The young, unstable Sun may have gone through a period of particularly powerful radiation that allowed the formation of solid inner planets, including Earth.
The planets were born from the matter of a gas and dust disk that revolved around a young Sun, unstable and weak. The heavier particles were more attracted to the star and eventually migrated closer to the center of the disk, giving rise to the rocky bodies of the inner solar system - Mercury, Venus, Earth and Mars, containing large amounts of silicon and iron. The problem is that these solid particles "stick" to each other badly - so much so that the birth of whole planets from them requires some kind of explanation.
In an article published by The Astrophysical Journal Letters, Alexander Hubbard of the American Museum of Natural History in New York draws attention to the young star FU Orion. In 1936, this large yellow star flared hundreds of times brighter than usual - and continues to glow like this to this day. It is assumed that additional radiation feeds the material of the gas and dust disk, which the star absorbs. Other stars are known that behave in the same way - but what if the young Sun also passed through such a period during the formation of its planets?
Hubbard concludes that only then could the solar system become what it has become. The most powerful radiation led to the heating and partial melting of solid particles of iron and other substances, allowing the future rocky planets to quickly form from them. According to the scientist, if there were no temporary increase in the brightness of the star, such melting could only occur much closer to it. This could give rise to a more compact system with hot and unsuitable planets - such as Kepler-11, whose farthest of six planets is twice as close to the star as Earth.
By the way, Hubbard's hypothesis also explains the modest size of Mars. Its small value is usually associated with the attraction of matter from Jupiter, but another reason may be the distance to the Sun. Even when young and - temporarily - exceptionally bright, it did not emit strongly enough to melt large amounts of particulate matter as far away as Martian orbit today.