In the hunt for exoplanets, astronomers are only rarely able to look upon a world directly with even the most powerful telescopes. So, it’s always notable when we can actually see a new exoplanet. Scientists from the University of Hawaii report they have spotted a new exoplanet only 35 light-years away, and we can see this one because it’s enormous and very far from its host star. In fact, it might set the record for most distant.
The exoplanet was discovered as part of the COol Companions ON Ultrawide orbiTS (COCONUTS) program. As the name implies, this project seeks exoplanets with very wide orbits around very cool stars. Both of those properties should make them easier to spot, as was the case for COCONUTS-2b — yes, there is finally an exoplanet with a good name.
Usually, detecting exoplanets means inferring their location and properties without even laying mechanical eyes on them. The most popular way is the transit method, which NASA’s Kepler Space Telescope used to discover thousands of exoplanets during its mission. By tracking the luminance of stars, we can detect when an exoplanet passes in front of them. Of course, this only works for solar systems that are aligned just right with somewhat large planets relative to the star. The other method detects changes in radial velocity — small wobbles in the star caused by the gravity of orbiting planets. Again, this works best with large planets.
Imaging exoplanets directly is difficult because they’re so much smaller and dimmer compared with stars. That’s why the COCONUTS program looks for “COol” exoplanets on “Ultrawide orbiTS.” These worlds should be easier to see in telescopes like the 2.2-meter unit at the University of Hawaii, and indeed that seems to be the case with the discovery of COCONUTS-2b by grad student Zhoujian Zhang. It’s the small red dot indicated in the above image.
This exoplanet is about six times more massive than Jupiter, and it orbits its host star at a distance of 6,471 astronomical units — one AU is the distance between Earth and the sun. By comparison, NASA’s Voyager probes left the solar system within the last few years at a distance of about 120-125 AU. Clearly, COCONUTS-2b is on a staggeringly wide orbit. The team estimates that it will take 1.1 million years to complete a single pass around the star.
Even with all that going for us, COCONUTS-2b was a lucky detection. The solar system is still relatively young at roughly 800 million years. Because COCONUTS-2b is so huge, it has retained a lot of heat from its formation — astronomers estimate it has a temperature of 322 degrees Fahrenheit (161 degrees Celsius). That makes it glow faintly in infrared. Finding more planets like COCONUTS-2b could help us better understand planet formation. The upcoming James Webb telescope could be uniquely capable of helping here with its enhanced infrared sensitivity compared with other instruments.
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