Saturday, July 25, 2015

Is Kepler 452b Really A "Cousin" Of Earth?

Artist's depiction of relative sizes of Earth and Kepler 452 b (right)

NASA's Kepler space telescope has been on a veritable planet-finding binge with thousands of exoplanets discovered the past 6 years. Now, the latest addition announced is named Kepler 452b and has been described as "a cousin of Earth" and even "Earth 2.0". (Several other worlds have also briefly held that label until a better candidate appeared.)

Kepler was launched in 2009 and has nearly 5,000 potential exoplanets to its credit — worlds beyond our solar system..  Boulder-based Ball Aerospace & Technologies Corp. built Kepler for NASA and still runs its operations in space, with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado.

Why is Kepler 452 b being described as a "cousin of Earth"? For one thing its star has the same spectral class (G2) as the Sun. Second, it's at about the same distance that Earth is from the Sun. As one investigator put it: this is now the nearest system found to an Earth-Sun system.

Some of the other comparisons made are as follows:

Age:

Earth at 3.5 billion years old vs. Kepler 452b at 6 billion years old

Length of Year:

Earth 365 days, vs. Kepler 452b at 385 days (given its 5% further away from its sun)

Gravity:

Earth value = 1 g or 9.8 m/s/s  =  9.8 N/kg

Kepler 452b: 19.5 m/s/s  = 19.5  N/kg

Since it is 60% larger by volume and with 5 times more mass, so we use the equation:

g = G M / r2

So here: r =   5R  (where R is Earth's radius or 6.4 x 10 6   m)

And M =  5 M E  where  M E     =   6.0 x 10 24   kg

Bear in mind weight w = mg

The individual mass times the acceleration of gravity.

So if one has a mass of 100 kg then his weight on Earth will be:

w = m g = 100 kg (9.8 N/ kg) =  980 N

And on Kepler 452 b:

w = m g = 100 kg (19.5 N/ kg) =  1950 N

For those who opt for English- British units, a 100 pound woman on Earth would weigh nearly 200 pounds on Kepler 452b

The latter difference in terms of g is important, so we can't simply think - as some have - of just colonizing Kepler 452b one day without calculating the consequences.

Another problem I have with referring to 452b as a "cousin" of Earth is that we don't even know if it possesses an atmosphere. Although it is certainly at the right distance and has a large enough g-value to retain an atmosphere we don't know: a) if one exists, or (b) - if one does - if its conducive to life as we know it (say Nitrogen and CO2 instead of Nitrogen, Oxygen).

We also don't know what kind of axial tilt, if any, exists. Bear in mind Earth has a tilt of 23.5 degrees which moderates our seasons. Thus, now in northern hemisphere summer,  the temperatures are warm though Earth is further away from the Sun. For Kepler 452b, imagine the same tilt orientation but occurring at orbital perihelion as opposed to near aphelion. Given the central star is 20% warmer than our own Sun (since its luminosity is 10 % greater) according to stats disclosed, that means the temperatures on Kepler 452b would be almost unbearable for humanoid life- even though it's 5% further from its Sun than we are from ours.

All this means that there is as yet too little hard data to really assert Kepler 452b is a legitimate "cousin" of our Earth. By the exterior trappings of distance to its sun, relative size, etc.  the indications are promising-  but still not a slam dunk. It is better to say it is a likely cousin of Earth, provided other factors (such as breathable atmosphere) also turn out to be present.