Two astronomers claim that when the sun was formed, it was brighter and more obscure than it is today
By: Marcus Cheon
Today's Mars is a frozen, windswept wasteland, but the planet's surface bears unmistakable signs of warmer times. Less than four billion years ago, huge rivers flowed through its steppes; Shallow days licked the lips of his sockets; Rainbows stretched over canyons so vast that even the channels that branched off from them were larger than the Grand Canyon.
But the golden age of Mars poses a difficult problem for the researchers of the planets. According to the accepted version of the evolution of the sun, it was much less bright in its youth than it is today. According to this opinion, there is no spring on Mars. The red star should have been frozen forever, steeped in perpetual winter.
Now, two astronomers have come up with a possible solution to the Martian paradox. According to Juliana Sackman, of the California Institute of Technology in Pasadena, and Arnold Boothroyd of the University of Toronto, the conventional wisdom among researchers about the early sun may be fundamentally wrong. "It is possible", the two claim, "that the young sun was brighter than it is today".
The reason for believing that the young sun was paler than it is today lies in the processes taking place in the sun's core. Nuclear reactions in the core convert hydrogen - the lightest element - into helium, the second lightest element, and as a result the core shrinks and heats up. The solar nuclear reactions - whose by-product is sunlight - accelerate with the increase in temperature. Thus, as the sun ages, it emits more light. To reach its current brightness, the Sun had to be at its birth, 4.55 billion years ago, 30% paler than it is today.
How is it possible, then, that the young sun was brighter than it is today? There is only one possibility: if it was more massive than researchers have thought so far. The temperature in the core of the sun - and hence, the speed of the nuclear reactions that produce light - depends on the mass of the material pressing on the core. According to Sackman and Boothroyd, if we assume that the mass of the Sun at its birth was only 7% greater than it is today, then it was 50% brighter than previously thought - that is, 5% brighter than it is today.
According to the researchers, this was enough to heat Mars to the extent that it would have allowed water to flow on its surface without freezing; This is until 3.8 billion years ago. So, according to planetary scientists, the planet lost the battle to preserve its atmosphere, and died. A more massive sun has another advantage. Such a sun would grip the planets with a greater gravitational force and pull the Earth and Mars closer to the wall.
But if the young sun was indeed more massive, where did all the mass go? She was lost in space, the researchers say. This could only have happened under the influence of the solar wind. Today, a hurricane of thin gas, moving at a speed of 1.6 million km/h, blows from the face of the sun into space. But the two astronomers hypothesize that when the sun was young, the solar wind was a thousand times stronger than today. A wind at this speed would have allowed the young sun to shed every million years a mass 10 times greater than the mass of the Earth, thus shrinking to its current size.
In the accepted view of the evolution of the sun, the gradual conversion of hydrogen to helium in the core of the sun causes it, as mentioned, to increase its brightness as it ages. But in Sackman and Boothroyd's scenario, the constant loss of mass through the extremely powerful solar wind caused the Sun to turn pale for its first billion to two billion years. At some point the trend reversed and since then the sun has been getting brighter.
It may be possible to test the new theory experimentally. If indeed the sun was more massive and brighter in its infancy, its internal composition is different than it is commonly thought. A change in the internal composition would affect the speed of sound waves in the sun - and this can be examined by examining the fluctuations of the sun, in a method known as helioseismology. "We think that soon, after the method is improved, it will be possible to confirm or refute our theory," said Boothroyd.
* The article originally appeared in Haaretz. The knowledge site was at that time part of the IOL portal
