Venus transit, an extremely rare event in which a planet passes between the Earth and sun, can now be used to make measurements about the way in which the atmosphere of Venus absorbs different kinds of light. Which, in turn is the scientists’ key to finding what elements are layered above the surface of Venus.
Similar to Earth, each of the layers of Venus’ atmosphere absorbs light in a different manner than another. For instance, some layers may absorb a certain wavelength of light completely, which another might not absorb it at all. As venus passes through the sun’s face, which emits light in almost every wavelength in the electromagnetic spectrum, scientists now have the chance of a lifetime to witness and find out the different types of light filter through Venus’ atmosphere.
A layer in the upper atmosphere around Earth’s twin Venus known as the thermosphere absorbs particular high-energy wavelengths of light. When looking at the planet against the sun in one of these wavelengths, the thermosphere, instead of appearing transparent, will appear surprisingly opaque.
“Radiation goes into the atmosphere and is absorbed, creating ions and a layer of the atmosphere called the ionosphere,” said Dean Pesnell, SDO project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Because the energy in this light is captured by the ions, it is not re-emitted on the other side. In certain wavelengths, Venus’s atmosphere is as solid as a wall, blocking light from traveling to our eyes. To our telescopes, the atmosphere is as dark as the planet itself — so, Venus will appear to have a different size, depending on the wavelength of the telescope’s pictures.”
Reale and his team selected images of the Venus transit taken in many X-ray and ultraviolet wavelengths and measured the apparent size of the planet to within several miles. For every set of pictures, the team calculated just how large the atmospheric blocking was, which is a measure of the amount of the wavelength in Venus’ atmosphere was completely absorbed.
Because of the variety of atoms, each with its own ability to absorb light, the height of the light absorptions gives a clue to the scientists about the molecular make-up of Venus’ atmosphere. This information is useful for planning missions to Venus since the molecules can lead to a large amount of the course-altering drag a spacecraft feels.
“Learning more about the composition of the atmosphere is very important for understanding the braking process for spacecraft when they enter the upper atmosphere of the planet, a process called aerobraking,” said Reale.
The shape of the atmosphere in Venus were also significant markers to the scientists relating to the effect of sun on the atmosphere. “If the atmosphere observed were asymmetric, that could tell us more about how the star is impacting the planet,” said Sabrina Savage, NASA project scientist for Hinode.
Only sides of the atmosphere were visible during the transit, but they were particularly interesting areas. From Venus’ perspective, these were the areas where the night turns into day and vice-versa. On Earth, these transition areas can host interesting effects in the ionosphere, the data from the Venus transit showed that these two transition areas have virtually nothing distinct from one another.
“The planet appeared very round in all wavelengths,” said Pesnell. “If the transition from day to night were different from the transition from night to day, you would expect a bulge in the atmosphere on one side of the planet.”
“In the future, there might be missions that have enough sensitivity to detect the difference in radius in different wavelengths,” said Reale. “In particular, if there are exoplanets with an extremely thick thermosphere, the size difference in different wavelengths will be larger and there will be a better chance of detecting the change.”