Australasian Science: Australia's authority on science since 1938

Seeing the Unseeable

By David Reneke

David Reneke’s wrap-up of space and astronomy news.

This dramatic new image of cosmic clouds in the constellation of Orion reveals what seems to be a fiery ribbon in the sky. This orange glow represents faint light coming from grains of cold interstellar dust, and was observed by the European Southern Observatory’s Atacama Pathfinder Experiment (APEX) in Chile.

This spectacular new picture shows just a part of a bigger complex called the Orion Molecular Cloud, in the constellation of Orion (The Hunter), a rich melting pot of bright nebulae, hot young stars and cold dust clouds.

This region is hundreds of light years across and located about 1350 light years from us. The sub-millimetre wavelength glow arising from the cold dust clouds is seen in orange, and is overlaid on a view of the region taken in the more familiar visible light. The dust clouds form beautiful filaments, sheets and bubbles, the effects of stellar winds.

The large bright cloud in the upper right of the image is the well-known Orion Nebula, which is also called Messier 42. It is readily visible to the naked eye as the slightly fuzzy middle “star” in the sword of Orion. The Orion Nebula is the brightest part of a huge stellar nursery where new stars are being born, and is the closest site of massive star formation to Earth.

Astronomers have used these and other data from APEX, along with images from the European Space Agency’s Herschel Space Observatory, to search the region of Orion for protostars – an early stage of star formation. They have so far been able to identify 15 newly discovered rare objects, probably among the youngest protostars ever found, bringing astronomers closer to witnessing the moment when a star begins to form.

Probing Hot Jupiters

Heather Knutson of Caltech made the first weather map of a “hot Jupiter” in 2007, and astronomers have since become more and more familiar with these extremely exotic planetary objects. Hot Jupiters are a class of extra-solar planets whose characteristics are similar to Jupiter but which have high surface temperatures because they orbit very close to their parent stars.

“It’s not as simple as taking a picture and bingo… we see the weather,” says Knutson. These planets are hundreds of light years from Earth and they are nearly overwhelmed by the glare of their parent stars. “Even to see the planet as a single pixel next to the star would be a huge accomplishment.”

Instead, Knutson and colleagues use a quirk of planetary science. The key, she explains, is that most hot Jupiters are tidally locked to their stars. This means they have a permanent day side and a permanent night side. As astronomers watch them orbit from our earthly vantage point, the planets exhibit phases like crescent, gibbous and full. By measuring the infrared brightness of the planet as a function of its phase, they can make a rudimentary map of temperature versus longitude.

NASA’s Spitzer Space Telescope is the only infrared observatory with the sensitivity to do this work. Since Knutson kickstarted the research in 2007, nearly a dozen hot Jupiters have been mapped by astronomers using Spitzer.

The most recent study, led by Nikole Lewis of MIT, shows a gas giant named HAT-P-2b. “We can see daytime temperatures as high as 2400°K, while the night side drops below 1200°K,” says Lewis. Even at night, this planet is ten times hotter than Jupiter.

These exoplanet maps may seem crude compared with what we’re accustomed to on Earth, but they are a fantastic accomplishment considering that the planets are trillions of kilometres away. The maps show huge day–night temperature differences typically exceeding 1000 degrees.

Researchers believe these thermal gradients drive ferocious winds blowing thousands of kilometres per hour, but without regular images researchers can’t say what this kind of windy weather looks like. They do agree on one thing, though: the weather on hot Jupiters is really big.

Over the years, planetary scientists have developed computer models to reproduce the storms and cloud belts in Jupiter’s atmosphere. If you take those models and turn up the heat, and slow down the rotation to match the tidally locked spin of a hot Jupiter, weather patterns become super-sized.

Astronomers speculating on what they’ve discovered believe even silicates will condense in such an environment. They’re already getting some hints that clouds might be common on these planets, but don’t yet know if they’re made of rock-strewn materials.

For now just one thing is certain: the meteorology of hot Jupiters is out of this world.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at www.davidreneke.com