New Planets Discovered

This July, Christian Marois, a young astrophysicist with Canada's National Research Council, was on a plane over the Pacific, poring over telescopic images of the star HR 8799 - an unremarkable pinprick in the Pegasus constellation - when things suddenly fell into focus.

"I thought 'this is crazy, this is amazing'," the 34-year-old research associate says.

"I discovered there was not one but two objects around this star."

And for the first time in the history of creation, a creature on a planet in our solar system was looking at an image of planets orbiting in another.

The discovery was released today in the journal Science.

"It was the first image of another planet system orbiting another star," says Marois, who is just completing a post-doctoral stint at the council's Herzberg Institute of Astrophysics in Victoria.

"I've been dreaming about astronomy since my this was a childhood dream come true."

His dream would capture three planets, as it turned out.

Circling HR 8799, 128 light years (128 X 9.46 trillion kilometres) from Earth, the planetary trio are between seven and 10 times the mass of Jupiter.

Some 50 per cent more massive and five times more luminous than our sun, HR 8799 is visible to the naked eye, if you just look towards Pegasus near its zenith in the northern latitudes.

Seeing the planets? That took a bit more work.

Some 300 planets have been detected around distant stars over the past 10 years. But these orbiting bodies have been inferred, rather than photographed, largely by the "wobble" they create in their stars as they pull it gravitationally in different directions during their circling orbits.

And while there have been "exoplanet" sightings reported in the literature - another is reported in this same Science edition - Marois says his images are the clearest and definitely the first to show a distant solar system.

"It might be seen in the future as the first unambiguous (images)," Marois says.

"It has all the elements that are strong arguments that these things are planets. There's no missing link, there's no missing information."

Getting the images was no easy task.

"We had to look at a lot of stars in order to be able to see these," says Marois, whose planetary quest began eight years ago.

Indeed, Marois says 80 stars, painstakingly pared down from the billions available, were scrutinized before the HR 8799 planets appeared.

Because stars are often 25 times brighter than their planets -- which simply mirror the starlight - they typically drown out any of the planetary glow that might be glimpsed by earthbound lenses.

Thus, Marois says, researchers needed to find stars with planets that were far enough out of their sun's glaring shadow to have some visible shine of their own.

This meant turning away from targets that resembled our sun - where Earth-like objects might exist --and towards larger A-class stars that are able to gravitationally hold onto larger planets in more distant orbits.

"Everybody had neglected those stars because, since they're more massive, they're brighter," Marois says.

But more massive stars, he says, can hold larger planets at wider separations, giving astronomers big optical targets that are farther away from the central light source.

"So even if they're brighter it doesn't mean they are bad targets to look for planets. They actually have a lot of good things going for them," Marois says.

"The planets could be distant enough and large enough to (picture)," he says.

Second, Marois says, the star had to be located outside of the galaxy's cluttered plane, where the light from backing stars would simply drown out any planetary light.

Our milky way is a spiral galaxy and most of the stars we can see from Earth are located within the circling arms that give a clear night sky it it's lactic hue.

"HR 8799 is well away from the galactic plain so there was not a dense star field," Marois says.

"And there was nothing else in the field, there was nothing, so it had to be a bound (planet)," he says.

Also well, Marois says, the star needed to be relatively young to ensure any orbiting planets would retain the formational heat that could add to their visibility.

The HR 8799 solar system is only about 60 million years old, compared to the 4.6 billion years that our planetary neighbourhood has been around.

And the trio of planets are between 5.3 and 6.6 times hotter than Jupiter.

As important as meeting these stellar criteria, Marois needed a new way to observe the skies that would separate the brighness of the stars from the puny, planetary glow.

That problem was solved by a software program he himself developed as a PhD. candidate at the University of Montreal, which allowed planetary bodies to come out from their sun's bright shadow far more readily than ever before.

"The new observing strategy that I developed ...enabled us extract very well the light from the star by a factor of 10 to 100, so these were the deepest images ever obtained on any telescope," he says

While hundreds of other exoplanets have been inferred, seeing is actually believing, says University of Western Ontario geologist Roger Osinski

"You're always wary in any kind of science about basing everything on assumptions and inferences," says Osinski, deputy director of Western's Centre for Planetary Science and Exploration.

"So for sure having direct observations is a very big thing," he says.

As well, Osinski says, actually sightings of other planets may eventually help in the future detection of extraterrestrial life, through atmospheric analysis.

Marois images were compiled from two of the world's largest telescopes; the W.M. Keck and Gemini Observatories on the summit of Hawaii's Mauna Kea.

Marois says these earthbound telescopes, with their 10 metre apertures, are actuall better than the space based Hubble telescope at planet detection. Indeed the Hubble already eyes HR 8799 in the 1990s and failed to reveal its planets.

There is, however, almost zero chance that anyone on the planets will be looking back at us, Marois says.

As gas giants far more massive that our behemoth Jupiter, the planets have virtually no capacity to support life, Marois says.

They orbit 25, 40 and 70 astronomical units from their star, with an astronomical unit representing the distance between our sun and the Earth (about 150 million kilometres).

"They are similar in distance (from HR 8799) as the outer planets in our own solar system are from the sun," Marois says, referring to the planets Neptune and Uranus.

There is a distinct possibility, however that smaller planets, perhaps even rocky ones, may be orbiting closer to HR 8799, Marois says.

"There's definitely a probability that something is there... but sadly we don't have the instrumentation yet to tell if there's anything closer," he says.

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