Tag: Kepler Space Telescope (page 2 of 2)

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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Counting Our Countless Worlds

The Milky Way has several hundred billion stars, and many scientists are now convinced it has even more planets and moons. (NASA)

The Milky Way is home to several hundred billion stars, and many scientists are now convinced it has even more planets and moons. (NASA)

Imagine counting all the people who have ever lived on Earth, well over 100 billion of them.

Then imagine counting all the planets now orbiting stars in our Milky Way galaxy , and in particular the ones that are roughly speaking Earth-sized. Not so big that the planet turns into a gas giant, and not so small that it has trouble holding onto an atmosphere.

In the wake of the explosion of discoveries about distant planets and their suns in the last two decades, we can fairly conclude that one number is substantially larger than the other.

Yes, there are many, many billions more planets in our one galaxy than people who have set foot on Earth in all human history. And yes, there are expected to be more planets in distant habitable zones as there are people alive today, a number upwards of 7 billion.

This is for sure a comparison of apples and oranges. But it not only gives a sense of just how commonplace planets are in our galaxy (and no doubt beyond), but also that the population of potentially habitable planets is enormous, too.   “Many Worlds,” indeed.

 

The populations of exoplanets identified so far, plotted according to the radius of the planet and how many days it takes to orbit. The circles in yellow represent planets found by Kepler, light blue by using ground-based radial velocity, and pink for transiting planets not found by Kepler, and green, purple and red other ground-based methods. (NASA Ames Research Center)

The populations of exoplanets identified so far, plotted according to the radius of the planet and how many days it takes to orbit. The circles in yellow represent planets found by Kepler, light blue by using ground-based radial velocity, and pink for transiting planets not found by Kepler, and green, purple and red other ground-based methods. (NASA Ames Research Center)

It was Ruslan Belikov, an astrophysicist at NASA’s Ames Research Center in Silicon Valley who provided this sense of scale.  The numbers are of great importance to him because he (and others) will be making recommendations about future NASA exoplanet-finding and characterization missions based on the most precise population numbers that NASA and the exoplanet community can provide.

Natalie Batalha, Mission Scientist for the Kepler Space Telescope mission and the person responsible for assessing the planet population out there, sliced it another way. When I asked her if her team and others now expect each star to have a planet orbiting it, she replied: “At least one.”

 

Kepler-186f was the first rocky planet to be found within the habitable zone -- the region around the host star where the temperature is right for liquid water. This planet is also very close in size to Earth. (NASA Ames/SETI Institute/JPL-Caltech)

Kepler-186f was the first rocky planet to be found within the habitable zone — the region around the host star where the temperature is right for liquid water.

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The Exoplanet Era

Many, and perhaps most stars have solar systems with numerous planets, as in this artist rendering of Kepler 11. (NASA)

Throughout the history of science, moments periodically arrive when new fields of knowledge and discovery just explode.

Cosmology was a kind of dream world until Edwin Hubble established that the universe was expanding, and doing so at an ever-faster rate. A far more vibrant and scientific discipline was born. On a more practical level, it was only three decades ago that rudimentary personal computers were still a novelty, and now computer-controlled, self-driving cars are just on the horizon. And not that long ago, genomics and the mapping of the human genome also went into hyperspeed, and turned the mysterious into the well known.

Most frequently, these bursts of scientific energy and progress are the result of technological innovation, coupled with the far-seeing (and often lonely and initially unsupported) labor and insights of men and women who are simply ahead of the curve.

We are at another of those scientific moments right now, and the subject is exoplanets – the billions (or is it billions of billions?) of planets orbiting stars other than our sun.

The 20th anniversary of the breakthrough discovery of the first exoplanet orbiting a sun, 51 Pegasi B, is being celebrated this month with appropriate fanfare. But while exoplanet discovery remains active and planet hunters increasingly skilled and inventive, it is no longer the edgiest frontier.

Now, astronomers, astrophysicists, astrobiologists, planetary scientists, climatologists, heliophysicists and many more are streaming into a field made so enticing, so seemingly fertile by that discovery of the ubiquitousness of exoplanets.

The new goal: Identifying the most compelling mysteries of some of those distant planets, and gradually but inexorably finding ever-more inventive ways to solve them. This is a thrilling task on its own, but the potential prize makes it into quite an historic quest. Because that prize is the identification of extraterrestrial life.

The presence of life beyond Earth is something that humans have dreamed about forever – with a seemingly intuitive sense that there just had to be other planets out there, and that it made equal sense that some of them supported life. Hollywood was on to this long ago, but now we have the beginning technology and fast-growing knowledge to transform that intuitive sense of life out there into a working science.

The thin gauzy rim of the planet in foreground is an illustration of its atmosphere. (NASA’s Goddard Space Flight Center)

The thin gauzy rim of the planet in foreground is an illustration of its atmosphere.

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