How Long Is a Day on Saturn?

How Long Is a Day on Saturn(ˈsadərn)?

The answer was hiding(ˈhīdiNG) in the planet’s(ˈplanət) rings.

By Nadia Drake

For decades, it was a nagging(ˈnagiNG) mystery(ˈmist(ə)rē) — how long does a day last on Saturn?

Earth pirouettes(ˌpirəˈwet) around its axis(ˈaksəs) once every 24 hours or so, while Jupiter(ˈjo͞opədər) spins(spin) comparatively(kəmˈperədivlē) briskly(ˈbrisklē), once in roughly(ˈrəflē) 9.8 Earth-hours. And then there is Venus(ˈvēnəs), a perplexingly(pərˈpleksiNG) sluggish(ˈsləgiSH) spinner(ˈspinər) that takes 243 Earth-days to complete(kəmˈplēt) a full rotation(rōˈtāSHən).

With Saturn, it turns out the answer rippled(ˈripəl) in plain(plān) view, in the planet’s lustrous(ˈləstrəs) rings.

After reading small, spiraling(ˈspīrəl) waves(wāv) in those bands, sculpted(skəlpt) by oscillations(ˌäsəˈlāSHən) from Saturn’s gravity(ˈɡravədē), scientists reported this month in the Astrophysical(ˌastrōˈfiziks) Journal(ˈjərnl) that one Saturnian(səˈtərnēən) day is a mere(mi(ə)r) 10 hours, 33 minutes and 38 seconds long, measured(ˈmeZHərd) in Earth time.

“The rings are not only beautiful, they’re very diagnostic(ˌdīəgˈnästik) of what’s going on inside the planet,” said Linda Spilker, project scientist for NASA’s(ˈnasə) Cassini mission(ˈmiSHən), which studied Saturn for more than a decade.

Saturn has been stubbornly(ˈstəbərnlē) secretive(ˈsēkritiv) about its days. Its buttery(ˈbətərē) clouds(kloud) don’t bear helpful markings that scientists might use to track(trak) the planet’s rotation, and they can’t easily use its nearly vertical(ˈvərdək(ə)l) magnetic(magˈnetik) axis — as they have for Jupiter’s more off-kilter(ˈkiltər) alignment(əˈlīnmənt) — to gather clues(klo͞o) about the planet’s interior(inˈti(ə)rēər).

Scientists long relied on other, ultimately(ˈəltəmitlē) misleading(misˈlēdiNG) clues to figure out how fast the ringed world turns. Not until the Cassini(kəsini) spacecraft(ˈspāsˌkraft) swooped(swo͞op), flipped and twirled(twərl) through the Saturn system did scientists realize that the answer was outside the planet itself, etched(eCH) into its icy(ˈīsē) rings.

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https://www.nytimes.com/2019/01/25/science/saturn-day-length.html