“Before the mid-90’s, when the first secure case of an exoplanet, 51 Peg was discovered orbiting around a star like our own, planets beyond our own solar system were thought to be out of the reach of humans. The idea that we could detect worlds beyond our own or even that worlds beyond on our own might be there was questioned,” says astrophysicist and dailygalaxy.com editor, Jackie Faherty. “But once the first few worlds were found, the floodgates were opened and the zoo of exoplanets started to reveal itself.”
A directly imaged exoplanet
Astronomers have since discovered thousands of exoplanets—planets beyond our solar system—but few have been directly imaged, because they are extremely difficult to see with existing telescopes. Now, a University of Hawaiʻi Institute for Astronomy (IfA) graduate student has beaten the odds and discovered a directly imaged exoplanet, and it’s the closest one to Earth ever found, at a distance of only 35 light years.
A gas-giant planet orbiting a low-mass red dwarf star
Using the COol Companions ON Ultrawide orbiTS (COCONUTS) survey, an international team of astronomers have identified a planet about six times the mass of Jupiter. The team’s research, published in The Astrophysical Journal Letters, led to the discovery of the low-temperature gas-giant planet orbiting a low-mass red dwarf star, about 6,000 times farther than the Earth orbits the sun. They dubbed the new planetary system COCONUTS-2, and the new planet COCONUTS-2b.
“With a massive planet on a super-wide-separation orbit, and with a very cool central star, COCONUTS-2 represents a very different planetary system than our own solar system,” astronomer Zhoujian Zhang at the University of Hawaii explained. The COCONUTS survey has been the focus of his recently-completed Ph.D. thesis, aiming to find wide-separation companions around stars of all different types close to Earth.
A Great Laboratory
COCONUTS-2b is the second-coldest imaged exoplanet found to date, with a temperature of just 320 degrees Fahrenheit, which is slightly cooler than most ovens used to bake cookies. The planet can be directly imaged thanks to emitted light produced by residual heat trapped since the planet’s formation. Still, the energy output of the planet is more than a million times weaker than the sun’s, so the planet can only be detected using lower-energy infrared light.
“Directly detecting and studying the light from gas-giant planets around other stars is ordinarily very difficult, since the planets we find usually have small-separation orbits and thus are buried in the glare of their host star’s light,” said Michael Liu, Zhang’s thesis advisor. “With its huge orbital separation, COCONUTS-2b will be a great laboratory for studying the atmosphere and composition of a young gas-giant planet.”
First Detected in 2011
The planet was first detected in 2011 by the Wide-field Infrared Survey Explorer satellite, but it was believed to be a free-floating object, not orbiting a star. Zhang and his collaborators discovered that it is in fact gravitationally bound to a low-mass star, COCONUTS-2A, which is about one-third the mass of the sun, and about 10 times younger.
A bright red star in the dark sky
Due to its wide-separation orbit and cool host star, COCONUTS-2b’s skies would look dramatically different to an observer there compared to the skies on Earth. Nighttime and daytime would look basically the same, with the host star appearing as a bright red star in the dark sky.
Beyond the range of deadly flares common to red-dwarf Star systems
Red dwarf stars can produce significant X-ray emission, and often have large flares of radiation and eruptions of particles in so-called coronal mass ejections (CMEs). X-ray radiation would cut through the atmosphere and reach the surface of an Earth-like planet. Life on land would be adversely impacted by a stellar flare and might only survive in the oceans. Recent research suggests that giant radiation flares could deplete the ozone layer of a planet by 94% for two years and could even be fatal for all life.
“COCONUTS-2b is almost 6500 times farther from its host star than the Earth is from our Sun. At that distance, COCONUTS-2b is well beyond the range of flares from the host star that could impact its environment and potential to host life,” wrote astronomer and co-author Will Best at the University of Texas in an email to The Daily Galaxy.
“Among all systems hosting imaged exoplanets known to date, COCONUTS-2 has the second widest separation between the host star and the planet,” added lead author Zhoujian Zhang told The Daily Galaxy.
Zhoujian Zhang led a team of astronomers, including Michael Liu and Zach Claytor (IfA), William Best (University of Texas at Austin), Trent Dupuy (University of Edinburgh) and Robert Siverd (Gemini Observatory/National Optical-Infrared Astronomy Research Laboratory)
Source: Zhoujian Zhang et al, The Second Discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) Program: A Cold Wide-Orbit Exoplanet around a Young Field M Dwarf at 10.9 pc,
Jackie Faherty via University of Hawaii at Manoa
Image credit: Red dwarf star system, NASA
Editor, Jackie Faherty, astrophysicist, Senior Scientist with AMNH. Jackie was formerly a NASA Hubble Fellow at the Carnegie Institution for Science. Aside from a love of scientific research, she is a passionate educator and can often be found giving public lectures in the Hayden Planetarium. Her research team has won multiple grants from NASA, NSF, and the Heising Simons foundation to support projects focused on characterising planet-like objects. She has also co-founded the popular citizen science project entitled Backyard Worlds: Planet 9 which invites the general public to help scan the solar neighbourhood for previously missed cold worlds. A Google Scholar, Faherty has over 100 peer reviewed articles in astrophysical journals and has been an invited speaker at universities and conferences across the globe. Jackie received the 2020 Vera Rubin Early Career Prize from the American Astronomical Society, an award that recognises scientists who have made an impact in the field of dynamical astronomy and the 2021 Robert H Goddard Award for science accomplishments.