In a recent study accepted Monthly Notices of the Royal Astronomical Society, an international team of researchers led by Texas A&M University has investigated how the James Webb Space Telescope (JWST) detects a variety of exoplanets orbiting the 15 closest white dwarfs to Earth using the Medium Infrared Instrument (MIRI). . This study holds the potential to expand our knowledge of exoplanets, their planetary structures, and whether they can support life.
A white dwarf is an incredibly dense star the size of Earth that is caused by a sun-like star exhausting all of its nuclear fuel. Basically, a white dwarf is what our Sun will be like at the end of its billions of years from now. So why are white dwarfs so important to the search for extraterrestrial life?
Mary Ann Limbach, a doctoral student in the Department of Physics and Astronomy at Texas A&M University and lead author of the study, explains how difficult it is to detect vital fingerprints on planets within the habitable zone (HZ) of Sun-like stars due to the Sun being 10 billion times brighter than Earth. It says this means that the JWST instruments will not be able to detect an exoplanet representative of Earth due to starlight drowning out the light of the Earth counterpart being imaged.
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“On the other hand, white dwarfs, the remnants of dead stars, are much smaller than the Sun,” Limbach said. “In fact, the size (radius) of a white dwarf is about the same as that of Earth. In the infrared, a white dwarf is about 100 times brighter than its terrestrial counterpart. Also, most white dwarfs do not have star spots or flares, but remain in Constant brightness over time.So, if we instead put a white dwarf and a quasi-Earth at 5 parsecs, we still couldn’t image the analog Earth, but we should detect 1% of the extra light we receive due to the presence of the Earth.This extra light is indicated As “extra-infrared” is the method we propose in the paper to discover white dwarf exoplanets.” For context, one parsec is 3.26 light years.
Using this method, the researchers discovered that JWST was able to detect infrared excess of cold gas giant exoplanets orbiting white dwarfs with 15 parsecs of Earth, along with temperate or hot terrestrial exoplanets, which include the isotopes of Earth and Mercury. , within 10 parsecs of Earth. The study also discusses how observations of follow-up spectroscopy with MIRI can be used to search for biosignatures on terrestrial worlds within the habitable zones of white dwarfs. While these results are unusual, could the James Webb Space Telescope be used to observe vital fingerprints on planets around stars other than white dwarfs?
“Transit spectroscopy, a method for characterizing the atmospheres of exoplanets, is another method that has been proposed to search for biosignatures using JWST,” Limbach explains. Other research papers have looked at using this technique for white dwarfs and M dwarf stars (which are less massive than the Sun, but still fuse with hydrogen). Using JWST transit spectroscopy, it would take hundreds of hours to discover the biosignatures on the Trappist-1 planets, the most suitable M dwarf for these observations. For comparison, to detect biosignatures on an analog Earth orbit orbiting a white dwarf at 5 parsecs, it would take about 25 hours using the proposed excess infrared method. However, there is one problem: We know about the Trappist-1 exoplanets, but we haven’t discovered any terrestrial exoplanets around white dwarfs. Hence, our goal is to first identify these exoplanets using excess infrared so that they can be distinguished.”
Trappist-1 is a star system located 12 parsecs (39 light years) from Earth with at least seven Earth-sized planets orbiting a star 12 times less massive than our sun, with a 2021 study indicating all planets. Seven planets share the same density, which suggests that they may be rocky worlds. So, what does the future hold for trying to find life beyond Earth?
“NASA has plans to build a telescope capable of imaging habitable exoplanets around Sun-like stars, but there are no upcoming infrared space observatories planned with a sensitivity comparable to JWST,” Limbach said. “So, observations with the JWST/MIRI instrument may be our only chance to search for life around nearby white dwarfs. If there is an abundance of life at this mysterious site, we will likely discover biosignatures on these worlds using JWST in the near future before long.” Observatories able to distinguish Earth analogues orbiting Sun-like stars.
As always, keep learning and keep researching!
Featured image: Artist’s depiction of a planet and a comet orbiting a white dwarf. (Credit: NASA, ESA and Z. Levy (STScI)