Tag: Earth

An “Elegant” New Theory on How Earth Became a Wet Planet

About 71 percent of the Earth’s surface is covered by water, and vast quantities of water are also locked up in minerals on and beneath the surface.  This image of Earth comes from NASA’s Earth Polychromatic Imaging Camera (EPIC) on NOAA’s Deep Space Climate Observatory (DSCOVR), orbits Earth from a distance of about 1 million miles away. (NASA)

One of the enduring puzzles of our planet is why it is so wet.

Since Earth formed relatively close to the sun,  planetary scientists have generally held that any of the water in the building blocks of early-forming Earth was baked out and so was unavailable to make oceans or our atmosphere.

That led to theories explaining the oceans and wet atmosphere of Earth as a later addition, brought to us by meteorites and comets formed beyond the solar system’s so-called “snow line,” where volatile compounds such as water can begin to condense into ice.

This snow line is a general area between Mars and Jupiter, and that means under this theory that our water would have had to come from awfully far away.   Further complicating this view is that the isotopic makeup of that distant water ice is somewhat different from much of the water on Earth.

Now, a new paper in the journal Science from Laurette Piani of  the Université de Lorraine and colleagues, argues that Earth’s water was simply acquired like most other of our materials, through accretion when the planet formed in the inner solar nebula.

To reach that conclusion, the group re-examined 13 meteorites of the parched type formed between Earth and the sun, and they found more than of enough hydrogen present to explain how Earth got so wet (wet for our solar system, that is.)

In fact, they extrapolated from their data that enough water was available in the nebular cloud  that accompanied the formation of our sun and formed those early meteorites — called enstatite chondrites — to create three times as much water as our oceans hold.

 

 

New measurements of enstatite chondrites indicate that water could have been primarily acquired from Earth’s building blocks. Additional water was delivered to Earth’s early oceans and atmosphere by water-rich material from comets and the outer asteroid belt. (Science)

“Our discovery shows that the Earth’s building blocks might have significantly contributed to the Earth’s water and that hydrogen bearing material was present in the inner solar system at the time of the Earth and rocky planet formation, even though the temperatures were too high for water to condense,'” Piani told me.… Read more

On Super-Earths, Sub-Neptunes and Some Lessons They Teach

Part 2 of 2

The Kepler-452 system compared alongside the Kepler-186 system and our solar system. Kepler-186 is a miniature solar system that would fit entirely inside the orbit of Mercury. The size of the habitable zone of star Kepler-452, considered one of the most “Earth-like” exoplanets found so far, is nearly the same as that of our sun. “Super-Earth” Kepler-452b orbits its star once every 385 days. (NASA Ames/JPL-CalTech/R. Hurt)

The Kepler-452 system compared alongside the Kepler-186 system and our solar system. Kepler-186 is a miniature solar system that would fit entirely inside the orbit of Mercury. The size of the habitable zone of star Kepler-452, considered one of the most “Earth-like” exoplanets found so far, is nearly the same as that of our sun. “Super-Earth” Kepler-452b orbits its star once every 385 days. (NASA Ames/JPL-CalTech/R. Hurt)

 

With such a large proportion of identified exoplanets in the super-Earth to sub-Neptune class, an inescapable question arises: how conducive might they be to the origin and maintenance of life?

So little is actually know about the characteristics of these planets that are larger than Earth but smaller than Neptune (which has a radius four times greater than our planet) that few are willing to offer a strong opinion.

Nonetheless, there are some seemingly good reasons to be optimistic, about the smaller super-Earths in particular. And there are some seemingly good reasons to be pessimistic –many appear to be covered in a thick layer of hydrogen and helium gas, with a layer of sooty smog on top, and that does not sound like an hospitable environment at all.

But if twenty years of exoplanet hunting has produced any undeniable truth, it is that surprising discoveries are a constant and overturned theories the norm. As described in Tuesday’s post, it was only several years ago that results from the Kepler Space Telescope alerted scientists to the widespread presence of these super-Earths and sub-Neptunes, so the fluidity of the field is hardly surprising.

One well-respected researcher who is bullish on super-Earth biology is Harvard University astronomy professor Dimitar Sasselov. He argues that the logic of physics tells us that the “sweet spot” for planetary habitability is planets from the size of Earth to those perhaps as large as 1.4 Earth radii. Earth, he says, is actually small for a planet with life, and planets with a 1.2 Earth radii would probably be ideal.

I will return to his intriguing analysis, but first will catalog a bit of what scientists have detected or observed so far about super-Earths and sub-Neptunes. As a reminder, here’s the chart of Kepler exoplanet candidate and confirmed planets that orbit G, K and M main sequence stars put together by Mission Scientist for the Kepler Space Telescope Kepler Natalie Batalha.

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Kepler exoplanets candidates, both confirmed and unconfirmed, orbiting G, K, and M type main sequence stars, by radii and fraction of the total.

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