There's No Place Like Earth

A survey of known exoplanets finds no real estate as valuable as Earth.

The most Earth-like exoplanet has come under fire. “Radiation blasts leave most Earth-like planet uninhabitable,” Science Daily says of Kepler 438b, thought before now to be an Earth twin. “Energy released by each superflare equivalent to 100 billion megatons of TNT.” Its real estate value just plummeted. “Regularly occurring every few hundred days, the superflares are approximately 10 times more powerful than those ever recorded on the sun,” the article says. HPF 438 required, but too late; the star’s activity has likely stripped off the planet’s atmosphere. That’s a nasty habit of red dwarfs like Kepler 438b’s angry parent.

Maybe relocating to a neighborhood around a sun-like star would help. Not for a star announced by PhysOrg, though: The “hot Jupiter around a sun-like star” would likely fling any Earth-like exoplanet out into outer darkness.

On The Conversation, Andrew Norton of The Open University analyzes “The five most Earth-like exoplanets (so far).” Number 1 on his list is Kepler 438b, but we can cross off that overcooked one. (2) Gliese 667Cc is likely on the same barbie, orbiting a red dwarf in a triple star system. (3) Kepler 442b is in a nicer neighborhood, but it is probably over twice the mass of Earth and orbits a cooler star. Those factors tend to have ripple effects. (4) Kepler 62e and 62f are over 30 times the mass of Earth, even though they exist in the star’s habitable zone. (5) Kepler 452b seems more congenial, possibly 1.6 times the radius of Earth (though estimated 5 times the mass), with temperature from -4°F to 50° F. Despite these close calls, Norton is not optimistic about these, or any of the first 1,978 exoplanets examined so far.

As we have seen, even the most Earth-like of these planets may not be able to support life due to the activity of its star, which can be very different to our sun. Others have a size or temperature that is slightly on the extreme side.

Planet-hunting is still in the early stages, however. There are thousands more “candidate” exoplanets, and more are bound to be identified by upcoming spacecraft. An infographic posted by Alexandra Witze for Nature shows the range of exoplanets by size, orbital period and radius, giving some indication of how likely they are to be habitable. A couple of dozen exoplanets fall in the Goldilocks zone (possibly just right for water), but the whole suite of habitability factors must be taken into consideration: obliquity, eccentricity, potential for superflares from its star, magnetic field, atmosphere, and much more (see list in 8/10/14 commentary).  For the time being, Earth remains uniquely suitable not only for life, but for complex life, ecosystems and civilizations of sentient beings.

Planet Formation

Do scientists know how planets form? The media are buzzing about a possible planet forming before our eyes. “First photo of planet in making captured,” PhysOrg announces. “Planet formation caught in the act,” Sid Perkins writes for Science. “Growing planet brought to light,” Nature boasts. “A planet is born – and we have the pictures to prove it” touts Forbes Magazine. That’s a lot of hype over some hydrogen-alpha spectral lines coming from a “protoplanet candidate” named LkCa 15. But gaps in dust disks do not always signal the presence of planets, Astrobiology Magazine warns.

If you look at the picture, there’s a whole lot of interpreting going on. According to the paper in Nature, hot hydrogen gas (10,000 Kelvins) appears to be “falling deep into the potential well of an accreting protoplanet,” according to the Editors, showing the “unambiguous formation of a planet” – the first out of all the exoplanets known so far. Despite their confidence that the H-alpha and infrared data “show that we are unambiguously witnessing planet formation,” and their trust in accretion theory,* they are not able to say for sure whether the observed infalling gas (if that’s what’s happening) is steady or stochastic. At best, multiple giant planets are involved—nothing Earthlike.

^{*They are not witnessing accretion. “Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful,” they admit, and they merely state that the H-alpha and infrared data are “best explained” by “an accretion disk model.”}

THERE’S NO PLACE LIKE EARTH

^{A song by David Coppedge}

1.  There’s no place like Earth;

Only God could give it birth.

Look out into space: you’ll never find such a place

So filled with His grace.

There’s no place like Earth;

Who could tell just what it’s worth?

A soul would be blind to say it wasn’t designed

With living in mind.

So fear the Lord your God,

And give Him glory,

And worship Him who made the Earth.

His riches so free,

On the land, and in the sea;

The works of His hand

Are part of His master plan,

Especially man.

2. But there’s there’s no place like Earth

Where God’s servants will not serve,

His laws won’t obey, His love won’t display,

His works won’t preserve.

But God’s still on the throne;

His word shall stand alone,

The hour has come, the judgment’s begun,

His will shall be done.

So fear the Lord your God,

And give Him glory,

And worship Him who made the Earth.

The Earth shall be filled

With the knowledge of His will.

His glory shall be

As waters cover the sea

Revealed in the Earth.

3. There’s no place like Earth,

Where a virgin brought to birth

A Savior, a son,

The promised ransoming One,

And hope was begun.

He lived among men,

Healed the sick, forgave their sin,

And dying displayed His power to save:

He rose from the grave!

So fear the Lord your God,

And give Him glory,

And Worship Him who made the Earth.

Across time and space

Who could find such wondrous grace?

Where justice met love

With such great drama thereof—

There’s no place like Earth!