An Easter Friday Reminder of the Shroud of Turin

In 1960 Willard Frank Libby was awarded the Nobel Prize for his method of using carbon-14 to find the age of objects ranging from ancient bows and arrows to trees buried in glacial ice. Since then, the technique of radiocarbon dating has been improved so that it can be used with much smaller samples—fractions of milligrams instead of the original 8 grams. This has made it less intrusive when dealing with precious art and in trying to figure out the authenticity of artefacts like the Shroud of Turin. Whereas, Libby modestly assumed that radiocarbon dating’s upper limit was 20 000 years old, it can currently estimate the age of objects as old as 55000 years old.

Carbon has 15 isotopes, of which only 3 are natural: ¹²C, ¹³C, ¹⁴C. The superscript refers to the sum of neutrons and protons in each atom. Any atom is characterized by its number of protons, so the trio of carbon’s isotopes ¹²C, ¹³C, ¹⁴C, have 6 protons each, but they contain 6, 7 and 8 neutrons, respectively. That last number seems to be too much for a nucleus to handle. Every 5730 ± 40 years, in half of ¹⁴C nuclei, a neutron transforms into a proton, an antielectron neutrino and a beta particle, becoming ¹⁴N in the process, the common isotope of nitrogen in the air. A beta particle is a highly energetic electron and is a form of radiation identical to what old “cathode ray” television sets and computer screens emitted from their long bulky bodies; it was blocked by lead (Pb) in the glass screen. The reason some ¹⁴C exists on earth is that neutrons released from violent cosmic ray-collisions in the Earth’s upper atmosphere cause a small portion of ¹⁴N in the air to become hydrogen and ¹⁴C.

This property of ¹⁴C has been very useful in dating old samples of bones, charcoal, seeds, wall paintings and in just about anything containing carbon.  While plants are still alive, through photosynthesis, they continuously absorb ¹⁴C from the small fraction of carbon dioxide which contains the isotope. This was first realized by Libby. Whether carbon dioxide contains ¹⁴C or the common ¹²C doesn’t affect the chemical properties of the vital gas. So plants can still use it to make glucose.

After organisms die, after bacterial decomposition, whatever ¹²C that remains behind does not undergo radioactive decay. Unlike ¹⁴C, ¹²C is a stable isotope. But ¹⁴C keeps transforming back into ¹⁴N. So the longer something has been dead, the less ¹⁴C it contains. The most efficient carbon-dating technique is accelerator mass spectrometry (AMS).

The ¹⁴C content is directly measured relative to the amount of ¹²C and to ¹³C present, which, like ¹²C, is also stable. From these ratios, the age of an object can be calculated. Unlike other methods, AMS does not measure the amount radiation emitted but determines the number of carbon atoms present in the sample and the age-dependent ratios. The 55000-year upper limit of radiocarbon-dating has only been reached in the past 15 years. As recently as 2008, the limit was a little less than half of that because sunspot activity affects the rate of cosmic rays reaching the earth, and hence the amount of ¹⁴C-formation in the atmosphere has not been constant. A calibration curve based on tree rings and their analyses takes the fluctuations into account. The improvement of the curve and the use of the AMS technique have been mainly responsible for giving the method more historical scope.

The Shroud of Turin is a  linen  cloth that Christian tradition associates with the crucifixion and burial of Jesus .   In 1988, scientists at three separate laboratories used carbon-14  to date samples from the Shroud to be from 1260 to1390 AD, coinciding with the first verified appearance of the shroud in the 1350s. Given that the burial of Jesus was in 30 or 33 AD, the evidence strongly suggests that the Shroud is not the real McCoy. 

35 years later, the 1988 tests continue to be debated. Is it because the conclusion clashed with longstanding belief about the cloth? About 10 years ago, Professor Christopher Ramsey of the Oxford Radiocarbon Accelerator Unit, one of three labs which carried out the research, said, “We’re pretty confident in the radiocarbon dates. There are various hypotheses as to why the dates might not be correct, but none of them stack up.” More recently, in 2019, Phillip Ball, former chief editor of Nature, wrote, “Nothing published so far on the shroud, including this paper, offers compelling reason to think that the 1989 study was substantially wrong – but apparently it was not definitive either.” Given ever-improving techniques and rigorous statistical analyses, the bar can always be raised.  But so far, more radiocarbon testing has not been given the OK by the Church. As Ball said, “As it stands, reticence looks more like fear of what further studies might reveal.”

Sources:

https://www.nature.com/articles/s43586-021-00063-w.pdf   2021

Nobel Prize Winners in Chemistry. Eduard Farber. Abelard-Schuman. 1962

https://www.acs.org/education/whatischemistry/landmarks/radiocarbon-dating.html

https://web.archive.org/web/20120107232043/http://blogs.telegraph.co.uk/news/tomchiversscience/100125247/the-turin-shroud-is-fake-get-over-it/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4853109/#b6-j92cur

https://www.chemistryworld.com/opinion/how-old-is-the-turin-shroud/3010341.article

Three Beautiful Effects of the Solar Wind

When astrologers randomly call our home, I tell them that astronomy is far more interesting than astrology. Whereas astrologers pretend they can predict people’s future, astronomers  realize that our individual fates are the combination of unpredictable contingencies and personal decisions.  Instead of relying on constellations as crystal balls, astronomers use observations, science and mathematics to predict the paths of heavenly bodies and to explain the behaviour of the universe.

For example, what is the solar wind? Heat from the sun’s 15 million ^oC core rises to its surface, but the atoms of the sun’s envelope are far less energetic; they’re only at 3300 ^oC. Then for reasons not fully understood, in the corona, the outermost layer of the sun’s atmosphere, the temperature shoots up again to millions of degrees. At such temperatures, electrons are stripped away from hydrogen atoms, leaving us with a mixture of positive and negative particles. This state of matter is called plasma, which also forms in a fluorescent bulb, except that there, electrons are not torn off by heat but by high voltage, and the electrons don’t come from hydrogen atoms but from those of noble gases and mercury.  The corona’s plasma is continually heated to the point that the Sun’s gravity can’t hold it down, so it leaks out into space. And that’s the origin of the solar wind.

_{The solar corona, the birthplace of the solar wind,as seen during a total solar eclipse on August 21, 2017  Credit: NASA/Aubrey Gemignani}

_{An artist’s depiction of the solar wind in the solar system. Credit: NASA}

Now let’s discuss 3 beautiful consequences of this phenomenon.

1. Aurora australis and Aurora borealis

The solar wind leaves the sun, travelling in all directions. Given that they move and are charged, solar wind particles create a magnetic field, which interacts with that of our planet. This is why the wind gets deflected towards Earth’s southern and northern extremities, where we get the beautifully colored displays of the aurora australis  and aurora borealis.  When deflected, solar wind particles collide with air’s most common atoms and molecules, and air’s electrons get excited to higher orbitals. During their return to their ground state orbitals, beautiful colors are emitted.  At what altitude the collision occurs indirectly influences the color produced. Why? It’s because above altitudes of 100 km, oxygen is monoatomic, and the orbitals of atoms are unlike those of the O₂ molecules they form, even when they bond with their own kind.

_{Image from aboard the International Space Station, shows the aurora australis as it streams across the Earth’s atmosphere as the station orbited over 400 km above the southern Indian Ocean. Notice the deep reds from atomic oxygen’s emissions at the highest altitude .}

Atomic oxygen’s brightest emissions are red and green. But the characteristic bright 630 nm “auroral red line” light occurs only at very high altitudes because below ~ 150 km, these atoms lose energy from collisions with nitrogen molecules.

_{Atomic oxygen’s emission spectrum}

In the absence of atomic oxygen, the green colors at lower altitudes(below 100 km) come from nitrogen molecules, which emit red, blue, and violet light. The interplay of molecular oxygen and nitrogen and their varying ratios at different altitudes cause the typical appearance of auroral colors.

2. The Colored Ion Tail Of Comets

The solar wind causes comets to grow tails as they approach the sun. Solar radiation ionizes gases that emanate from cometary surfaces, and the momentum of the solar wind knocks the ions behind the comet’s head. The tail’s blue color is from the emissions of its ions. The comet’s second coda, the dust tail, only reflects sunlight. Due to its more massive particles, this tail is not pushed back as much by the sun’s charged particle-stream, so it appears not in line with the sun and at an angle to the ion tail.

_{Comet Leonard was discovered by G.J. Leonard on Jan. 3, 2021. A piece of its tail was pinched off and carried away by the solar wind, seen in this image by Gerald Rhemann.}

Incidentally green comets have green comas, not green tails. In their case, the solar wind is not a factor in their formation. It is solar radiation that causes tenuous diatomic carbon from the surface of the coma to fluoresce.

3. Protection from Cosmic Rays.

_{By NASA/JPL-Caltech – https://photojournal.jpl.nasa.gov/figures/PIA22835_fig1.png, Public Domain, https://commons.wikimedia.org/w/index.php?curid=74978307}

The solar wind travels past all the planets to about three times the distance to Pluto before it gets stopped by the interstellar medium. This forms a giant bubble around the sun and its planets, known as the heliosphere. The heliosphere plays a crucial role because it acts as a giant shield, protecting Earth and all the planets from galactic cosmic radiation. On average, cosmic radiation is far more energetic than the solar wind because the former comes from the remnants of supernovas. The range of energies for solar wind particles is between 0.002 and 10 MeV per nucleon (with the lower end being far more common), but those of intergalactic cosmic rays are in the range of 1 MeV up to ~1000 MeV, based on Voyager I measurements.

There are such beautiful and important consequences of the fact that the sun does not have the gravitational strength to hold on to its own charged particles! Our faults may not lie in the stars, as Shakespeare’s Cassius said, but the star belonging to us, underlings, is the cause of some of the beauty we witness.

Sources

https://news.uchicago.edu/explainer/what-is-solar-wind#about

https://science.nasa.gov/heliophysics/focus-areas/heliosphere#

https://www.nasa.gov/image-feature/aurora-australis-lights-up-the-sky

https://www.windows2universe.org/earth/Magnetosphere/tour/tour_earth_magnetosphere_09.html