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Webb Telescope finds water on very hot exoplanet named GJ 486 b

The vast universe is filled with an abundance of red dwarf stars, the most common type of star known to exist. Consequently, rocky exoplanets are most likely to be found orbiting these cool stars. Not GJ 486 b.

To be within the habitable zone, where liquid water could exist, a planet must maintain a tight orbit around its red dwarf star. However, these stars are known for their activity, particularly during their early years, emitting ultraviolet and X-ray radiation that could potentially destroy planetary atmospheres. 

This has led to a significant and unresolved question in astronomy: can a rocky planet maintain or reestablish an atmosphere in such a harsh environment?

To shed light on this question, astronomers employed NASA’s James Webb Space Telescope to observe a rocky exoplanet called GJ 486 b. 

Although this planet orbits too closely to its star to be within the habitable zone, with a blistering surface temperature of approximately 800 degrees Fahrenheit (430 degrees Celsius), the telescope’s Near-Infrared Spectrograph (NIRSpec) detected hints of water vapor.

If the water vapor is indeed associated with GJ 486 b, this would suggest that the planet has an atmosphere despite its scorching temperature and close proximity to its star. While water vapor has been observed on gaseous exoplanets before, no atmosphere has been definitively detected around a rocky exoplanet. 

However, the research team urges caution, as the water vapor could be emanating from the star itself, specifically from cool starspots, rather than the planet.

Sarah Moran, lead author of the study from the University of Arizona in Tucson, explains that while the observed signal is “almost certainly due to water,” it remains unclear whether the water is part of the planet’s atmosphere or simply a signature coming from the star. 

Kevin Stevenson, the principal investigator on the program from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, reiterates the importance of this distinction, stating that finding water vapor in the atmosphere of a hot, rocky planet would be “a major breakthrough for exoplanet science,” but it is crucial to ensure the star is not responsible for the detected signal.

How the GJ 486 b study was done

GJ 486 b, a rocky world with stronger gravity than Earth, is approximately 30 percent larger and three times as massive as our home planet. It orbits its red dwarf star in just under 1.5 Earth days and is believed to be tidally locked, possessing a permanent day side and a permanent night side.

The planet’s transit in front of its star, as viewed from Earth, offers astronomers a unique opportunity to study its potential atmosphere. If an atmosphere is present, starlight passing through the gaseous layer would leave detectable fingerprints that can be decoded through a technique known as transmission spectroscopy. 

The team investigating the rocky exoplanet GJ 486 b has observed two transits, each lasting approximately an hour. They analyzed the resulting data using three distinct methods, all of which consistently revealed a mostly flat spectrum with a notable rise at the shortest infrared wavelengths. 

What the researchers found at GJ 486 b

After running computer models that considered various molecules, the team concluded that water vapor was the most likely source of the signal.

Although the presence of water vapor could potentially indicate an atmosphere on GJ 486 b, it is equally plausible that the water vapor originates from the star itself. Interestingly, even our own Sun can sometimes harbor water vapor in sunspots, as these areas are significantly cooler than the surrounding star surface. 

GJ 486 b’s host star is much cooler than the Sun, which means that even more water vapor could concentrate within its starspots, potentially creating a signal that mimics a planetary atmosphere.

Ryan MacDonald, a co-author of the study from the University of Michigan in Ann Arbor, explains that while they did not observe evidence of the planet crossing any starspots during the transits, this does not necessarily mean that there are no spots elsewhere on the star. 

Such a scenario could imprint the water signal into the data, making it appear as though it is coming from a planetary atmosphere.

If a water vapor atmosphere does exist, it would be expected to gradually erode due to stellar heating and irradiation. Consequently, if an atmosphere is present, it would likely need to be continuously replenished by volcanic activity ejecting steam from the planet’s interior. 

The study of GJ 486 b continues

To determine whether the water vapor is indeed in the planet’s atmosphere, additional observations are required to assess the amount of water present.

Future observations using the James Webb Space Telescope’s Mid-Infrared Instrument (MIRI) may provide further insight into this system. 

An upcoming program will observe GJ 486 b’s day side, and if the planet has no atmosphere or only a thin one, the hottest part of the day side should be directly under the star. However, if the hottest point is shifted, this would suggest the presence of an atmosphere capable of circulating heat.

In order to differentiate between the planetary atmosphere and starspot scenarios, observations at shorter infrared wavelengths by another Webb instrument, the Near-Infrared Imager and Slitless Spectrograph (NIRISS), will be necessary. 

Kevin Stevenson, the principal investigator on the program, emphasizes the importance of utilizing multiple instruments to conclusively determine whether GJ 486 b has an atmosphere.

As scientists continue to study GJ 486 b, the results of these observations could significantly impact our understanding of rocky exoplanets and their potential to maintain atmospheres in harsh environments.

More about exoplanets and the search for extraterrestrial life

Exoplanets, or extrasolar planets, are planets that orbit stars outside of our solar system. Since the discovery of the first exoplanet in 1992, thousands more have been identified, and ongoing research continues to unveil new and diverse worlds. 

The search for water and life outside our solar system is of great interest to scientists, as it could offer insights into the prevalence of life in the universe and help us better understand the conditions necessary for its emergence and survival.

Water is considered an essential ingredient for life as we know it. It serves as a solvent for biochemical reactions and regulates temperature in living organisms. The presence of liquid water on an exoplanet is therefore seen as a key factor in determining its potential habitability. 

The habitable zone, or the “Goldilocks zone,” is the region around a star where conditions are just right – not too hot, not too cold – for liquid water to exist on a planet’s surface. Identifying exoplanets within this zone is a priority in the search for life beyond our solar system. GJ 486 b is found outside of the goldilocks zone.

A variety of techniques are employed to detect exoplanets and analyze their atmospheres for signs of water or life. Some of the most widely used methods include:

Transit method

Astronomers observe the decrease in a star’s brightness when an orbiting planet passes in front of it, or “transits.” By analyzing the resulting light curves, scientists can deduce the planet’s size, orbit, and atmospheric composition.

Radial velocity method

This technique measures the motion of a star caused by the gravitational pull of an orbiting planet. As the star moves towards and away from Earth, the Doppler effect causes its light to shift to blue and red wavelengths, respectively. By analyzing these shifts, astronomers can determine the planet’s mass, orbit, and sometimes its atmospheric composition.

Direct imaging

High-contrast imaging techniques and advanced instruments, like the James Webb Space Telescope, enable scientists to capture images of exoplanets directly. By studying these images and the light emitted or reflected by the planets, researchers can analyze their atmospheres for signs of water or other potential biomarkers.

In addition to water, astrobiologists look for other chemical signatures, such as methane, oxygen, and ozone, which could indicate the presence of life or at least the potential for habitability. These “biosignatures” are distinctive chemical compounds or patterns that are typically produced by living organisms.

The discovery of an exoplanet with both water and biosignatures would be a significant breakthrough in the search for extraterrestrial life. While no such planet has been found yet, the growing catalogue of exoplanets and advancements in detection techniques continue to bring us closer to answering the profound question of whether or not we are alone in the universe.

More about the James Webb Space Telescope

The James Webb Space Telescope (JWST), named after the former NASA administrator James E. Webb, is a large, infrared-optimized space observatory developed through a collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). 

The telescope is designed to succeed the Hubble Space Telescope as the premier space observatory of the next decade, offering significant advancements in terms of sensitivity and capabilities.

The main scientific goals of the JWST include:

  1. Investigating the formation of the first galaxies, stars, and black holes in the early universe.
  2. Observing the formation of stars and planetary systems, and understanding the conditions necessary for the emergence of life.
  3. Studying the physical and chemical properties of solar systems, including our own, and examining the potential for life on other planets.
  4. Exploring the mysteries of dark matter, dark energy, and the nature of the universe itself.

The JWST is equipped with a 6.5-meter (21.3 feet) primary mirror, significantly larger than Hubble’s 2.4-meter (7.9 feet) mirror, allowing it to capture more light and achieve much higher resolution. Its instruments are optimized for infrared wavelengths, which enables it to peer through dust and gas to observe distant celestial objects and study the early universe.

The main instruments aboard the JWST include:

Near-Infrared Camera (NIRCam)

This camera serves as the primary imager for the telescope, capturing high-resolution images in near-infrared wavelengths. It can detect faint light from the earliest galaxies and help study the formation of stars and planets.

Near-Infrared Spectrograph (NIRSpec)

This spectrograph separates light into its constituent wavelengths, allowing scientists to analyze the chemical composition, temperature, and other properties of celestial objects.

Mid-Infrared Instrument (MIRI)

Operating at mid-infrared wavelengths, MIRI is designed to study cooler objects, such as distant galaxies, forming stars, and exoplanets. It combines imaging and spectroscopy capabilities to provide detailed information about the observed objects.

Fine Guidance Sensor and Near-Infrared Imager and Slitless Spectrograph (FGS/NIRISS)

The FGS ensures the telescope remains stable and accurately pointed during observations, while NIRISS is designed for high-contrast imaging and the study of exoplanet atmospheres.

The JWST will be positioned at the second Lagrange point (L2), approximately 1.5 million kilometers (about 930,000 miles) from Earth. This location provides a stable environment with minimal interference from the Earth and Moon, allowing the telescope to maintain a constant temperature and perform sensitive observations. This helps when searching for exoplanets like GJ 486 b.

The James Webb Space Telescope is expected to revolutionize our understanding of the universe, shedding light on the formation of celestial objects, the nature of dark matter and dark energy, and the potential for life beyond our solar system. Its unprecedented capabilities and sensitivity promise to uncover new discoveries and insights, transforming the field of astronomy and our knowledge of the cosmos.


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