The planets and their star grow together

From a cloudcloud of gasgas and dust present around a starstar. Of the mattermatter which first agglomerates a bit like “dust bunnies” then under the effect of gravitygravity. This is the idea that scientists have formed of how planets are formed. But they still struggle to specify the finer processes. But a new study by Cambridge University Astronomers (United Kingdom) provides some details today.

Unpublished: the first stages of the formation of a planet observed live

Details of a chronological order, in particular. Because the researchers imagined that planets would only appear once their star had reached its final size. However, the work carried out here on some of the oldest stars in our UniverseUniverse suggest the opposite, namely that the constituent elements of giant planetsgiant planets Of type JupiterJupiter Where SaturnSaturn begin to form as the star grows. Understand that stars and planets could grow together!

To come to this astonishing conclusion, the astronomersastronomers have studied somewhat special stars. White dwarfs which they call “polluted”. Let us first recall that a white dwarf is what remains of a star comparable to our Sun, once it has burned up all its fuel. And white dwarfs “polluted” have the particularity of containing heavy elements — from magnesiummagnesiumfrom ironiron or even calciumcalcium — deposited there by asteroid-like objects that crashed into these stars.

Planets that appear very early

Thanks to spectroscopic observations of white dwarfs “polluted”, researchers can therefore have access to the compositions of these asteroids and the conditions under which they formed. It’s interesting. Because, according to the commonly accepted idea, the asteroids are formed when the planets also begin to appear. Like the accretionsaccretions of dust that will never go further.

The mixture of elements that astronomers at the University of Cambridge have observed by spectroscopy in the atmospheresatmospheres of the white dwarfs studied can only be explained if many of the original asteroids had once melted, causing heavy iron to flow towards their cores while the lighter elements remained on the surface. This process, our Earth has known it. It caused it to exhibit an iron-rich core. Scientists talk about differentiation.

The Solar System would have formed only in 200,000 years!

Above all, this meltingmelting can only be attributed to radioactive elements with a very short durationduration of life. They exist in the early stages of a planetary system. But they decay in just a million years. If these asteroids have melted, this means that the process of planet formation must start very quickly. The first bodies of a system forming at the same time as the star. A chronology that would be valid for all exoplanetsexoplanets known. But also for our own solar system. With a Jupiter and a Saturn which would have had a long time to reach their current size.


Birth of the planets: should we review the theory of their formation?

Around the stars in formation float envelopes of dust that are difficult to fathom. Astronomers have just had the surprise of discovering relatively large grains there, already formed less than 100,000 years after thecollapsecollapse of the initial gas cloud. A result that could challenge the established chronology of planet formation.

Article of Nathalie MayerNathalie Mayer published on 10/15/2019

Although discoveries have been made in recent years, the physicalphysical of the youngest forming stars — those known as protostarsprotostars class 0 — remains mysterious. Because the envelopes of gas and dust that surround them are difficult enigmas to solve. Especially since these gases mainly emit in the so-called (sub)millimeter range. And it is in the hope of lifting the veil that astronomers from CEA-Paris Saclay (France) are exploring the environment of such protostars thanks in particular to the large interferometerinterferometer Noema (Northern Extended Millimeter Array) placed on the plateau of Bure (Hautes-Alpes, France).

Last February, they had discovered that the protostars studied had embryosembryos much smaller than expected protoplanetary disks. And today, they show that the emissivity index β of the dust they contain is not only surprisingly low, but decreases as one approaches the forming star.

Large dust grains present very early

These low values ​​indicate the presence of relatively large grains — grains larger than 100 microns — in the environments of very young stars. A surprise for astronomers who do not yet explain how such grains could grow in less than 100,000 years after the start of the star formation process.

But, as these are the raw material from which planets form, they are in any case an additional clue that planets could start to emerge much earlier than astronomers thought. What may lead to a total revision of the established chronology of the process.


The formation of planets would begin before the birth of stars

The formation of planets could begin even though the birth of the host star is not complete. This is indicated by observations made with the radio telescoperadio telescope Alma. Indeed, the device made it possible to scrutinize a protoplanetary disk located around a very young protostar, and to flush out dust grains the size of a millimeter.

Article of Laurent SaccoLaurent Sacco published on 03/07/2018

Molecular Cloud 1 of Taurus Taurus Molecular Cloud 1so TMC 1) is a molecular cloud located at about 450 light yearslight years of the Sun in the Milky Way. As far as we know, it is the closest star nursery to the Solar systemSolar systemmaking it an ideal target for an instrument like theAtacama Large Millimeter/submillimeter Array (abbreviated as Alma, which also means “soul” in Spanish). Indeed, one of the main scientific objectives of this radio telescope is to help us understand the formation of stars and their processions of exoplanets through the observation of molecular clouds.

The astrophysicistsastrophysicists therefore turned Alma’s gaze to TMC 1A, a protostar of massmass already comparable to that of the Sun and located in TMC 1. It is surrounded by a protoplanetary disk and its formation would have begun only about 100,000 years ago.

It is also estimated that it would contain only half or even three quarters of its final mass, because the accretion of matter from the envelope of the protostar on its accretion diskaccretion disk then on thestarstar itself is not complete. This system is still very young and the thermonuclear reactions that will transform the protostar into a real star have not yet begun.


Mojo, for Modeling the Origin of JOvian planets, i.e. “modeling of the origin of the Jovian planets”, is a research project that has resulted in a series of videos presenting the theory of the origin of the Solar System, in particular that of the giants carbonated. We owe these videos to two renowned specialists, Alessandro Morbidelli and Sean Raymond. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles then appear. Then click on the cogwheel to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © Laurence Honnorat

Large grains of dust that block radiation

A team of European researchers has just made an astonishing discovery regarding TMC 1A, as they explain in an article published in Nature Astronomy and available in free access on arXiv. This discovery obviously concerns cosmogony, more precisely the birth of planets, because it is reasonably possible to think that the example of TMC 1A is general (however, prudence imposes to make additional studies to firmly establish that we are not faced with an exception with regard to the formation of planetary systems for stars of solar type or close to it). It is therefore possible to think that the lesson drawn from these observations also concerns the birth of the Solar System and that it thus helps us to understand one of the stages that led from the Big Bang to life.

In this case, the astrophysicists have demonstrated an absence of emission lines from the carbon monoxidecarbon monoxide (CO) while it was possible to expect their presence, given what is known of the composition of molecular clouds and protoplanetary discsprotoplanetary discs. Of the numerical simulationsnumerical simulations concerning the transfer of radiation in the disk of TMC 1A have accredited a hypothesis put forward to account for this observation.


A computer-generated video showing a dive into a protoplanetary disk. We then descend to the scale of colliding rock dust and grains. Sometimes, these dusts and these grains stick to each other, and this is how objects can grow until the formation of planetesimals from grains of silicate and carbonaceous dust. © ESO, YouTube

The process of planet formation quickly began

The moleculesmolecules of CO must have been there but their radiation must have been blocked by the presence of millimeter-sized dust grains. These grains are a stage leading to the birth of pebbles then of planetesimals from a few kilometers to a few hundred kilometers as a prelude to the formation of the embryos of planets and the planets themselves.

However, these grains do not exist with such a large size initially in molecular and dusty clouds on the point of collapsing to form proto-stars and protoplanetary disks; indeed, they are smaller, of the order of a micron.

The researchers therefore conclude that, contrary to what scientists thought before, the process of planet formation very quickly got under way in the protoplanetary disk around TMC 1A and that it began even before the protostar has reached maturity.

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