![]() ![]() Over a long period, typically a million years, the majority of the planetesimals and smaller protoplanets are accreted by the more massive protoplanets, leaving only a few protoplanets remaining. To then form Proxima b, the protoplanets and planetesimals undergo significant gravitational interactions with each other, resulting in numerous collisions, allowing the protoplanets to grow. ![]() ![]() When using this scenario to form Proxima b, it is assumed that enough solid material in the form of protoplanets and planetesimals has been able to form and migrate to the general location of Proxima b before the end of the disc lifetime. Scenario (i) in situ planet formation: It is thought that the terrestrial planets in the Solar System formed near their current orbits from a group of smaller protoplanets embedded within swarms of even smaller planetesimals in a gas-free environment, after the end of the disc lifetime. I will now explain these scenarios and their implications for the composition and structure of Proxima b, and also the multiplicity of the Proxima Centauri system – that is whether we should expect more planets to be discovered. Now this is a very general view of planet formation what happens when we begin to examine the specific case of Proxima b? When looking at individual systems, there are many different scenarios that branch off of the general case described above. Figure 1: Diagram showing the formation of a star and planetary system from a protostellar nebula. This all occurs during the lifetime of the protoplanetary disc, so that the only objects surviving once the disc has accreted on to the star are the star itself, any surviving planets, and all the remaining asteroids, pebbles and dust. If these protoplanets can accrete enough material they may become massive enough to hold a substantial atmosphere and then grow into gas giants similar to Jupiter and Saturn. As they continue orbiting the star, they interact with other planetesimals – occasionally colliding and forming larger planetesimals – until they eventually become planetary-sized objects (what we call protoplanets) similar to the terrestrial planets today (Mercury, Venus, Earth, Mars). The dust in the disc begins to settle to the middle of the disc, whilst simultaneously clumping together and coagulating into larger pebbles, and eventually into asteroid sized bodies. This gas and dust disc then accretes on to the protostar over a period between 1 and 10 Myr, and this is the time and location that we expect planet formation to take place. The nebula then collapses in on itself to form a protostar surrounded by a protoplanetary disc. But before we examine the specific case of Proxima b, it is useful to understand just what planets form from and how they do it in a very general case.īefore a star system is born, the entirety of its material is held in a protostellar nebula in the form of gas and dust this includes the parent star (composed of mostly hydrogen and helium), along with all of the planets, asteroids and dust particles (which are mostly heavy elements such as carbon, oxygen, etc). ![]() How did it form and evolve into the planet that is detected today? Knowing how and where it formed can give valuable insights into its composition and atmospheric properties, whilst understanding its evolution can give hints at to what else, if anything, should be expected to be discovered orbiting Proxima Centauri. Whilst these pieces of work are important in looking at the present state of the planet, (well the state of the planet 4.25 years ago) one important question from its past needs to be answered. Living earth red oak how to#At the time of writing, there are already 8 papers discussing a wide variety of topics concerning Proxima b: ranging from its potential habitability and the impact of flares, to how to characterise the planet’s atmosphere with NASA’s new James Webb Space Telescope. The recent discovery of Proxima b has not only excited much of the public, but also scores of scientists who are attempting to explain its many different aspects. Gavin Coleman, Queen Mary University of London ![]()
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