Sunday, 29 July 2012

Astrophysics stuff from the week 23-29/7/12

[video] They've already put a probe on Titan - a moon of Saturn (built by a team working at the University of Kent) - now ESA's going to put a lander on the Moon, which will arrive in 2018
The best thing about this article, is the video simulation of the project, from launch to finish.

[video] 'A taste of solar maximum'
As we approach solar maximum, in 2013, we've been getting tastes of what the Sun can do.
On the 12th July, a CME (Coronal Mass Ejection) occurred; on the 14th July, it reached Earth, compressing the Earth's atmosphere, exposing satellites to radiation, which fortunately did no harm.
As the CME's wake washed across Earth, aurorae lit the atmosphere up, from Pole to Pole, in red, green, blue, and purple.

What causes the colours of aurorae?
Low aurorae shine in green, the next highest shine in red, and the highest shine in blue. When aurorae involve excitation of atoms at multiple heights, the combination causes differing hues, such as this beautiful purple.

The orbital line of planets matches up to their star's spin on its axis (orbits its equator) varyingly, according to their size.
Hot jupiters (large, gassy planets) are far more likely to orbit their stars at a wacky angle, close up to their host star -- smaller more Earth-massed planets, are more likely to orbit in line with their star's equator.
This means that although there are plenty of uninhabitable planets out there, the ones that are small enough to be like Earth, and orbit far enough out to be in the 'Goldilocks zone', are more likely than just random variable alignment.

When planets form, they accrete out of the proto-planetary disk into blobs which then stratify to have a core of metal, a mantle of silicate surrounding it, and a crust on the surface.
For this differentiation to happen, heating is required. The energy that does this comes from radiactive elements with low half-lives (and therefore high activity), which thereby emit energy quickly, into the surrouding rocks.
Also, from separation enthalpies, when dense metals separate from silicates, and the energy of impacts wit hother objects.
Earth and the Moon's mantles formed more than 4.4 billion years ago, and Mars' formed more than 4.5 billion years ago.
Highly siderophile (iron-loving) elements, such as osmium, iridium, ruthenium, platinum, palladium, and rhenium, are segregated to the core (where a lot of the iron is), but...
the mantles of the Earth, Moon, and Mars, contain more of this siderophiles than expected, meaning they must have been supplied since stratification.
The source: diogenites -- fragments of asteroids, that were pulled to Earth, and supplied the extra siderophile elements, before the formation of the crust locked them out.
The diogenites found scattered across Earth's surface today meean geophysicists reckon there was a window of just 2 or 3 million years in which this doping could happen.

A huge storm of comets has been seen around star Eta Corvi, similar to what would have been seen around our own star, when our solar system was 600-800 million years old.
Some of these comets are inevitably slingshotted by the outer planets, outward, and in toward the inner planets, providing water and elements to seed, for example, the Earth.

“After the discovery we were very surprised that the pulsar was initially only visible until September 2009. Then it seemed to suddenly disappear.”
Only a complex follow-up analysis enabled an international team led by Pletsch to solve the mystery of pulsar J1838-0537: it did not disappear, but experienced a sudden glitch after which it rotated 38 millionths of a Hertz faster than before. “This difference may appear negligibly small, but it’s the largest glitch ever measured for a pure gamma-ray pulsar,” explains Allen. And this behaviour has consequences.
“If the sudden frequency change is neglected, then after only eight hours, a complete rotation of the pulsar is lost in our counting, and we can no longer determine at which rotational phase the gamma-ray photons reach the detector aboard Fermi,” adds Pletsch. The “flashing” of the neutron star then disappears. If the researchers take the glitch into account and correct the change in rotation, the pulsar shows up again in the observational data.

"This scene lies between Mercury’s Moody and Amaral craters, spanning an area of about 1200 km (745 miles). The patch of dark blue Low Reflectance Material (LRM) in the upper left of the image and the bright rayed crater on the right make this a diverse view of Mercury’s surface. Note the curious small, dark crater just below the bright rayed crater on the right."