Planets that can potentially support life... - Page 41

Scientists say they have detected an atmosphere around an Earth-like planet for the first time.

They have studied a world known as GJ 1132b, which is 1.4-times the size of our planet and lies 39 light years away.

Their observations suggest that the "super-Earth" is cloaked in a thick layer of gasses that are either water or methane or a mixture of both.

The study is published in the Astronomical Journal.

Discovering an atmosphere, and characterising it, is an important step forward in the hunt for life beyond our Solar System.
But it is highly unlikely that this world is habitable: it has a surface temperature of 370C.

Dr John Southworth, the lead researcher from Keele University, said: "To my knowledge the hottest temperature that life has been able to survive on Earth is 120C and that's far cooler than this planet."

Could there be life under the icy surface of Saturn's moon Enceladus?

Scientists have found a promising sign.

NASA announced on Thursday that its Cassini spacecraft mission to Saturn has gathered new evidence that there's a chemical reaction taking place under the moon's icy surface that could provide conditions for life. They described their findings in the journal Science.

"This is the closest we've come, so far, to identifying a place with some of the ingredients needed for a habitable environment," Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate in Washington, said in a statement.

However, the scientists think that because the moon is young, there may not have been time for life to emerge.

In 2015, researchers said that there was evidence of a warm ocean under the moon's surface, as NPR's Geoff Brumfiel reported.

This posed an exciting prospect — researchers wondered whether that warm ocean might be interacting with rock to create a form of chemical energy that could be used by some forms of life.

If true, it would be analogous to ancient organisms on Earth fueled by the energy in deep-sea ocean vents.

[b]under the surface of Enceladus. By flying through a plume spraying out of its icy shell, Cassini was able to detect molecular hydrogen.

NASA said in a press release that the presence of hydrogen in the sub-surface ocean "means that microbes – if any exist there – could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in water." Called methanogenesis, it's a reaction that it says is "at the root of the tree of life on Earth."

As the lead author Hunter Waite put it, the reaction would basically provide a "candy store for microbes."

So what exactly could be lurking under the surface?

"Most of us would be excited with any life, and certainly when we're talking about the sources of energy, this is to feed the base of a food web. So we're going to start with bacteria and if we get lucky, maybe there's something that's larger," NASA astrobiology senior scientist Mary Voytek said at a news conference.

Astronomers have added 219 candidates to the growing list of planets beyond our solar system, 10 of which may be about the same size and temperature as Earth, boosting their chances of hosting life.

Scientists found the candidates in a final batch of Nasa’s Kepler Space Telescope observations of 200,000 sample stars in the constellation Cygnus.

They include 10 newly discovered rocky worlds that are the right distance from their parent stars for water, if it exists there, to pool on the surface. Scientists believe liquid water is a key ingredient for life.

“An important question for us is, ‘Are we alone?’” Kepler program scientist Mario Perez said in a conference call with reporters. “Maybe Kepler today is telling us indirectly ... that we are not alone.”

Nasa launched the Kepler telescope in 2009 to learn if Earth-like planets are common or rare. With the final analysis of Kepler data in hand, scientists said they will now work on answering that question, a key step in assessing the chance that life exists beyond Earth.

During a four-year mission Kepler found 2,335 confirmed planets and another 1,699 candidates, bringing its tally to 4,034. That number includes about 50 worlds that may be about the same size and temperature as Earth.

Including other telescope surveys, scientists have confirmed the existence of nearly 3,500 planets beyond the solar system.

Kepler’s data also provided a new way to assess whether a planet has a solid surface, like Earth, or is made mostly of gas, like Neptune. The distinction will help scientists home in on potential Earth-like planets and better the odds for finding life.

The Kepler team found that planets which are about 1.75 times the size of Earth and smaller tend to be rocky, while those two to 3.5 times the size of Earth become gas-shrouded worlds like Neptune.

“It’s like finding what we thought was a single species of animal is really two different things,” said Benjamin Fulton, a graduate student in astronomy who analysed the Kepler data.

So far, these planets, which scientists refer to as “super-Earths” and “mini-Neptunes”, have not been found in Earth’s solar system, though scientists are on the hunt for a potential ninth planet far beyond Pluto.

“It is interesting that we don’t have what appears to be the most common type of planet in the galaxy,” Fulton said.

On June 21 2017 04:29 CuddlyCuteKitten wrote:
The cool thing is that even without some amazing breakthrough in technology we could be looking at humans living on other planets in a reasonable time frame (a few hundred years).

We need perhaps a hundred more years to develop the tech to build a colony ship staffed by robots as well as a synthetic womb and the ability to print DNA chemically.
If we can get the thing to accelerate to 20 % the speed of light it would take ~200-300 years to get to a habitable planet, set up an outpost and clone up the first human being.

So essentially we should only need to not wipe our self out in a hundred years give or take and we could be a multi planet species given some times, if we wanted too. Not that anyone on Earth would ever get to experience a message from the actual planet but it would still be awesome.

On June 21 2017 04:29 CuddlyCuteKitten wrote:
The cool thing is that even without some amazing breakthrough in technology we could be looking at humans living on other planets in a reasonable time frame (a few hundred years).

We need perhaps a hundred more years to develop the tech to build a colony ship staffed by robots as well as a synthetic womb and the ability to print DNA chemically.
If we can get the thing to accelerate to 20 % the speed of light it would take ~200-300 years to get to a habitable planet, set up an outpost and clone up the first human being.

So essentially we should only need to not wipe our self out in a hundred years give or take and we could be a multi planet species given some times, if we wanted too. Not that anyone on Earth would ever get to experience a message from the actual planet but it would still be awesome.

Scientists have identified two planets circling round a dim dwarf star as especially likely candidates for habitable worlds, with probable water and a source of heat, conditions thought necessary for life beyond Earth.

Since their discovery last year, the seven planets and their star, called Trappist-1, have thrilled astronomers hunting for a world resembling Earth. Never before had scientists found so many Earth-sized planets around a single star, or in a zone where the extreme temperatures of space would not obliterate the chances of life.

The finding suggested that there may be planets as rocky and large as Earth all over the Milky Way, and scientists quickly set to work analyzing the Trappist-1 system.

With colleagues in Hungary, Dr Amy Barr, of the Planetary Science Institute built mathematical models of the seven planets and their interiors, and found that six of the seven worlds likely have water, as liquid or ice, with a global ocean possible on one. The team then modeled the planets’ orbits to determine a likely surface temperature on the worlds.

“That’s one of the main innovations of the paper,” Barr told the Guardian. “The planets are also on eccentric orbits – kind of egg shaped – so every time the planet goes around the star it gets stretched and squeezed.”

Jupiter’s moon Io, experiences the same kind of push-pull, called tidal heat. Io’s surface is riven by erupting volcanoes, lava flows, scars and caldera. Barr said the same forces are probably at work in the Trappist-1 system: “The planet kind of works its own internal friction, because that stretching and squeezing creates heat in the interior.”

In the paper, set to be published in the journal Astronomy & Astrophysics, the team concluded that planets b and c (each world goes by a lower-case letter), experience tidal heat, and that planet c likely has little to no water, but mostly iron and rock. Planets d and e – the two identified as most likely to be habitable – also experience tidal heat, they found, but much less.

They calculated that those planets are “in this kind of temperate region”, Barr said, with a “very reasonable surface temperatures”. Planet d, the team estimates, has a temperature around 15C (59F) or perhaps as low as slightly warmer than the melting point of ice. Planet e was colder, Barr said: “the temperatures you would get in Antarctica, but also reasonable”.

The likelihood of tidal heating is encouraging to scientists in search of planets with the conditions for life. Tidal heat not only warms a planet, but also drives chemistry and flow in its mantle, conditions amenable to the development of life – at least as humans know it.

Because Nasa has yet to launch its next generation space telescope, the James Webb, scientists like Barr and her colleagues have turned to computers to investigate puzzles with limited data. A paper last year found that Trappist-1, although older and more dim than our sun, projects a stellar wind far more severe than the solar wind that lashes Earth from our sun. This wind likely stripped away the atmosphere – another condition for life – from the planets closest to Trappist-1, while the more distant planets fared better. Another team investigated whether the Trappist-1 worlds could hold water – another condition – and found that four of the seven might.

But while the pieces of research by various teams have generally supported each other, Barr and other astronomers, astrophysicists and geophysicists are most eager for more observations. Should the James Webb launch on schedule this year, it will provide far more data about specific exoplanets, and ease the challenge of writing about a system as a whole.

“It’s hard to write a paper about seven planets all at once,” Barr said.

On June 21 2017 04:29 CuddlyCuteKitten wrote:
The cool thing is that even without some amazing breakthrough in technology we could be looking at humans living on other planets in a reasonable time frame (a few hundred years).

We need perhaps a hundred more years to develop the tech to build a colony ship staffed by robots as well as a synthetic womb and the ability to print DNA chemically.
If we can get the thing to accelerate to 20 % the speed of light it would take ~200-300 years to get to a habitable planet, set up an outpost and clone up the first human being.

So essentially we should only need to not wipe our self out in a hundred years give or take and we could be a multi planet species given some times, if we wanted too. Not that anyone on Earth would ever get to experience a message from the actual planet but it would still be awesome.

Astronomers have discovered a pretty interesting multi-planetary system orbiting a nearby star. Each of the exoplanets is apparently a gas giant, but two of them orbit the star in the habitable zone, where liquid water could exist!

To be clear, gas giants don’t have a surface — they have such tremendous atmospheres that as you go down inside them the air just gets thicker, merges into a liquid mantle, then finally gets crushed into a solid deep down near the core — but they do tend to have moons, some of them quite large. And that makes this system very interesting indeed…

The planets orbit the star HD 34445 (the 34,445th entry in the Henry Draper catalog of brightish stars). The star itself is at first glance a lot like the Sun: It’s a type G0 star, just slightly warmer and just a scosh more massive than the Sun (1.07 times as massive, to be specific).

I was surprised, however, to see it’s bigger than I expected, about 1.38 times the Sun’s diameter, and twice as luminous. I’d think those numbers would be much closer to the Sun’s, but then I saw the age and understood: It’s 8.5 billion years old, nearly twice as old as the Sun, and that means it’s starting to run out of fuel in its core. It’s starting the slow expansion into red giant territory.

It’s pretty close to us as stars go, about 150 light years away, so it appears relatively bright as well — about 7th magnitude, which is a little bit fainter than you can see with the naked eye, but could easily spot in binoculars.

Through a big telescope, then, it’s really bright, and that makes it a good target to look for planets. Bright stars mean lots of photons for your camera, and that helps when you’re looking for small effects.

The first planet, HD 34445b, was announced in 2010. They found it using what’s called the reflex velocity method. The way I like to think of that is this: Imagine a big person facing a smaller person, and they hold hands. Now they swing each other around. The smaller person makes a big circle, and the bigger person makes a small circle. The “reflex” part comes in because as one person moves away from you the other moves toward you, and vice versa.

Same with stars and planets. A planet orbits the star due to the star’s gravity, but the planet has mass and gravity too, so the star responds by making a smaller circle. They actually both orbit their mutual center of gravity/center of mass, what astronomers call the 'barycenter.' We can’t see that planet directly because the star is bright and the planet faint, and the circle the star makes is far too small to see directly either.

But, as the star moves in a circle it sometimes approaches us, and sometimes moves away. When it approaches us its light is slightly shifted to the blue due to the Doppler effect, and it shifts to the red as it moves away. That can indeed be measured, though it's a small effect. The very first exoplanets were found this way!

After the first planet was found around HD 34445, astronomers concentrated on this star, using bigger and better telescopes and instruments to look for more. In October of 2017, another team announced they had found five more planets, for a total of six! They had taken 333 observations over 18 years to get them, so this is a really long-term project.

As is the convention, the planets are named HD 34445 b through g, in the order of their discovery. HD 34445 b takes 1057 days to orbit the star (about 3 years), and the rest take 215, 118, 49, 677, and 5,700 days (that last one is pretty far out from the star). And they're all pretty big: In terms of Jupiter's mass, they are (again in order) 0.63, 0.17, 0.1, 0.05, 0.12 and 0.38 as big as our own biggest planet.

For comparison, Saturn is about 1/3rd of Jupiter's mass, and Neptune about 1/20th. Jupiter is over 300 times the mass of Earth, so it seems like a decent bet that all these planets in the HD 34445 system are gas giants.

Right away that's interesting; this is clearly a very different solar system from our own! We only have four such big planets. They're also spread out around HD 34445, ranging from 40 million to a billion kilometers out from their star. There might be more farther out, but they would be very hard to detect; the reflex velocity method is easier to use for massive planets closer in to the star.

I'll note there could be more Earth-sized planets here too; there's room for them between the bigger ones or closer in to the star, but again this method makes it hard to spot them because of their lower mass.

But don't fret about not finding habitable worlds around HD 34445 just yet. This is where things get interesting indeed.

Two of the planets — HD34445b and f — are located in the star's habitable zone: the region around the star where liquid water can exist on the surface of a body. For this star, that's about 200 – 350 million kilometers out. Closer than the inner edge and it gets too hot (for a terrestrial (rocky) planet, you get a runaway greenhouse effect and the planet gets scorched), and farther than the outer edge and even the best greenhouse effect won't keep you from freezing.

HD 34445b is 311 million km out, and HD 34445f is 230 million. Not bad.

Now again, these are gas giants! HD 34445 b is 200 times the mass of the Earth, and HD 34445f, while smaller, is still about 40 times our heft. These are not going to be planets our Earth.

But they might have moons. Exomoons! Our own solar system's gas giants have huge retinues of such satellites, and some are big: Ganymede (orbiting Jupiter) and Titan (Saturn) are about as big as Mercury! And it’s not too ridiculous to think even bigger ones might exist, making some of these moons potentially Earth-sized, and maybe, maybe, Earth-like.

Heck, Titan is well over a billion kilometers from the Sun, and it has an atmosphere thicker than ours! If it were in a more Earth-like orbit around the Sun, it could possibly be a pretty nice place to live. Could there be such habitable moons around these alien worlds?

If so, I have to wonder. Their star is old and slowly expanding, becoming more and more luminous over time. If these moons exist and if they are habitable and if there is life there, it's in trouble. As the star turns into a proper red giant those moons will get good and truly cooked. It's a story played out over and again in the galaxy, and will here too with our own Sun. Eventually, like in a few billion years or so.

One interesting bit, though, is that moons farther out from HD 34445 will go from frozen to quite clement. Will they get a chance for life? Maybe, but then their warm season won’t last that long; eventually the star sheds its outer layers in a series of violent paroxysms and finally reveals its core: a white dwarf that’s very hot but so small it provides very little warmth. Everything in the system will eventually freeze.

Now, this is all speculation. We don't know there are moons orbiting these planets, and we have no idea if it's possible to have a habitable moon orbiting a gas giant just because they're in the habitable zone around their star. I can think of lots of reasons this could be a nasty place (the radiation around the gas giant incited by a strong magnetic field, huge tidal stresses causing endless seismic activity, and so on).

… but the Universe is vast, and in such an expanse even the unlikely is bound to happen many times. Finding an example of gas giants like these in a fairly nearby star implies it's common in the galaxy (if it were very rare what are the odds it would happen in a star that's only a tenth of a percent of the galaxy’s diameter away from us?).

Right now, we just don't know. But our collection of known exoplanets grows nearly every day, as does our ability to explore them. Nature has a way of surprising us the deeper we investigate it. And the science fiction fan in me would love to see these be true. Let's hope.

A faraway planet in the constellation of Leo has been named the most habitable known world beyond the solar system after astronomers detected water vapour in its atmosphere.

It is the first time a planet in its star’s “Goldilocks zone” – where the temperature is neither too hot nor too cold for liquid water to exist – has been found to bear the life-sustaining substance in the blanket of gases that surround it.

The discovery has raised hopes that the planet, and similar worlds spotted in recent years, not only have conditions that can be suited to life, but in some cases may host living organisms.

“This is the first potentially habitable planet where the temperature is right and where we now know there is water,” said Angelos Tsiaras, an astronomer at University College London. “It’s the best candidate for habitability right now.”

The planet, named K2-18b, was first spotted in 2015 by Nasa’s Kepler space telescope. Roughly twice as big as Earth and eight times as massive, it orbits a cool red dwarf less than half the size of the sun, 110 light years away.

Red dwarfs produce far less heat than the sun, but K2-18b is warmed to about 10C (50F) by circling close to its star. From a mere 14m miles out, a sixth of the distance from the Earth to the sun, the planet completes an orbit every 33 days, making a year there pass as swiftly as a month on Earth.

Today’s technology is too feeble to take photos of the surfaces of such distant worlds, and they are too far away to send probes to. But space-based telescopes can glean some information about the atmospheres on alien planets.

The UCL team turned to Nasa’s veteran Hubble space telescope, which observed K2-18b in the two years after its discovery. In particular, they analysed measurements of starlight from the red dwarf as the planet wandered across its face on eight separate occasions.

The data revealed that as K2-18b crossed in front of its star, wavelengths of light that are absorbed by water suddenly dropped off, and then rose again as the planet moved on. The effect is seen as a smoking gun for water vapour in the planet’s atmosphere.

“To our great surprise we saw a pretty strong signature of water vapour,” said Giovanna Tinetti, a member of the UCL team. “It means first of all that there’s an atmosphere, and second that it contains a significant amount of water.”

Nothing has driven the search for life elsewhere more than the presence of water. On Earth, there is no life without the substance, and the same is expected on other planets, at least for life as we know it.

The discovery of water vapour on K2-18b does not prove there is water on the surface. But it ticks one more box in the hunt for worlds where the conditions are ripe for life. “We don’t know any other planet with the right temperature that has water in its atmosphere,” Tsiaras told the Guardian. According to the report in Nature Astronomy, K2-18b has between 0.01% and 50% water in its atmosphere.

In astronomy jargon, K2-18b is a super-Earth, putting its size between Earth’s and Neptune’s. But rather than Earth’s twin, K2-18b is more like our home planet’s cousin. It is two-thirds the density of Earth and though it may have a rocky surface, it could equally be a water world.

Humans would not fare well on the planet. If it has a hard surface, it would be impossible to stand. With gravity eight times stronger than on Earth, the average human would weigh half a tonne. Added to that are intense UV rays that would drive cancer-causing mutations. But get around these and the view, at least, might be pleasing to the eye: wispy clouds, a giant red sun, and an inner planet that rises like Venus. As Ingo Waldmann, a researcher on the team, said: “It’s maybe not quite your vacation destination just yet.”

Ryan Cloutier at the Harvard and Smithsonian Center for Astrophysics said an independent analysis, or fresh observations, would be valuable to confirm the detection of water vapour. But he added that the apparent presence of water was promising for K2-18b’s habitability.

“It’s a good sign,” he said. “Overall, the presence of water in its atmosphere certainly improves the prospect of K2-18b being a potentially habitable planet, but further observations will be required to say for sure.”

Astronomers now hope to study more super-Earths for signs of water in their atmospheres. That work is due to be transformed in coming years with the launch of Nasa’s James Webb space telescope in 2021 and the European Space Agency’s Ariel mission in 2028. Observations from these telescopes should reveal more about the makeup of atmospheres on distant worlds, including the presence of methane and other gases that could be direct signs of life.

On September 12 2019 07:10 Amui wrote:
That's a pretty neat discovery.

Gravity might be 8x stronger from mass, but the planet is twice as large so you'd only have 2G on the surface. It'd be very hard for most people, but if you were very fit you could definitely walk around and do some light activity.

I don't think we'll leave our solar system in my lifetime though, so it's kind of a moot point anyways.

On September 12 2019 06:37 {CC}StealthBlue wrote:
Huge bump.



Source

On September 12 2019 22:32 pmh wrote:


8 times the mass of the earth around a red dwarf. Maybe there can be life but it wont be highly developed.
Seeing the enormous amount of effort in detecting those planets I find the results very disappointing. There has not been found even ONE planet that is somewhat similar to earth. The longer it takes to find one,the more we should realize how incredibly lucky we are with having earth.

.

On September 12 2019 09:10 Dav1oN wrote:


Gravity 2g means you won't survive for long, our body is designed for 1g excusivly.

Such gravity means you'll have to grow bigger hearth, possibly even two, because a proper blood circulation require so.

In addition your muscular apparatus would suffer roughly two times harder. Atmospheric pressure also usually much higher in such conditions.

I also should correct myself, humans designed for 1g, specific pressure, atmosphere, land, temerature, only for Earth.

Well, and the worst thing is that the closest star is ~4,5 light years away, impossible to reach at the moment and maybe never at all. Unless you take some kind of "Pandorum" try. Wormholes is a fiction at the moment also.

On September 13 2019 02:40 Yurie wrote:


We could build generation ships and go there (4,5 light years) with current technology. We would likely die upon reaching there and not having a habitable planet waiting though.

Slightly future tech is artificial wombs, frozen eggs and embryos. That requires less from the craft going there but probably half a century of robot development. A thing to note, removing people fully from the trip makes it much simpler.

Terraforming or having a civilisation viable in space without a habitable planet is the deal breaker though. If we manage living full time in space with 0 resources required to be supplied from Earth there isn't any major hindrances for going. If we did a solid push for it I don't see why we couldn't have it all done in 50 years. More likely 100 years since we aren't pushing for it.

High in the toxic atmosphere of the planet Venus, astronomers on Earth have discovered signs of what might be life.

If the discovery is confirmed by additional telescope observations and future space missions, it could turn the gaze of scientists toward one of the brightest objects in the night sky. Venus, named after the Roman goddess of beauty, roasts at temperatures of hundreds of degrees and is cloaked by clouds that contain droplets of corrosive sulfuric acid. Few have focused on the rocky planet as a habitat for something living.

Instead, for decades, scientists have sought signs of life elsewhere, usually peering outward to Mars and more recently at Europa, Enceladus and other icy moons of the giant planets.

The astronomers, who reported the finding on Monday in a pair of papers, have not collected specimens of Venusian microbes, nor have they snapped any pictures of them. But with powerful telescopes, they have detected a chemical — phosphine — in the thick Venus atmosphere. After much analysis, the scientists assert that something now alive is the only explanation for the chemical’s source.

Some researchers question this hypothesis, and they suggest instead that the gas could result from unexplained atmospheric or geologic processes on a planet that remains mysterious. But the finding will also encourage some planetary scientists to ask whether humanity has overlooked a planet that may have once been more Earthlike than any other world in our solar system.

“This is an astonishing and ‘out of the blue’ finding,” said Sara Seager, a planetary scientist at the Massachusetts Institute of Technology and an author of the papers (one published in Nature Astronomy and another submitted to the journal Astrobiology). “It will definitely fuel more research into the possibilities for life in Venus’s atmosphere.”

“We know that it is an extraordinary discovery,” said Clara Sousa-Silva, a molecular astrophysicist at Harvard University whose research has focused on phosphine, and another of the authors. “We may not know just how extraordinary without going back to Venus.”

Sarah Stewart Johnson, a planetary scientist and head of the Johnson Biosignatures Lab at Georgetown University who was not involved in the work, said, “There’s been a lot of buzz about phosphine as a biosignature gas for exoplanets recently,” referring to the search for life on worlds that orbit other stars. “How cool to find it on Venus.”

She added: “Venus has been ignored by NASA for so long. It’s really a shame.”

David Grinspoon of the Planetary Science Institute in Tucson, Ariz., who was not part of the work but has long promoted the possibility of life in Venus’s clouds, said, “That is pretty damn exciting!”

The work needs to be followed up, he said, “but this could be the first observation we’ve made which reveals an alien biosphere and, what do you know, it’s on the closest planet to home in the entire cosmos.”

Venus is one of the most beautiful objects in Earth’s sky. But at a closer glance, the less lovely it becomes.

Often called Earth’s twin, Venus is roughly the same mass as Earth. Many scientists think that Venus was once covered in water and possessed an atmosphere where life as we know it could have flourished.

In earlier days of the solar system, Earth was not so hospitable to the likes of us. There was life here then, even an entire biosphere that did not survive in the oxygen-rich environment that later developed. And much as Earth over time became a home for jellyfish, ferns, dinosaurs and Homo sapiens, Venus was transformed by something into a hell.

Today, the second planet from the sun has an atmosphere stifled by carbon dioxide gas, and surface temperatures that average more than 800 degrees Fahrenheit. The dense atmosphere of Venus exerts a pressure of more than 1,300 pounds per square inch on anything at the surface. That is more than 90 times the 14.7 pounds per square inch at sea level on Earth, or the equivalent to being 3,000 feet underwater in the ocean.

It is hardly a place that makes visiting or research easy, although that doesn’t mean people haven’t tried. Space programs have tried dozens of robotic missions to Venus, many of them in the Soviet Union’s Venera series. But the planet eats metal, within minutes melting down and crushing spacecraft that have landed there. Of all those attempts, only two managed to directly capture images of the planet’s surface.

Whereas frigid Mars is currently ringed by orbiters and prowled by NASA rovers, Venus is being studied by only one probe, the lonely Japanese spacecraft Akatsuki. Future missions to the planet are still mere concepts.

Although the surface of Venus is like a blast furnace, a cloud layer just 31 miles below the top of its atmosphere may reach temperatures as low as 86 degrees Fahrenheit, and has a pressure similar to that at ground level on Earth. Many planetary scientists, including Carl Sagan and Harold Morowitz, who proposed the idea 53 years ago, have hypothesized life may exist there.

Jane Greaves, an astronomer at Cardiff University in Wales, set out in June 2017 to test that hypothesis using the James Clerk Maxwell Telescope in Hawaii, looking for signs of various molecules on Venus. Different species of molecules will absorb radio waves coming through the clouds at different characteristic wavelengths. One of the chemicals was phosphine. She did not expect to find it.

“I got intrigued by the idea of looking for phosphine, because phosphorus might be a bit of a sort of go-no-go for life,” Dr. Greaves said.

Chemists compare phosphine to a pyramid — one atom of phosphorus topping a base of three hydrogen atoms. The NASA spacecraft Cassini detected it in the atmospheres of Jupiter and Saturn. In that setting, Dr. Sousa-Silva said, life is not necessary to form phosphine. The immense heat and pressures can jam the phosphorous and hydrogen atoms together to form the molecule.

But on smaller, rocky planets like Earth and Venus, the researchers say, there is not enough energy to produce copious amounts of phosphine in the same way. There is one thing, however, that appears to be very good at producing it: anaerobic life, or microbial organisms that don’t require or use oxygen.

On such worlds, “as far as we can tell, only life can make phosphine,” Dr. Sousa-Silva said. She has long studied the gas, on the theory that finding it being emitted from rocky planets that orbit distant stars could be proof that life exists elsewhere in the Milky Way.

Here on Earth, phosphine is found in our intestines, in the feces of badgers and penguins, and in some deep sea worms, as well as other biological environments associated with anaerobic organisms. It is also extremely poisonous. Militaries have employed it for chemical warfare, and it is used as a fumigant on farms. On the TV show “Breaking Bad,” the main character, Walter White, makes it to kill two rivals.

But scientists have yet to explain how Earth microbes make it.

”There’s not a lot of understanding of where it’s coming from, how it forms, things like that,” said Matthew Pasek, a geoscientist at the University of South Florida in Tampa. “We’ve seen it associated with where microbes are at, but we have not seen a microbe do it, which is a subtle difference, but an important one.”

Dr. Sousa-Silva was surprised when Dr. Greaves said that she had detected phosphine.

“That moment plays in my mind a lot, because I took a few minutes to consider what was happening,” she said.

If there really was phosphine on Venus, she believed there could be no other obvious explanation than anaerobic life.

“What we find circumstantially also makes complete sense with what we know thermodynamically,” she said.

The team needed a more powerful telescope, and the scientists next used the Atacama Large Millimeter Array, in Chile, in March 2019.

This time, they found, all signs pointed to phosphine, and a lot of it, ranging from 5 to 20 parts per billion. Although those numbers might seem small, that’s thousands of times more than what is in Earth’s atmosphere.

Dr. Sousa-Silva, Dr. Greaves and their colleagues had planned to complete additional telescope observations earlier this year. But the coronavirus pandemic and Venus’s limited time above the horizon interfered with their ability to gather more evidence, leaving many questions unanswered.

“The finding itself is astonishing,” said Paul Byrne, a planetary scientist at North Carolina State University in Raleigh who was not involved in the research. He said that although he was “skeptical of it being life, I don’t have a better explanation for what it is.”

The team spent a year recreating the Venusian environment in computer simulations to test different explanations for the phosphine’s source and abundance.

“The light is constantly breaking the phosphine down, so you have to continuously replenish it,” said William Bains, a biochemist at M.I.T. and one of the co-authors of the papers.

Volcanic activity and lightning on Venus would not be sufficient to add more of this constantly disappearing phosphine, according to the researchers’ models. But living things could emit enough of the gas.

“What we’ve done is rule out all other sources of phosphine other than life,” Dr. Bains said.

Other planetary scientists counter that a non-biological origin cannot be ruled out.

“Despite prior speculation (mostly by the same authors), this can hardly be taken as a biosignature,” Gerald Joyce, a biologist at the Salk Institute in California who has experimented with creating life in the lab, said in an email. In their own paper, he noted, the researchers wrote that “the detection of phosphine is not robust evidence for life, only for anomalous and unexplained chemistry.”

A similar note of caution was voiced by James Kasting, a geoscientist and expert on planetary habitability at Pennsylvania State University in State College, who said, “The model atmospheric composition that they show is, at best, incomplete.”

The finding also follows a history of detections of gases on other worlds that can be byproducts of life. But these gases, such as burps of methane or oxygen on Mars, can also be produced by chemical reactions that do not involve life at all. So far, such signals have been intriguing, but they are not convincing proof of aliens.

While few doubt whether this phosphine is there, what kind of life in the clouds of Venus would it take to actually make the gas?

Such living things would have had to evolve to survive in a high-acid environment, perhaps with protective outer layers similar to microscopic organisms in Earth’s most extreme environments.

In a paper published in August, Dr. Seager and her colleagues suggested that microbes borne aloft on air currents called gravity waves could live, metabolize and reproduce inside drops of sulfuric acid. And given the amount of gas being produced, the population of these microbes would be ample.

As to how these microbes got there, the best guess, she said, is that they originated on the surface when Venus had oceans as late as 700 million years ago, but they were forced into the skies when the planet dried up.

And nobody knows whether the microbes, if real, are based on DNA like us, or something entirely different.

“When looking for life elsewhere, it’s so hard to not be Earth-centric,” Dr. Sousa-Silva said. “Because we only have that one data point.”

Before their imaginations run away, the researchers want to gather more telescope data and see their models tested and challenged. Robotic space missions to Venus could also advance the search.

India’s space agency has proposed a mission, in the coming years, as has a private rocket company, Rocket Lab.

And NASA, which has declined to fund a number of Venus missions in recent decades, announced in February that it would consider a pair of proposed spacecraft among four finalists competing for a round of funding.

“For the last two decades, we keep making new discoveries that collectively imply a significant increase of the likelihood to find life elsewhere,” said Thomas Zurbuchen, the head of NASA’s science directorate, who helps select missions to explore the solar system. “Many scientists would not have guessed that Venus would be a significant part of this discussion. But, just like an increasing number of planetary bodies, Venus is proving to be an exciting place of discovery.”