Recent sighting of planet TRAPPIST-1 raises concerns about stellar 'pollution’: Science Alert

Earlier this year, the James Webb Space Telescope shattered hopes for life on one of the Earth-like exoplanets discovered in the Milky Way.

TRAPPIST-1b, a world 1.4 times the mass of Earth and 1.1 times the radius, just 40 light-years away, has no atmosphere to protect it from its host star’s scorching radiation.

The discovery, made using mid-infrared photometric observations, was not unexpected; The research was more about closely examining a small, rocky world at cooler temperatures than we usually do.

Now, there are new JWST infrared spectroscopic observations—and they suggest that the behavior of an exoplanet’s host star may interfere with the exoplanet’s ability to make accurate measurements.

TRAPPIST-1b is still uninhabitable, as far as we know, mind you. But the discovery, led by astronomer Olivia Lim of the University of Montreal, suggests that stellar contamination could create false detections of molecules unrelated to the exoplanet.

An artist’s impression of TRAPPIST-1b. (NASA, ESA, CSA, J. Olmsted/STScI, TP Greene/NASA Ames, T. Bell/BAERI, E. Ducrot & P. ​​Lagage/CEA)

„Our observations show no signs of an atmosphere around TRAPPIST-1 b. This tells us that the planet may be bare rock, have an atmosphere rich in clouds, or contain a very heavy molecule, such as carbon dioxide, that is too small to detect an atmosphere. ,” says astrophysicist Ryan McDonald of the University of Michigan.

„But what we see is that the star is the dominant effect in our observations, and it will do the same for the other planets in the system.”

The problem is that stars don’t sit at the same brightness all the time. Star points cause fading; Faculae are points of brightness. These variations in a star’s brightness can influence spectral observations of exoplanet atmospheres.

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Such observations are taken when an exoplanet passes between us and its host star. It dims the star’s light little by little; But some starlight passes through the exoplanet’s atmosphere around the edge of the planetary disk.

Scientists can look for changes in the spectrum of light when an exoplanet transits, and use those changes to hunt for signatures of molecules that absorb and re-emit specific wavelengths of light.

If the brightness of the star is constant, it will be much easier. But the researchers found that stellar activity can heavily contaminate spectroscopic observations.

„In addition to contamination from star points and faeculae, we observed a stellar flare, an unpredictable event during which a star remains bright for several minutes or hours.” Lim says.

„This flare affected our measurement of the amount of light blocked by the planet. Such signatures of stellar activity are difficult to model, but we need to calculate them to make sure we understand the data correctly.”

A diagram of changes in a star’s light as an exoplanet orbits it. (J. Win, arXiv, 2014)

The team created a model of stellar pollution and then conducted two analyzes of the data: the first with stellar pollution removed, and the second with it intact. Both results are similar; That is, the spectrum with TRAPPIST-1b was more or less the same without the spectrum.

This is a confirmation of previous mid-infrared spectroscopy results that showed the exoplanet has no atmosphere. But the team’s work also showed the importance of taking stellar contamination into account before analyzing the data.

Good to find this out now. There are seven exoplanets in the TRAPPIST-1 system, three of which are in the star’s habitable zone — a nice, moderate distance away that isn’t too hot or too cold as we know it. JWST hasn’t seen these habitable zone worlds yet, but now we know that stellar contamination can skew the results, and scientists can take that into account.

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„Because of the star model’s lack of reliability,” The researchers conclude„Further theoretical work and/or observations of the host star are necessary to provide better constraints on the contribution of stellar contamination to future transmission spectra.”

Published in the thesis Astrophysical Journal Letters.

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