Scientists calculate length of Saturn’s day
Using Cassini data of the rotation rate of Saturn’s rings, scientists have calculated what they think is the precise rotation rate of the planet itself.
Using new data from NASA’s Cassini spacecraft, researchers believe they have solved a longstanding mystery of solar system science: the length of a day on Saturn. It’s 10 hours, 33 minutes and 38 seconds. The figure has eluded planetary scientists for decades, because the gas giant has no solid surface with landmarks to track as it rotates, and it has an unusual magnetic field that hides the planet’s rotation rate.
The answer, it turned out, was hidden in the rings. During Cassini’s orbits of Saturn, instruments examined the icy, rocky rings in unprecedented detail. Christopher Mankovich, a graduate student in astronomy and astrophysics at UC Santa Cruz, used the data to study wave patterns within the rings. His work determined that the rings respond to vibrations within the planet itself, acting similarly to the seismometers used to measure movement caused by earthquakes. The interior of Saturn vibrates at frequencies that cause variations in its gravitational field. The rings, in turn, detect those movements in the field.
…Mankovich’s research, published Jan. 17 by Astrophysical Journal, describes how he developed models of Saturn’s internal structure that would match the rings’ waves. That allowed him to track the movements of the interior of the planet – and thus, its rotation. [emphasis mine]
This work certainly seems ingenious, clever, and somewhat convincing, but I must admit I laughed when I read their estimate of the day length above, to the second. That is ridiculous. Their margin of error cannot possibly be that small. Mankovich has for sure narrowed the uncertainty in the length of Saturn’s day, but forgive me if I remain skeptical as to the precision claimed.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Using Cassini data of the rotation rate of Saturn’s rings, scientists have calculated what they think is the precise rotation rate of the planet itself.
Using new data from NASA’s Cassini spacecraft, researchers believe they have solved a longstanding mystery of solar system science: the length of a day on Saturn. It’s 10 hours, 33 minutes and 38 seconds. The figure has eluded planetary scientists for decades, because the gas giant has no solid surface with landmarks to track as it rotates, and it has an unusual magnetic field that hides the planet’s rotation rate.
The answer, it turned out, was hidden in the rings. During Cassini’s orbits of Saturn, instruments examined the icy, rocky rings in unprecedented detail. Christopher Mankovich, a graduate student in astronomy and astrophysics at UC Santa Cruz, used the data to study wave patterns within the rings. His work determined that the rings respond to vibrations within the planet itself, acting similarly to the seismometers used to measure movement caused by earthquakes. The interior of Saturn vibrates at frequencies that cause variations in its gravitational field. The rings, in turn, detect those movements in the field.
…Mankovich’s research, published Jan. 17 by Astrophysical Journal, describes how he developed models of Saturn’s internal structure that would match the rings’ waves. That allowed him to track the movements of the interior of the planet – and thus, its rotation. [emphasis mine]
This work certainly seems ingenious, clever, and somewhat convincing, but I must admit I laughed when I read their estimate of the day length above, to the second. That is ridiculous. Their margin of error cannot possibly be that small. Mankovich has for sure narrowed the uncertainty in the length of Saturn’s day, but forgive me if I remain skeptical as to the precision claimed.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
The Astrophysical Journal, linked to by the NASA article, article states that the rotation is “10h33m38s +1m52s -1m19s (median and 5%/95% quantiles)”. So it actually has a fairly wide margin of error, which the NASA article should have mentioned.
This goes to the lack of critical understanding of the propagation of error and what it means to reporting results. By one decimal point to many, people can lie!
Andi: Thank you for finding this. It is not surprising that press release was essentially dishonest, or incompetently written. Since it came out late today, we shall see tomorrow how the press covers it. Will we see many stories citing this exact number, or will most or all catch what you did? It will be quite interesting to see.
I admit that I did not do this digging, but at least I had the sense to recognize this claim for what it was.
Science has spoken and we must all accept the conclusion as the ultimate truth right up until it isn’t and then we must mock and belittle anyone stupid enough to believe it in the first place. Thus sayeth the scientific method may it continue to bless us though we do not deserve it for our sins against nature, women, and cultures that science through means other than science.
I just checked a few references I had on hand that are over 50 years old. They gave Saturn’s day variously as “10 1/2 hrs” or “10 hr 14 min” or other figures over 10 hours. Clearly, we’ve had a fair idea of the length of Saturn’s day for much longer than the press release would have us believe.