Since the first detection in 1995, awarded a Nobel Prize very recently, more than 4000 exoplanets have been discovered outside of our Solar System, around nearby stars. The size range goes from planets about the size of Mars to gigantic objects several times the size of Jupiter. Among the most common objects we found, are planets between 1 and 2 times as big as the Earth. We strongly suspect these objects to be rocky (made mostly of oxygen, silicon, magnesium, iron and nickel) that is why we nickname them: Super-Earth. On average almost every single star has a Super-Earth which means they are very common and we might find life on one/some of them. However little is known about these exoplanets and the ABISSE project aims at better understanding these objects. One of the key question that ABISSE is looking at answering is: is it possible for a Super-Earth to have a magnetic field? For a planet to produce a magnetic field, it needs to have a conducting fluid in a convective motion (the convection is what happens when you heat up water in a pan). Inside Earth the magnetic field is produced by a portion of the iron core in a liquid state and where a dynamo process occurs. On Super-Earths the iron core may very well be fully crystallized making a dynamo process impossible there. ABISSE is dedicated to finding where such a process could occur. Yet, a magnetic field would be an important feature to characterize the habitability of a planet. A magnetic field helps protecting the surface from deadly radiations coming from the host star and it is also likely to protect the atmosphere from being blown away by the stellar winds. Thus, determining the conditions for the existence of a magnetic field on large rocky objects is a step further in finding habitable planets and life outside of Earth.
The ultimate goal of ABISSE is to characterize the materials inside a Super-Earth and to determine if their properties offer the possibility for magnetic fields to be produced. The Earth is made basically of three areas: a thin crust of the order of 10 km, a mantle of 2,900 km and a core of 3,300 km in thickness. The highest pressure in the mantle is ~140 GPa which is 1,400,000 times the atmospheric pressure. In the core it goes up to 350 GPa. For Super-Earths it is anticipated that it could go higher than 500 GPa, just shy of 1000 GPa. Under these conditions, matter is highly compressed and its properties change. Using sophisticated numerical simulations, ABISSE characterizes matter under such conditions and answers questions such as: Is iron liquid? Solid? What happens to the mantle, do we have a magma ocean? Is the planet differentiated as in Earth? Are the conditions compatible with a dynamo process? All these pieces of information are necessary to determine if a magnetic field can exist and, consequently, help constraining the habitability of a Super-Earth.
In the coming decade, many space programs as well as ground-based observation campaigns are going to be dedicated to the study of exoplanets and the search for life outside the Earth and the Solar System. It is thus very timely to perform such studies allowing a better understanding of these new worlds.