James Webb provides groundbreaking data from the TRAPPIST-1 system

trappist 1b

In 2017, a group of researchers employing the TRAPPIST telescope found seven rocky planets orbiting a very cool red dwarf 40 light-years from Earth. The TRAPPIST-1 star system was widely welcomed by the general public thanks to the tentative possibility of finding some form of life in the habitable zone. However, before Webb, there was no ability to confirm the existence of an atmosphere in them. Finally, the data have been compiled and released by NASA and ESA.

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Illustration of the exoplanet TRAPPIST-1b together with its star. Credits: NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)

A very particular system

The seven planets are very similar to each other. If they were in the solar system, they could be placed without major problem in a radius smaller than the orbit of mercury, but receiving a similar amount of energy.. That closeness to the main TRAPPIST-1 implies that all or most of them are tidally coupled. That is, they always offer the same face towards the star.

TRAPPIST-1b, the closest of the planets to the star, has a mean orbital radius equivalent to one tenth that of the Earth and receives up to 4 times more energy. Although it is not in the habitable zone, it is desired to be able to know it in order to better understand planetary processes in other as yet undiscovered systems.

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Comparison of temperature on the diurnal side of predictions and measurements of exoplanet TRAPPIST-1 and Earth.

Hunting for an atmosphere

Previous observations of TRAPPIST-1b by the Hubble and Spitzer telescopes did not provide conclusive data on the absence and presence of a dense atmosphere. Therefore, an alternative was needed in order to be certain of the presence of a dense atmosphere.. For this the temperature was measured, comparing the data over time would allow to find the heat flow over the planet. Comparing them with the theoretical models, the density of the atmosphere can be inferred.

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Light curve of the star TRAPPIST-1 in the phenomenon known as secondary eclipse, in which the planet passes behind the star.

This was done using the secondary eclipse photometry technique. In this, the MIRI instrument measured changes in the system's brightness as the planet apparently moved behind the star. Since TRAPPIST-1b does not emit any light of its own, it is necessary to filter out the necessary data from the entire received data.

Achieving such data was in itself a great feat to demonstrate Webb's incredible detection capabilities. He needed a resolution to filter out differences similar to 0.01 %. There was also the possibility of not even seeing the eclipse, since the mutual gravity of all the planets strongly alters their orbits. However, the measurements agreed with the time predictions.

Analysis of the data revealed a temperature on its constant diurnal side of approximately 500 kelvins or 230 degrees Celsius. Based on this, the researchers consider TRAPPIST-1b to have no atmosphere. The data agree with theoretical predictions of light emission from a rock blackbody and no gases trapped in the gravitational field.

The hope of finding life

TRAPPIST-1b is the closest planet to the star, and although it was previously expected not to find favorable conditions for life, these results offer a good insight into what other worlds may be hiding. In the future James Webb will continue to point his instruments at this enigmatic system.

Francisco Andrés Forero Daza