The origin of comet material formed at high temperatures

ScienceDaily (July 22, 2011) — Comets are icy bodies, yet they are made of materials formed at very high temperatures. Where do these materials come from? Researchers from the Institut UTINAM(1)(CNRS/Université de Besançon) have now provided the physical explanation behind this phenomenon. They have demonstrated how these materials migrated from the hottest parts of the solar system to its outer regions before entering the composition of comets.See Also:Space & TimeSunAsteroids, Comets and MeteorsAstronomySolar FlareSolar SystemStarsReferenceComet Hale-BoppComet Shoemaker-Levy 9Orion NebulaNear-Earth asteroid

Their results are published in the July 2011 issue of the journal Astronomy & Astrophysics.

On 15 January 2006, after an eight-year voyage, NASA's Stardust Mission (Discovery program) brought dust from Comet Wild 2 back to Earth. Comets are formed at very low temperatures (around 50 Kelvin, i.e. -223°C). However, analyses have revealed that Comet Wild 2 is made of crystalline silicates and CAIs (Calcium-Aluminium-rich Inclusions). Considering that the synthesis of these minerals requires very high temperatures (above 1 000 Kelvin or 727°C), how can this composition be explained?

A team from the Institut UTINAM1 (CNRS/Université de Besançon), in collaboration with researchers from the Institut de Physique de Rennes (CNRS/Université de Rennes), the University of Duisburg-Essen (Germany) and the Laboratoire Astrophysique, Instrumentation et Modélisation (CNRS/CEA/Université Paris Diderot), have provided the answer on the basis of a physical phenomenon called photophoresis. This force depends on two parameters: the intensity of solar radiation and gas pressur e. At the birth of the solar system, the comets were formed from the protoplanetary disk(2). Inside this disk, a mixture of solid grains ranging in size from a few microns to several centimeters was bathed in a dilute gas that let sunlight through.

According to the researchers, photophoresis drove the particles towards the outer regions of the disk. Under the effect of solar radiation, one face of the grains was "hotter" than the other and the behavior of gas molecules on the surface of these grains was modified: on the "sunny" side, the gas molecules were more unstable and moved about more rapidly than on the "cold" side. By causing a pressure difference, this imbalance moved the grains away from the Sun. Through digital simulations, the researchers have borne out this photophoresis phenomenon. They demonstrated that the grains of crystalline silicates formed in the inner, hot region of the protoplanetary disk near to the Sun migrated to its outer, cold region before playing a part in the formation of the comets! . This novel physical explanation could account for the position of certain dust rings observed in protoplanetary disks and thus shed light on the conditions of planet formation.

(1)Institut "Univers, Transport, Interfaces Nanostructures, Atmosphère et Environnement, Molécules" (CNRS/Université de Besançon). (2)The protoplanetary disk of a young star (for example the Sun) is the disk of gas and dust that surrounds it, and in which planets are likely to form.

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The origin of malaria: The hunt continues

ScienceDaily (July 22, 2011) — The agent of malaria has been found in the greater spot-nosed monkey, also known as putty-nosed monkey (Cercopithecus nictitans), a small African primate derived from a line different to that of humans, gorillas and chimpanzees. This discovery challenges current thinking on the origin of the parasite and introduces a key element in the fight against malaria: knowing how it has adapted to the human species will make it possible to target its weaknesses.See Also:Health & MedicineMalariaHealth PolicyHuman BiologyPlants & AnimalsPests and ParasitesMonkeysApesReferenceInfectious diseaseHominidaeMonkeyPathogen

This work stems from research carried out by CNRS researchers in association with other organizations(1) and is published on the 4 July 2011 in the journal PNAS.

Malaria, also known as paludism, is one of the greatest global scourges. This pathology, which causes a million human deaths each year, is especially rampant in Africa. The question of whether the primary infection originated from rodents or birds has long remained unanswered. Also found in gorillas, it was thought that the parasite was specific to hominids(2).

By working on the subject, a team of CNRS researchers headed by Franck Prugnolle and François Renaud of the Laboratoire MIVEGEC(1)(CNRS/IRD/Université Montpellier 1), jointly with the Centre International de Recherches Médicales de Franceville in Gabon, and in collaboration with other organizations(4), has demonstrated the presence of Plasmodium falciparum, the agent of malaria, in the greater spot-nosed monkey (Cercopithecus nictitans), a small African monkey derived from a line different to that of humans. The origin of the parasite probably predates the origins of the African hominids line.

The presence of Plasmodium falciparum in this Old World Monkey opens the way to the analysis of the genome of the parasite found in this species. Comparing its sequence with that (already known) of falciparum in humans will enable researchers to discover the molecular signatures of the human parasite and to find out how it has adapted to humans. Knowing the weaknesses of the parasite will be a major asset in combating malaria.

(1)Centre International de Recherches Médicales de Franceville au Gabon, IRD, Université Montpellier 1, Université de la Méditerranée, Université de Toulouse, University of California and Université de Brazzaville.

(2)The hominids line comprises two branches: humans and large monkeys (gorillas, chimpanzees and orangutans).

(3)Laboratoire "Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle"

(4)Université de la Méditerranée, Université de Toulouse, University of California and Université de Brazzaville.

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