Session H04: Physical Review Invited Session: Looking Ahead as we Look Far through the JWST

The Exciting First Years and the Upcoming Long Legacy of the James Webb Space Telescope

The James Webb Space Telescope is the culmination of thirty years of planning, twenty years of construction, and ~11 billion dollars of funding, and for the past ~20 months it has been dazzling astronomers and the public alike with spectacular early science images. It is the most expensive and complex astronomical observatory ever built and it was designed specifically to perform superlative new observations, such as the first systematic exploration of stars, galaxies, and black holes in the early universe, or detailed atmospheric characterization of potentially habitable exoplanets. Luckily for us, this first systematic exploration is happening right now. I will provide an overview of this flagship telescope and discuss some of the early, and sometimes tentative, discoveries that have been made in Webb's first deep fields from the first light of galaxies and black holes, and finish by touching on some of the exciting scientific directions JWST is likely to probe in the near future.   

Exploring the Diversity of Planetary Systems

JWST has transformed the study of exoplanets by obtaining exquisitely precise spectroscopic observations. Although some planets appear to be shrouded by hazes or clouds, JWST has constrained the atmospheric compositions of multiple planets and revealed that several potentially terrestrial worlds are likely to be airless. At larger orbital separations, JWST has achieved new sensitivity levels in directly imaging and obtaining direct spectroscopy of young, massive planets. In 2027, the Roman Space Telescope will further advance studies of distant planets via direct imaging and spectroscopy with the Coronagraphic Instrument, which will be capable of imaging even fainter planets and disks. Roman will also significantly expand knowledge of exoplanet demographics by using gravitational microlensing to detect hundreds of planets with masses as small as that of Mars. Roman’s microlensing detections will be at orbital separations of roughly 0.5 astronomical units and beyond, thereby complementing previous studies of the demographics of close-in planets by radial velocity and transit surveys, especially the NASA Kepler, K2, and TESS missions. From the ground, extremely precise radial velocity spectrographs, sophisticated analysis techniques, and an improved understanding of stellar astrophysics will improve planet mass measurements and ideally lead to precise mass measurements for planets with similar masses, radii, and temperatures as the Earth. Future direct imaging and spectroscopy observations with extremely large ground-based telescopes will probe the atmospheres of small, potentially habitable planets orbiting the coolest stars and search for signs of life. From space, the upcoming Habitable Worlds Observatory (HWO), a large aperture telescope with sensitivity from the UV to the NIR, will conduct transformative studies in general astrophysics and search for signs of life by directly imaging and obtaining spectra of roughly 25 habitable zone planets orbiting Sun-like stars. The observatory will also obtain near-flyby quality observations of solar system objects and observe hundreds of exoplanets with a range of masses, radii, atmospheric compositions, and orbital properties.   

The Hubble Tension and JWST

We present high-definition observations with the James Webb Space Telescope of Cepheid variables used to calibrate the luminosity of Type Ia Supernovae and the Hubble constant. The superior resolution of JWST negates crowding noise, the largest source of variance in the NIR Cepheid Period-Luminosity relations (Leavitt laws) measured with HST. Together with the use of two-epochs to constrain Cepheid phases and three filters to remove reddening, we reduce the dispersion in the Cepheid PL relations by a factor of 2.5. We find no significant difference in the mean distance measurements determined from HST} and JWST, with a formal difference of -0.01 +/- 0.03 mag. This result is independent of zeropoints and analysis variants including metallicity dependence, local crowding, choice of filters, and slope of the relations. We can reject the hypothesis of unrecognized crowding of Cepheid photometry from HST that grows with distance as the cause of the ``Hubble Tension'' at 8.2 sigma, i.e., greater confidence than that of the Hubble Tension itself. We conclude that errors in Cepheid measurements across the distance ladder are not the source of the decade-long Hubble Tension.