本帖最后由 人与自然 于 2014-1-13 23:41 编辑
这是每日邮报的一篇报道，G版有兴趣的话，不妨看一看
http://www.dailymail.co.uk/sciencetech/article-2538549/Could-super-Earths-climate-like-Giant-worlds-huge-amounts-water-hidden-beneath-surface.html
Massive alien worlds, known as ‘super-Earths’, could be more like our own planet than first thought.
Scientists now suggest that tectonically active super-Earths store most of their water in the mantle- the rocky part that makes up most of the volume and mass of the planet.
If this model proves to be true, it could mean that our galaxy is home to giant worlds that have a stable climate similar to Earth with potential to harbour life.
Super-Earths are giant planets that have between one and 10 times the mass of our world. About 40 per cent of all red dwarf stars - the most common stars in our galaxy - have a super-Earth orbiting in the habitable zone
Super-Earths are giant planets that have between one and 10 times the mass of our world.
About 40 per cent of all red dwarf stars – the most common stars in our galaxy - have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet.
Super-Earths are expected to have deep oceans that will overflow their basins and inundate the entire surface, but we show this logic to be flawed,’ said Nicolas Cowan, at Northwestern University in Illinois.
Terrestrial planets have significant amounts of water in their interior. Super-Earths are likely to have shallow oceans to go along with their shallow ocean basins.’
Scientists suggest that tectonically active super-Earths store most of their water in the mantle- the rocky part that makes up most of the volume and mass of the planet. The mantle in this image is shown in orange, the crust is in red and the core in yellow
WHAT ARE SUPER-EARTHS?
Super-Earths are giant planets that have between one and 10 times the mass of our world
About 40 per cent of all red dwarf stars – the most common stars in our galaxy - have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet.
The first super-Earths were discovered by Aleksander Wolszczan and Dale Frail in 1992.
In April 2007, a team in Switzerland announced the discovery of two new super-Earths around Gliese 581.
Both wereon the edge of the habitable zone around the star where liquid water may be possible on the surface.
In their model, the researchers treated the intriguing exoplanets like Earth, which has water in its mantle - the rocky part that makes up most of the volume and mass of the planet.
The rock of the mantle contains tiny amounts of water, which quickly adds up because the mantle is so large. Because of this, deep water cycle moves water between oceans and the mantle.
Water is constantly traded back and forth between the ocean and the rocky mantle because of plate tectonics, the researchers said. The division of water between ocean and mantle is controlled by seafloor pressure, which is proportional to gravity.
Accounting for the effects of seafloor pressure and high gravity are two novel factors in their model. As the size of the super-Earths increase, gravity and seafloor pressure also go up.
We can put 80 times more water on a super-Earth and still have its surface look like Earth,’ Professor Cowan said. ‘These massive planets have enormous seafloor pressure, and this force pushes water into the mantle.’
And it doesn’t take that much water to tip a planet into being a water world, the researchers said.
If Earth was one per cent water by mass, we’d all drown, regardless of the deep water cycle,’ Professor Cowan said.
The first super-Earths were discovered by Aleksander Wolszczan and Dale Frail in 1992. In April 2007, a team in Switzerland announced the discovery of two new super-Earths around Gliese 581 (pictured on the right)
The surface would be covered in water. Whether or not you have deep water cycle really matters for planets that are one one-thousandth or one ten-thousandth water.’
Professor Cowan admits that there are two major uncertainties in his model: that super-Earths have plate tectonics and the amount of water Earth stores in its mantle.
These are the two things we would like to know better to improve our model,’ he added. ‘Our model is a shot from the hip, but it’s an important step in advancing how we think about super-Earths.’
Researchers claim that Earth-sized planets can support life at least ten times further away from stars than previously thought
Last week, researchers in Scotland said that Earth-sized planets can support life at least ten times further away from stars than previously thought.
This means that cold rocky planets previously considered uninhabitable may be teeming with life beneath the surface.
Academics at the University of Aberdeen and University of St Andrews claim the definition of the ‘Goldilocks’ zone - the area of space around a star, or sun, which can support life – is flawed.They argue this definition fails to take into account life that can exist beneath a planet’s surface.
As you get deeper below a planet’s surface, the temperature increases, and once you get down to a temperature where liquid water can exist – life can exist there too,’ said Aberdeen University PhD student Sean McMahon.
In a galaxy of 200 billion stars of various types, scientists estimate there are 11 billion potentially habitable planets in the Goldilocks zone as it is currently defined.Factor in smaller, dimmer red dwarf stars, and the number of planets with mild temperatures similar to Earth rises to 40 billion. |
置顶卡
变色卡
千斤顶
显身卡
