Getting close to the Sun
Ken Tapping, August 21, 2018
We are seriously interested in understanding the Sun for two reasons. First of all it is the only star in the universe that is close enough to study in fine detail. Knowing how the Sun works is an important step in making sense of the many different types of stars that in their billions populate our and other galaxies. The other reason is that it is the engine driving our environment on Earth. All the energy we use, with the exception of nuclear energy, comes from the Sun, either now or in the past, stored in fossil fuels. It also can degrade or completely disrupt our power, transportation and communication infrastructure.
Until now we have been confined to observing the Sun from a safe distance, using ground-based optical and radio telescopes, orbiting telescopes, and a selection of space probes. So our information has been partly second-hand; we find out what is going on by observing the emissions produced, rather than studying the processes and their environment directly. This autumn things will change, when we expect to have the closest encounter we have ever had.
A NASA spacecraft has been launched which is in an orbit that will eventually take it to within 6 million kilometres of the "surface" of the Sun, and then, over the following seven years or so repeat this encounter 24 times. During those encounters the spacecraft will encounter more than 600 times the amount of heat reaching the Earth. To survive such heat levels it is equipped with some exotic cooling technologies plus a heat shield made from a special carbon composite material. The objective is to make direct measurements of what is going on in the solar corona, close to the Sun. It will be exploring the environment where the solar wind begins, solar flares happen and coronal mass ejections (solar storms) start their journeys to Earth. Our radio telescopes pick up emissions from a complex menagerie of plasma processes in the solar corona. Now we can hope for direct measurements of what is going on. This spacecraft has the potential to be a real solar research and space weather game changer.
The spacecraft is named the "Parker Solar Probe", after the eminent American solar physicist Eugene Parker, who, apart from writing a series of important text books found on the bookshelves of most solar physicists, predicted the existence of the solar wind – 60 years ago. This is one of those rare cases where the spacecraft is named after a scientist who is still living.
The Sun is a very difficult object to get to for a spacecraft launched from Earth. Our planet is orbiting the Sun at over 110,000 km/h. To get the spacecraft into an orbit that closely approaches the Sun, we need to cancel almost all that speed; that is, launch the spacecraft backwards from Earth at close to 110,000 km/h. We currently have nothing able to do that. So the vehicle has been launched backward along the Earth's orbit at around 88,000 km/h. There are launchers just capable of doing that. This will get the spacecraft to Venus, where it will use the planet's gravity to change its course and speed so that it can continue on to its close encounter with the Sun. Eventually the probe will succumb to the Sun's heat and radiation, but for a while it will be the fastest spacecraft ever launched from Earth, reaching around 720,000 km/h during its closest passes to the Sun.
This close to the Sun it is not only the heat that poses a problem. The spacecraft will be exposed to blasts of high-energy particles and X-rays, which can damage or destroy instruments and electronics that are not radiation hardened. This is a challenging mission any way we look at it, but the science we expect will be really exciting.
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