exoplanet J1407b -- 1/20/21

Today's selection -- from Cosmos: Possible Worlds by Ann Druyan. The rings of the exoplanet J1407b. By the way, Neptune and Uranus have rings too:

"Gravity has a big bag of tricks. Some of the loveliest are the rings around worlds. Half the planets in our own solar system are ringed. But of the thousands of extrasolar worlds we've discov­ered since 1995, we weren't able to discern a single ringed planet until we found J1407b in 2012. And, wow, is it a doozy.

"Imagine a world 20 times as large as Jupiter, with a ring system that would more than fill half the 93 million miles between Earth and the sun. That's what awaits us 420 light-years from Earth, in orbit around an infant yellow dwarf star, a ring system so extensive it makes its gigantic planet look tiny. Why haven't we found more ringed planets in our galaxy? Is it that rings are so unusual, or are the methods we use to find exoplanets not very good at seeing the ring systems that may surround them?

"One method of searching is to look at a star with a spectroscope, which produces a picture of the signals hidden in the starlight. Looking at J1407, we see thin, dark vertical lines running across the spectrum are shifting back and forth by a small amount. That's the gravity of the exoplanet tugging on its star.


"And then there's the transit method, a kind of interstellar electrocardiogram, or EKG. A graphic exhibits a series of blips against the blackness of the graph, and the yellow dwarf star at the same time. As the planet transits across the disk of the star, the light blips stop because the planet's rings are blocking out its star's light.

"A light curve is a measure of the variations of brightness from a distant object. The most interesting part in the one from J1407 is the darkness. It tells us that something mysterious is passing between us and the star ... something very large. J1407b's ring system is so vast that it eclipsed its star for days. These rings extend across an astonishing 112 million miles. But as enormous as they are, they're shockingly thin. If the ring system of J1407b were the size of a dinner plate, it would have to be a hundred times thinner­ as thin as a human hair. This surprising contrast between the immense territory of a ring system, and its thinness, is just as strik­ing in our own solar system. The outermost ring of Neptune is so dainty that it was first thought to be the fragments of a ring. Not a ring, but a collection of arcs. That was, until NASA's Voyager 2 spacecraft revealed that the so-called arcs were clumps, the thicker parts of a fainter, complete ring.

"Uranus also has rings. Why is it that the weirdest planet in the solar system has attracted the least attention? Voyager 2 is the only spacecraft that has ever been sent on a reconnaissance mission to Uranus, one of the two ice giant planets that circle the sun. Uranus looks like it's on its side, skating around the sun on the blade of its rings. Amid its 13 faint rings are 27 small orbiting moons. During Uranus's 20-year-long summers, the sun never sets. The winters are equally as long-20 years of unbroken night. Unlike its fellow gas planets, Uranus is cold-hearted. It doesn't generate any internal heat.

"Uranus is one crazy world. The outer edge of Uranus's atmo­sphere is hot-hotter than 500 degrees above zero. If we could dive into them we would find that the clouds become thicker, more blue, colder. Uranus also has the coldest clouds in the solar system­ nearly 400 degrees below zero. Scientists speculate that its vast, interior ocean might be made of ammonia, water, or liquid dia­monds. It may rain diamonds on this world."

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Ann Druyan


Cosmos: Possible Worlds


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Copyright 2020 Ann Druyan


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