Venus, second planet from the Sun and sixth in the solar system in size and mass, is our closest planet. When it is visible, since it can only be seen in the hours around sunrise or sunset, it is the brightest planet in the sky. Now, a team of astronomers has used Earth-based radar observations to measure some of the fundamental properties of this planet. Specifically, we now know the precise length of a day, the tilt of its axis, and the size of its core.
How long is a day on Venus?
After 15 years of observations, we can say that one day on Venus is equivalent to 243.0226 Earth days , approximately two-thirds of a year on Earth. And, in addition, it changes with a variation of about 20 minutes. According to experts, this variation in the length of the day is probably caused by the very dense atmosphere, 93 times more massive than that of the Earth, exchanging momentum with the solid ground and speeding it up or slowing it down, affecting the planet’s spin. “This also happens on Earth, but the exchange adds or subtracts only one millisecond from each day,” say the researchers. It is a quantity perceptible only by an atomic clock.
Are you surprised that we still do not know this fact with how close Venus is to us? It is easy to calculate the rotational speed of most planets if they have identifiable features on the surface. However, the dense atmosphere of Venus makes this difficult, so the astronomers had to be creative when making the measurements.
First, they used the 70-meter-wide Goldstone antenna located in California’s Mojave Desert to send radio waves to Venus. This was between 2006 and 2020. Radio waves can travel through the atmosphere and then reflect off the surface. Later, a few minutes later, they are collected again at the Goldstone Observatory and about 20 seconds later at the Green Bank Observatory in West Virginia. The difference between the two detections, the exact delay between reception at the two facilities, has revealed how fast the planet is spinning.
What is the size of its core?
The team discovered that the core of Venus is about 3,500 kilometers in diameter, quite similar to Earth, although they do not know if it is liquid or solid. Venus is quite an enigma and understanding the size of its core, the speed of rotation and the exact inclination of the axis will help to plan future landing missions in this infernal twin of the Earth (remember that both planets have a lot in common: almost the same size, mass and density).
Venus evolved quite differently from Earth, since in it a runaway greenhouse effect was unleashed that made it the hottest planet in the solar system with temperatures of up to 500 ºC (the minimum never falls below 400 ºC) and a landscape with clouds sulfuric acid and carbon dioxide atmosphere.
Changes in the spin and orientation of Venus reveal how mass is distributed within the planet, which in turn drives understanding of its original formation, the team said.
And the inclination of its axis?
The study found that Venus tilts to one side at exactly 2.64 degrees, an improvement from previous estimates by a factor of 10 in precision. Given the minimal tilt, the planet does not experience seasons.
Referencia: J.-L. Margot et al. Spin state and moment of inertia of Venus. Nat Astron, published online April 29, 2021; doi: 10.1038/s41550-021-01339-7
