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MOST Satellite

Small Scope, Big Science

Canada's MOST space telescope reveals the secret lives of alien stars and planets

Approaching its seven year anniversary, Canada's space telescope, MOST (Microvariability and Oscillation of Stars) is continuing to challenge our understanding of the cosmos by making ground-breaking stellar discoveries. The Canadian Space Agency's suitcase-sized technological wonder has been measuring and analyzing the minute variations in the light of thousands of distant stars uncovering surprises about their inner clockwork and planetary systems that are leaving the astronomical community abuzz.

By continuously staring at stars for up to two months at a time and applying photometric precision better than one part per million, "MOST has been very good at seeing things in the Universe that most people never expected or thought possible," says Jaymie Matthews, MOST mission Principal Investigator and astronomy professor at the University of British Columbia.

Bubble, Bubble, Toil and Trouble

Stars across our galaxy come in wildly different colours, sizes and ages, but MOST is discovering that some of the largest and hottest may have more in common with our Sun than ever thought. The stars under study were about twice the diameter and mass of the Sun, and blue-white – quite similar to the brilliant Vega that rides high in the summer night sky. The little telescope that could has helped reveal that these behemoth stars, those that are considerably bigger and hotter than our Sun, surprisingly experience similar circulatory movement of energy near their surfaces.

This bubbling activity astronomers call convection (seen on the Sun's disk as "granulation" because it looks like grains of salt scattered on a dark floor in magnified images) occurs in a layer or zone where hotter gas rises to a star's surface carrying energy with it, as cooler plasma sinks towards the interior to pick up more energy from within. This same convection process brings bubbles to the surface of boiling water on a stovetop. Until now, it was thought that only Sun-like stars have their convective zone near the surface, while stars several times larger have convection zones buried deep in their cores.

It turns out however, thanks to MOST, that there is more activity going on at the surface of these stars than what astronomers ever thought possible. Matthews believes that if we can see this convection or granulation in massive stars, then it is possible that we could find activity cycles like the Sun's 11-year cycle in these stars which would teach us more about the life stories of stars very different from our familiar Sun. "This may be opening up the door to searching for behaviours in stars that we never ever thought about looking at before," he says.

Adding to the excitement are the latest MOST measurements taken of the famous red supergiant star Betelgeuse 600 light years away in the constellation Orion, which has revealed convection near its own searing surface for the first time. Cool supergiants like Betelgeuse are stars where the dynamics of convection structures have also remained a mystery until now; it seems they too obey the same stellar life cycle rules as our own Sun does.

"It's mind-blowing when you realize that right across the range of ages and properties of stars, the rules governing the way things happen at their surfaces are essentially all the same," says Matthews. "With these results, MOST is rewriting astronomy textbooks."

Alien Weather

The holy grail of astronomy is to find an Earth-like world orbiting another star. It seems that MOST has taken us one step further in reaching this historic goal by studying the most bizarre weather conditions ever seen on a far-off planet. Matthews and his team recently finished monitoring a gas giant planet orbiting the star HD 80606 located 190 light years away in the constellation Ursa Major. The planet, dubbed HD 80606b is estimated to be about three times the mass of Jupiter, the biggest planet in our solar system. It has a 112-day-long year, circling a star similar to our Sun. However the planet has an extremely elongated orbit, taking it from a distance similar to Earth from our Sun, only to plunge twenty times closer in less than two months. As HD80606b swings so close to its Sun the planet's atmosphere heats up from 500 to 1200 degrees Celsius in a matter of days.

By looking at the tiny dip in starlight intensity as the planet transits in front of its parent star, MOST has been able to help determine how this alien planet's environment responds to these extreme conditions in a matter of hours not centuries. "We hope to couple our results with [NASA's infrared] Spitzer Space Telescope data to model the planet's atmosphere, clouds and even global climate change on another planet," says Matthews. Data like this could also help Earth scientists better understand atmospheric changes on our own planet and tweak their climate models as well.

Now MOST has begun hunting for transits of other exoplanets and already has its sights on about 40 targets which are thought to be super-Earths: rocky worlds with deep oceans and icy layers. While studying extreme weather patterns on alien planets may sound like science fiction, Mathews hints that there are more surprises in store. "Avatar's Pandora is actually quite a mundane world compared to the worlds MOST is discovering and studying."