Another Earth?

We just get used to seeing those magnificent images of Pluto, then we find an attempt to upstage it with the discovery from the Kepler space telescope of a planet circling a star (Kepler 452) of similar size to our sun at a similar distance to us. More specifically, it is 1.046 times as far from a star that is 1.037 times the mass of our sun. The star is approximately 6 Gy old (our sun is approximately 4.56 Gy old) and it has a moderately higher metallicity than our star. In the absence of a greenhouse effect, it would have an average temperature of about minus 8 degrees Centigrade, which is a little warmer than Earth would be. The orbital eccentricity is quite low, although because the discovery was by transiting, this is a little less certain. So far there is only one planet known, but we can draw little from that. Look up the number of times we see a transit of Venus, and that is in our system, and solar systems are more or less in a plane, at least for significant planets.

So, what do we know about such a planet? The short answer is, not much more than what is listed above. However, if I assume that my theory of planetary formation is correct, as outlined in my ebook “Planetary Formation and Biogenesis”, this is most likely to be an Earth equivalent. The alternatives would be an ice-world, such as something dislodged from the Jupiter orbits, but this is less likely because the eccentricity would be expected to be higher. If it were a rocky planet, as an earth equivalent, it would have formed in the same way Earth did, and should have granitic continents, and a good layer of water. Here I have the first uncertainty. According to this theory, the first stage of the accretion of a rocky planet involves small rocky material being cemented together with material separated during the hot phase of stellar accretion, and it is this cement that separates early and forms the continents. When the planet gets big enough, it accretes everything by gravity, and this material mainly forms basalt. How much basalt depends on how much rock is around, how much water is available to set cement, and how long it grows. This latter length of time is dependent on how soon the star expels the accretion dust, and our star apparently did this rather quickly. This rocky planet is somewhat bigger than Earth, so it may have a greater fraction of basalt. Venus has a higher fraction of basalt, presumably because it grew later, in part because the temperatures were hotter and it is harder to set the cement, which is why it is smaller than Earth.

Materials such as nitrogen and carbon (essential for life) are accreted as solids, and become volatile on reaction with water within the planet. (In my view, it is because in reactions involving water, hydrogen reacts faster than deuterium, which explains why Venus has high levels of deuterium in the atmosphere.) So, what about this planet? Because we don’t know how long the star stayed accreting, I cannot predict how much water would be there, but there should be a reasonable amount, as apart from hydrogen and helium, water is one of the most common ingredients of the material that forms stars, and it accreted at a similar temperature. Similarly, the nitrogen and the carbon are dependent on the temperatures reached in forming the star, and since the star is about the same size as sol, the planet should have accreted similar amounts of carbon and nitrogen.

So, what would it be like? I would expect continents just like those on Earth but because the gravitational field on the surface would be stronger (because the planet has more mass, being roughly twice as big as Earth) the mountains would not be as tall. The climate would be similar, but perhaps a bit warmer (because the star is slightly hotter and bigger) and trees would be shorter and thicker. The distribution of continents is important, because if this is unsatisfactory, even if there are large seas, there can still be a lot of desert.

Accordingly, I think the prospects for life there are quite strong. So, why do we not see signs of intelligence, given that it has had a lot more time to evolve? There can be many reasons. If the star is 1.5 billion years older, it has possibly formed and died out. It could be there, but is somewhat disinterested in us. It could be studying us. There is no way of knowing, short of going there, and that is not going to happen any time soon.