Hycean worlds are also called ocean worlds. They're planets covered in oceans that also have thick hydrogen atmospheres. There are no confirmed Hycean worlds—also called ocean worlds—but many candidates. Even though they're only candidates so far, researchers are curious about their habitability. New research examines the role tidal heating plays in their potential habitability.

If hycean planets do exist, they're likely common around red dwarfs (M dwarfs.) Red dwarfs are the most plentiful type of star in the galaxy, and Hycean worlds' thick hydrogen atmospheres might protect them from the devastating flaring behaviour of these small, long-lived stars. Hycean worlds may have larger habitable zones because of all their water, but their hydrogen atmospheres may contribute to the runaway greenhouse effect. When it comes to habitability, these hypothetical worlds are intriguing and mysterious.

In new research to appear in The Astrophysical Journal, the authors argue that for Hycean worlds close to their low-mass stars, tidal heating may be an important factor in determining their habitable zones. It's titled "Tides Tighten the Hycean Habitable Zone," and the lead author is Joseph Livesey. Livesey is from the Department of Astronomy and the Wisconsin Center for Origins Research, both at the University of Wisconsin-Madison.

When a new exoplanet is discovered, one of the first things scientists and the public want to know is if it's in the star's habitable zone. Researchers have made significant progress understanding the habitable zones for rocky planets. "Many studies have parameterized the habitable zone (HZ) for terrestrial exoplanets," the authors write. "The exact HZ boundaries can vary based on key characteristics such as stellar host type, planetary mass, atmospheric composition, and more."

But hycean worlds are much different than terrestrial worlds. They're sub-Neptunes with significant water layers and atmospheres dominated by hydrogen. They're oddballs, and determining if they are in habitable zones requires a different approach than with rocky planets.

In our Solar System, some of the gas giant moons have frozen shells with liquid oceans underneath. They're far too distant for the Sun to warm them. It's tidal flexing that maintains their liquid oceans. As moons like Europa and Enceladus orbit Jupiter and Saturn, the much-larger gas giants pull on the moons and they flex in response. That action creates heat. So, in effect, tidal flexing creates a habitable zone that's isolated from the Sun.

Since many hycean worlds are expected to orbit their stars closely, can tidal heating alter their habitable zones?

The researches say that the Hycean Habitable Zone (HHZ), when compared to the terrestrial habitable zone, may include smaller semi-major axes and could even extend to unbound planetary orbits. A near total absence of GHGs other than hydrogen along with a high albedo allows closer orbital proximity to the star, while internal heating from radiogenic sources, high pressures, a liquid water layer, and larger planet masses extend the HHZ outward.

Tidal heating creates another heat source aside from stellar radiation. Hycean worlds following moderately eccentric orbits experience tidal flexing and heating that shifts the HHZ outward. This creates a smaller HZ than previous estimates based on stellar heating.

Moderately eccentric orbits are common. Our Solar System has massive outer planets that have shifted the orbit of smaller planets into eccentricity. Many other solar systems are likely to have them too, meaning they're shifting smaller planets into eccentricity.

"These outer companions do occur in planetary systems around M dwarfs; the occurrence rate of giants in such systems has been found to be ∼ 10%, and the occurrence rate of planets in the range 10–100M⊕ is ∼ 20%," the authors write.

This figure shows The HHZ (blue shaded regions) and dark HHZ (red shaded regions) around a 0.12M⊙ star for a 7M⊕, 1.7R⊕ Hycean planet with tidal heating. The dark HHZ indicates a tidally-locked Hycean planet that can be habitable on its nightside. The low-opacity contours show the habitable zone locations without tidal heating, and the high-opacity contours show the habitable zone location where tidal heating is included. The dotted and dashed lines indicate the conservative and optimistic habitable zones for terrestrial planets.

Image Credit: Livesey et al. 2025. The Astrophysical Journal.

The above image shows how tidal heating shifts the HHZ around low-mass stars. However, most hycean candidates are orbiting more massive stars. The researchers found that the effect of tidal heating on the HHZ depends on the star's mass. They found that around more massive stars, the tidal heating effect isn't as pronounced.

This figure shows the HHZ and dark HHZ around stars of various mass for a 7M⊕, 1.7R⊕ Hycean planet. The orbital eccentricity for this planet is based on the Hycean candidate world K2-18 b, a planet known for evidence of potential biosignatures. The dotted line represents the stellar mass in the previous figure of 0.12 solar masses. "Clearly, the effect of tides on the extent of the habitable zone becomes negligible at high stellar masses," the researchers explain. Image Credit: Livesey et al. 2025.

The Astrophysical Journal.

This research shows that tidal flexing on ocean worlds shifts their habitable zones outward. The effect relies on a more massive companion planet that can introduce eccentricity into the hycean world's orbit.

"Hycean planets are likely to exhibit stronger tidal responses than a fiducial terrestrial world," the researchers explain. "We expect tides to have little effect on a lone planet at such small orbital radii. However, the presence of a large outer companion with moderate eccentricity will force an eccentricity cycle that periodically and indefinitely heats the interior of the planet in question, and push out the inner boundaries of the HHZ."

Though hycean worlds are only hypothetical at this point, their confirmation may not be too distant. Exoplanet scientists are intrigued by them because of their potential for habitability. Their extended atmospheres also make them desirable targets for atmospheric spectroscopy with telescopes like the JWST. K2-18b is a prime example of their potential. It's a candidate hycean world that repeatedly generated headlines when astronomers found evidence of water vapor, then carbon dioxide and methane, then the potential biosignature dimethyl sulfide in its atmosphere.

"A recent possible detection of dimethyl sulfide (DMS) in the atmosphere of the potential hycean exoplanet K2-18 b may indicate the presence of ocean-faring life; the only major source of DMS on Earth is phytoplankton," the authors write. They point out that on hycean worlds with deep oceans, the ocean tides generate a significant amount of heat that can be used by organisms. This sets them apart from Earth, where the tidal energy is dissipated. "We suggest, therefore, that strong tides on hycean planets could yield a significant power source for life and ultimately accelerate biological evolution," they explain.

If our Solar System seems stable, it's because our short lifespans make it seem that way. Earth revolves, night follows day, the Moon moves through light and shadow, and the Sun hangs in the sky. But in reality, everything is moving and influencing everything else, and the fine balance we observe can easily be disrupted. Could passing stars have disrupted Earth's orbit and ushered in dramatic climatic changes in our planet's past?

A stellar flyby is when another star passes close enough to our Solar System to cause some disruption. Our neighbourhood in the Milky Way is relatively sparsely populated, so stellar flybys are rarer than in other parts of the galaxy. But they still occur.

The most well-known one was probably Scholz's star. About 70,000 years ago, it passed through the Oort Cloud, our Solar System's outlying repository of long-period comets and icy planetesimals. It may have perturbed some comets from the Oort Cloud, but if it did, we won't know for a couple of million years. That's how long it would take for a comet to reach the inner Solar System.

Scholz's star illustrates the risk of stellar flybys. Scientists have wondered if these flybys have affected Earth's climate in the past by altering the planet's orbit. New research that will appear in The Astrophysical Journal examines stellar flybys to see if this is true. It's titled "No influence of passing stars on paleoclimate reconstructions over the past 56 million years." The authors are Richard Zeebe and David Hernandez. Zeebe is from the School of Ocean & Earth Science & Technology at the University of Hawaii, and Hernandez is from the Department of Astronomy at Yale University.

"Passing stars (also called stellar flybys) have notable effects on the solar system’s long-term dynamical evolution, injection of Oort cloud comets into the solar system, properties of trans-Neptunian objects, and more," the authors write. "Based on a simplified solar system model, ... it has recently been suggested that passing stars are also an important driver of paleoclimate before ∼50 Myr ago, including a climate event called the Paleocene-Eocene Thermal Maximum (PETM) (∼56 Myr ago)."

The PETM saw a 5–8 °C (9–14 °F) rise in global temperature and a massive influx of carbon into the atmosphere and oceans. It took 10,000 or 20,000 years for the temperature to rise and it lasted for about 100,000 or 200,000 years. Its effect on the biosphere was massive. Many marine organisms went extinct, tropical and sub-tropical regions extended toward the poles, and primates and other mammals appeared.

The Paleocene–Eocene Thermal Maximum was a prominent hyperthermal episode in Earth's climatic history. Its cause is unclear.

Image Credit: Svensen 2012. https://doi.org/10.1038/483413a

The cause is still debated, and there are several hypotheses. They include volcanic eruptions, comet impact, the release of methane clathrates, and orbital forcing. Researchers think that the giant planets play an important role during stellar flybys. When a roaming star passes by, the giant planets' gravitational fields can amplify the effect of the flyby and then alter the orbits of the smaller planets.

To find out if stellar flybys could be responsible for the PETM and other climatic changes, the researchers used a state of the art model of the Solar System and random stellar parameters in 400 simulations. The total number of stellar flybys was 1,800.

Other researchers who examined the same issue found that stellar flybys could've altered Earth's paleoclimate. [Kaib & Raymond (2024)] (https://iopscience.iop.org/article/10.3847/2041-8213/ad24fb) said, "Here we present simulations that include the Sun's nearby stellar population, and we find that close-passing field stars alter our entire planetary system's orbital evolution via their gravitational perturbations on the giant planets." They also wrote "Although it takes tens of Myr for the effects of stellar passages to significantly manifest themselves, the long-term orbital evolution of the Earth and the rest of the planets is linked to these stars."

However, Zeebe and Hernandez reached a different conclusion. "In contrast to Kaib and Raymond, we find no influence of passing stars on paleoclimate reconstructions over the past 56 Myr," they write.

This global map shows what Earth looked like 45 million years ago.

Image Credit: By Scotese, Christopher R.; Vérard, Christian; Burgener, Landon; Elling, Reece P.; Kocsis, Ádám T. - "Phanerozoic-scope supplementary material to "The Cretaceous World: Plate Tectonics, Paleogeography, and Paleoclimate (doi:10.1144/sp544-2024-28)" from the PALEOMAP project". doi:10.5281/zenodo.10659112 https://zenodo.org/records/10659112, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=155112444

One of the reasons for the different results is the completeness of the models used to understand the flybys. Some Solar System models, for example, excluded the Moon.

"Running accurate state-of-the-art solar system models that include all known secondary effects is computationally expensive," the authors write. "As a result, long-term studies on, e.g., Gyr-timescale tend to be based on simplified solar system models, or the outer planets alone."

By using a more complete Solar System model, Zeebe and Hernandez showed that stellar flybys are not likely behind Earth's dramatic paleoclimate shifts, like the PETM. They point out that the Moon has a stabilizing effect, and models that exclude it reach suspect conclusions.

"In contrast, using a state-of-the-art solar system model, including a lunar contribution and J2 (the Moon and Sun's quadrupole moment), and random stellar parameters, we find no influence of passing stars on paleoclimate reconstructions over the past 56 Myr," the authors explain. Even extremely close flybys seem to have no effect.

There have been many stellar flybys in the past and there'll be many more in the future. The orange dwarf Gliese 710 is expected to come within 0.1663 light-years or 10,520 astronomical units in about 1.29 million years. It has an 86% chance of passing through the Oort Cloud, and some researchers say it could trigger a swarm of comets into the inner Solar System. Could this flyby trigger a dramatic shift in Earth's climate?

There's a lot of uncertainty, and understanding the past and future of stellar flybys and how they might affect Earth's climate comes down to how detailed our scientific models are.

"Our results indicate that a complete physics model is essential to accurately study the effects of stellar flybys on Earth’s orbital evolution," the authors conclude.

In March 2025, NASA's Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission launched into orbit to monitor the Sun's outer atmosphere to reveal more about solar wind. Developed and led by the Southwest Research Institute (SwRI), this constellation consists of four microsatellites that observe the Sun's corona and heliosphere using continuous 3D deep-field imaging. While completing its commission phase, the Wide Field Imagers (WFIs) aboard the four PUNCH spacecraft captured high-resolution images of a Coronal Mass Ejection (CME) in greater detail than any previous mission.

SwRI heliophysicist Dr. Craig DeForest discussed the latest accomplishments of the PUNCH mission at the 246th American Astronomical Society meeting, which took place from June 8th to 12th in Anchorage, Alaska. DeForest is the Director of the SwRI's Department of Solar and Heliospheric Physics, the former Chair of the AAS's Solar Physics Division, and PUNCH's principal investigator. As he explained:

These preliminary movies show that PUNCH can actually track space weather across the solar system and view the corona and solar wind as a single system. This big-picture view is essential to helping scientists better understand and predict space weather driven by CMEs, which can disrupt communications, endanger satellites and create auroras at Earth. These first integrated images of our home in space are astonishing, but the best is yet to come. Once the spacecraft are in their final formation and the ground processing is fully sighted over the next few months, we'll be able to track the solar wind and space weather in 3D throughout our neighborhood in space.

• https://www.youtube.com/shorts/g88s4r_skxQ?feature=share

These images were taken by PUNCH's four cameras, which work together as a single "virtual instrument," measuring 12,875 km (8,000 mi) across. Their WFIs work with a Narrow Field Imager (NFI) chronograph that blocks out the Sun's bright light, allowing scientists to observe the outermost portion of the corona and the continual stream of charged particles from the Sun (solar wind). The images the spacecraft took were stitched together to create a video (see below) that shows giant CMEs erupting and spreading across the inner Solar System. The images also show Venus, Jupiter, the Moon (visible as bright spots), and several constellations like Orion and Pleiades in the background.

During its two-year primary mission, PUNCH will continue to make global 3D observations of the Sun's outer atmosphere and the inner solar system. These detailed images will help scientists better understand space weather, which can disrupt communications, satellites, and missions in Low Earth Orbit (LEO), and will improve predictive models. "These first images are astonishing, but the best is still yet to come," said DeForest. "Once the spacecraft are in their final formation, we'll be able to routinely track space weather in 3D across the entire inner solar system."

Further Reading: 

• NASA, 
• SwRI

Most scientists agree that supernova explosions have affected Earth's climate, though the details are not all clear. They likely cooled the climate several times in the last several thousand years, just as humanity was becoming established around the world. The evidence is in telescopes and tree rings.

We live in the Quaternary period which spans from 2.58 million years ago to the present. The Quaternary is characterized by climatic and environmental changes, most significantly the Ice Ages. The Quaternary also encompasses human existence and evolution from early hominids to our species.

New research in the Monthly Notices of the Royal Astronomical Society examines the role supernovae explosions played in the Quaternary climatic changes. It's titled "Late Quaternary supernovae in Earth history," and the author is Robert Brakenridge. He's a senior research associate in the Institute of Arctic and Alpine Research at the University of Colorado.

The Late Quaternary is loosely defined as the time period from 50,000 years ago to the present. It featured several abrupt, dramatic changes in Earth's climate. These include the Older Dryas and the Younger Dryas, abrupt shifts to a colder climate while the Earth was experiencing a warming trend after the last ice age, at the end of the Pleistocene epoch.

There are several ways that SN can cool Earth's climate. They can weaken or destroy Earth's ozone layer, which would allow more UV light to reach the surface. That leads to knock-on effects that can cause cooling. SN also contribute to cooling by degrading atmospheric methane, a greenhouse gas. The primary way that SN can cool Earth's climate is by increasing the cloud cover.

The idea that supernovae could be responsible for abrupt climate shifts is supported by evidence from tree rings. Trees absorb three isotopes of carbon, carbon-12 (12C), carbon-13 (13C), and carbon-14 (14C). When researchers examine ancient tree rings, they find different ratios of the carbon isotopes in different rings. 12C and 13C are stable isotopes, while 14C isn't. 14C is created continuously in the upper atmosphere all of the time.

When supernovae explode, they send high-speed energetic particles outward in all directions. When some reach Earth, they collide with nitrogen in the atmosphere and generate 14C. Because of this, the atmospheric level of 14C spikes when a nearby supernova (in astronomical terms) explodes.

Tree rings can be dated, and when scientists date tree rings with raised levels of 14C, it indicates that a supernovae explosion occurred somewhere nearby at a specific time.

It's not that cut and dried, however, and not all researchers agree that we can link tree rings with supernovae. Miyaki events also create a burst of 14C that can be identified in tree rings, but they're caused by the Sun. However, the the idea that supernovae could be responsible for 14C and climate shifts won't go away.

“We have abrupt environmental changes in Earth’s history. That’s solid, we see these changes,” study author Brakenridge said. “So, what caused them?”

The question rings out as we try to understand our own history and what the future might hold for Earth.

“When nearby supernovae occur in the future, the radiation could have a pretty dramatic effect on human society,” he said. “We have to find out if indeed they caused environmental changes in the past.”

Tree rings and carbon-14 are only part of the story. The other part is told by our powerful telescopes that search the heavens. When stars explode as supernovae, they don't just simply disappear. They leave behind remnants, an expanding shock wave of dead star material and swept up interstellar medium that's lit up by the explosion and depending on the type of supernova, a white dwarf.

Supernova remnants (SNR) are some of Nature's most dazzling displays. The most well-known one is probably the Crab Nebula, the remnant from the 1054 supernova. The crab nebula was the first astronomical object successfully linked with a historical supernova.

The Crab Nebula is the remnant from the 1054 AD supernova. Ancient astronomers in China and other places observed the explosion at the time and recorded it.

Image Credit: By NASA, ESA, J. Hester and A. Loll (Arizona State University) - Public Domain

As our telescopes have grown in power, scientists have learned a lot about the radiation that comes from supernovae. The struggle is to understand exactly how the radiation interacted with Earth and affected its climate. There's no clear picture of how far away SN can be and still affect Earth.

"All known Late Quaternary SNRs are much further away than the solar system neighbourhood," the author writes in his research. "SNe at distances of >0.1 kpc have sometimes been considered too remote to affect Earth's biosphere and atmosphere." Brakenridge explains that this conclusion is based on catastrophic effects rather than significant effects. "Such a criterion is not appropriate for Late Quaternary time, as there is no known global extinction event comparable to, for example, those in the late Ordovician and the Cretaceous-Tertiary boundary," he explains, mentioning two of Earth's major extinctions.

"Instead, there is abundant evidence of global climate changes of lesser magnitude and also major mammalian extinction events," Brakenridge explains. "It is thus not possible with present knowledge to rule out SNe at a few 0.1 kpc as causing significant effects observable in Late Quaternary records."

In this research, Brakenridge created a new model of how SN radiation affects the planet's atmosphere.

No SN are affecting Earth right now, so Brakenridge tested the model the only way he can: with tree rings. He examined tree rings over the last 15,000 years and found 11 carbon spikes. Eventually, he determined that four supernovae could have affected Earth's climate during the Late Quaternary.

“The events that we know of, here on earth, are at the right time and the right intensity,” Brakenridge said.

The Hoinga SNR closely aligns with the Older Dryas abrupt cooling about 14,000 years ago.

The Hoinga SNR may be linked to the Earth's Older Dryas abrupt cooling period.

Image Credit: Team New Horizons/Australia Telescope National Facility.

The Vela SNR is associated with the Younger Dryas cooling about 12,000 years ago.

The Vela SNR may be linked to Earth's Younger Dryas cooling period.

Image Credit: By (Credit) ESO/TIMER survey

- https://www.eso.org/public/news/eso2214/, CC BY 4.0

Two other C14 events, the largest of the Holocene, at about 9,000 and 7,000 years ago, are also closely aligned with nearby SNR.

The Older and Younger Dryas affected our human ancestors, who were struggling to survive. The Younger Dryas was particularly difficult for humans, who saw a significant population decrease during this time. We may be buffered from similar climatic changes by technology, but these types of rapid climate shifts could be catastrophic for civilization as we know it.

Tree rings and telescopes aren't the only evidence showing how SN could've affected Earth. There's also sediments, ice cores, and other evidence. The challenging part is to piece all of it together and understand how the past played out.

The other challenge is to look around and us and determine what nearby stars may be about to explode, and what threat they might pose to the climate. It's possible that we could be thrust back into a difficult survival situation like our ancestors were.

“As we learn more about our nearby neighboring stars, the capability for prediction is actually there,” Brakenridge said. “It will take more modeling and observation from astrophysicists to fully understand Earth’s exposure to such events.”

• Press release: Supernovae may have kicked off abrupt climate shifts in the past, and they could again
• Published Research: Late Quaternary supernovae in Earth history

In this series we are exploring NASA's top five challenges as detailed in its Civil Space Shortfall Ranking, which is basically NASA's Christmas wish list. These are the technologies that NASA believes we need to develop if we want to go to space…and stay there.

And finally, after multiple rounds of voting from NASA centers, industry partners, and academic researchers, the highest priority goal we need to accomplish to make all our space dreams come true: surviving the Lunar night.

Now I know this sounds like a low-budget knockoff of Five Nights at Freddy's, but it's the real deal. The Lunar night is no fun at all. For one, it typically lasts two weeks at a time (although there are some peaks that receive sunlight almost permanently, but there are also regions where the sun never strikes at all). For another, temperatures can plummet down to 35 degrees above absolute zero. This is absolutely unprecedented; there is no analogy to anything we have experienced on the Earth. Even in arctic regions, where the Sun can disappear for months at a time, are helped by the fact that we still have an atmosphere that can retain and distribute heat. When the Sun shines on the equator, some of that heat makes it up to the poles. But the Moon has no atmosphere, so the only heat you get is from the Sun. When it's gone, it's gone. This makes nighttime operations are a serious challenge. It's really hard to design electronics, and especially batteries, that can function for long periods of time at low temperatures, because almost all of our battery designs rely on chemical processes to generate electricity – processes that slow down at low temperatures, and all of our electronics are designed to work…you know, on Earth.

There has been some headway in the direction of surviving the lunar night. In early 2024 the Japanese lander SLIM, for Smart Lander for Investigating Moon, also known by the much cooler anime nickname of "Moon Sniper", made history by surviving three lunar nights – that's three four-week cycles of light and darkness. But to survive the nights the lander had to shut down and enter a hibernation state, hoping that its batteries would stay warm enough to power itself back up once daylight hit again.

So while that technically counts as surviving the lunar night, that's not exactly what NASA and its partners had in mind when they ranked this as their number one challenge. We can't just go into low-power sleep mode every two weeks, especially if we're talking about extended human or even robotic activities on the lunar surface.

Surviving the Lunar night means transitioning from a daylight temperature of over a blistering 120 degrees Celsius (or 260 degrees Fahrenheit) all the way down to -240 Celsius at night, which is…negative a lot in Fahrenheit. On the other side of the coin, our own robotics and electronics are going to generate their own heat, anywhere from 5 Watts to 10,000 Watts. We need to efficiently manage that heat and make sure it doesn't warp or destroy other vital components on its way out of the spacecraft, especially when the outside temperatures will vary so much.

What will it take to enable lunar night operations? We need components that can manage those kinds of massive temperature swings and still efficiently operate in frigid conditions. We need systems that can efficiently dump heat in both freezing and boiling outside conditions. We need large solar panels that can absorb energy during the daytime and low-temperature batteries that can continue to supply that power through the night. We can't just have these components specialized to one temperature extreme or the other – they need to be able to handle both.

I see this challenge as the culmination of all the other ones. Surviving the lunar night isn't easy, but it serves as a critical milestone in our advance into space. If we want to survive the lunar night and maintain activities and exploration for those two weeks of darkness, we need to solve the other four challenges. This will be our true test. We can't just content ourselves with literal day-trips or low-power night modes. We have to be able to maintain the same level of activity regardless of the daylight conditions. We need high-powered, capable robotics. We need reliable systems for timing and navigation. We need more sophisticated computers, and most importantly we need a lot of electricity. If we can maintain robotic or crewed activities through lunar night after night, then we will have the technological base we need to create a more robust presence on the Moon and extend even further into the solar system.

It won't be easy. The lunar night is unforgivingly cold, depressingly dark, and depressingly long. But hey, at least we'll get a great view of the stars.

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In this series we are exploring NASA's top five challenges as detailed in its Civil Space Shortfall Ranking, which is basically NASA's Christmas wish list. These are the technologies that NASA believes we need to develop if we want to go to space…and stay there.

Coming in second place is nothing less thanmore power. Which is kind of obvious: we want bigger and faster computers, we want more powerful robotics, and we want more sophisticated navigation systems. All that is going to take a lot of juice.

What we have now just…isn't going to cut it. Right now if you want power in space you essentially have two options: solar panels, and a kind of nuclear power called radioisotope thermoelectric generators.

Solar panels are exactly what you think of, because it's very similar to what we have on the Earth. On the plus side, solar panels are relatively cheap to make and deploy, and contain no moving parts, which is always a bonus when it comes to space applications. There are major downsides, however. One, anything outside the Earth's orbit is going to be tight on energy relying on solar panels, because…not a lot of sunlight. Also there's no Sun in the shade, which I know is an incredibly obvious statement to make but matters if you're, say, on the Moon and get plunged into darkness for two weeks at a time.

Even the International Space Station, which receives the same amount of sunlight as the Earth (because it's in Earth orbit), has over 262,000 individual solar cells spanning over an acre – which is over 2,500 square meters for you metric folks that generates on average an impressive 84 to 120 kilowatts of electricity, which could power…a handful of typical homes.

Hm.

NASA's Juno spacecraft currently holds the record for the most distant deployed solar panels in the system, orbiting around Jupiter at a distance of over 800 million kilometers. Its gigantic solar array could generate 14,000 watts of power on the Earth, but at the distance sunlight is so feeble it only managed a measly 500 watts of power…which could run a kitchen blender. You know, if you needed to make a smoothie at Jupiter. But Juno was able to turn that juice into the most detailed images ever taken of the storms and cloud-tops of the giant planet, and use slight variations and gravity and magnetic fields to give us a sense of what's happening deep beneath the surface.

The alternative for deep-space missions is the RTG, or radioisotope thermoelectric generator. This device is essentially a chunk of radioactive material that decays. As it does it releases heat, which can be used to generate electricity. It's like a nuclear battery. On the upside these thigs last basically forever, giving spacecraft decades of reliable power. But on the downside they don't deliver a lot of power, they slowly lose power over time, and there's the whole nuclear thing which makes some people a little twitchy.

But there's thing. If we're going to stay in space for the long haul, we have to get over the whole nuclear thing real quick. And that doesn't mean more RTGs. That means full on nuclear power plants on lunar and Martian bases. Yes, you heard me right. Look, it's not like we don't know how to make relatively compact nuclear power plants: submarines and aircraft carriers around the world all carry their own little power plants. But those things are beyond heavy, which make them impractical to launch in a single mission, and nobody really likes the idea of trying to assemble one in Earth orbit.

So we have to get clever. We're going to have to figure out how to make smaller, launchable fission power plants. And the most difficult challenge will be convincing the public that we can launch nuclear material into space and totally not have it blow up in the atmosphere, we promise. I mean, it's kind a legit concern. It's not like we'll have a nuclear bomb going off or anything, but also nobody wants some rocket blowing up and rain radioactive material across a sizeable fraction of a continent. It's not likely to happen, but there's a possibility, and NASA and its partners will have its work cut out to convince the public that it's a small enough risk, and a great enough reward.

In the meantime, while we're figuring out all the bits and pieces that will make safe, efficient nuclear power in space a viable option, we have to up our game with solar panels. That's really the only other power source we can rely on. It's not like there are coal or oil deposits on the Moon or Mars. So we need more efficient solar panels, lighter solar panels, and the ability to deploy solar farms in sunlit areas and transmit that generated power to our bases and stations.

Those solar panels are going to have to be more durable than current ones, as they have to deal with micrometeorite impacts and the destruction caused by the Sun's unfiltered UV radiation. Oh, and don't forget the dust. The always-present, always-persistent dust that just gets…everywhere. The only reason that the Spirit and Opportunity rovers were able to go past their planned mission lifetimes was that random Martian dust devils would wipe the dust off their solar panels. And we can't rely on dust devils as a long-term solution.

In this series we are exploring NASA's top five challenges as detailed in its Civil Space Shortfall Ranking, which is basically NASA's Christmas wish list. These are the technologies that NASA believes we need to develop if we want to go to space…and stay there.

That brings us to the number 3 highest-priority technology for long-term space activities: better computers.

Computers have been involved in spaceflight since almost the very beginning. Just like on the Earth, computers aid in a variety of tasks, like navigation and communication. But unfortunately, space is really, really unkind to electronics.

It's not so much the vacuum of space; a circuit board does just fine. And freezing cold temperatures aren't that big of an issue either. No, it's our old friends, the cosmic rays. Each cosmic ray consists of a single proton or atomic nuclei, and the most powerful ones have the energy equivalent to a thrown baseball – which doesn't sound like much, but when you cram that baseball down to the size of a subatomic particle, it can be rather nasty.

Most cosmic rays slip through tissues and computer circuitry with ease; they're so small they literally miss the atoms and molecules of larger objects. But every once in a while they can strike, delivering all their energy to whatever they encounter. In humans, this can lead to an increased risk of cancer. In computers, it can lead to fatal glitches.

In 2022 the Voyager 1 spacecraft, launched all the way back in 1977 and is currently sailing beyond the borders of our solar system, started sending back garbled transmissions. By this point, voyager had spent decades cruising the outer solar system, giving us the most pristine images of the giant planets and our first taste of interstellar space. Most of the spacecraft was operating normally, but not the attitude articulation and control system, which is responsible for keeping Voyager's radio antenna pointed back to Earth, was just creating nonsense. Engineers were able to fix the issue by uploading the equivalent of a software update to route around the malfunctioning circuitry, although they never discovered the root cause of the problem. Many suspect that a cosmic ray struck a piece of circuitry at just the wrong moment to cause the problem.

More sophisticated computers are vulnerable as well. In 2023 the James Webb Space Telescope, the largest and most advanced telescope ever sent into space, suffered a minor malfunction when it's Near infrared Imager and Slitless Spectrograph, or Niriss, an important scientific instrument used to study exoplanets, become unsynchronized with the rest of the spacecraft, rendering it useless. NASA engineers suspected a cosmic ray led to the malfunction, but thankfully they were able to restore order by, essentially, turning it off and turning it back on again.

These issues were easy to solve, but it's only a matter of time before a cosmic ray strikes at a critical moment, shutting down a much more important mission. To protect against the ever-present threat of cosmic rays, spacecraft engineers take years to develop onboard computers and ensure that they are hardened against radiation. It's for this reason that computers going into space tend to be a couple…or more…generations behind the curve.

In 1969, the Apollo 11 mission's guidance computer weighed 70 pounds and was capable of performing about 40,000 instructions per second, which is over 100,000 times slower than the smartphone you're probably using right now. The International Space Station featured several custom-build computers with took nearly a decade to develop.

If we're going to maintain a larger presence in space, this isn't going to cut it. We need advanced hardware to handle a variety of complex tasks: more sophisticated navigation and tracking, much larger data communication loads, assistance with scientific surveys and studies, and more. Plus, we need our computers to be more fault tolerant, so that a stray cosmic ray doesn't derail an entire mission, and we need to be able to easily swap out computing modules when they go space crazy on us, because we need maximum adaptability to achieve our long-term plans.

Ironically, one of our biggest challenges with sending more powerful computers into space is how to deal with the heat. Yes, away from the Sun, space is cold, just a few degrees above absolute zero. But it's also a vacuum, which means there's no air or water to easily transport away heat. It's not just you can just plop a fan on the side of the CPU. So heat can easily build up to dangerous – for delicate circuitry – levels. Plus, shielding against cosmic rays isn't as simple as putting up a wall. That's because cosmic rays can strike the molecules in the wall itself and send out a shower of still-energetic particles that can disrupt circuitry.

We'll have to come up with many clever solutions if we want our space-based computers to be as fast and reliable as our Earthbound ones.

In this series we're exploring NASA's top five challenges as detailed in its Civil Space Shortfall Ranking, which is basically NASA's Christmas wish list. These are the technologies that NASA believes we need to develop if we want to go to space…and stay there.

Next we have number four: improved navigation.

We all take for granted our handy little cell phones, these magical rectangles that let us communicate instantly with anyone in the world…or scroll social media until our brains go numb. Related to that is the ease of navigation. Or you can plug in an address or drop a pin, and boom there you, the fastest route to grandma's house. Oh yeah, and you always know what time it is, day or night or season of the year…so that you know you're late for dinner.

All of this is easy for us to use because it was hard for someone else to create. To make a call, our cell phone connects to a nearby tower, of which there are approximately a bajillion, which is then connected to a vast globe-spanning network of wires and undersea cables. As for our position and navigation, that's all handled by hundreds of satellites in orbit around the Earth, with several different networks: The United State's Global Position System (the OG), Russia's Global Navigation Satellite System, China's BeiDou, and the European Union's Galileo. We have all that, plus a host of regional and local space- and ground-based location services, all overlapping and working together to provide that pinpoint accuracy.

But in space, like on the Moon or Mars, we have…none of that. Zero. No GPS satellites, no globe-spanning networks. Just radio broadcasts from command centers here on Earth to tell our robots and crews what to do.

And so we have the next high priority challenge we have to navigate (ha, ha) to achieve a permanent presence in space: all that stuff, but in space. So what would this look like?

The most important step is to create a mini-GPS for the Moon, with a constellation of satellites doing for the Moon what they already do for the Earth. Plus we need to augment that with relay stations and repeaters at lunar bases or centers of exploration, because we probably won't have enough signal strength to whip out our cell phones in the middle of Mare Vaporum. The hope is that our first generation of lunar GPS will be enough to match our first explorations, and then we can expand the system to match the needs of further lunar activities.

But in order to make that lunar GPS system, we need to deploy in space one critical piece of technology: atomic clocks. Atomic clocks are ultra-precise…well, clocks, that rely on the resonant frequency of atoms to monitor the passage of time. We already have atomic clocks in space, because every single GPS satellite has several of them onboard – that's the key component to the entire navigation system. But for deep-space work we need to be much more sophisticated. Earth-based atomic clocks can get away with some uncertainty, because they are always cross-checking and correcting each other. That won't be an option around the Moon or Mars, where a small network of satellites will have to keep perfect time.

Precise timing is necessary for pinpointing a satellite's location. If you receive a signal from the satellite from a ground station, you need to know how long it took for you to receive the signal to figure out where the satellite is.

In June of 2019 NASA launched the Deep Space Atomic Clock, or DSAC, which operated for two years, maintain an accuracy of better than 1 nanosecond in 10 days – the means after ten years, the clock would only be off by a microsecond. NASA has recognized that to enable long-term deep-space activities,we need to be even more accurate than that.

Lunar and Martian spacecraft are going to have to be able to navigate autonomously, without human input. As a complement to a space-based GPS system, these spacecraft could also employ a few other tricks. One trick is called radiometric tracking, which uses incoming radio signals to judge the distance to the source of those radio signals. We already use this technique quite frequently, but it's limited to one dimension: the direction towards the Earth, which is the origin of any radio signal that a spacecraft might pick up. Decades from now, we hope to have radio signals coming from lunar and Martian bases, and even asteroids, and a sufficiently sophisticated spacecraft might be able to pick up all these signals and figure out where it is in the solar system.

Speaking of weak radio signals, Lunar operations would benefit from our existing GPS network. Yes, those GPS satellites are aiming their signals down to the Earth, but some of that signal leaks out into outer space. We might be able to piggyback off that signal to at least get our navigation game started.

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