Mercury's core is huge for the planet's size, about 85% of the planetary radius, even larger than previous estimates. The planet is sufficiently small that at one time many scientists thought the interior should have cooled to the point that the core would be solid. However, subtle dynamical motions measured from Earth-based radar combined with parameters of the gravity field, as well as observations of the magnetic field that signify an active core dynamo, indicate that Mercury's core is at least partially liquid.Moving out ...
|Venus in transit|
(I find Eratosthenes' calculation of the Earth's size -- more than two millennia ago -- equally amazing. Geometry really is useful -- and it's handy to be reminded that geometry means something: Earth measurement.)
And that's a good segue to astronomical news of Earth. We'll begin with what is not quite a finding, but is nonetheless interesting: the implications of a simulation. To wit: "Earth Must Have Another Moon, Say Astronomers." As in:
The way our planet temporarily captures asteroids suggests Earth should have at least one extra moon at any one time.Speaking of our home world, which has been home to life for about, oh, four billion years ... there's long been a mystery. Conventional stellar evolution theory has it that the sun has become more luminous with age. Calculations based on that theory show that good ole Sol started out only 70% as bright as we measure it today. So why wasn't the early Earth a snowball, rather than -- luckily for us -- a cradle of life? Really ferocious greenhouse effect? The geological record doesn't support that premise. So, from io9, see speculations that "A super-sized Sun could explain why Earth didn’t freeze to death long ago."
|PHAs in orange. Earth's orbit in gre|
Off Earth (but still in the neighborhood), "A New Count of Potentially Hazardous Asteroids." PHA, for short.
How interesting are asteroids? Very (in one blogger's opinion, anyway). The DAWN probe's observations suggest that "huge asteroid Vesta is a battered protoplanet left over from the solar system's early days."
To group asteroid stories, I jumped over Mars. (Take that cow who merely jumped over the moon.) So in Part II (in about a week) we'll explore outward, starting with Mars.