The plan­ets: what can JWST tell us?

De­spite cen­turies of ob­ser­va­tion, the plan­ets still hold mys­ter­ies. Here is what the JWST will aim to re­veal about each one

Sky at Night Magazine - - JAMES WEBB SPACE TELESCOPE -

an ob­serv­ing win­dow of around 50 days ap­prox­i­mately ev­ery six months, the gi­ant plan­ets Jupiter, Saturn, Uranus and Nep­tune will all be view­able, as well as their as­so­ci­ated rings and 170 known moons.

While the plan­ets them­selves will be mon­i­tored by JWST, some of the most in­ter­est­ing sci­ence will con­cern their satel­lites. From help­ing to solve the tidal heat­ing co­nun­drum on Jupiter’s moon Io to tak­ing over the task of watch­ing the Satur­nian moon Ti­tan af­ter the Cassini mis­sion comes to an end or even es­tab­lish­ing whether Nep­tune’s ret­ro­grade-or­bit moon Tri­ton has a sub­sur­face ocean, JWST of­fers the chance to view and try to un­der­stand the most dy­namic pro­cesses of the So­lar Sys­tem’s satel­lites.

Fo­cus on the small things

How­ever, the bread and but­ter for JWST’s So­lar Sys­tem sci­ence will be even less stud­ied, smaller and dis­tant bod­ies: comets, the main belt as­teroids sit­u­ated be­tween Mars and Jupiter, the Tro­jan as­teroids that share Jupiter’s or­bit, and the Kuiper Belt ob­jects – in­clud­ing dwarf planet Pluto and the yet-to-be-seen Planet Nine. All could yield clues to how the So­lar Sys­tem came to be the home we know.

“Be­cause they re­tain ma­te­rial from the very start of So­lar Sys­tem his­tory, they re­veal the chem­i­cal makeup of the plan­ets and how plan­ets form,” says Andy Rivkin, plan­e­tary as­tronomer from Johns Hop­kins Univer­sity.

For these smaller dis­tant bod­ies and ring sys­tems, NASA has an­other trick

up its sleeve: stel­lar oc­cul­ta­tions, where a star is tem­po­rar­ily blocked by a pass­ing So­lar Sys­tem body.

“If you can take data very quickly as an ob­ject passes in front of a star, you can mea­sure var­i­ous things about the ob­ject it­self,” ex­plains Stans­berry. By look­ing at the changes to the star’s light as it dis­ap­pears be­hind a planet, Webb will be able to look at ring mi­crostruc­tures, and may dis­cover rings around mi­nor plan­ets or even find at­mo­spheres around var­i­ous Kuiper Belt ob­jects.

All of these pro­posed tar­gets for Webb sug­gest the So­lar Sys­tem’s most well­hid­den mys­ter­ies may soon be solved, but one pa­per re­ally sticks out as hav­ing the po­ten­tial to cap­ti­vate the pub­lic’s imag­i­na­tion. In it, the au­thors pro­pose us­ing JWST and Hub­ble to­gether to cre­ate stereo 3D movies of the plan­ets and moons am­a­teur as­tronomers have been fas­ci­nated by for cen­turies.

“I worked with a vi­sion sci­en­tist col­league to un­der­stand the lim­its of hu­man depth per­cep­tion,” says Joel Green, a project sci­en­tist at STScI, who led the study. “It turned out that if you had eyes one mil­lion miles apart, and the res­o­lu­tion of Hub­ble and Webb (roughly 1,000 times bet­ter than 20/20 vi­sion), you could ac­tu­ally see ob­jects like Mars, or Jupiter’s moon sys­tem or Saturn’s rings in stereo 3D!”

Not only might this be a boon to as­tronomers, of­fer­ing stereo data on weather changes, col­li­sional stud­ies, ring sys­tem shocks, and many more, but would also be a first for sci­ence ed­u­ca­tion, mak­ing an­cient as­tro­nom­i­cal bod­ies come to life in the class­room. As Green notes: “These are the sorts of im­ages that could in­spire a gen­er­a­tion”.

Does Nep­tune’s moon Tri­ton har­bour an ocean be­neath its crust? JWST could tell us

How much more might we learn about Pluto and other Kuiper Belt ob­jects once JWST is trained on them?

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