JWST Verifies Coldest Exoplanet Found Around A Dead Star

In 2020, astronomers discovered WD 1856+534 b, a gas giant about 81 light-years from Earth. With about six times Jupiter’s mass, this “super-Jupiter” became the first known exoplanet to transit a white dwarf.

JWST Observations Confirm WD 1856+534 b as the Coldest Exoplanet Ever Detected

In a recent study, an international team of astronomers reported their observations of the exoplanet WD 1856+534 b using the James Webb Space Telescope  Mid-Infrared Instrument (MIRI). They confirm that it is the coldest exoplanet ever detected.

Acording to the research was led by  Mary Anne Limbach an Assistant Research Scientist in the Department of Astronomy at the University of Michigan, Ann Arbor, with collaborators from institutions including MIT’s Kavli Institute, Johns Hopkins University Applied Physics Lab, University of Victoria, University of Texas at Austin, CIERA, Centre for Astrophysics at the University of Southern Queensland, NSF NOIRLab, and the Gemini Observatory.

The team conducted the observations as part of the JWST Cycle 3 General Observation (GO) program, which aimed to directly study the planet using Webb’s advanced infrared imaging and spectroscopic tools.

This aligns with one of JWST’s core goals: to analyze exoplanets through the  Direct Imaging Method. This technique captures reflected light from a planet and analyzes it with spectrometers to identify chemicals.

JWST’s Role in Detecting Biosignatures Beyond Our Solar System

This approach helps astronomers detect possible biosignatures like oxygen, methane, and water, and understand a planet’s composition and formation.

Powerful telescopes like JWST could eventually reveal the first evidence of life beyond our Solar System.

Therefore, emission spectra from exoplanets can also provide valuable information about their chemical makeup and migration patterns.

However, researchers note that a host star’s brightness often drowns out an exoplanet’s light.

Consequently, direct imaging has mostly targeted large planets—such as gas giants—with wide orbits or very hot atmospheres. So far, scientists have not directly observed any rocky (terrestrial) exoplanets in close orbits around their stars.

So far, scientists haven’t found any exoplanets with emission spectra below 275 K—similar to Earth’s temperature. White dwarf stars offer a rare chance to find and study these colder planets. As the researchers highlighted:

“The faint luminosity of white dwarfs greatly lessens the contrast issues that usually complicate direct detection around main-sequence stars. As the remnants of stars like the Sun, white dwarfs give us a glimpse into the future of planetary systems after stellar death. Studying how planets interact with and endure the post-main-sequence phase is key to understanding orbital stability, dynamical migration, and the potential for planetary engulfment.”

Moreover, studying planetary systems around white dwarfs can help determine if planets can survive this advanced stage of stellar evolution and whether habitable conditions could persist around stellar remnants.

Limbach and Team Use JWST’s MIRI to Confirm WD 1856+534 b

Astronomers and astrobiologists are eager to explore these questions using Webb’s advanced capabilities. For their research, Limbach and her team confirmed the existence of WD 1856+534 b by employing the Infrared (IR) excess method with data from JWST’s Mid-Infrared Instrument (MIRI).

This method enabled the team to determine the mass of WD 1856+534 b and assess its atmospheric temperature. Their analysis showed an average temperature of 186 K (-87 °C; -125 °F), making it the coldest exoplanet ever discovered.

They also confirmed that the planet’s mass is no more than six times that of Jupiter, compared to earlier estimates of 13.8 Jupiter masses.

Their findings provide the first direct evidence that planets can survive and migrate into close orbits within the habitable zones of white dwarfs.

The team is eager for upcoming observations of WD 1856 b by the JWST, set for 2025. These additional observations may help identify more planets and determine if WD 1856 b was disturbed into its current orbit.

Moreover, results from earlier observations made by Webb’s Near-Infrared Spectrograph (NIRSpec) during Cycle 1 will be released soon, offering an initial analysis of the planet’s atmosphere.

Read the original article on: Sciencealert

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