The Telescope That Didn't Need JWST
Helium Leaking For Billions
Collin Cherubim, who finished his Harvard PhD this year, modeled what he expected before anyone looked: a rocky planet orbiting a red dwarf, close enough for temperate surface temperatures, should shed a thin layer of helium from its upper atmosphere if it had an atmosphere left to shed. Then his team pointed the WINERED spectrograph, mounted on the 6.5 meter Magellan Clay Telescope in Chile, at LHS 1140 b as it crossed its star, and watched helium absorb starlight exactly where the model said it would.
The planet is 48 light-years out, 5.6 times Earth's mass, wrapped in enough atmosphere to register a helium leak. Red dwarfs are dim, so their habitable zones sit close in, and close in means decades of flares and stellar wind aimed at whatever air a planet has. Earlier searches for atmospheres around red-dwarf rocky planets kept coming back empty, air presumed stripped by exactly that flare history. Helium escaping now, measurably, means the tank was never emptied. The team's read, published in Science on July 16, is that the atmosphere has held for more than three billion years, not that it appeared last week. A leak that old is evidence of a reservoir, not a puff of gas.
Where JWST Gets Spent
JWST is the only instrument sensitive enough to look for the actual signature of life, a specific ratio of gases like oxygen and methane that shouldn't coexist without something replenishing one of them. But that search is expensive: a real biosignature pair can take 30 to 700 transits to confirm, sometimes over 100 hours of an oversubscribed telescope's time, per candidate. Before Cherubim's result, every one of those hours had to do double duty: first prove the planet has kept an atmosphere at all, then start hunting for the specific molecules that would matter. Most candidates fail at the first step, air stripped away by their star long before anyone gets to ask about biosignatures.
Cherubim's team did that first step from the ground, on the Magellan Clay, an existing 6.5 meter telescope with no queue measured in years. Ground-based helium spectroscopy becomes the filter, and JWST is reserved for the planets that clear it. Harvard's Robin Wordsworth called this proof that at least one rocky habitable zone world can keep its air. The more useful sentence is the one nobody's saying yet: JWST just got some of its hours back.
An atmosphere is not a biosignature, and everything interesting about LHS 1140 b, whatever sits under that helium layer, is still unmeasured. Thin, largely inert air can survive three billion years of red dwarf flares without telling you a thing about life. Whether that is a genuine first step toward a livable world or just proof that a planet can hold its breath a very long time will not be settled here: it waits on further observation of LHS 1140 b.
Sources
- Science (journal) (doi.org)
- Harvard FAS (current.fas.harvard.edu)
- EarthSky (earthsky.org)
- TechTimes (techtimes.com)
- phys.org (phys.org)