My astronomy textbook includes this graph of the temperature of the Sun's Corona versus the distance above the photosphere. It appears to go up from 4,500 K to over 1 million K at 20,000 km above the photosphere. But at what point does it come back down? Or does it not? Does that mean the temperature of the interplanetary space in our solar system is really over 1 million degrees K? (Source: Astronomy Today, 9th edition, by Chiasson and McMillan. Pearson Publishing, 2017).