A Mars orbiter has captured stunning pictures of the largest canyon in the solar system, called Valles Marineris. It stretches across 2,500 miles of the red planet’s equator, a distance that is roughly equivalent to the diameter of the continental United States.

Mars Express, a European Space Agency (ESA) mission that arrived at Mars in 2003, recently imaged the deepest reaches of this epic canyon, where its slopes descend more than four miles into the Martian surface, which is five times deeper than the Grand Canyon, according to an ESA statement. 

The observations reveal two massive “chasma,” or trenches, that run parallel along the western portion of Valles Marineris, known as Tithonium Chasma in the south and Ius Chasma in the north. These trenches are each about 500 miles in length, making them twice as long as the Grand Canyon—and they encompass only about a fifth of Valles Marineris’ full extent.  

Perspective view of Tithonium Chasma. Image: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO​​

Mars Express snapped these shots of the chasma in April with its High Resolution Stereo Camera, during its 23,123th orbit around the planet. The images are so sharp that ESA scientists used them to generate close-up perspectives of Tithonium Chasma that resemble aerial photographs. The pictures show dark dunes, huge mountains, and the fallout of landslides within the chasma, which are annotated in an accompanying map.

Canyons on Earth are usually whittled out by the flow of rivers over millions of years, but scientists believe Valles Marineris was formed by tectonic activity on Mars more than 3 billion years ago. 

While the immense rift is dry today, scientists recently detected surprising stores of water ice under its surface. Valles Marineris may have also hosted liquid water billions of years ago, when Mars was wetter, warmer, and potentially habitable. NASA’s Perseverance rover is currently looking for signs of past life on Mars in Jezero Crater, an ancient lakebed, but scientists have also speculated that Valles Marineris may have also hosted aliens in the past.

Mars was “very likely” habitable to life more than 3.7 billion years ago and may still be home to resilient organisms today, according to a new study that presents a tantalizing glimpse of how microbial aliens could have emerged and survived on the red planet—and where we might be able to find signs of them.

Modern Mars is cold and desiccated, making it inhospitable to most imaginable forms of life. But there is abundant evidence that this world was warmer, wetter, and more welcoming to life in the past. For instance, NASA’s Perseverance rover is currently exploring the parched remains of what was once a vast ancient lakebed on Mars, known as Jezero Crater, in part to search for traces of extinct aliens that might have lived there billions of years ago. 

While there’s no concrete evidence that life has ever existed on Mars, scientists have speculated that microbial organisms called methanogens, which are among the most ancient life forms on Earth, could have been well-suited to conditions on early Mars. Methanogens derive energy from hydrogen and carbon dioxide, which were available on ancient Mars, and they release methane as a waste product.

Now, scientists led by Boris Sauterey, a biologist at the Institut de Biologie de l'École Normale Supérieure in France, have presented a first-of-its-kind study that assesses the viability of hydrogen-eating methanogens on early Mars, and speculates about the survival of any descendants of these hypothetical organisms to the present day. 

The team discovered that “subsurface habitability was very likely” on early Mars and that “biomass productivity could have been as high as in the early Earth’s ocean,” according to a study published on Monday in Nature Astronomy. 

The results support the exciting prospect that life may commonly arise on other worlds, but also reveal an unexpected dark side: Life may frequently be the agent of its own destruction.

“We evaluated the habitability of Mars and we evaluated the influence that this biosphere, that  could have been similar to the primitive terrestrial biosphere, would have had on the Martian climate—and we were surprised,” Sauterey told Motherboard in a call.

“What did not surprise us was the fact that we found Mars to be likely habitable; we had an expectation of that based on previous works,” he continued. “What was surprising was the fact that when we assumed that a biosphere inhabited Mars, the climatic effects of that biosphere were opposite [of Earth]. Instead of warming the planet, and consolidating the planetary habitability, this biosphere would instead cool it down dramatically, degrading the habitability of the planet.” 

In other words, the researchers discovered that the activities of early Martian microbes would have triggered a global cooling effect that may have led to their own extinction. Here on Earth, life also has also affected the climate for billions of years, but these feedback loops have generally maintained and even enhanced our planet’s habitability. The new study suggests that transient life forms may emerge on many worlds, but the type of long-term habitability we’ve enjoyed on Earth may be an outlier.

“As soon as you put methanogens on Mars, the climate cools down by 20 to 40 degrees [Kelvin], the planet gets covered in ice, and potentially becomes completely uninhabitable,” Sauterey said. This could be the general rule in the universe and Earth might be an exception.”

“The ingredients of life may be everywhere, but potentially life is just making a mess of it every time,” he continued. “Right now we are a good example of the fact that we can make a mess of a habitable planet,” referring to human-driven climate change and other anthropogenic pressures on Earth, “but even a really primitive ecosystem could do the same.”

This may seem like a bittersweet scenario, but it is tempered by other promising revelations in the study. For one thing, Sauterey and his colleagues conclude that early Mars was almost certainly habitable under certain parameters and in key areas, such as Hellas Planitia or Jezero Crater. This finding bolsters the evidence that habitable environments may have emerged in multiple places not only within our solar system, but also the wider galaxy and universe. Not every habitable location is necessarily inhabited by aliens—and Sauterey cautioned that “we still have no idea how inert matter becomes alive”—but the abundance of these hospitable environments is still an encouraging sign in the search for extraterrestrial life.

The team also examined the possibility that methanogens that thrived on Mars billions of years ago could have taken refuge from the cold deep under the Martian surface. Cut off from access to their atmospheric energy sources, these hypothetical survivors would have had to find a new source of power, but Sauterey noted that methanogens on Earth have managed to make these kinds of shifts in the past. 

If descendents of ancient Martians are hidden in subterranean lairs, it might be possible to detect them by scanning Mars to look for underground biomass or sniffing out chemical traces of their activities at the surface. Indeed, NASA’s Curiosity rover has detected unexplained  emissions of methane gas at its location on Mars, which could have either a biotic or abiotic origin. 

Sauterey hopes that future missions might be able to definitively distinguish whether the elusive methane detections are geological in origin, or are the exhalations of ancient subterranean organisms. 

“We can try to detect, for instance, emissions of methane that are not expected even with what we know of the geological process going on at the surface of Mars,” he said.

“Assuming that actually some of them survived, if there are still habitable pockets for those types of organisms on Mars, it's possible to see if we can characterize chemical signals,” Sauterey concluded. “Maybe we can use life to explain stuff that we have no other explanation for so far.”

Scientists have captured the first image of the black hole at the center of the Milky Way, the galaxy we live in, an achievement decades in the making that offers a never-before-seen glimpse of the closest supermassive black hole to Earth. 

This enormous object, called Sagittarius A*, is four million times more massive than the Sun and is located some 27,000 light years from Earth in the dense and chaotic region at the core of our galaxy.

“This is the first image of the supermassive black hole at the heart of our Milky Way galaxy,” said Sara Issaoun, a NASA Einstein Fellow and an astrophysicist at the Harvard & Smithsonian Center for Astrophysics, at a press conference about the breakthrough on Thursday. 

“​​For decades, we have known about a compact object at the heart of our galaxy that is four million times more massive than our Sun,” Issaoun added. “Today, right at this moment, we have direct evidence that this object is a black hole.”

The groundbreaking new image was snapped by the Event Horizon Telescope (EHT), a network of radio telescopes that spans our planet, enabling it to achieve the level of high resolution necessary for a photoshoot of a supermassive black hole. 

The EHT collaboration previously snapped a mesmerizing picture of the supermassive black hole at the center of Messier 87, a giant galaxy located about 55 million light years from the Milky Way, which made history and captured the public’s imagination as the first image of a supermassive black hole ever taken, after its release in April 2019. 

Because nothing escapes the boundaries of a black hole, not even light, both images only show the dark shadow at the center of their galaxies, where the black hole resides, which is circled by the bright glow of gas surrounding these enormous cosmic objects.

“Imaging this black hole would not have been possible without a big telescope of very high magnifying power, or angular resolution as we astronomers call it,” said Thomas Krichbaum, a scientist at the Max Planck Institute for Radio Astronomy, at the press conference. “To achieve this, astronomers combine radio telescopes located around the globe to create a super-telescope which has the size of the Earth.”

“With this, the EHT achieves an angular resolution which is sufficient for the imaging of such distant black holes, and also sufficient for the matter surrounding these black holes,” Krichbaum added. “To give you an idea, EHT can see three million times sharper than the human eye, so when you are sitting in a Munich beer garden for example, one could see the bubbles in the glass of beer in New York.”

The incredible image of Sagittarius A* closely resembles the EHT’s initial picture released in 2019, even though our local black hole is a thousand times smaller than the one at the center of Messier 87, known as Messier 87*. The resemblance suggests that many of the mysterious properties of supermassive black holes are similar at different scales, though differences may show up in the images of the material surrounding a black hole, which is made up of stars, gas, and dust. 

But while the two supermassive black holes may look the same in these images, the new picture of Sagittarius A* was significantly more challenging to capture. 

“The gas in the vicinity of the black holes moves at the same speed—nearly as fast as light—around both Sagittarius A* and Messier 87*,” said Chi-kwan (‘CK’) Chan, a scientist at Steward Observatory at the department of astronomy of the University of Arizona, in a statement. 

“But where gas takes days to weeks to orbit the larger Messier 87*, in the much smaller Sagittarius A it completes an orbit in mere minutes,” Chan noted. “This means the brightness and pattern of the gas around Sagittarius A were changing rapidly as the EHT Collaboration was observing it—a bit like trying to take a clear picture of a puppy quickly chasing its tail.” 

Despite these challenges, the EHT collaboration, which involves more than 300 scientists across the world, eventually captured this long-sought look at Sagittarius A during observations made in 2017. While evidence of this object’s existence has piled up for decades—and its discovery even earned the 2020 Nobel Prize for Physics—the new image makes it real, for the first time, not only to scientists, but to anyone who is awed by the mind-boggling evolution of our universe.

“This is it,” said J. Anton Zensus, director of the Max Planck Institute for Radio Astronomy, during Thursday’s press conference. “This is a big—no, it is a huge—moment for everyone in the Event Horizon Telescope collaboration. It’s the next level, and I’m proud of everyone in our entire worldwide team. They have worked so hard for this latest breakthrough.”

“You are the first to see our image of the black hole in the center of our galaxy—as close as it gets,” Zensus said. “Imagine this: We have combined the world’s greatest radio telescopes into one Earth-sized camera. To be honest, after doing this for 40 years, I’m still astonished each time we pull this off.”