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Humans have been developing new methods of space exploration and travel steadily over time. Although there have been many groundbreaking achievements, the Sun was once one of the most impenetrable objects in our solar system. However, the NASA Parker Solar Probe, designed to get close to and investigate the Sun, has finally entered the sun’s atmosphere.
13 million kilometers above the sun, the Alfvén critical surface marks the boundary between space and the Sun. It was not announced until recently at the fall meeting of the American Geophysical Union, but on April 28, 2021, Parker crossed into this territory. Solar physicists mostly believed in the surface’s existence prior to the discovery, but its exact location could not be determined and its appearance was questionable.
The Alfvén critical surface marks where plasma can separate from the sun and become a part of the Sun’s constantly emanating solar wind. Solar wind and space weather in general often causes problems for satellites and even life. Understanding where the solar wind begins would be extremely beneficial for scientists attempting to understand its impact.
Additionally, the surface may help explain why the sun’s corona, or outer atmosphere, is drastically hotter than the sun’s atmosphere. Usually, temperatures decrease as you get further out, but the corona is more than a million degrees Celsius. Now that the boundary of the Alfvén critical surface has been identified, scientists can observe coronal heating more closely.
As for the appearance of the surface, Parker’s measurements determined that it was wrinkly. Scientists had long been debating about the surface’s identity, with theories ranging from a smooth sphere to a ragged and nearly imperceptible boundary. The Parker Solar Probe crossed through the boundary three times, all of which were noticeable due to the surface’s relative smoothness.
The Parker Solar Probe is still orbiting the Sun and is planned to approach the Sun and its corona, getting up to 6 million kilometers close to the Sun. Although this spacecraft has already done the impossible, it isn’t done just yet!
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