Life in Space?

• ENVIRONMENT: rocky surface with an extremely hot, thick atmosphere made of carbon dioxide gas and sulfuric acid clouds.

• Environment: rocky surface with an extremely hot, thick atmosphere made of carbon dioxide gas and sulfuric acid clouds

Venus is the second planet from the sun, which makes conditions there extremely hot. The rocky planet has an average surface temperature of more than 470°C (878°F). No living thing on Earth could survive such extreme heat.

For a long time, Venus seemed an unlikely candidate for hosting alien life. But last September, scientists made an interesting discovery that could prove otherwise. The team of researchers used powerful telescopes to analyze the chemical makeup of Venus’s atmosphere. They found that the layer of gases surrounding the planet contains the molecule phosphine. Phosphine is a stinky and toxic gas naturally produced by some microbes on Earth. The scientists’ hypothesis: The phosphine on Venus may have been produced by microscopic organisms living within the planet’s clouds.

Venus is the second planet from the sun. That’s why conditions there are extremely hot. The rocky planet’s average surface temperature is more than 470°C (878°F). No living thing on Earth could survive such extreme heat.

For a long time, Venus seemed an unlikely place for alien life. But last September, scientists made an interesting discovery. It could prove that idea wrong. The team of researchers studied Venus’s atmosphere with powerful telescopes. They looked at the chemical makeup of this layer of gases around the planet. And they found the molecule phosphine. Phosphine is a stinky and toxic gas. On Earth, some microbes produce it naturally. The scientists think that microscopic organisms may live in Venus’s clouds. These microbes may have produced the phosphine.

Any creatures that could survive Venus’s harsh environment would be nothing like those found on Earth. “If there is life there, it’s hard to imagine what that life might be like,” says Clara Sousa-Silva, who was part of the Venus study. She’s an astrochemist at Harvard University in Massachusetts. She examines the chemistry of objects in space.

As soon as the new research went public, many scientists around the world raised doubts. Different teams of researchers tried to replicate the results, but so far only one group has been able to detect phosphine. Now, Sousa-Silva and her team are redoing their analysis using improved data, and they hope to confirm their original results. Repeating a study is an important part of scientific research to help ensure findings are accurate. “This is exactly how science works,” says Sousa-Silva.

Creatures on Earth couldn’t survive Venus’s harsh environment. Any creatures on Venus would be nothing like them. “If there is life there, it’s hard to imagine what that life might be like,” says Clara Sousa-Silva, who worked on the Venus study. She’s an astrochemist at Harvard University in Massachusetts. She studies the chemistry of objects in space.

When the new research went public, many scientists around the world raised doubts. Different teams of researchers tried to get the same results. But only one group has found phosphine so far. Now Sousa-Silva and her team are doing their study again. They’re using improved data, and they hope to confirm their first results. Repeating a study is important to science. It helps make sure the findings are correct. “This is exactly how science works,” says Sousa-Silva.

• ENVIRONMENT: about the size of Earth’s moon; frozen surface; extremely cold; thin atmosphere made of oxygen (O)

• ENVIRONMENT: about the size of Earth’s moon; frozen surface; extremely cold; thin atmosphere made of oxygen (O)

Europa is a frozen moon of Jupiter. Its surface is covered by a layer of ice with a giant ocean underneath. The icy shell is 15 to 25 kilometers (10 to 15 miles) thick—possibly thin enough for radiation from Jupiter and the sun to penetrate. These high-energy particles and rays could provide enough heat and light to allow the ocean to sustain life.

A phenomenon called tidal flexing could also warm Europa’s ocean. Jupiter’s enormous force of gravity constantly tugs on Europa. Scientists believe this strain leads to increased volcanic activity within the moon. As a result, Europa’s ocean could have formations similar to Earth’s deep-sea hydrothermal vents. These openings in the seafloor spew mineral-rich hot water that could make Europa’s ocean hospitable to life.

Scientists also believe these vents could spray huge plumes of water from the depths of Europa’s ocean onto its surface—and even into space. Water in the plumes could contain compounds that indicate the existence of life in the ocean below. NASA hopes to someday send a spacecraft to orbit Europa and sample the spray from these plumes. Another possible mission could drill through Europa’s ice and send a probe into the ocean to look for alien life.

Europa is a frozen moon of Jupiter. A layer of ice covers its surface. A giant ocean lies underneath the ice. The icy shell is 15 to 25 kilometers (10 to 15 miles) thick. That might be thin enough for radiation from Jupiter and the sun to get through. These high-energy particles and rays provide heat and light. Those could be enough to support life in the ocean.

Europa’s ocean could also be warmed by tidal flexing. Jupiter’s enormous force of gravity always tugs on Europa. Scientists believe this pull increases volcanic activity within the moon. As a result, openings could form in Europa’s ocean floor. These formations could be like Earth’s deep-sea hydrothermal vents. Hot water, rich in minerals, flows from these vents. That could make life possible in Europa’s ocean.

Scientists believe these vents could spray huge jets of water from Europa’s ocean floor onto its surface. The jets might even reach into space. Compounds in this water could show that life exists in the ocean below. Someday, NASA hopes to send a spacecraft to orbit Europa. It would sample the spray from these jets. Another possible mission could drill through Europa’s ice. Then it would send a probe into the ocean to look for alien life.

• ENVIRONMENT: rocky and dry surface with some frozen water near poles; extremely cold; a thin atmosphere made of CO₂ gas

• ENVIRONMENT: rocky and dry surface with some frozen water near poles; extremely cold; a thin atmosphere made of CO₂ gas

Today, the surface of Mars looks like an immense desert. But scientists think it was once covered in oceans that could have supported life. About 3.1 million years ago, charged particles streaming from the sun stripped away most of Mars’s atmosphere. Most of its water turned from liquid to gas and evaporated into space. As a result, the planet turned into a cold, dry wasteland.

Any life that may have existed in Mars’s ancient oceans probably would have been microbial. If any of these organisms remain on Mars, they’re likely living below the planet’s surface, where there may still be some liquid water. “It’s very possible there was, and is, microbial life on Mars,” says Sarah Hörst, a planetary scientist at Johns Hopkins University in Maryland.

Today, the surface of Mars looks like a vast desert. But scientists think oceans used to cover it. And life could have existed in those oceans. Charged particles streamed from the sun and stripped away most of Mars’s atmosphere. That happened about 3.1 million years ago. Most of Mars’s water turned from liquid to gas and evaporated into space. The planet turned into a cold, dry wasteland.

If life existed in Mars’s ancient oceans, it was probably microbial. Do any of these organisms still live on Mars? If so, they’re probably below the planet’s surface. That’s where some liquid water may still exist. “It’s very possible there was, and is, microbial life on Mars,” says Sarah Hörst. She’s a planetary scientist at Johns Hopkins University in Maryland.

Unfortunately, finding signs of microbial life on Mars isn’t easy. Scientists learn about past life on Earth by studying fossils—the preserved remains of ancient organisms. “But microbes don’t leave fossils because this type of life has no bones or skeleton,” says Hörst. Instead, scientists are looking for traces of chemicals that organisms on Mars may have once created.

Most recently, NASA sent the Perseverance rover to Mars. The remote-controlled robot was scheduled to land on the planet in February 2021. The rover will collect dirt and rock samples that will be stored on the planet’s surface until they can be picked up during a later mission and returned to Earth for study. These samples may hold the key to understanding whether life did, and possibly still does, thrive on Mars.

But it’s not easy to find signs of microbial life on Mars. Scientists study fossils to learn about past life on Earth. These are the preserved remains of ancient organisms. “But microbes don’t leave fossils because this type of life has no bones or skeleton,” says Hörst. Organisms on Mars may have created chemicals in the past. So scientists are looking for traces of these chemicals instead.

Most recently, NASA sent the Perseverance rover to Mars. The remote-controlled robot was scheduled to land on the planet in February 2021. The rover will collect dirt and rock samples. They’ll be stored on the planet’s surface. Later, another mission will pick them up and return them to Earth for study. These samples may hold the answers to the questions: Did life ever thrive on Mars? Does it still?

• ENVIRONMENT: about the size of the planet Mercury; frozen surface; extremely cold; atmosphere made mostly of nitrogen (N) gas

• ENVIRONMENT: about the size of the planet Mercury; frozen surface; extremely cold; atmosphere made mostly of nitrogen (N) gas

Saturn’s largest moon, Titan, is unlike any other in the solar system. It’s the only moon with a dense atmosphere. It’s also the only known place in the solar system besides Earth with liquid bodies currently on its surface. But instead of containing water, Titan’s lakes, seas, and rivers are made up of liquid methane and ethane. While life as we know it on Earth could never survive in these chemicals, alien organisms may have found a way. “The universe is much more creative and much better at solving problems than people are, so we shouldn’t rule it out,” says Sarah Hörst, a planetary scientist at Johns Hopkins University in Maryland.

Beneath the liquid on Titan’s surface is a shell of ice 200 to 300 kilometers (125 to 186 miles) thick. Underneath it lies an ocean of liquid water. Liquid water is a necessary ingredient for life on Earth—so could Titan’s hidden ocean be another likely place to find alien organisms? Probably not, says Hörst. That’s because sunlight can’t penetrate Titan’s icy outer layer to provide the light and heat energy needed to sustain life in the ocean below.

There is one other place on this moon where life might have existed long ago. In the past, huge asteroids and comets crashed into the moon’s surface. Such collisions caused enormous explosions. Heat from these blasts melted portions of Titan’s icy surface. That created pools of mineral-rich liquid water—a potential spot where microbes could have thrived, says Hörst.

Titan is Saturn’s largest moon. It’s unlike any other in the solar system. It’s the only moon with a dense atmosphere. And it has liquid bodies on its surface. Earth is the only other known place in the solar system with this feature. But Titan’s lakes, seas, and rivers don’t contain water. Instead, they’re made up of liquid methane and ethane. Life on Earth could never survive in these chemicals. But alien organisms may have found a way. “The universe is much more creative and much better at solving problems than people are, so we shouldn’t rule it out,” says planetary scientist Sarah Hörst. She works at Johns Hopkins University in Maryland.

A shell of ice is beneath the liquid on Titan’s surface. The ice is 200 to 300 kilometers (125 to 186 miles) thick. Under it is an ocean of liquid water. Liquid water is needed for life on Earth. So could alien organisms live in Titan’s hidden ocean? Probably not, says Hörst. That’s because sunlight can’t get through Titan’s icy outer layer. And light and heat energy would be needed for life in the ocean below.

One other place on this moon might have held life long ago. In the past, huge asteroids and comets crashed into the moon’s surface. These blows caused enormous explosions. Heat from these blasts melted parts of Titan’s icy surface. That created pools of liquid water, rich in minerals. Microbes could have thrived in this spot, says Hörst.