Rosetta’s Comet Contains Ingredients of Life

Rosetta’s Comet Contains Ingredients of Life

Ingredients regarded as crucial for the origin of life on Earth have been discovered at the comet that ESA’s Rosetta spacecraft has been probing for almost two years.

They include the amino acid glycine, which is commonly found in proteins, and phosphorus, a key component of DNA and cell membranes.

Scientists have long debated the important possibility that water and organic molecules were brought by asteroids and comets to the young Earth after it cooled following its formation, providing some of the key building blocks for the emergence of life.

While some comets and asteroids are already known to have water with a composition like that of Earth’s oceans, Rosetta found a significant difference at its comet – fuelling the debate on their role in the origin of Earth’s water.

But new results reveal that comets nevertheless had the potential to deliver ingredients critical to establish life as we know it.

Rosetta’s comet contains ingredients for life.

Amino acids are biologically important organic compounds containing carbon, oxygen, hydrogen and nitrogen, and form the basis of proteins.

Hints of the simplest amino acid, glycine, were found in samples returned to Earth in 2006 from Comet Wild-2 by NASA’s Stardust mission. However, possible terrestrial contamination of the dust samples made the analysis extremely difficult.

Now, Rosetta has made direct, repeated detections of glycine in the fuzzy atmosphere or ‘coma’ of its comet.

“This is the first unambiguous detection of glycine at a comet,” says Kathrin Altwegg, principal investigator of the ROSINA instrument that made the measurements, and lead author of the paper published in Science Advances today.

“At the same time, we also detected certain other organic molecules that can be precursors to glycine, hinting at the possible ways in which it may have formed.”

The measurements were made before the comet reached its closest point to the Sun – perihelion – in August 2015 in its 6.5 year orbit.

The first detection was made in October 2014 while Rosetta was just 10 km from the comet. The next occasion was during a flyby in March 2015, when it was 30–15 km from the nucleus.

Glycine was also seen on other occasions associated with outbursts from the comet in the month leading up to perihelion, when Rosetta was more than 200 km from the nucleus but surrounded by a lot of dust.

“We see a strong link between glycine and dust, suggesting that it is probably released perhaps with other volatiles from the icy mantles of the dust grains once they have warmed up in the coma,” says Kathrin.

Glycine turns into gas only when it reaches temperatures just below 150°C, meaning that usually little is released from the comet’s surface or subsurface because of the low temperatures. This accounts for the fact that Rosetta does not always detect it.

“Glycine is the only amino acid that is known to be able to form without liquid water, and the fact we see it with the precursor molecules and dust suggests it is formed within interstellar icy dust grains or by the ultraviolet irradiation of ice, before becoming bound up and conserved in the comet for billions of years,” adds Kathrin.

Another exciting detection made by Rosetta and described in the paper is of phosphorus, a key element in all known living organisms. For example, it is found in the structural framework of DNA and in cell membranes, and it is used in transporting chemical energy within cells for metabolism.

“There is still a lot of uncertainty regarding the chemistry on early Earth and there is of course a huge evolutionary gap to fill between the delivery of these ingredients via cometary impacts and life taking hold,” says co-author Hervé Cottin.

“But the important point is that comets have not really changed in 4.5 billion years: they grant us direct access to some of the ingredients that likely ended up in the prebiotic soup that eventually resulted in the origin of life on Earth.”

“The multitude of organic molecules already identified by Rosetta, now joined by the exciting confirmation of fundamental ingredients like glycine and phosphorous, confirms our idea that comets have the potential to deliver key molecules for prebiotic chemistry,” says Matt Taylor, ESA’s Rosetta project scientist.

“Demonstrating that comets are reservoirs of primitive material in the Solar System and vessels that could have transported these vital ingredients to Earth, is one of the key goals of the Rosetta mission, and we are delighted with this result.”


Loop Quantum Gravity Theory Offers Glimpse Beyond the Event Horizon

Loop Quantum Gravity Theory Offers Glimpse Beyond the Event Horizon

Black holes are still very mysterious celestial bodies which, according to the majority of physicists, do not, however, escape the laws of thermodynamics. As a result, these physical systems possess an entropy though no real agreement has been reached about the microscopic origin of this propriety and how it should be calculated. A SISSA/Max Planck Institute (Potsdam) group has achieved important results in this calculation by applying a new formalism (Group Field Theory) of Loop Quantum Gravity (LQG), a very popular approach in the area of quantum gravity. The result is consistent with the famous Bekenstein/Hawking law, whereby the entropy of a black hole is proportional to a quarter of its surface area, while it avoids many of the assumptions and simplifications of previous LQG theory attempts. Additionally, it lends support to the holography hypothesis, whereby the black hole that appears three-dimensional can be mathematically reduced to a two-dimensional projection.

In principle, nothing that enters a black hole can leave the black hole. This has considerably complicated the study of these mysterious bodies on which generations of physicists have debated ever since 1916, the year their existence was hypothesized as a direct consequence of Einstein’s Theory of Relativity. There is, however, some consensus in the scientific community on the fact that black holes possess an entropy, because their existence would otherwise violate the second law of thermodynamics. In particular, Jacob Bekenstein and Stephen Hawking have suggested that the entropy – which we can basically consider a measure of the inner disorder of a physical system – of a black hole is proportional to its area and not to its volume, as would be more intuitive. This assumption also gives rise to the “holography” hypothesis of black holes, which (very roughly) suggests that what appears to be three-dimensional might in fact be an image projected onto a distant two-dimensional cosmic horizon just like a hologram which, despite being a two-dimensional image, appears to us as three-dimensional.

As we cannot see beyond the event horizon (the outer boundary of the back hole), the internal microstates that define its entropy are inaccessible: so how is it possible to calculate this measure? The theoretical approach adopted by Hawking and Bekenstein is semiclassical (a sort of hybrid between classical physics and quantum mechanics) and introduces the possibility (or necessity) of adopting a quantum gravity approach in these studies, in order to obtain a more fundamental comprehension of the physics of black holes.

Planck’s length is the (tiny) dimension at which space-time stops being continuous as we see it, and takes on a discrete graininess made up of quanta, the ”atoms” of space-time. The Universe at this dimension is described by quantum mechanics. Quantum gravity is the field of inquiry that investigates gravity in the framework of quantum mechanics: this force is a phenomenon that has been very well described within classical physics, but it is unclear how it behaves at the Planck scale.

Daniele Pranzetti and colleagues, in a new study published in Physical Review Letters, present an important result obtained by applying a second quantization formulation of Loop Quantum Gravity (LQG) formalism. LQG is a theoretical approach within the problem of quantum gravity, and Group Field Theory is the “language” through which the theory is applied in this work.

“The idea at the basis of our study is that homogenous classical geometries emerge from a condensate of quanta of space introduced in LQG in order to describe quantum geometries” explains Pranzetti. “This way, we obtained a description of black hole quantum states, suitable to describe also ‘continuum’ physics, that is, the physics of space-time as we know it”.

Condensates, quantum fluids and the universe as a hologram

A “condensate” is a collection of ‘atoms’ – in this case space quanta – all of which share the same properties so that, even though there are huge numbers of them, we can nonetheless study their collective behavior simply, by referring to the microscopic properties of the individual particle. So now the analogy with classical thermodynamics seems clearer: just as fluids at our scale appear as continuous materials despite their consisting of a huge number of atoms, similarly, in quantum gravity, the fundamental constituent atoms of space form a sort of fluid, that is, continuous space-time. A continuous and homogenous geometry (like that of a spherically symmetric black hole) can, as Pranzetti and colleagues suggest, be described as a condensate, which facilitates the underlying mathematical calculations, keeping in account an a priori infinite number of degrees of freedom.

“We were therefore able to use a more complete and richer model compared with what done in the past in LQG, and obtain a far more realistic and robust result”, continues Pranzetti. “This allowed us to resolve several ambiguities afflicting previous calculations  due to the comparison of these simplified LQG models with the results of semiclassical analysis, as carried out by Hawking and Bekenstein”.  Another important aspect of Pranzetti and colleagues’ study is that it proposes a concrete mechanism in support to the holographic hypothesis, whereby the three-dimensionality of black holes could be merely apparent: all their information could be contained on a two-dimensional surface, without having to investigate the structure of the  inside (hence the link between entropy and surface area rather than volume).

The other two authors of the study are Daniele Oriti, of the Max Planck Institute for Gravitational Physics in Potsdam, Germany, and Lorenzo Sindoni, former SISSA research fellow, now also at the Max Planck Institute in Potsdam.