Agreed. When you say two times larger, you have to specify whether you mean diameter or volume. Since the article also says you would be two times heavier, I assume it means twice the diameter. This is the interesting thing about gravity. Other things being equal (like density), the surface gravity of a planet is linear with respect to radius -- it increases in direct proportion to its radius. So even though a so-called "super Earth" that is twice Earth's diameter would have eight times its mass (2^3), it's surface gravity would "only" be twice Earth's.The author did not spent too much time on examining the science of this article. For example when size is mentioned, say, 2x to 10x that of earths, what does that mean? Is it radius or mass? The mass increases with the cube of the radius so a planet of 2 times earths radius would have a mass of 2³ = 8 times our mass, other things being equal which they aren't density being the primary variable. And surface area varies as the square of radius so 2 x the diameter would give 4 x the surface area. This is an awful lot bigger planet than that of earth and leaves lots of extra area for meteors to fall on maybe!
Gravity is not a linear function either since it depends on the mass of a sphere which is not a linear function of radius, as I mentioned above. Your weight will decrease by the square of the distance from the centre of a planet according to the formula F ~ Mm/r², where M = the mass of the planet and m = your mass, divided by the square of the distance from you to the centre of the planet. For your consideration, if you had two planets of equal mass but one was lower density then you would weigh less on the larger planet (the low density one) because you are farther from its centre.
This is not complex math but the article was way too simple and therefore wrong.
From the article "If the hypothetical super-Earth were even bigger, say, 10 times its current size, dramatic changes could start happening in Earth's interior. The iron core and liquid mantle would also be 10 times larger, "
This is also quite wrong. First, the problem of size. Again what does 10 x larger mean? If size were radius the core would be 10 times the radius all other things being equal again. But mass is proportional to the cube of radius as I mentioned in my first reply. This means the core would be 10³ = 1000 times more massive not 10! No small difference.
Galaxies like grains of sand on a beach, random nonintelligent variation in planets is sufficient to explain a rare but present incidence of a planet like Earth. It's perhaps the astonishment of being a Being on such a rarity would create the tendency of a sentient on such an object to hypothecate an intelligence of enormous powers as necessary to it's existence. I too am a sentient impressed by the wonder of it all. This only peripherally skirts G.R.A.P.E.S.As Edward pinpoints to the greater difference in mass, additionally it woud mean a greater gravity which would affect just about everything including the retention of poisonous gases like CO2, ammonia, sulfur and the likes. Ife would just not be supported at all! This planet exhibits precise specifications that supports life and evidences a Highly intelligence at work.