Israeli researchers accurately measured the length of the day on Saturn: "It is amazing to see that in 2015 we still lack basic details about bodies in the solar system"

According to Dr. Royat Haled, who headed the research, measuring the length of the day on a gaseous planet is not a simple matter, there are no fixed sites where you can measure the time when they reappear in order to accurately know the length of the day

What is the length of the day on the planet Saturn? Apparently this is a fundamental question in space exploration: for most of the planets in our solar system, the length of the day is a clear and unequivocal physical data, well known to modern science. But it turns out that in Saturn the situation is different. Even today, in 2015, scientists do not have certain and definitive information regarding the self-rotation time - which is the length of the day - of this planet. Now a team of young scientists from Tel Aviv University and the Weizmann Institute has developed a new calculation method, which may finally yield an accurate solution to this puzzle - and even be a key to other mysteries in our solar system and throughout the galaxy.

The research was carried out by Dr. Roit Chaled, a planetary science researcher in the Department of Earth Sciences of Tel Aviv University, in collaboration with Dr. Eli Galanti and Dr. Yohai Caspi from the Weizmann Institute of Science. The article is published today (25.3.15) in the journal Nature. Dr. Khaled is involved in space missions of NASA and the European Space Agency - among them the research spacecraft 'Cassini' orbiting Saturn, 'Juno' which will reach the planet Jupiter in 2016, and JUICE which will explore Jupiter and its moons in the next decade.

In an interview with the Hidan website, Dr. Khaled, who specializes in the study of gas giants (planets of the type of Jupiter and Saturn and even larger) in the solar system and beyond, explains that measuring the length of the day on a gaseous planet is not a simple matter, there are no fixed sites that can measure the time when they appear Again to accurately know the length of the day (perhaps with the exception of Tzedek and his 'eye').

"Saturn is a gas giant planet - a planet made entirely of gases, mainly hydrogen and helium," explains the leader of the study, "because Saturn is made of gases, it does not have a stable surface, and therefore its rotation time cannot be determined using the usual method for solid planets: choosing An ID mark on the surface, and measuring the time that passes until it is seen again. In addition, the gas giants are always covered by a layer of clouds, which makes the job of measurement even more difficult."

When Cassini arrived she got a different number - 10 hours and 47 minutes. Such a planet cannot change its rotation speed in eight minutes in such a short time.
It is clear that the measurement does not give exact data and during the Cassini journey they saw that the radio frequency changes with time. Then there were theoretical models that talked about 10 hours and 32-33 minutes and then we had an uncertainty of fifteen minutes.

"In 1977, NASA launched the Voyager 2 spacecraft, which brought us valuable information about the four outer planets of our solar system - Saturn, Jupiter, Uranus and Neptune," says Dr. Khaled. "According to Voyager 2 observations, it was determined that Saturn's rotation time is 10 hours, 39 minutes and 22 seconds, and this figure has been considered reliable for about 30 years. That was until measurements from the Cassini spacecraft, which entered orbit around Saturn in 2004, showed that the measurement method used by Voyager 2 did not actually reflect the planet's rotation time. The mystery of the length of Saturn's day has been reopened."

According to Dr. Khaled, both Voyager and Cassini measured its rotation speed by measuring SKR radiation (Saturn Kilometer Radiation), radiation in the radio field with a wavelength of kilometers created by the currents between the ionosphere and magnetosphere of the planet. Since Cassini has been orbiting Saturn for about a decade, the test was performed again a few years after Cassini's arrival, and a different result was obtained. If this is not enough, there are theoretical models that stated that the length of Saturn's day should be ten hours and 32-33 minutes.

Dr. Khaled and her colleagues chose to attack the question using a calculation method known as 'statistical optimization', with which they estimated the planet's rotation speed by linking it to its gravitational field, the density of the material and its flattened shape. In this way they calculated a rotation time that optimally fits the existing information: 10 hours, 32 minutes and 45 seconds. To test the reliability of their method, the researchers also used it to calculate the rotation time of Jupiter, which is well known to science - and reached the correct result.

"Our findings have a wide meaning, far beyond finding a solution to an interesting puzzle," explains Dr. Khaled. "First, the time of rotation greatly affects the winds and the prevailing weather on the planet Saturn. And perhaps more importantly: in a previous study we found that a difference of 7 minutes in the rotation time has far-reaching consequences for the study of the internal structure of the planet. From the internal structure, important conclusions can be drawn about the formation of Saturn in particular, and gas giants in general, and the conditions that prevailed around it when it was formed, in the creation nebula of the solar system. This information, in turn, adds an important layer to the study of the development of our solar system and other systems in the vastness of the galaxy."

"It sounds little, but it is a very basic physical quantity in the solar system, so we obviously want to know it with greater precision. In addition, the speed of rotation affects the speed of the winds - for example, the fact that winds blow on it in both directions - from east to west and vice versa, as in Jupiter. Knowing the length of the day also makes it possible to analyze how many heavy substances (substances heavier than hydrogen and helium, in fact most of the elements in the periodic table and of course compounds such as methane and ammonia) are in Saturn's atmosphere. Subtracting seven minutes from Saturn's rotation period on its axis means a smaller core.

The Scientist: As someone who studies planets outside the solar system, does this information help with insights for this research?

"Indeed, I am also involved in space missions that study planets outside the solar system. A better understanding of bodies in the solar system allows us to compare our solar system with thousands of other solar systems that have already been discovered."

"Space missions designed for this have not only discovered the planets but also their mass and diameter. We use the planets in the solar system to calibrate this information. We actually have one solar system about which we have many details, and many solar systems about which we have no detailed information except for the number of planets and their orbits and as mentioned just their diameter and diameter, but nothing more, but this little bit allows us to do statistics. The condition for their correctness is that the calibration is accurate and for that we need to know our solar system."

The scientist: What is the state of our knowledge about the gas giants?
Jupiter has been and will be studied a lot, as will Saturn. In contrast, Uranus (Uron) and Neptune (Rahab) were only briefly visited by the Voyager 2 spacecraft in the XNUMXs, and the knowledge about them originates mainly from observations from Earth. The planetary scientists appealed to NASA and the European Space Agency to send a mission to one or both of them. This is because we discover a lot of planets whose masses are relatively small and similar to those of Uranus and Neptune, and when we check our knowledge of these planets, it turns out that it is poor."
In their next studies, Dr. Khaled and her partners will seek to apply the innovative approach they developed to other gas giants in the solar system - mainly Uranus and Neptune, and even use it in the study of planets of other suns.

Dr. Khaled hopes that the publication of the research and findings of the Israeli groups specializing in astrophysics and the study of planets will attract young people to take an interest in the field.