Earth’s magnetic field maintained by Moon

The Earth’s magnetic field permanently protects us from the charged particles and radiation that originate in the Sun. This shield is produced by the geodynamo, the rapid motion of huge quantities of liquid iron alloy in the Earth’s outer core. To maintain this magnetic field until the present day, the classical model required the Earth’s core to have cooled by around 3 000 °C over the past 4.3 billion years. Now, a team of researchers from CNRS and Université Blaise Pascal, Clermont-Ferrand, France, suggests that, on the contrary, its temperature has fallen by only 300 °C. The action of the Moon, overlooked until now, is thought to have compensated for this difference and kept the geodynamo active. Their work is published on 30 march 2016 in the journal Earth and Planetary Science Letters.

More information from

http://www2.cnrs.fr/en/2735.htm

Historic First Observation of Gravitational Waves

On September 14, 2015 at 09:50:45 UTC, for the first time in history, the two detectors of the Laser Interferometer Gravitational-Wave Observatory both observed a transient gravitational-wave signal. Based on previous simulations of possible observations, the Ligo Collaboration Team was able to conclude that what their revolutionary experiment had detected was the result of two black holes merging 1 billion years ago.

Not since Galileo first turned a telescope on the night sky in 1609 have men taken such a profound step forward in observing the universe. But, whereas all telescopes since Galileo have been limited to using electromagnetic waves at one of it’s many frequencies, Ligo’s observations are based on an entirely different principal: it uses the distortions of space-time itself to make deductions about what caused these distortions. In this case, the movement and final fusion of two massive black holes.

The signal that they observed was a mere 20 millisecond blip.For the layman it might seem strange to think that the astronomers are not actually seeing anything concrete, but merely comparing a tiny observation with computer-based predictions and thereby coming to dramatic conclusions.

But this is the way that cutting-edge science works. It is exactly the same at CERN, for example, and many other physics experiments.

This is just the beginning of a revolution in astronomy. Know we know that laser interferometry really can detect gravitational waves, scientists will be pressing governments for the money to build more, bigger and more sophisticated observatories. And just as Galileo could never have predicted the discoveries to which his first observations have led us in the past 400 years, so we have no idea what incredible new things we are going to learn about the universe. But results are certainly not going to take another 400 years to arrive.

For more information see the following:

A summary of the scientific paper carrying the announcement:
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 

A podcast of a 30 minute BBC radio program on the day the discovery was announced http://www.bbc.co.uk/programmes/b06zj4dl

A BBC news story with useful images
http://www.bbc.co.uk/news/science-environment-35524440

A Scientific American Feature on the story
http://www.scientificamerican.com/article/gravitational-waves-discovered-from-colliding-black-holes1/

A Guardian newpaper story
https://www.theguardian.com/science/2016/feb/11/gravitational-waves-discovery-hailed-as-breakthrough-of-the-century?CMP=share_btn_link

 

Astronomers say a Neptune-sized planet lurks beyond Pluto

The solar system appears to have a new ninth planet. Today, two scientists announced evidence that a body nearly the size of Neptune—but as yet unseen—orbits the sun every 15,000 years. During the solar system’s infancy 4.5 billion years ago, they say, the giant planet was knocked out of the planet-forming region near the sun. Slowed down by gas, the planet settled into a distant elliptical orbit, where it still lurks today.

Source: Astronomers say a Neptune-sized planet lurks beyond Pluto | Science | AAAS

Could There Be a Crisis in Physics?

Great Podcast on Science Friday

If you don’t know Science Friday podcasts, this is a good place to start.

Physicist Lawrence Krauss and Nobel Laureates Frank Wilczek and Brian Schmidt discuss cosmic challenges.

Episode Download Link (24 MB): http://www.podtrac.com/pts/redirect.mp3/traffic.libsyn.com/sciencefriday/scifri201401312.mp3

Show Notes: http://www.podtrac.com/pts/redirect.mp3/traffic.libsyn.com/sciencefriday/scifri201401312.mp3

Podcast Feed: Science Friday Audio Podcast (http://www.npr.org/rss/podcast.php?id=510221)

Colossal star explosion detected – BBC News

Astronomers have seen what could be the most powerful supernova ever detected. The exploding star a super-luminous supernova, was first seen 3.8 billion light-years from Earth by the All Sky Automated Survey for SuperNovae (ASAS-SN) in June 2015 and is still radiating vast amounts of energy.

At its peak, the event was 200 times more powerful than a typical supernova, making it shine with 570 billion times the brightness of our Sun. Researchers think the explosion and ongoing activity have been boosted by a very dense, highly magnetised, remnant object called a magnetar.

This object, created as the supernova got going, is probably no bigger than a major city, such as London, and is likely spinning at a fantastic rate – perhaps a thousand times a second.

Source: Colossal star explosion detected – BBC News

Pebble accretion helps explain origin of gas giants in Solar System

It is widely held that the first step in forming gas-giant planets, such as Jupiter and Saturn, was the production of solid cores each with a mass roughly ten times that of the Earth. Getting the cores to form before the solar nebula dissipates (in about one to ten million years has been a major challenge for planet formation models. Recently models have emerged in which “pebbles” (centimetre-to-metre-sized objects) are first concentrated by aerodynamic drag and then gravitationally collapse to form objects 100 to 1,000 kilometres in size. These “planetesimals” can then efficiently accrete left-over pebbles and directly form the cores of giant planets. This model is known as “pebble accretion” theoretically, it can produce cores of ten Earth masses in only a few thousand years. Unfortunately, full simulations of this process show that, rather than creating a few such cores, it produces a population of hundreds of Earth-mass objects that are inconsistent with the structure of the Solar System. Here we report that this difficulty can be overcome if pebbles form slowly enough to allow the planetesimals to gravitationally interact with one another. In this situation, the largest planetesimals have time to scatter their smaller siblings out of the disk of pebbles, thereby stifling their growth. Our models show that, for a large and physically reasonable region of parameter space, this typically leads to the formation of one to four gas giants between 5 and 15 astronomical units from the Sun, in agreement with the observed structure of the Solar System.

References

http://www.nature.com/nature/journal/v524/n7565/full/nature14675.html
http://www.skyatnightmagazine.com/news/do-planetary-pebbles-solve-gas-giant-mystery
http://www.swri.org/9what/releases/2015/planetary-pebbles-building-blocks-large-planets.htm#.VnltGRWLTDc

Did Asteroid Impact or Volcanic Eruption Kill the Dinosaurs?

Compelling new evidence supports the hypothesis that the Chicxulub asteroid off the coast of the Yucatan Peninsula in Mexico 66 million years ago ignited volcanoes around the globe, most catastrophically in India, and that, together, these two planet-wide catastrophes caused the extinction of many land and marine animals, including the dinosaurs.

See more at: http://drexel.edu/now/archive/2015/October/Volcano-Asteroid/#.dpuf

Primordial O2 perhaps incorporated into comet during formation

The European Space Agency (ESA) announced today that its Rosetta spacecraft has made the first in situ detection of oxygen molecules outgassing from a comet, a surprising observation that suggests they were incorporated into the comet during its formation.

“We weren’t really expecting to detect O2 at the comet – and in such high abundance – because it is so chemically reactive, so it was quite a surprise,” says Kathrin Altwegg of the University of Bern, and principal investigator of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument, ROSINA.

Photolysis and radiolysis of water ice rejected

Her team explored various possibilities to explain the presence and consistently high abundance of Oand its relationship to water, as well as the lack of ozone. They first considering whether processes called photolysis and radiolysis of water ice could have converted ice into oxygen. They seemed the most likely sources, but finally they rejected these mechanisms.

“The instantaneous generation of O2 also seems unlikely, as that should lead to variable O2 ratios under different illumination conditions. Instead, it seems more likely that primordial O2 was somehow incorporated into the comet’s ices during its formation, and is being released with the water vapour today.”

Oxygen dissolved in water ice rejected

In one scenario, gaseous O2 would first be incorporated into water ice in the early protosolar nebula stage of our Solar System. Chemical models of protoplanetary discs predict that high abundances of gaseous O2 could be available in the comet forming zone, but rapid cooling from temperatures above –173ºC to less than –243ºC would be required to form water ice with O2 trapped on dust grains. The grains would then have to be incorporated into the comet without being chemically altered.

Possible warm molecular cloud

“Other possibilities include the Solar System being formed in an unusually warm part of a dense molecular cloud, at temperatures of 10–20ºC above the –263ºC or so typically expected for such clouds,” says Ewine van Dishoeck of Leiden Observatory in the Netherlands, co-author of the paper cited below.

“This is still consistent with estimates for the comet formation conditions in the outer solar nebula, and also with previous findings at Rosetta’s comet regarding the low abundance of N2.”

Radiolysis on dust grains also possible

Alternatively, radiolysis of icy dust grains could have taken place prior to the comet’s accretion into a larger body. In this case, the O2 would remain trapped in the voids of the water ice on the grains while the hydrogen diffused out, preventing the reformation of O2 to water, and resulting in an increased and stable level of O2 in the solid ice. Incorporation of such icy grains into the nucleus could explain the observed strong correlation with H2O observed at the comet today.

“Regardless of how it was made, the O2 was also somehow protected during the accretion stage of the comet: this must have happened gently to avoid the O2 being destroyed by further chemical reactions,” adds Kathrin.

“This is an intriguing result for studies both within and beyond the comet community, with possible implications for our models of Solar System evolution,” says Matt Taylor, ESA’s Rosetta project scientist.

References

Abundant molecular oxygen in the coma of 67P/Churyumov–Gerasimenko,” by A. Bieler et al is published in the 29 October 2015 issue of the journal Nature.

http://www.esa.int/Our_Activities/Space_Science/Rosetta/First_detection_of_molecular_oxygen_at_a_comet