Young, Jupiter-like planet 51 Eridani b discovered by Gemini Planet Imager
Like Jupiter, planet has an atmosphere awash in methane
Scientists have discovered a baby planet that may be very similar to what Jupiter would have looked like in its infancy – and have taken some amazing baby photos.
The new planet 51 Eridani b is about twice as massive as Jupiter and orbits a star that is just 20 million years old – "born … 40 million years after the dinosaurs died out," noted Eric Nielsen, a postdoctoral researcher at Stanford University and the SETI Institute, in a news release announcing the discovery.
That makes the planet itself even younger.
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51 Eridani b is a little farther from its star than Saturn is from our sun – putting in the right region for a gas giant similar to those in our solar system.
But what has scientists most excited is that, like Jupiter, 51 Eridani b has an atmosphere awash with methane.
It's the first time large amounts of methane have been directly detected in the atmosphere of an exoplanet, says Julien Rameau, a postdoctoral researcher at the University of Montreal who first spotted the chemical signature for the gas.
"In Jupiter, we know that there is huge content of methane so it makes 51 Eridani b very similar to what Jupiter was when the solar system was young," Rameau told CBC News. "I was like 'This is awesome, this is amazing."'
The new discovery, led by Bruce Macintosh, a physics professor at Stanford University and the Kavli Institute for Particle Astrophysics and Cosmology, was described today in the journal Science.
51 Eridani b is the first planet ever found using a new, high-tech camera specially designed to take pictures of distant planets: the Gemini Planet Imager. And it couldn't have been discovered with any other existing instrument.
NASA's Kepler space telescope has discovered thousands of planets by looking for the slight dimming of distant stars as nearby planets pass in front of them. That means the planets' orbits have to have just the right orientation so they appear to pass in front of the star as viewed from Earth. Kepler is also best at finding planets very close to older, dimmer stars – ones that complete an orbit just once every few days.
The Gemini Planet Imager, installed on Chile's Gemini South Telescope in 2013, works more like a normal camera – rather than looking for blips in data, it captures images of the actual light given off by young, hot planets – the temperature on 51 Eridani b is about 400 C — as they cool down in the 100 million years after they form.
That means it's better at finding planets farther from their stars, and the orientation of their orbit doesn't matter as much.
51 Eridani b takes about 15 years to orbit its star, and the researchers aren't sure it ever crosses in front when viewed from Earth.
Discovering it with other techniques, if even possible, would take decades, says Christian Marois, a researcher at the National Research Council Herzberg Astronomy and Astrophysics in Victoria who co-authored the study.
"Direct imaging takes an hour."
Molecules in the atmosphere
Another advantage of the Gemini Planet Imager is that scientists can use it to get lots of information that you can't get with other planet-finding techniques. For example, it can look for chemical signatures for compounds like methane in the different colours of light coming from a planet.
"You can see molecules in the atmosphere, you can derive its temperature… you can even derive the surface gravity which gives you an idea of the mass of planet," Marois said.
"You can also trace its orbit around the star… and understand something about its formation process as well."
The Gemini Planet Imager isn't the first planet imager of its kind, but it is the most advanced. Previous versions could find planets that were larger than five times Jupiter's mass, very hot, farther from their stars and unlike anything that exists in our solar system. Those all had dusty, star-like atmospheres with barely any detectable methane.
Marois said 51 Eridani b is the first planet discovered with this technique that appears to have been formed the same way as planets in our own solar system – from tiny dust particles clumping together into rocks and eventually the core of a planet.
This single discovery isn't enough to make more general conclusions about planet or solar system formation, Marois said. That will require the discovery and analysis of many other planets around different kinds of stars. Scientists don't even yet know if there are other planets orbiting the same star as 51 Eridani b.
But it's an exciting first discovery for the international team of scientists, including many Canadians, who have been working on the Gemini Planet Imager for a decade.
Marois helped design the instrument itself, which was partially assembled at the National Research Council in Victoria.
Both he and Rameau were also involved in processing the raw images captured by the instrument and subtracting off the overpowering glare of the starlight to make the planet visible.
Rameau, who worked on the project for four years, was also very involved in teasing out the signature of methane from the planet's light.