article_snippet: But Mercury and the sun also reveal certain characteristics of Earth and the other rocky planets, which would have formed later than the outer ones from a depleted supply of material.
article_snippet: Before this this’s plausible that rocky planets with deep atmospheres would have been forming close to the sun from a dense disk of gas and dust on their way to becoming typical ‘super-Earths’ like so many of the planets astronomers have found around other stars.
article_snippet: A second generation of inner planets would have formed later from the depleted material that was left behind, consistent with evidence that our solar system’s inner planets are younger than the outer planets.
article_snippet: The resulting inner planets - Mercury, Venus, Earth and Mars - are also less massive and have much thinner atmospheres than would otherwise be expected.
article_snippet: One of the predictions of our theory is that truly Earth-like planets - with solid surfaces and modest atmospheric pressures - are rare,’ added Professor LaughlinProfessor Laughlin.
article_snippet: The rocky inner planets of the ‘typical’ planetary system, with relatively low masses and thin atmospheres, may turn out to be fairly anomalous.