"Mega Earth" discovered

[omega_tyrant]

A new class of exoplanet has been discovered. 17 times Earth's mass, yet still rocky. If we use this in the setting, what type of life/ environment could you see this type of world having?

http://news.discovery.com/space/alien-li...140602.htm

[radtech497]

A new class of exoplanet has been discovered. 17 times Earth's mass, yet still rocky. If we use this in the setting, what type of life/ environment could you see this type of world having?

http://news.discovery.com/space/alien-li...140602.htm

A few quick BOTE calculations gives a tide-locked planet with a day and year of 45 days (semi-major axis = 0.239 AU), a surface temperature of at least 750 K at the substellar point (cooling to at least 500 K before reaching the terminator), high surface winds blowing in from the "dark side" toward the substellar point, a mean surface gravity of 3.211 g, and mostly (if not totally) cloud-free skies. If there is any liquid on the surface, it is likely to be liquid sulfur. Depending on the thickness of the atmosphere, the "dark side" is probably much cooler than the starlit hemisphere.

This environment is inhospitable to carbon-based life-forms composed of proteins and other Terragen biomolecules, which would decompose at those temperatures. However, silicon-based life might be possible there. [IIRC, my "sandbox" has a silicone-based species living under similar thermal conditions]

Just a thought or three,

Radtech497

[stevebowers]

Let's see. Assume it has a radius of 2.31 Earths, (the lower bound) and a mass of 19 Earths, (the upper bound), then it has a surface gravity of 3,58 gees and an escape velocity of 32.1km/s.

The atmosphere on a planet like that would retain hydrogen, even at the planet's likely average temperature of 485K. Looking at the density, at 8.5g/cm3 this is more dense than Earth, but actually less dense than a ball of Earth-like material at that mass (compression would raise the density of such a ball to 9.1g/cm3). So this planet is made of material less dense than Earth's composition.

What does this mean? I think it means it has a moderately thick atmosphere and probably a layer of hot or supercritical water; a hot-water world, in fact. Alternately it might have no metallic core and be predominately silicates, with a hot dry atmosphere - but this seems less likely. Any other options? A massive carbon world?

[omega_tyrant]

Steve, I think you're right. I'm not quite sure why nobody presented a large water world as an option here.

[radtech497]

Many of the properties of Kepler-10c are dependent on the planet's formation history. For example, if the world formed in its current orbit, then the availability of water vapor would be minimal, leading to a hot, dry planet with a primarily hydrogen-helium reduced atmosphere (plus gases evolved from reactions with surface minerals or captured from the protoplanetary disk). Had it formed farther out and later migrated starward, then the fraction of volatiles would be enhanced, increasing the fractions of those gases in the resulting atmosphere. Even then, the atmosphere will be a reducing one, dominated by hydrogen and helium.

Assuming the surface temperature and pressure is below 647.096 K and 217.755 atmospheres (respectively), allowing for the presence of liquid water on the surface, the planet would have a high albedo on the daylit side, due to extensive cloud cover, and a much darker nightside where clouds precipitate in the (slightly) cooler temperatures (the atmosphere conducts heat between the hemispheres, so long as the surface pressure is greater than 0.1 atmosphere). If the water vapor is, instead, a supercritical fluid, then the skies will be cloudless and the albedo uniformly low on both hemispheres (there would be no bodies of liquid water on the surface).

Life on such a world, if it exists at all, would probably not be very similar to Terragen life. For one thing, the atmosphere is relatively anoxic, though the small fraction of atmospheric oxygen might, when multiplied by the ambient pressure, have a partial pressure similar to that found on Earth (if that were true, however, then nitrogen toxicity might be a problem). For another, in a reducing atmosphere, the biochemistry would be unlike that found in most terrestrial organisms.

Regardless of the biochemistry involved, any organisms would need to contend with the high temperatures, gravity (2.6 to 3.6 g, depending on the uncertainties), and atmosphere of their world. They might be flat, pancake-like creatures designed to minimize their body's volume while maximizing their surface area to better radiate heat. Others may take to the skies, drawing moisture from the humid atmosphere (in the case of a hot and humid world).

Due to the uncertainties in the properties of both the planet and its star, it is difficult to pin down what the planet's environment is actually like. A range of possible values can, however, be calculated fairly easily, from which a corresponding set of conditions can be surmised (depending on initial assumptions). Kepler-10c could, then, be anything from a lifeless version of Mercury (albeit much larger with a much thicker atmosphere of hydrogen and helium) to a larger, warmer version of Earth obscured on its daylit side by thick clouds of water vapor. Or anything in between.

Radtech497

[stevebowers]

I wonder what an organism evolved to live in a supercritical atmosphere might be like? The atmosphere would be denser than any gas we are familiar with, but less dense than liquid- perhaps a foam might be the closest analogy. Creatures might evolve to be foam-like themselves - or maybe like filmy jellyfish, or fractal aerial graptolites of some sort.

[stevebowers]

Something weird like this, perhaps...