new technique, the team was able to tease out the weak signal of the planet from a much stranger one from the parent star.

“Thanks to the high quality observations provided by the VLT and CRIRES we were able to study the spectrum of the system in much more detail than has been possible before," Lead author of the study Matteo Brogi said. "Only about 0.01% of the light we see comes from the planet, and the rest from the star, so this was not easy."

The majority of planets around other stars were revealed through their gravitational effects on their parent stars, which limits the information that astronomers can take about their mass.

By using the new technique, astronomers are able to see the planet's light directly, allowing them to measure the angle of the planet's orbit and work out its mass precisely.

They traced the changes in Tau Boötis b's motion as it orbits its parent star, which helped them determine that the planet orbits its star at an angel of 44 degrees, and has a mass six times that of the planet Jupiter.

“The new VLT observations solve the 15-year old problem of the mass of Tau Boötis b. And the new technique also means that we can now study the atmospheres of exoplanets that don´t transit their stars, as well as measuring their masses accurately, which was impossible before”, Ignas Snellen, co-author of the paper, wrote. “This is a big step forward.”

The team also was able to measure the amount of carbon monoxide present in the planet's atmosphere, and measure the temperature at different altitudes by comparing observations and theoretical models.

The new observations indicate that the higher up in the atmosphere on Tau Boötis b, the lower the temperature gets, which is the opposite result seen on Jupiter and other similar exoplanets.

The research shows how high resolution spectroscopy from ground-based telescopes can be a valuable tool for getting a detailed analysis of non-transiting exoplanets' atmospheres, according to ESO.

Detecting different molecules in the future will allow astronomers to learn more about the planet's atmospheric conditions.

Astronomers may even be able to track atmospheric changes between the planet's morning and evening by making measurements of the planet's orbit.

"This study shows the enormous potential of current and future ground-based telescopes, such as the E-ELT. Maybe one day we may even find evidence for biological activity on Earth-like planets in this way”, Snellen concludes in the journal.