To prepare for one of the most advanced searches for life on other planets, astronomers have examined the stars that a new multibillion-dollar telescope might target. They discovered some may be better suited than others to hunt for potential alien life.
In the 2040s, NASA plans to launch the Habitable Worlds Observatory (HWO), a successor to the James Webb Space Telescope. Its primary goal is to image 25 Earth-like planets in the habitable zones of sun-like stars – where water, or even life, could exist. Before construction on the HWO begins in the next decade, scientists are tackling some of the key technological and scientific hurdles it will face.
One of those is selecting the stars within about 100 light years of Earth that the telescope might target. at the University of California, Berkeley, and their colleagues have analysed 164 candidate stars so far to see what we do and don’t know about them. “We’re trying to get the ball rolling so we can fill in our knowledge gaps,” says Harada. These may become some of the most studied stars in history.
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The list of candidates includes Tau Ceti, a sun-like star 12 light years away that is believed to host multiple planets, and 82 G. Eridani, 20 light years away, which is known to have at least three super Earths, with masses bigger than Earth’s but smaller than Neptune’s. So far, about 47 of the stars have been ranked as “Tier A”, the most promising targets for HWO. However, at NASA’s Jet Propulsion Laboratory in California, who drew up the , says the full list is “very much provisional” at the moment.
Harada and their team showed that 102 of the total list are binary stars, which could complicate the search for life. HWO will use an advanced technique known as a coronagraph to block out light from the stars and attempt to image the planets in orbit, while also picking apart the gases in the planets’ atmospheres. “If they’re too close together, the unblocked star would swamp the image and you wouldn’t be able to see planets,” says , the director of the University of California Observatories.
Of the stars, 33 are also known to have debris discs – like our solar system’s Kuiper Belt – which could make imaging planets difficult. “It’s an extra source of flux,” says Harada. It is likely that HWO’s coronagraph will be designed to cope with such discs. Some of the stars are also prone to flaring events. These are not necessarily deadly to life, considering our sun emits solar flares, but researchers will need to study them to make sure they are not too intense. “These can affect life and habitability,” says Harada.
The composition of many of the stars is known, which can directly translate to the composition and habitability of any planets orbiting them as well. “We might want to [focus our search on stars with] the chemical elements that are essential for life, including carbon, nitrogen and phosphorus,” says Harada. But scientists don’t know the make-up of all the stars in such detail, making them prime targets for follow-up studies.
Any one of these stars could be the location where life is first definitively detected outside our solar system. That makes them extraordinarily valuable objects that will be widely observed before HWO launches, says Macintosh. “People are going to study the heck out of them,” he says.
arXiv
