Once launched in 2021, NASA’s long-awaited James Webb Space Telescope (JWST) will spend the first few months of operations focusing in part on Pluto, its moon Charon and a panoply of other bizarre, frozen worlds in the planetary graveyard of our outer solar system.
NASA’s New Horizons spacecraft’s magnificent 2015 flyby of the dwarf planet Pluto, and its moon Charon, revealed that these objects are far more active and far more interesting than previously thought. In fact, Pluto and Charon arguably act as gatekeepers to an outer region of our solar system that is made up of thousands of dwarf planets and other relatively small objects.
“These are objects that are in the graveyard of solar system formation,” Cornell University’s Jonathan Lunine, a Webb Interdisciplinary Scientist who will use Webb to study some of these targets, said in a statement. “They’re in a place where they could last for billions of years, and there aren’t many places like that in our solar system. We’d love to know what they’re like.”
So-called Kuiper Belt Objects, objects that lie in a circumstellar disk of planetary leftovers extending from beyond Neptune to some 50 Earth-Sun distances, are inherently cold and faint. Yet because they glow in infrared light, at wavelengths Webb is specifically designed to detect, the telescope should be extremely adept at detecting such bodies’ wide range of colors, says NASA. This, in turn, should provide clues as to their formation histories.
And while JWST can’t get the very close up images that New Horizons provided, it provides a different way at getting at the composition, Lunine told me.
These objects include Eris, the second-largest dwarf planet in our solar system. Nearly the size of Pluto, at its farthest point, mysterious Eris is more than 97 times as far from the Sun as the Earth is, says NASA. But as part of its guaranteed time observations, Webb should provide lots of data about what types of ices cling to its surface. Another, Sedna, is so far distant that it takes some 11,400 years to complete one orbit around our Sun, says NASA. And a strange 250-km asteroid Chariklo is the first asteroid discovered with a miles-wide ring system.
The few spacecraft that have flown by Kuiper Belt Objects could only study these intriguing objects for a very short period of time, says NASA. With Webb, astronomers can target more Kuiper Belt Objects over an extended time, says the agency. In fact, A Target of Opportunity will observe a Kuiper Belt Object passing in front of a star, if such an alignment should occur during the first two years of Webb’s lifetime, says NASA. This sort of occulting transit can reveal a given object’s size.
Lunine’s own JWST Guaranteed Time (GTO) investigation covers other Kuiper Belt objects, including Haumea, Quaoar, the Centaur Chiron. Haumea and Quaoar sit on opposite sides of the predicted divide between objects big enough to retain their non-water volatiles and those that do, says Lunine. And perhaps discover something new about the Centaurs by observing Chiron with JWST, he says.
“What is the nature of these objects which may have been kicked out of the Kuiper Belt by some unknown gravitational perturbation?” Lunine wonders.
As for what these objects tell us about architecture of our solar system?
These are the remnants of the formation of the giant planets, says Lunine. Some were too far from the Sun to begin with to be consumed by the gas and ice giants, and others survived the melee by being ejected beyond Neptune, he says.
We know the giant planets consumed Earth masses worth of heavy elements (elements other than hydrogen and helium), says Lunine. Thus, he says that the Kuiper belt is a collection of the uneaten remnants of the feast that engorged the planetary cores until they became massive enough to be giant planets.
“One learns a lot about the gourmands by studying what they left behind on their plates,” said Lunine.