Astronomers were able to accurately measure the length of the day, the inclination of the axis and the size of the core of Venus

The history of research on Venus goes back more than four centuries, and for the last 60 years it includes the work of automatic interplanetary stations.

But even such seemingly basic parameters of this planet as the duration of the day and the inclination of its axis of rotation have so far been measured with a very large error. American astronomers, based on data obtained over 15 years of observations, were able to radically clarify not only these two characteristics, but also to estimate the size of the Venusian nucleus.

An article with the new measurements was published in the peer-reviewed journal Nature Astronomy. In this scientific paper, staff at the University of California, Los Angeles (UCLA) analyzed the results of radar observations of Venus conducted by the Green Bank (West Virginia) and Goldstone (California) observatories. Both radio telescopes used are remarkable in their own way: the first – the world’s largest all-turn astronomical antenna, the second – is part of the complex long-range space communications NASA Deep Space Network (DSN).

It took fifteen years to collect the necessary information – from 2006 to 2020 inclusive. Such an impressive period was required not only because of the high workload of radio astronomical observatories. In addition to this factor, different noise in the data had a great influence. A large part of the observations had to be rejected because of interference and insufficient number (or accuracy) of measurements. But as a result, over a decade and a half, scientists have accumulated enough high-quality observations to clarify the fundamental parameters of Venus.

First of all, scientists found that the second planet from the Sun rotates with an inclination of 2.6392±0.0008 degrees relative to its orbital plane. This value, obtained empirically, is no less than an order of magnitude more accurate than earlier estimates. If we compare it with the Earth, Venus moves in space “standing still”: the inclination of our native planet relative to the orbital plane is 23 degrees, 26 minutes and 21 seconds.

Measuring the speed of rotation of Venus around its axis, American astronomers checked the average duration of day on it – 243,0226±0,0013 Earth days. And, most interestingly, from observation to observation this value varied within 20 minutes. Such deviations may be associated with the rapid movement of the Venusian atmosphere. Its mass is 93 times greater than Earth’s, and its speed of movement relative to the surface reaches one revolution in 96 hours. As a result, the exchange of momentum between such a massive atmosphere and the planet becomes noticeable. On Earth, such a phenomenon is also observed, but its effect is incomparably lower – about a millisecond per day.

Finally, by measuring the tilt of the axis of rotation and its precession, we were able to estimate the size of the core of Venus. If we imagine the second planet from the Sun as a yula, its upper prong will describe a circle of 29 millennia (44.58±3.3 angular seconds per year). Incidentally, this is slightly slower than the precession of the Earth’s axis of rotation: it will take 26 thousand years for the same circle. Based on these deviations, the U.S. astronomers calculated the moment of inertia of Venus (0.337±0.024), from which derived the size of the core – 3500 kilometers in diameter (almost like the Earth). However, from this data we cannot yet conclude whether it is liquid or solid.

Despite the large time expense, the clarified data is extremely important for astronomers, so the work done by UCLA certainly deserves respect. After Venus, they plan to shift their focus to Jupiter’s large satellites, Europa and Ganymede. They are so massive and complex that they are comparable in many characteristics to the planets. It is hard to say how long it will take to study them with radio telescopes, but hopefully less than a decade.

Venus is of great interest to scientists – of all the planets in the solar system, it is the most similar to Earth in many ways. Because of this, it has even been called the “sister” of humanity’s home celestial body. But since last year, after a careless statement by the head of Roskosmos, it is better known as the “Russian planet”. There is some truth in these words: it was the Soviet Union that made the most impressive space missions to Venus. However, over the past three decades, only three spacecraft (American, Japanese, and European) have entered orbit around it. Some scientific data were also provided by “passing by” probes, but it is difficult to call it a full-fledged study of the second planet from the Sun.

Exploration of Venus is complicated by extremely adverse conditions on its surface and in its atmosphere. Landing platforms must rely on high temperatures (over 460 degrees Celsius) and pressures (more than 90 times higher than at sea level on Earth). And aircraft risk encountering high levels of acid in the clouds. Well, probes in orbit face the fact that these clouds completely cover the planet and are transparent only in the radio range – for optical instruments they are impermeable (except for small “windows” in the infrared part of the spectrum).

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