Young stars and exoplanets

Figure 1. β Pictoris, its disk of debris and a giant planet (courtesy of ESO)

The study of exoplanets goes hand in hand with the study of young stars. As they evolve, planetary systems pass through a number of phases before reaching that of our current solar system, dominated by several rocky planets (e.g. our Earth) and some gas planets (e.g. Jupiter) in near-circular orbits. In the early phases, young systems contain a large quantity of dust and gas, making them much easier to detect than older systems like ours (4.5 billion years) with current techniques.

In a mature planetary system like ours, planets reflect light from their star. In a young system, the newly formed planets are much hotter and emit light in the infrared domain as they cool. This makes them much easier to detect. β Pictoris (Figure 1), which has both a disk of dust and a giant planet, is a good example of a young planetary system.

Figure 2. A giant planet discovered around a low-mass star. They were discovered by doctoral students Marie-Ève Naud and Lison Malo, supervised by René Doyon and Étienne Artigau.

Consequently, it is much easier to search for planets around young stars, typically less than 100 million years old, than around mature systems like our own. The survey of young stars in the neighbourhood of our Sun is far from complete, particularly for low-mass stars (less than half of the mass of the Sun). Two dissertation projects by Institute students Lison Malo and Jonathan Gagné concern the detection of new young stars in the solar neighbourhood. A recent article by Lison Malo details the discovery of 214 young stars in the solar neighbourhood. As part of her doctoral studies, another student at the Institute, Marie-Eve Naud, is conducting research into giant planets around the stars in this sample. A 1st planet has already been discovered at a tremendous distance (2000 AU) from one of these stars (Figure 2).

Work by Jonathan Gagné, under the supervision of René Doyon and David Lafrenière, has made it possible to detect several very young brown dwarfs and a handful of planetary-mass objects (less than 13 times that of Jupiter), although they are not orbiting a star (Figure 3). One of the brown dwarfs identified by Jonathan Gagné in fact proved to be a system with an unusual structure; the brown dwarf itself is a binary system and a giant planet is orbiting this odd pair. This discovery, resulting from a France-Quebec collaboration, was published in 2013 (Figure 4).

 

Artist’s impression of the free-floating planet CFBDSIR J21494

Figure 3. Artist’s impression of a starless planet, discovered in 2012 by researchers from the Institute in collaboration with a French team.

Figure 4. A giant planet orbiting a brown dwarf pair. This system, with its unusual configuration, was discovered by researchers from the Institute and from Université Joseph Fourier (Grenoble, France).

 

 

 

 

 

 

 

 

The few planets orbiting young stars that have been discovered to date probably represent just the tip of the iceberg. They have a mass several times that of Jupiter, and there are good reasons to think that lighter planets are much more abundant than such massive ones. With the introduction of the JWST and observation modes like slitless spectroscopy (for planets far from their star) and non-redundant aperture masks (for planets very close to their star), it should be possible to detect an entire class of planets invisible up until now, and to describe objects that were previously impossible to study.