Webb confirms the coldest planet ever found. It's orbiting a white dwarf

 

Credit: NASA, GSFC

The gas giant WD 1856+534 b was discovered by researchers in 2020. It orbits a star 81 light-years away from Earth.  An exoplanet described as a "super-Jupiter" orbited a white dwarf (WD) star for the first time. It has about six times the mass of Jupiter.  An international group of astronomers just published a report detailing their observations of this exoplanet with the James Webb Space Telescope's (JWST) Mid-Infrared Instrument (MIRI).  WD 1856+534 b is the coolest exoplanet ever detected, according to their observation.

Mary Anne Limbach, an Assistant Research Scientist in the University of Michigan, Ann Arbor's Department of Astronomy, led the study.  Researchers from the Johns Hopkins University Applied Physics Lab (JHUAPL), the University of Victoria, the University of Texas at Austin, the Center for Astrophysics, University of Southern Queensland, the Center for Interdisciplinary Research and Exploration in Astrophysics (CIERA), the Kavli Institute for Astrophysics and Space Research at MIT, the NSF NOIRLab, and the Gemini Observatory joined her.

Their observations were a part of the JWST Cycle 3 General Observation (GO) mission, which sought to directly characterize the planet using Webb's advanced infrared optics and spectrometers.  This aligns with one of the goals of the JWST mission, which is to use the Direct Imaging Method to characterize exoplanets.  This involves using spectrometers to examine light reflected from the surface or atmosphere of an exoplanet in order to search for chemical fingerprints.

 By doing so, astronomers can ascertain whether possible biosignatures—such as oxygen, nitrogen, methane, water, etc.—are present and deduce information about the planet's composition and genesis.  This approach may yield the first concrete proof of extrasolar life using cutting-edge next-generation telescopes like the JWST.

These planets' emission spectra can also provide information about their composition and migration history. However, because of the enormously obscuring light from their host stars, it is still difficult to detect light straight from an exoplanet, as the authors point out in their paper published on the arXiv preprint service.

Because of this, direct imaging has mostly been limited to huge planets with broad orbits or exceptionally hot atmospheres (such as gas giants). As of right now, no rocky or terrestrial exoplanets have been seen orbiting nearer to their stars. Furthermore, there have been no exoplanets discovered with emission spectra lower than 275 K (1.85°C; 35.33°F), which is equivalent to Earth. A rare chance to find and describe cooler planets is provided by WD stars. As the group observed:

The contrast issues that usually prevent direct detections of WDs surrounding their main-sequence counterparts are greatly lessened by their low brightness.  WDs provide information about what happens to planetary systems following stellar death since they are the evolutionary remains of stars like the sun.  Knowledge of how planets interact with and endure post-main-sequence evolution is essential for understanding dynamical migration, orbital stability, and possible planetary engulfment.

Furthermore, studying WD planetary systems can help determine whether planets can endure this final phase of star evolution and whether there is still a chance for habitable circumstances to persist near stellar remnants.  With Webb's capabilities, astronomers and astrobiologists hope to explore these mysteries.  Limbach and her colleagues used data from the JWST Mid-Infrared Instrument (MIRI) and the Infrared (IR) excess approach to validate the presence of WD 1856+534 b for their investigation.

This enabled them to measure the atmosphere temperature of WD 1856+534 b and constrain its mass. With an average temperature of 186 K (-87°C; -125°F), according to their calculations, WD 1856+534 b is the coldest exoplanet ever discovered. Additionally, they verified that the exoplanet's mass is no more than six times that of Jupiter, contrary to earlier measurements that estimated its mass to be 13.8 Jupiter masses. Their findings also represent the first concrete evidence that planets can live and move into close orbits close to WDs' habitable zones.

The JWST is expected to make additional observations of WD 1856 b in 2025, which the team is eager to see.  With any luck, these observations will find more planets, which would indicate if WD 1856 b was disturbed into its present orbit.  Additionally, Webb’s Near-Infrared Spectrometer (NIRSpec) will shortly share the findings of earlier observations from Cycle 1.  These will offer a preliminary description of the atmosphere of the planet.

Reference