JWST | "The ultimate goal of our work? To answer the question: does life exist elsewhere in the universe?

Initially, the JWST was designed to observe the most distant galaxies possible, in order to study the first phases of the Universe. Indeed, the speed of light being finite, the farther we observe, the more we can "go back in time". This first objective of the JWST explains why it was designed to detect infrared light: because of the expansion of the Universe, the further away an object is, the more its light is red-shifted. 

The telescope will also address the problem of "dark matter", the mysterious cosmic ingredient that must be added to our models to fit not only the Universe as a whole, but also the dynamics of its large structures (clusters of galaxies, galaxy, etc.).   

Finally, and most importantly, it will allow us to study exoplanets in a much more advanced way than what has been done so far. The large size of its primary mirror combined with the infrared capability of its instruments will indeed allow us to study the atmospheric composition of a large number of exoplanets, including rocky and potentially habitable planets orbiting small cool stars like TRAPPIST-1. In the worst case scenario, it will tell us that these planets are generally unable to maintain a substantial atmosphere because of their proximity to their small star. In the best case, it will reveal for some of these planets atmospheric compositions that can only be explained by the presence of life on their surface.  

But this list is far from being exhaustive, the JWST mission being open to the whole scientific community, it will be used for many other projects, as, for example, in the study of objects of our solar system.  

I plan to use JWST primarily to study the atmospheric composition of telluric exoplanets orbiting small nearby stars, especially those of TRAPPIST-1 and those to be discovered by SPECULOOS. In this context, I have developed with my colleague Victoria Meadows at the University of Washington a community initiative to bring together researchers interested in studying TRAPPIST-1 with JWST to maximize the scientific return from this study.  

As our national motto says, there is strength in numbers, and this is also the case in science. The detailed study of the seven TRAPPIST-1 planets will require hundreds of hours of observing time withJWST, and only by avoiding fruitless competition and combining our expertise and resources will we be able to obtain these data and learn more about these mysterious planets. 

Via collaborations with GTO GTO (Guaranteed Time Observations), teams, we will have access to some of the first JWST observations of TRAPPIST-1. The TRAPPIST-1 community initiative will also give us access to a lot of data, as some of the initiative's member teams have obtained JWST time to observe TRAPPIST-1 during the first cycle of observations (cycle 1). Personally, I introduced two ambitious proposals to study in depth two of the planets of the system. They were not selected, probably because they were too ambitious at this stage of JWST. Indeed, we do not know yet its real performances in space, so NASA preferred not to grant hyper-ambitious programs spread over several cycles, which is understandable. 

I'm banking mainly on the NIRSpec (Near InfraRed Spectrograph) instrument, which will be able to measure the "transit spectrum" of the planets very precisely over a wide range of wavelengths. The concept of these observations is to observe the passage (transit) of the planet in front of the star. When this happens, some of the light emitted by the star in our direction passes through the atmosphere of the planet and is filtered by it. For example, if the atmosphere is rich in CO2 , it will absorb part of the light coming from the star at certain wavelengths (which we know well thanks to physics), and we will observe a deficit of flux that will be added to that caused by the body of the planet hiding part of the star. By measuring the amplitude of this deficit in a wide range of wavelengths, we obtain the transit spectrum of the planet which gives access to rich information on its composition and its atmospheric properties.  

The information can in principle allow us to constrain the surface conditions of the planet, but also reveal a chemical disequilibrium of the atmosphere indicative of a biological activity on its surface. Ultimately, this is the ultimate goal of our work: to answer the question "does life exist elsewhere in the Universe?" 

Yes, in part, because the Hubble data suffer from many systematic effects related to its geocentric orbit, which the JWST will not suffer from, as it will be orbiting the Sun at 1.5 million kilometers from the Earth. Nevertheless, we do not expect huge surprises in this field, for the simple reason that Hubble data are far from being precise enough to detect a compact atmosphere around planets and to reveal their compositions. We have used Hubble to reject the (a priori unlikely) hypothesis of extended hydrogen-rich atmospheres around the TRAPPIST-1 planets. With JWST, we will enter a completely different range of precision, and thus have access to very different atmospheres, similar to those of the Earth or Venus.   

In Cycle 1, none other than TRAPPIST-1, but we intend to use JWST from Cycle 2 onwards to study some planets that will be detected by SPECULOOS, and others detected by TESS (Transiting Exoplanet Survey Satellite) and confirmed by our telescopes. These will all be small planets orbiting very low mass, very cold stars.  

Of course we will! The detailed study of the TRAPPIST-1 planets will require the accumulation of data over the entire JWST mission, we are involved in the discovery of other interesting targets for the JWST mission through our contribution to the TESS project, and we expect to detect other systems similar to  TRAPPIST-1 with SPECULOOS that we will then study with JWST. JWST will usher in a new era in exoplanetology, that of the detailed study of temperate rocky exoplanets, and we aim to contribute as much as we can. 

At the space level, no equivalent mission has yet been selected for the post-JWST era. There are several mission concepts in development, but given the time needed to go from concept to realization of a space mission, and given the enormous costs of these missions, we should not expect to see the launch of a real successor to JWST before at least 2040.  On the other hand, several giant ground-based telescopes are under construction. Because of the Earth's atmosphere, they will unfortunately not have the capabilities of JWST for the study of transiting exoplanets, but we can hope that they will lead to the detection of potentially habitable "super-Earths" around Sun-like stars by 2040. In any case, they should greatly improve our ability to detect exoplanets in direct imaging, even if the detection of a true twin of the Earth will not be within their reach yet.