Pluto’s un­ruly moons are noth­ing like our own

The China Post - - LIFE -

Some of Pluto’s moons have a rugby ball-like shape and spin around er­rat­i­cally in or­bit, ac­cord­ing to an up­dated por­trait Wed­nes­day of the dis­tant dwarf planet sys­tem.

Mea­sure­ments by the Hub­ble Space Tele­scope re­vealed that Hy­dra and Nix, the sec­ond- and third-big­gest of Pluto’s five known moons, are elon­gated and be­have in a very dif­fer­ent way than Earth’s own satel­lite.

“They tum­ble. They flip over so that some­times the north pole be­comes the south pole. It’s a very, very pe­cu­liar dance,” study coau­thor Mark Showalter of the SETI re­search in­sti­tute told AFP.

The moons do not change their po­si­tion in or­bit, but their ori­en­ta­tion in space, he ex­plained, “just tum­bling, spin­ning in a ran­dom di­rec­tion.”

Pluto and its largest moon, Charon, to­gether form what is called a “bi­nary planet,” the only one in our so­lar sys­tem, with four smaller moons or­bit­ing the cen­tral duo.

The im­bal­anced and shift­ing grav­i­ta­tional field cre­ated by Pluto and Charon is what sends the smaller moons tum­bling un­pre­dictably, ac­cord­ing to a Uni­ver­sity of Mary­land state­ment.

And the ef­fect was am­pli­fied by the satel­lites’ el­lip­ti­cal shape.

“Like good chil­dren, our moon and most oth­ers keep one face fo­cused at­ten­tively on their par­ent planet,” said the uni­ver­sity’s Dou­glas Hamil­ton, the sec­ond au­thor of the study pub­lished in the jour­nal Na­ture.

“What we’ve learned is that Pluto’s moons are more like ornery teenagers who refuse to fol­low the rules.”

Yet de­spite their er­ratic ro­ta­tions, the or­bits of Hy­dra and Nix, along with that of Styx, fol­low a “clock­work pat­tern of reg­u­lar­ity,” said the state­ment.

The study also re­vealed that the other moon, Ker­beros, is as dark as char­coal, while the rest are as bright as white sand.

“Be­cause we be­lieve that all of Pluto’s moons formed at the same time, from the same im­pact, we would have ex­pected that they would all look alike. We now know that isn’t so,” said Showalter.

Sci­en­tists do not know how the sys­tem came to be, but a lead­ing the­ory is that a large ob­ject slammed into proto-Pluto, cre­at­ing a de­bris cloud from which the planet’s moons were formed.

Showalter and Hamil­ton’s find­ings are based on anal­y­sis of all avail­able Hub­ble images of the sys­tem.

As­tronomers hope that stud­ies of the Pluto sys­tem may help ex­plain how plan­ets and satel­lites form and re­main in sta­ble or­bits for bil­lions of years — also in other so­lar sys­tems.

“We are learn­ing that chaos may be a com­mon trait of bi­nary sys- tems,” said Hamil­ton. “It might even have con­se­quences for life on plan­ets or­bit­ing bi­nary stars.”

Pluto was long con­sid­ered the ninth planet in our so­lar sys­tem — the fur­thest from the Sun. It was re­clas­si­fied a dwarf planet in 2006.

Its moons Ker­beros and Styx were dis­cov­ered in 2011 and 2012, and Hy­dra and Nix in 2005.

NASA’s New Hori­zons space­craft is set to pass the Pluto sys­tem next month for an even closer look.

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