Tag Archives: Earth

The Remnants of Theia May Still Exist Deep Inside the Earth

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There are two enormous provinces of unusual rock that sit at the bottom of the mantle, just above the Earth’s core. One of them is located underneath Africa and one is under the Pacific Ocean. They’re called Large Low Shear Velocity Provinces (LLSVPs) and they may shape hotspot formation and volcanic activity across the globe.

The LLSVPs are areas where seismic shear waves propagate much more slowly. They extend laterally for thousands of miles (we think), and they may be up to 1,000km “tall.” Geologists have considered a variety of potential explanations for the origin of the LLSVPs, and now a team has put forth a new argument: The LLSVPs may represent the remains of Theia, the protoplanet thought to have smashed into the world some 4.5 billion years ago, creating the Moon. There are a number of hotspots around the world associated with the margins and boundaries of the LLSVPs:

Image by DR Davies et al, The Australian National University

The hotspots associated with the LLSVP sometimes create a type of lava known as ocean island basalts, which are often compared with mid-ocean ridge basalts. In some cases, ocean island basalts are found with isotopic ratios that are believed to reflect the primordial Earth, especially when they’re located above one of the LLSVPs.

This suggests that at least some of the material down at the mantle/core boundary has been there since the formation of the planet. Mid-ocean ridge basalts are more likely to contain magma drawn from the upper layers of the mantle. This material has typically melted, cooled, and then subducted and melted again more than once across billions of years. This cycling results in magma with different isotope ratios and characteristics compared with the magma welling up from the mantle/core boundary.

Qian Yuan, a Ph.D. student in geodynamics at Arizona State University (ASU), presented his hypothesis on the topic at the Lunar and Planetary Science Conference. According to him, the Theia impactor could have formed the LLSVPs if Theia’s mantle material was 1.5 – 3.5 percent heavier than Earth’s. Under this model, some parts of Theia’s original mantle remained contiguous and never completely mixed with the Earth. This is not a problem; it is very difficult to create a Theia – Earth impact model that achieves uniform mixing, even if you assume a post-impact global magma ocean. Yuan’s work suggests Theia’s mantle material would form 3-15 percent of the mantle volume of the Earth, which lines up with the 3-9 percent of the mantle the LLSVPs are thought to occupy.

Image by Sanne Cottaar, CC BY-SA 4.0. Animated version available.

Alternate Explanations

The Theia impact hypothesis is not the only explanation for the LLSVPs. A number of causes have been proposed. They may be plumes of upwelling magma or represent differentiation that occurred entirely on Earth early in its history. They may be created by thermochemical convection or be comprised of ancient slabs of subducted ocean crust that fell to the bottom of the core/mantle boundary hundreds of millions to billions of years ago.

There’s even a chance that the LLSVPs don’t exist, at least not in their currently theorized size and shape. We track seismic waves as they propagate through the Earth to learn about its composition and structure, but it’s not the same as taking an X-ray. Some researchers have argued that the enormous size and unusual shape of the LLSVPs are due to resolution limits in our seismic data.

Image by Sanne Cottaar, CC BY-SA 3.0

The idea that we might find pieces of Theia inside the mantle is a solid one, even if the LLSVPs turned out to be something other than they’re currently theorized to be. There are other, smaller pockets of low seismic velocities inside the mantle. They’re often near also associated with the LLSVPs, but much smaller. These ultra-low-velocity zones are thought to be enriched with iron. They may represent core fragments of other planetesimals that struck Earth during its formation and became trapped in the mantle. The long-term sequestration of such primitive material would explain why we occasionally find lava that looks as if it came straight from the early solar system.

If the LLSVPs or ultra-low-velocity zones prove to be of extraterrestrial origin, it would mean the planetesimals that helped form the Earth have continued to shape its geology ever since. It’s one thing to know the Moon was created in an impact some 4.5 billion years ago, and another to imagine that some of the core of the planetesimal that shaped our entire Earthly existence might still exist itself, trapped below an ocean of liquid rock.

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Europe Plans 20,000 GPU Supercomputer to Create ‘Digital Twin’ of Earth

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Anyone who’s tried to buy a graphics card lately knows how tough it can be to find something in stock, let alone for a reasonable price. The European Union, however, thinks this is a grand time to slap 20,000 GPUs into a supercomputer with the aim of studying climate change with a simulated twin of our planet. The plan to create a digital twin of Earth might end up delayed due to the relative lack of available GPUs, but this isn’t going to be an overnight project. 

The EU calls the upcoming computer Destination Earth, or DestinE for short. This massive raft of GPUs will allegedly be able to create a highly accurate copy of Earth down to kilometer-scale that simulates how climate change will affect us. Users will be able to vary conditions and project the effects on food security, ocean levels, global temperature, and so on. 

This level of detail will allow researchers to predict the future, at least in some small way. Peter Bauer is deputy director of the European Centre for Medium-​Range Weather Forecasts and lead author on the new study detailing DestinE. Bauer uses The Netherlands as an example of what a digital Earth clone could do. “If you are planning a two-​metre high dike in The Netherlands, for example, I can run through the data in my digital twin and check whether the dike will in all likelihood still protect against expected extreme events in 2050,” says Bauer. DestinE could guide decisions large and small as Europe seeks to reduce emissions and plan for the impacts of climate change. 

The team planning DestinE have ballparked 20,000 GPUs based on the Cray Piz Daint supercomputer in Zurich (above). That device runs on more than 5,000 Pascal-based Nvidia Tesla GPUs, and scientists believe it will take about four times the computing power to create a digital twin of Earth. That’s how the scientists arrived at the 20,000 number. We will take their word for it that this isn’t some crazy scheme to build a secret crypto mega-mining rig. 

DestinE is part of the EU’s $ 1 trillion initiative to reach carbon neutrality by 2050. That would just about cover 20,000 GPUs if the EU were buying everything right now, but thankfully, it’s not working to assemble DestinE just yet. Researchers hope to have the supercomputer up and running within the next seven to ten years. That many GPUs are sure to draw a ton of power, even if they’re more efficient cards from a few generations in the future. Hopefully, the EU’s climate change computer doesn’t contribute to climate change itself.

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Earth Will Lose Its Oxygen in a Billion Years, Killing Most Living Organisms

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Humans haven’t been great for the health of the planet, but even if we pollute ourselves into extinction, Earth will continue on. It’s survived enormous asteroid impacts and megavolcanoes, after all. A few primates aren’t going to do worse in the long-run. The ultimate fate of life on Earth lies a billion years in the future. A new study supported by NASA’s exoplanet habitability research lays out how the sun will eventually bake the planet, turning Earth from a lush, oxygen-rich world to a dried-up husk with no complex life. 

NASA is interested in the future of Earth because it’s the only habitable planet we can study up close. As such, scientists have attempted to extrapolate the properties of Earth-like planets we might be able to detect from great distances. Kazumi Ozaki at Toho University in Japan and Chris Reinhard at the Georgia Institute of Technology created a model of Earth’s climate, biology, and geology to see how it will change. 

According to Ozaki and Reinhard, Earth’s oxygenated atmosphere is not a permanent feature. There was very little of it in the atmosphere until 2.4 billion years ago when cyanobacteria evolved to absorb carbon dioxide and expel oxygen — this is known as the Great Oxidation Event. This gave rise to all the forms of multicellular life we see on Earth today. There’s just one problem: the Sun. As stars age, they get hotter, and the Sun is about a billion years from roasting Earth. 

The study predicts that in a billion years, the Sun will become so hot that it breaks down carbon dioxide. The levels of CO2 will become so low that photosynthesizing plants will be unable to survive, and that means no more oxygen for the rest of us. When that happens, the changes will be abrupt. Ozaki and Reinhard say in the study, published in Nature Geoscience, that it could take a little as 10,000 years for oxygen levels to drop to a millionth of what it is now. That’s a blink of the eye in geological terms. Methane levels will also begin to rise, reaching 10,000 times the level seen today. 

Cyanobacteria like these oxygenated the atmosphere, but the era of oxygen may be fleeting.

This harsh, choking atmosphere will be incompatible with any multicellular life as it exists today. The globe will be given over to bacteria and archaea, the heartiest of living organisms to see the planet through the rest of its existence until it’s swallowed by the Sun. Even if more complex life did survive, it would be irradiated by the increasingly luminous Sun. Without oxygen, the ozone layer will evaporate and expose the surface to more intense UV radiation. 

Ozaki and Reinhard conclude that oxygen is an important biomarker, but it may not be a permanent feature of planets with life. That could change how we categorize exoplanets going forward — even without oxygen, there could be plenty of single-celled life.

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NASA’s OSIRIS-REx Asteroid Sampler Will Head Back to Earth on May 10

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NASA’s OSIRIS-REx mission has been a smashing success so far. After reaching the asteroid Bennu at the very end of 2018, the spacecraft surveyed the surface and collected a sample. Now, NASA is making plans for OSIRIS-REx to head back to Earth with its precious cargo. According to the team, OSIRIS-REx will begin that journey on May 10th, but there are good reasons for the delay. 

OSIRIS-REx collected its sample from the “Nightingale” site on Bennu several months ago. Using its collection arm, OSIRIS-REx dropped down to the carefully chosen location and blasted the asteroid with a stream of compressed nitrogen gas. The surface material ejected by the puff of air fell neatly in the probe’s sample container. Initially, NASA planned to conduct tests to make sure it had successfully scooped up some of the asteroid’s soil, but the container was visibly overflowing. Rather than tempt fate, NASA locked everything down and began planning for the return trip. 

NASA says that OSIRIS-REx will leave the vicinity of Bennu on May 10th. There are a few reasons for this. First, it gives NASA the opportunity to plan one last flyby of Bennu. The team hopes to skim the surface over Nightingale to see how the spacecraft’s excavation changed the terrain. It will also give scientists a chance to assess the functionality of the probe’s onboard instruments after several years of use. The other reason for the wait is that OSIRIS-REx can use less fuel leaving Bennu’s orbit if it waits until May. 

The trip back to Earth will be a long one. NASA projects OSIRIS-REx will be able to drop off the sample container on September 24, 2023. The capsule with a bit of Bennu will parachute down over the Air Force’s Utah Test and Training Range, where NASA will be waiting to retrieve it. Once on Earth, the canister will head to Johnson Space Center in Houston for analysis and processing. NASA believes it may have several kilograms of material in OSIRIS-REx, far more than the 60g design minimum. That would be enough to distribute samples of Bennu’s regolith to laboratories around the world.

So, why go to all the trouble? Collecting samples from asteroids like Bennu can help scientists piece together the history of our solar system. Unlike space rocks that have fallen into Earth’s atmosphere, a C-type asteroid like Bennu is like a time capsule of unaltered molecules from billions of years ago. That’s why missions like OSIRIS-REx and Japan’s Hayabusa2 are so important. 

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Earth Is Spinning Faster After Decades of Slowing Down

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We all know that a day on planet Earth is 24 hours long — except it isn’t. It’s actually a few fractions of a second longer, which is why we have February 29th every four years. Still, Earth isn’t a clock, and the actual length of a day can vary slightly. Scientists now say that the days have started trending shorter because the Earth is spinning faster, which could require additional, potentially confusing adjustments. 

Before you get stressed about yet another existential threat to the future of the planet, scientists don’t believe the increased rate of spin is a danger. The mechanisms for this effect are well-understood. Factors like lunar gravity, snowfall levels, and mountain erosion can affect the speed at which the globe rotates. The effect is that days can be a few milliseconds shorter or longer than the 84,400 number we use to keep track of time. 

Over the past several decades, the availability of precise atomic clocks has allowed humanity to make more accurate adjustments to our measurement of time. For example, on several occasions, we’ve added a “leap second” to keep clocks aligned outside of the traditional leap year adjustment. Since we began measuring time like this, the length of days has been trending longer, usually by a fraction of a millisecond. However, that trend has now reversed. 

538914-nasa-apollo-photo-moon-earth

The moon’s gravity is one of several things that can change the Earth’s rotation speed.

Scientists note that days in the last year have been on the shorter side by the same small margins. However, July 19 was a notably shorter day, clocking in at 1.4602 milliseconds below the standard. The earlier record for the shortest day was set in 2005, but it’s been beaten 28 times in 2020.

Should this trend continue, we may very well need a negative leap second in the next few years to keep our clocks synchronized with “real time.’ That would be a first as all previous adjustments have added time. While it’s impossible to say for certain that this speed-up will continue, most scientists believe that it will. Regardless, the quicker rotation is itself not a problem — the causes might be, though. Some have started to wonder aloud if large-scale changes from global warming have started to have a noticeable impact on the spin. Shaving a few milliseconds off the day won’t hurt anyone, but it’s not exactly a good sign.

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Hayabusa2 Spacecraft Completes Mission, Returns Asteroid Sample to Earth

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The Japanese Hayabusa2 spacecraft launched a few years back with an ambitious mission ahead of it: orbit an asteroid, deploy rovers, shoot the asteroid, and collect samples for return to Earth. In the last couple of years, Hayabusa2 has accomplished every single one of those objectives. After six years in space, the Hayabusa2 sample container landed on Earth, providing scientists with the first significant samples collected directly from an asteroid. 

The Japan Aerospace Exploration Agency (JAXA) launched Hayabusa2 in 2014. It took about two years for the probe to rendezvous with a space rock known as Ryugu, which is a rare spectral type Cb asteroid, with qualities of both a C-type and B-type asteroids. Asteroids like Ryugu have remained mostly unchanged since the earliest era of the solar system. So collecting a sample could allow us to look back in time and learn about this part of our history. Getting pristine samples from an asteroid is no simple feat, though. 

Hayabusa2 reached Ryugu in summer 2018 and spent the next several months gathering data so the team on Earth could evaluate sample collection locations. The team found that Ryugu was much more craggy than expected, a finding confirmed when NASA’s OSIRIS-REx probe reached the asteroid Bennu. Along the way, Hayabusa2 dropped off its robotic surface explorers and mapped the entire surface of Ryugu. 

Last year, Hayabusa2 dropped down to the surface and fired a tantalum slug into the asteroid. This launched the regolith upward into the collection mechanism. Later, the probe deployed its Small Carry-on Impactor (SCI), which fired an explosive-accelerated impactor into the surface to produce a small crater. After bombing the asteroid, Hayabusa2 dropped down to get another sample from the newly uncovered area. 

Hayabusa2 began the journey home in late 2019, using its ion engines to leave Ryugu behind forever. The spacecraft reached Earth over the weekend and released the 35-pound (16 kilograms) sample return capsule. As planned, the container entered Earth’s atmosphere over Australia, deploying its parachute as it descended in the Woomera test range. Teams recovered the capsule after spotting its parachute snagged on a bush. 

The team set up a “quick look” facility at Woomera to inspect the payload. They siphoned off gas from the inside of the container, but it’s unclear at this time if the gas came from the asteroid. The mission was designed to collect about 100 micrograms of material — that might not sound like a lot, but it’s by far the most asteroid material we’ve ever had to analyze. JAXA will send some of the samples to NASA (among others), which will have its own asteroid samples in a few years when OSIRIS-REx returns to Earth. That mission may have collected several kilograms of material from Bennu, so scientists will have plenty of material to conduct experiments.

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NASA Probe Stows Huge Asteroid Sample for Return to Earth

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OSIRIS-REx has been in orbit of Bennu since late 2018, which gave NASA ample time to find just the right landing zone on the unexpectedly rocky surface. It apparently chose well. Following the recent successful touch and go operation, NASA has reported a sizeable sample of the asteroid has now been locked away in the probe’s sample return container

Earlier this month, OSIRIS-REx descended and tapped the surface, or rather, it was supposed to be a tap. NASA now says the sampling arm may have punched through 19 inches (48 centimeters) of loose soil before the nitrogen blast fired. That puff of air was supposed to blow about 60g of material into the sampling container. Instead, it harvested a whole lot more. 

There was a brief but scary period earlier this week when NASA confirmed that large pebbles had jammed open the sample container’s lid. As a result, asteroid particles were falling out whenever the spacecraft moved. NASA opted to forego the planned sample measurement over the weekend as that would have caused more sample material to drift away. It also scrapped any plans to conduct a second sampling run at the backup Bennu site. Instead, NASA worked to secure its impressive haul. 

The latest images from OSIRIS-REx show the sample safely locked inside the sample capsule. This module will eventually drop into Earth’s atmosphere, and the heat shield will protect it from atmospheric reentry. We don’t know exactly how much sample OSIRIS-REx grabbed from Bennu, but we know it’s a lot more than the 60g minimum. NASA estimates OSIRIS-REx could have as much as a kilogram (1,000g or 2.2 pounds) of pristine asteroid soil in the return canister. That’s huge — the payloads of past sample return missions could best be measured in milligrams. The recent Hayabusa2 mission hopes to have 100mg (a tenth of a gram) of asteroid regolith when it lands in the coming months. 

Getting that much of Bennu back to Earth could be a watershed moment for science. Most asteroid samples on Earth have been scorched by the atmosphere and smashed to bits on impact. Bennu has remained mostly unchanged since the formation of the universe, and we’ll have enough for lots of teams to run lots of tests that will no doubt teach us a great deal about the early solar system. 

Bennu and OSIRIS-REx are currently millions of miles away, so it’ll take time for the probe to return home. NASA plans to break orbit in March 2021 when Bennu and Earth are in close proximity. The sample return capsule should be back on Earth in September 2023.

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NASA: Asteroid Could Still Hit Earth in 2068

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Earth has been bombarded by space rocks throughout its history, but we’re lucky no large ones have slammed into the planet lately. Astronomers keep a careful watch on the skies, hoping to spot potential impactors far enough in advance that we can do something about it, and one of the most worrying objects is 99942 Apophis. This skyscraper-sized asteroid might still hit Earth in 2068, according to a new analysis from the University of Hawaii and NASA’s Jet Propulsion Laboratory. 

Scientists discovered Apophis in 2004, sounding the alarm when initial observations suggested it had a worryingly high 2.4 percent chance of hitting Earth in 2029. Thankfully, further study lowered that probability to zero. Still, astronomers have been keeping an eye on Apophis ever since — it’s currently considered the third-highest impact threat to Earth, behind 101955 Bennu and 29075 (1950 DA). However, the highest impact risks for those objects are centuries out. 

NASA’s Sentry Risk Table shows a 1 in 150,000 chance of Apophis hitting Earth in 2068, but that doesn’t take into account a phenomenon known as the Yarkovsky effect. As asteroids tumble through space, they absorb energy from the sun. That energy is radiated back into space as heat, but the process is not uniform over the object’s entire surface. The result is a small but measurable push that alters the object’s orbit. Davide Farnocchia at NASA and Dave Tholen from the University of Hawaii used data from the Subaru Telescope to try and pin down how much the Yarkovsky effect changes our odds. 

This is our best guess at Apophis’ shape.

Tholen says the true impact risk is probably closer to 1 in 530,000, a number used by the NEODyS impact monitor service that includes the Yarkovsky effect. The new observations will probably push NASA’s Sentry risk to a similarly low level. So yes, it’s probably less likely Apophis will hit Earth in a few decades, but astronomers will need to monitor its orbit over time to make sure. There is still a very real, non-zero chance that Apophis will get caught in Earth’s gravity in 2068. 

You don’t want to take any risks with an object like Apophis. While it’s not quite “mass extinction” big, an impact would be catastrophic. It’s a simple matter of physics — Apophis hitting Earth results in an explosion equivalent to 1,151 megatons of TNT. By comparison, the largest nuclear weapon ever detonated by humans was around 57 megatons. The 1883 eruption of Krakatoa clocked in at about 200 megatons. Apophis could level a small country, cause massive tidal waves, and spark widespread wildfires. All in all, a pretty bad day for Earth. 

In the event Apophis is ever on a collision course, astronomers should be able to tell us well in advance. Maybe it’ll even be early enough to try one of those pie-in-the-sky asteroid deflection systems we always hear about.

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There Are 1,004 Nearby Stars Where an Alien Astronomer Could Detect Life on Earth

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We are in the very early stages of exploring the universe, and our efforts have uncovered thousands of exoplanets. We don’t yet know if any of them support life, but maybe one day we’ll know. In the meantime, Earth is the only planet we know for certain does host life. Researchers from Cornell University and Lehigh University turned this question around. We know Earth has life, but does anyone else? The new study says that, yes, there are 1,004 nearby stars where an alien looking at Earth could potentially know we’re here. 

There are more than 4,000 known exoplanets currently, and most of them were identified with the Kepler Space Telescope. We can’t just point any old telescope at a star and say, “Yep, there’s a planet there.” Stars are so much brighter by comparison that we can’t make out individual worlds. The most common way to spot exoplanets, and the method Kepler used, is to watch for the planet to transit in front of the star. When you hear about a new exoplanet discovery, that’s usually how astronomers found it. 

Here’s the catch: we can only see transits if the plane of an alien solar system is aligned with ours. Otherwise, the planet doesn’t pass in front of the star from our perspective. Professors Lisa Kaltenegger and Joshua Pepper looked at this from the other side — which solar systems would be able to make a transit observation of Earth and detect life-associated molecules in our atmosphere? 

Using NASA’s Transiting Exoplanet Survey Satellite (TESS) star catalog, the pair looked 300 light-years in all directions to find candidate solar systems, ruling out stellar remnants like white dwarfs that cannot (as far as we know) host alien life. There are a huge number of main-sequence stars in this region of space, but only a fraction of them would be able to see Earth passing in front of the sun from where they are. 

The final count, according to Pepper and Kaltenegger, is 1,004. Of those, 508 have angles that would give them at least 10 hours of observational data every time Earth transited the sun. However, 5 percent of the total are stars too young to have developed planets or life. The rest, though, could hypothetically have habitable planets, and two of them have known exoplanets.

In every one of those solar systems, beings like us with an understanding of planetary transits could be seeing Earth darken the sun every year. They might be able to estimate Earth’s size and distance from the sun, and that would indicate the possibility of liquid water on the surface. If they’re a little more advanced than us, they might already have the equivalent of the James Webb Space Telescope, which NASA hopes to launch in the next few years after numerous delays. An instrument such as that could detect the presence of water vapor, methane, phosphine, and other compounds that suggest life. Maybe an alien astronomer is, right at this moment, having a eureka moment as they realize someone is looking back at them from Earth. You should wave hello to be polite just in case.

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Better Than Earth? Scientists Identify 24 ‘Superhabitable’ Planets

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Our observations of distant stars have revealed more than 4,000 exoplanets, and some of them have been labeled as potentially habitable. That doesn’t mean there’s anyone living there, but it’s possible. It may also be possible that there are so-called “superhabitable planets” in the cosmos where the chances are higher. A new analysis published in the journal Astrobiology seeks to identify these worlds, and the researchers say we might have already detected 24 of them

When we talk about habitable planets, that usually means worlds that are very much like Earth — the kind of place where there’s liquid water and an atmosphere. A human, plopped down on such a world, would not immediately curl up and die. A superhabitable planet isn’t just one that’s better for human life. The team led by astrobiologist Dirk Schulze-Makuch from the Technical University Berlin defines a superhabitable planet as one that is even more likely than Earth to have life. The research argues that these are the worlds we should focus on when hunting for aliens. 

We only have this one living ecosystem on which to base our assumptions about what’s “habitable.” It’s possible that Earth isn’t anything special as a home for life. Perhaps an alien observing Earth from a great distance would be surprised intelligence could evolve on such an unsuitable hunk of rock. The authors note that restraining our anthropocentric view of the universe could be vital to finding life among the stars. 

So, what makes a planet superhabitable? We know that Earth’s warmer regions have greater biological diversity, so a planet somewhat warmer than Earth could host more life. That might not make it very comfortable for humans, but that’s not the point. Likewise, the team looked for exoplanets that are about 1.5 times as massive as our home planet. These worlds are more likely to have a dense atmosphere, and there would be more surface area for life to occupy. 

eso exoplanet

Credit: ESO

The star an exoplanet orbit is also an important factor. The sun is a yellow dwarf, and it does a good job of keeping Earth livable, but maybe this isn’t the best kind of star for life. The sun has a lifespan of about nine billion years, and we’ve only got another billion years or so before it heats up and boils Earth like an egg. If you’re playing the odds, planets that orbit longer-lived stars like orange dwarfs could have a higher chance of hosting life. 

The team surveyed the known exoplanet catalog and found 24 worlds that might qualify as superhabitable. One such planet is KOI 5715.01, which is 3,000 light-years away. It’s 1.8 times Earth’s mass and orbits an orange dwarf. However, none of the exoplanets cited in the paper are within 100 light-years. The hunt for superhabitable worlds may be at an impasse until more advanced instruments like the James Webb Space Telescope come online.

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