“Recently, a team of astronomers including NASA scientists discovered a Jupiter-like planet within a young system that could serve as a decoder ring for understanding how planets formed around our sun,” NASA announced earlier today.
Called “51 Eridani (Eri) b,” it is the first exoplanet (planets outside our own solar system) discovered by the Gemini Planet Imager (GPI), a new instrument that was installed on the 8-meter Gemini South Telescope in Chile in 2013 and is operated by an international collaboration.
“This is exactly the kind of planet we envisioned discovering when we designed GPI,” James Graham, professor at the University of California, Berkeley, and project scientist for GPI, said in a statement.
Located 100 light years away, “51 Eri b” is not only the lowest-mass exoplanet ever imaged – roughly twice the mass of Jupiter – it’s also the coldest at 800 degrees Fahrenheit compared to 1,200 F of other, similar exoplanets.
However, based on data gathered through GPI, scientists concluded that “51 Eri b” features the strongest atmospheric methane signal ever detected on an alien planet, which is a key factor in determining if it might show signs of what Jupiter was like in its infancy. That’s because, in context of the cosmic clock, the newly discovered exoplanet is very young – “only” 20 million years old.
“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,” said Mark Marley, an astrophysicist at NASA’s Ames Research Center in Moffett Field, California, co-lead for theory and a team member responsible for helping to interpret GPI observations.
Previous Jupiter-like exoplanets have shown only faint traces of methane, far different from the distinctive signatures of methane seen in the atmospheres of the gas giants in our own solar system – Jupiter, Saturn, Uranus, and Neptune.
“In addition to expanding the universe of known planets, GPI will provide key clues as to how solar systems form… and how common that planet-forming mechanism is throughout the universe,” says NASA, adding that, “Astronomers believe that the gas giants in our solar system formed by building up a large core over a few million years and then pulling in a huge amount of hydrogen and other gasses to form an atmosphere. But the Jupiter-like exoplanets that have been discovered are much hotter than models [based on our own solar system] have predicted, hinting that they could have formed much faster as material collapsed quickly to make a very hot planet.”
“The newly discovered 51 Eri b is the first planet that’s cold enough and close enough to the star that it could have indeed formed right where it is the ‘old-fashioned way. This planet really could have formed the same way Jupiter did – the whole solar system could be a lot like ours,” Bruce Macintosh, a professor of physics at Stanford University, concluded.
The Gemini Planet Imager
NASA explains that 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.”
That light – and other forms of light near-infrared wavelengths (Y – K bands) – is what GPI was built for to measure and analyze. More specifically, it looks for faint, young planets orbiting bright stars via “’direct imaging,’ in which astronomers use adaptive optics to sharpen the image of a target star, then block out its starlight. Any remaining incoming light is then analyzed, and the brightest spots indicate a possible planet.” (See example image above.)
Compared to the GPI method, other techniques of planet detection are more indirect. NASA’s Kepler mission, for example, applies the “transit method” as part of which planets can be discovered when they pass in front of the star (or sun) they orbit and briefly block that starlight. That momentary loss of light can be measured and translated into data that helps determine if it was indeed caused by a planet.
As Macintosh described the difference perfectly, to detect planets, Kepler sees their shadow while GPI sees their glow.
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Image Credit: “Artistic conception of the Jupiter-like exoplanet 51 Eridani” byDanielle Futselaar and Franck Marchis, SETI Institute | “Gemini Observatory at sunset” by Mailseth, CC BY-SA 3.0 via Wikimedia Commons | “Hy4796aGPI” by Source (WP:NFCC#4), Licensed under Fair use via Wikipedia