Researchers just discovered a planetary system located 40 light years from Earth that hosts three possibly habitable planets each the size of Earth. Based on the calculated dimensions and surface temperatures of the planets, the scientists established that parts of each planet might have conditions ideal for life.

According to a new report in the journal Nature, researchers have now found the two innermost planets are rocky and have tight, dense atmospheres, like those found on Earth and Mars.

To make their discovery, the team borrowed NASA’s Hubble telescope and pointed it at the system’s star, TRAPPIST-1. The team commandeered the telescope in order to capture a rare double transit, when two planets in a system nearly simultaneously pass in front of their star.

The team was able to document a combined transmission spectrum of TRAPPIST-1b and c, which means that as one planet then the other crossed in front of the star, they could evaluate the modifications in starlight wavelengths as the quantity of starlight dipped with each pass.

“The data turned out to be pristine, absolutely perfect, and the observations were the best that we could have expected,” study author Julien de Wit, a planetary scientist at MIT, said in a news release. “The force was certainly with us.”

The drops in starlight were identified over a thin array of wavelengths and turned out not to fluctuate significantly over that range. Had the dips varied considerably, it would have shown the planets have light, puffy atmospheres, comparable to that of the gas giant Jupiter.

Looking at the Planets’ Atmospheres

However, the data indicated both transiting planets have compact atmospheres, very similar our own.

“Now we can say that these planets are rocky. Now the question is, what kind of atmosphere do they have?” de Wit said. “The plausible scenarios include something like Venus, where the atmosphere is dominated by carbon dioxide, or an Earth-like atmosphere with heavy clouds, or even something like Mars with a depleted atmosphere. The next step is to try to disentangle all these possible scenarios that exist for these terrestrial planets.”

The researchers are currently trying to identify ground-based telescopes to delve further into this planetary system, as well as look for other similar systems.

The planetary system’s star, TRAPPIST-1, is referred to as an ultracool dwarf star, a kind of star that is normally chiller than the sun, giving off radiation in the infrared as opposed to the visible spectrum. De Wit’s colleagues from the University of Liège came up with the idea to check for planets around these stars, because they are much fainter than standard stars, meaning their starlight would not overwhelm the signal from planets themselves.

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Image credit: NASA, ESA, AND STSCI

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