水星可能起源于稀有流星体

Around 4.6 billion years ago, the universe was a chaos ¹ of collapsing ² gas and spinning debris ³. Small particles of gas and dust clumped ⁴ together into larger and more massive meteoroids that in turn smashed together to form planets. Scientists believe that shortly after their formation, these planets -- and particularly Mercury -- were fiery ⁵ spheres of molten material, which cooled over millions of years. Now, geologists ⁶ at MIT have traced part of Mercury's cooling history and found that between 4.2 and 3.7 billion years ago, soon after the planet formed, its interior temperatures plummeted ⁷ by 240 degrees Celsius ⁸, or 464 degrees Fahrenheit ⁹. , ,They also determined ¹⁰, based on this rapid cooling rate and the composition of lava ¹¹ deposits on Mercury's surface, that the planet likely has the composition of an enstatite chondrite -- a type of meteorite ¹² that is extremely rare here on Earth. , ,Timothy Grove ¹³, the Cecil and Ida Green Professor of Geology in MIT's Department of Earth, Atmospheric ¹⁴, and Planetary Sciences, says new information on Mercury's past is of interest for tracing Earth's early formation. , ,"Here we are today, with 4.5 billion years of planetary evolution, and because the Earth has such a dynamic interior, because of the water we've preserved on the planet, [volcanism] just wipes out its past," Grove says. "On planets like Mercury, early volcanism is much more dramatic, and [once] they cooled down there were no later volcanic ¹⁵ processes to wipe out the early history. This is the first place where we actually have an estimate of how fast the interior cooled during an early part of a planet's history.", ,Grove and his colleagues, including researchers from the University of Hanover, in Germany; the University of Liége, in Belgium; and the University of Bayreuth, in Germany, have published their results in Earth and Planetary Science Letters.