The Third Rock From Another Sun Shows No Signs of Life So Far

New York Times

a day ago

In the search for signs of life on what seemed like a promising little exoplanet, astronomers' hopes have dimmed.
Living things, as we understand them, seem to flourish best in an atmosphere like the one on Earth. But scientists who have been using the James Webb Space Telescope to examine the planet known as Trappist-1 d have found no sign of an earthlike atmosphere, according to a study published on Wednesday in The Astrophysical Journal.
Exoplanets revolve around stars other than our sun. And the exoplanet in question is the third of seven that orbit Trappist-1, a star some 40 light-years from our place in the Milky Way. It is a red dwarf, so named because this type of star emits reddish light and tends to be small.
In the search for life elsewhere in the galaxy, the discovery of the Trappist-1 planetary system was a big deal. Researchers announced in 2017 that the seven planets around Trappist-1 seemed to have excellent potential as hosts for living things.
But in the years since, astronomers have not detected habitable atmospheres on the two innermost planets. They are still examining the outer ones.
The star Trappist-1, which was named for a telescope in the Atacama Desert of Chile, is just a little bigger than Jupiter. Red dwarves are the most common stars in our galaxy, but this particular star and its planets are a bit easier to study than other known planetary systems. The system is fairly close to Earth, and the seven planets follow a tight, fast orbit.
That makes them good candidates for a method of observation called transmission spectroscopy. When light from a star shines through a planet's atmosphere on its way to the Webb telescope, scientists can find clues about the chemical makeup of that atmosphere by determining which wavelengths of light it absorbed.
The third world from the Trappist-1 star, a rocky planet, had appeared promising, according to Caroline Piaulet-Ghorayeb, a postdoctoral researcher at the University of Chicago and the study's lead author.
But the starlight that passed the exoplanet before reaching the Webb telescope did not appear to have been filtered through the kinds of atmospheric molecules that are essential to life on Earth, like water or carbon dioxide.
The research of Dr. Piaulet-Ghorayeb and her team did not completely rule out the possibility of an atmosphere there, she said. But it did suggest that cool red dwarves — or, at least, this cool red dwarf — might be too volatile to support life.
'Maybe that tells us that it's going to be harder than we thought to find atmospheres on these rocky planets,' she added.
Astronomers may need to turn their attention to planets that circle brighter stars, like our sun.
Those planets are more difficult to observe and will probably require another telescope, said Jacob Bean, an astronomer at the University of Chicago who advises Dr. Piaulet-Ghorayeb but was not involved in the study. 'We still have this burning question: Can life develop elsewhere?' he said.
Dr. Piaulet-Ghorayeb agreed that other planets might be better candidates for life than Trappist-1 d, but she was not ready to give up on the exoplanet just yet. 'There are different ways of figuring out whether these planets have atmospheres,' she said. 'Transmission spectroscopy is just one of them.'
Based on the results of her study, she said, 'our job is going to be a little bit harder.'
'But it definitely doesn't kill our prospects,' she added.
Dr. Bean called the Trappist-1 system 'a fantastic laboratory for studying terrestrial planets around other stars,' and said that the research so far had yielded plenty of interesting data despite the largely negative result of the latest study.
'If we go look, sometimes we come up disappointed,' Dr. Bean said. 'But if we hadn't looked, we wouldn't know. And it's always better to know.'