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Western University researcher plays key role in planetary discovery

Press Release From: Western University
Posted: Friday, August 14, 2015

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The first planet detected by the Gemini Planet Imager is 100 light years away but shares many of the characteristics of an early Jupiter.

The out-of-this-world discovery, which generated international media headlines, was revealed last month and a new paper outlining the findings in full detail was published in the current issue of Science.

Stanimir Metchev, a Physics & Astronomy professor at Western University and Stony Brook University, is a co-investigator on the scientific study.

The Canada Research Chair in Extrasolar Planets, Metchev is also a faculty member at Western's Centre for Planetary Space and Exploration (CPSX).

Metchev is quoted extensively in the media release below in the section titled, "The key to the solar system?"

To interview Metchev, please contact Jeff Renaud, Senior Media Relations Officer, Western University, 519-661-2111, ext. 85165, jrenaud9@uwo.ca, @jeffrenaud99

For downloadable images and animation, please visit http://mediarelations.uwo.ca/2015/08/13/western-university-researcher-plays-key-role-in-planetary-discovery/

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Astronomers discover 'young Jupiter' exoplanet

One of the best ways to learn how our solar system evolved is to look to younger star systems in the early stages of development. Now, a team of astronomers has discovered a Jupiter-like planet within a young star system that could serve as a decoder ring for understanding how planets formed around our sun.

The new planet, called 51 Eri b, is the first exoplanet discovered by the Gemini Planet Imager, a new instrument operated by an international collaboration headed by Bruce Macintosh, a professor of physics in the Kavli Institute at Stanford. It is the 'faintest' exoplanet on record, and also shows the strongest methane signature ever detected on an alien planet, which should yield additional clues as to how the planet formed.

The results of the study are published in the current issue of Science.

A clear line of sight

The Gemini Planet Imager (GPI) was designed specifically for discovering and analyzing faint, young planets orbiting bright stars. NASA's Kepler mission indirectly discovers planets by the loss of starlight when a planet blocks a star.

"To detect planets, Kepler sees their shadow; GPI sees their glow," says Macintosh. "What GPI does is referred to as direct imaging."

The astronomers use adaptive optics to sharpen the image of a star, and then block out the starlight. Any remaining incoming light is then analyzed, the brightest spots indicating a possible planet.

After GPI was installed on the 8-meter Gemini South Telescope in Chile, the team set out to look for planets orbiting young stars. To date, the astronomers have looked at nearly 100 stars.

"51 Eridani is only 20 million years old, a little more massive than our sun – a perfect target," says James Graham, a professor at UC Berkeley and Project Scientist for GPI.

As far as the cosmic clock is concerned, 20 million years is young for a star, and this is exactly what made the direct detection of the planet possible, explains Macintosh.

"When planets coalesce, material falling into the planet releases energy and heats it up. Over the next hundred millions years they radiate that energy away, mostly as infrared light," says Macintosh.

Once the astronomers zeroed in on the star, they blocked its light and spotted 51 Eri b orbiting a little farther away from its parent star than Saturn does from the sun. Even though the light from the planet is very faint – nearly a million times fainter than its star – subsequent observations revealed that it is roughly twice the mass of Jupiter. Other directly-imaged planets are five times the mass of Jupiter or more.

In addition to being the faintest planet ever imaged, it's also the coldest – 400 Celsius (°C), whereas others are around 700 °C – and features the strongest atmospheric methane signal on record. Previous Jupiter-like exoplanets have shown only faint traces of methane, far different from the heavy methane atmospheres of the gas giants in our solar system.

All of these characteristics, the researchers say, point to a planet that is very much what models suggest Jupiter was like in its infancy.

"All of the exoplanets astronomers have imaged before have atmospheres that looks like stars – very cool stars, but still stars," says Macintosh, who led the construction of GPI and now leads the survey. "This is the first one that really looks like a planet."

Of course, it's not exactly like Jupiter. The planet is so young and still has a temperature of 400 °C, which is hot enough to melt lead.

"In the atmospheres of the cold giant planets of our solar system carbon is found as methane, unlike most exoplanets where carbon has mostly been found in the form of carbon monoxide. Since the atmosphere of 51 Eri b is also methane rich, it signifies that this planet is well on its way to becoming a cousin of our own familiar Jupiter," says Mark Marley, an astrophysicist at NASA’s Ames Research Center.

The key to the solar system?

“What makes 51 Eridani particularly interesting is that it also harbours dust and ice in the planetary system," explains Stanimir Metchev, a professor of Physics & Astronomy and a Canada Research Chair in Extrasolar Planets at Western University, Canada. "These are much like the dust and the ice grains produced by collisions among asteroids and comets in the Solar System."

Metchev's team conducted a study with data from NASA's Wide-field Infrared Survey Explorer (WISE) to search for any thermal glow that such dust and ice can produce.

"We found that 51 Eridani is surrounded by warm dust that indicates the presence of an asteroid belt," says Rahul Patel, a PhD student at Stony Brook University, who led the WISE study.

Metchev adds, "And more data from the European Space Agency's Herschel Space Observatory reveal that 51 Eridani is also surrounded by a more distant and colder cometary belt, much like the Kuiper Belt of comets beyond Neptune in the Solar System."

The two belts – the asteroid and the cometary belt around 51 Eridani – fall on either side of the newly discovered planet 51 Eridani b.

"The overall structure bears striking resemblance to our own Solar System, with Jupiter as the most massive planet orbiting between a belt of asteroids and a belt of comets," explains Metchev. "In 51 Eridani, we are therefore seeing what the Solar System resembled at a very young age, around the time when the Earth was still forming."

The GPI Exoplanet Survey team, led by Macintosh, is now conducting a three-year program to detect new extrasolar planets and to study their home systems. Using GPI to find more young solar systems such as 51 Eridani will help astronomers understand the formation of our neighbouring planetary systems, and how similar or different they are from our own.

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