Le cerveau humain est un organe feignant si on lui en donne les moyens : ChatGPT est l'outil parfait pour cela. Le prix de la productivité est-il l'abdication de notre propre conscience ?

Les plus grands mathématiciens se sont cassés les dents sur ce problème pendant plus d'un siècle, ils pensaient même qu'il était impossible de le résoudre.

Les plus grands mathématiciens se sont cassés les dents sur ce problème pendant plus d'un siècle, ils pensaient même qu'il était impossible de le résoudre.

Derrière chaque race, un cerveau ; et des manières très différentes de réfléchir.

More molecules and compounds vital to the origin of life have been detected in asteroid samples delivered to Earth by NASA’s OSIRIS-REx mission. The discovery strengthens the case that not only did life’s building blocks originate in space, but that the ingredients of RNA, and perhaps RNA itself, were brought to our planet by asteroids.

Two new papers in Nature Geoscience and Nature Astronomy describe the discovery of the sugars ribose and glucose in the 120 g of samples returned from the near-Earth asteroid 101955 Bennu, as well as an unusual carbonaceous “gum” that holds important compounds for life. The findings complement the earlier discovery of amino acids and the nucleobases of RNA and DNA in the Bennu samples.

A third new paper, in Nature Astronomy, addresses the abundance of pre-solar grains, which is dust that originated from before the birth of our Solar System, such as dust from supernovae. Scientists led by Ann Nguyen of NASA’s Johnson Space Center found six times more dust direct from supernova explosions than is found, on average, in meteorites and other sampled asteroids. This could suggest differences in the concentration of different pre-solar dust grains in the disc of gas and dust that formed the Solar System.

Space gum

It’s the discovery of organic materials useful for life that steals the headlines, though. For example, the discovery of the space gum, which is essentially a hodgepodge chain of polymers, represents something never found in space before.

Scott Sandford of NASA’s Ames Research Center, co-lead author of the Nature Astronomy paper describing the gum discovery, tells Physics World: “The material we see in our samples is a bit of a molecular jumble. It’s carbonaceous, but much richer in nitrogen and, to a lesser extent, oxygen, than most of the organic compounds found in extraterrestrial materials.”

Sandford refers to the material as gum because of its pliability, bending and dimpling when pressure is applied, rather like chewing gum. And while much of its chemical functionality is replicated in similar materials on our planet, “I doubt it matches exactly with anything seen on Earth,” he says.

Initially, Sandford found the gum using an infrared microscope, nicknaming the dust grains containing the gum “Lasagna” and “Neapolitan” because the grains are layered. To extract them from the rock in the sample, Sandford went to Zack Gainsforth of the University of California, Berkeley, who specializes in analysing and extracting materials from samples like this.

Platinum scaffolding

Having welded a tungsten needle to the Neapolitan sample in order to lift it, the pair quickly realised that the grain was very delicate.

“When we tried to lift the sample it began to deform,” Gainsforth says. “Scott and I practically jumped out of our chairs and brainstormed what to do. After some discussion, we decided that we should add straps to give it enough mechanical rigidity to survive the lift.”

By straps, Gainsforth is referring to micro-scale platinum scaffolding applied to the grain to reinforce its structure while they cut it away with an ion beam. Platinum is often used as a radiation shield to protect samples from an ion beam, “but how we used it was anything but standard,” says Gainsforth. “Scott and I made an on-the-fly decision to reinforce the samples based on how they were reacting to our machinations.”

With the sample extracted and reinforced, they used the ion beam cutter to shave it down until it was a thousand times thinner than a human hair, at which point it could be studied by electron microscopy and X-ray spectrometry. “It was a joy to watch Zack ‘micro-manipulate’ [the sample],” says Sandford.

The nitrogen in the gum was found to be in nitrogen heterocycles, which are the building blocks of nucleobases in DNA and RNA. This brings us to the other new discovery, reported in Nature Geoscience, of the sugars ribose and glucose in the Bennu samples, by a team led by Yoshihiro Furukawa of Tohoku University in Japan.

The ingredients of RNA

Glucose is the primary source of energy for life, while ribose is a key component of the sugar-phosphate backbone that connects the information-carrying nucleobases in RNA molecules. Furthermore, the discovery of ribose now means that everything required to assemble RNA molecules is present in the Bennu sample.

Notable by its absence, however, was deoxyribose, which is ribose minus one oxygen atom. Deoxyribose in DNA performs the same job as ribose in RNA, and Furukawa believes that its absence supports a popular hypothesis about the origin of life on Earth called RNA world. This describes how the first life could have used RNA instead of DNA to carry genetic information, catalyse biochemical reactions and self-replicate.

Intriguingly, the presence of all RNA’s ingredients on Bennu raises the possibility that RNA could have formed in space before being brought to Earth.

“Formation of RNA from its building blocks requires a dehydration reaction, which we can expect to have occurred both in ancient Bennu and on primordial Earth,” Furukawa tells Physics World.

However, RNA would be very hard to detect because of its expected low abundance in the samples, making identifying it very difficult. So until there’s information to the contrary, “the present finding means that the ingredients of RNA were delivered from space to the Earth,” says Furukawa.

Nevertheless, these discoveries are major milestones in the quest of astrobiologists and space chemists to understand the origin of life on Earth. Thanks to Bennu and the asteroid 162173 Ryugu, from which a sample was returned by the Japanese Aerospace Exploration Agency (JAXA) mission Hayabusa2, scientists are increasingly confident that the building blocks of life on Earth came from space.

The post Components of RNA among life’s building blocks found in NASA asteroid sample appeared first on Physics World.

Retatrutide, originally developed by Eli Lilly, has found a loyal fan base—even though clinical trials of the drug still haven’t finished.

Researchers found a chasm between the health reasons for which the public seeks out cannabis and what gold-standard science actually shows about its effectiveness.

© Mohamed Sadek for The New York Times

Zohran Mamdani isn’t just a superfan. Until recently, he was a key player on the Talking Headers, a rec-league team in Brooklyn.

Si jamais l'agence américaine ne le retrouve pas, les rovers Perseverance et Curiosity perdraient leur principal appui.

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Selon les projections des géologues, la planète Terre n'aura plus rien à voir avec ce que l'on connaît aujourd'hui dans 250 millions d'années. Si la France existe toujours d'ici là, elle occupera une place de choix sur le planisphère.