Some 25 underwater mines mysteriously exploded in the summer of 1972. A newly declassified report points its finger at a surprising culprit: the sun.
Something very strange happened on Aug. 4, 1972 in the waters near Vietnam. Dozens of undersea mines detonated for seemingly no reason. The matter was classified, as was a report trying to get to the bottom of what happened. Initial hypotheses focused on a malfunctioning self-destruct feature meant to prevent lost mines from posing an underwater hazard for decades after hostilities were over, but there was no corroborating evidence. Soviet subs might have accounted for one or two, but not systematic detonations across the whole minefield, not to mention their defensive countermeasures.
But one of the suggestions seemed to very neatly explain the observed phenomenon. The mines were magnetic, meaning that they reacted to the natural magnetism of metals in ships’ hulls and the changes in the strengths of their magnetic fields as those ships approached. It was an old, reliable technology and it would’ve taken a massive magnetic event to have set them off. And wouldn’t you know it, some of the most intense solar activity on record happened in that exact time frame, causing numerous power surges and telegraph outages across North America.
On the day Navy aircraft saw the mines go off, the sun erupted in what’s known as an X-class flare, a burst of energy more than 10,000 times more powerful than the high end of typical solar emissions. With the path to Earth cleared by supercharged solar winds, the resulting coronal mass ejection hit Earth in just 14.6 hours instead of the typical three days and caused massive magnetic and electrical disruptions in the atmosphere, quite possibly powerful enough to set off detectors on the underwater mines off the coast of Hon La Port as the plasma slammed into our planet.
So, case closed? Not exactly. We measure the intensity of the disruption in the Earth’s magnetic field caused by solar storms in negative nTs, or nano-Teslas. By itself, a nano-Tesla isn’t much. Your run of the mill fridge magnet is a million times stronger, although it’s only spread over tens of square centimeters, instead of millions of square kilometers like the fraction of a coronal mass ejection that hits Earth and lingers in the upper layers of the atmosphere. In 2003, a massive flare hit us with a magnetic disruption measuring almost -400 nT without melting anything down, although it did cause problems with air traffic.
By comparison, the ejection in 1972 measured a third of that at just -125 nT. Was it really strong enough to set off underwater mines? We’ll probably never know for sure, but it’s still entirely possible. Over the decades, we’ve learned much more about solar storms and what they can do, developed better shielding and early warning systems, more sophisticated equipment, and unwittingly created a shield of radio emissions to reroute charged particles from Earth. It’s quite plausible that older, less insulated technology was more sensitive to major solar storms and the trigger mechanisms for those mines were just one example.
When rains came to one of the driest places on Earth, an unprecedented mass extinction ensued.
The assumption was that this rainfall would turn this remote region of the Atacama Desert in Chile into a wondrous, floral haven — dormant seeds hidden in the parched landscape would suddenly awake, triggered by the “life-giving” substance they hadn’t seen for centuries — but it instead decimated over three quarters of the native bacterial life, microbes that shun water in favor of the nitrogen-rich compounds the region has locked in its dry soil.
In other words, death fell from the skies.
“We were hoping for majestic blooms and deserts springing to life. Instead, we learned the contrary, as we found that rain in the hyperarid core of the Atacama Desert caused a massive extinction of most of the indigenous microbial species there,” said astrobiologist Alberto Fairen, who works at Cornell Cornell University and the Centro de Astrobiología, Madrid. Fairien is co-author of a new study published in Nature’s Scientific Reports.
“The hyperdry soils before the rains were inhabited by up to 16 different, ancient microbe species. After it rained, there were only two to four microbe species found in the lagoons,” he added in a statement. “The extinction event was massive.”
Climate models suggest that these rains shouldn’t hit the core regions of Atacama more than once every century, though there is little evidence of rainfall for at least 500 years. Because of the changing climate over the Pacific Ocean, however, modern weather patterns have shifted, causing the weird rain events of March 25 and Aug. 9, 2015. It also rained more recently, on June 7, 2017. Besides being yet another reminder about how climate change impacts some of the most delicate ecosystems on our planet, this new research could have some surprise implications for our search for life on Mars.
Over forty years ago, NASA carried out a profound experiment on the Martian surface: the Viking 1 and 2 landers had instruments on board that would explicitly search for life. After scooping Mars regolith samples into their chemical labs and adding a nutrient-rich water mix, one test detected a sudden release of carbon dioxide laced with carbon-14, a radioisotope that was added to the mix. This result alone pointed to signs that Martian microbes in the regolith could be metabolizing the mixture, belching out the CO2.
Alas, the result couldn’t be replicated and other tests threw negative results for biological activity. Scientists have suggested that this false positive was caused by inorganic reactions, especially as, in 2008, NASA’s Phoenix Mars lander discovered toxic and highly reactive perchlorates is likely common all over Mars. Since Viking, no other mission has attempted a direct search for life on Mars and the missions since have focused on seeking out water and past habitable environments rather than directly testing for Mars germs living on modern Mars.
With this in mind, the new Atacama microbe study could shed some light on the Viking tests. Though the out-gassing result was likely a false positive, even if all the samples collected by the two landers contained microscopic Martians, the addition of the liquid mix may well have sterilized the samples — the sudden addition of a large quantity of water is no friend to microbial life that has adapted to such an arid environment.
“Our results show for the first time that providing suddenly large amounts of water to microorganisms — exquisitely adapted to extract meager and elusive moisture from the most hyperdry environments — will kill them from osmotic shock,” said Fairen.
Another interesting twist to this research is that NASA’s Mars rover Curiosity discovered nitrate-rich deposits in the ancient lakebed in Gale Crater. These deposits might provide sustenance to Mars bacteria (and may be a byproduct of their metabolic activity), like their interplanetary alien cousins in Atacama.
As water-loving organisms, humans have traditionally assumed life elsewhere will bare similar traits to life as we know it. But as this study shows, some life on Earth can appear quite alien; the mass extinction event in the high deserts of Chile could teach us about how to (and how not to) seek out microbes on other planets.
When ʻOumuamua visited our solar system last year, the world’s collective interest (and imagination) was firing on all cylinders. Despite astronomers’ insistence that asteroids from other star systems likely zip through the solar system all the time (and the reason why we spotted this one is because our survey telescopes are getting better), there was that nagging sci-fi possibility that ʻOumuamua wasn’t a natural event; perhaps it was an interstellar spaceship piloted by (or at least once piloted by) some kind of extraterrestrial — “Rendezvous With Rama“-esque — intelligence. Alas, any evidence for this possibility has not been forthcoming despite the multifaceted observation campaigns that followed the interstellar vagabond’s dazzling discovery.
Still, I ponder that interstellar visitor. It’s not that I think it’s piloted by aliens, though that would be awesome, I’m more interested in the possibilities such objects could provide humanity in the future. But let’s put ʻOumuamua to one side for now and discuss a pretty nifty project that’s currently in the works and how I think it could make use of asteroids from other stars.
Obviously, this is a long-term goal; humanity is currently having a hard enough time becoming a multiplanetary species, let alone a multistellar species. But from projects like these, new technologies may be developed to solve big problems and those technologies may have novel applications for society today. Central to ESA’s role in the project is an exciting regenerative life-support technology that is inspired by nature, a technology that could reap huge benefits not only for our future hypothetical interstellar space fliers.
Called the MELiSSA (Micro-Ecological Life Support System Alternative) program, scientists are developing a system that mimics aquatic ecosystems on Earth. A MELiSSA pilot plant in Barcelona is capable of keeping rat “crews” alive for months at a time inside an airtight habitat. Inside the habitat is a multi-compartment loop with a “bioreactor” at its core, which consists of algae that produces oxygen (useful for keeping the rats breathing) while scrubbing the air of carbon dioxide (which the rats exhale). The bioreactor was recently tested aboard the International Space Station, demonstrating that the system could be applied to a microgravity environment.
Disclaimer: Space Is Really Big
Assuming that humanity isn’t going to discover faster-than-light (FTL) travel any time soon, we’re pretty much stuck with very pedestrian sub-light-speed travel times to the nearest stars. Even if we assume some sensible iterative developments in propulsion technologies, the most optimistic projections in travel time to the stars is many decades to several centuries. While this is a drag for our biological selves, other research groups have shown that robotic (un-crewed) missions could be done now — after all, Voyager 1 is currently chalking up some mileage in interstellar space and that spacecraft was launched in the 1970’s! But here’s the kicker: Voyager 1 is slow (even if it’s the fastest and only interstellar vehicle humanity has built to date). If Voyager 1 was aimed at our closest star Proxima Centauri (which it’s not), it would take tens of thousands of years to get there.
But say if we could send a faster probe into interstellar space? Projects like Icarus Interstellar and Breakthrough Starshot are approaching this challenge with different solutions, using technology we have today (or technologies that will likely be available pretty soon) to get that travel time down to less than one hundred years.
One… hundred… years.
Sending robots to other stars is hard and it would take generations of scientists to see an interstellar mission through from launch to arrival — which is an interesting situation to ponder. But add human travelers to the mix? The problems just multiplied.
The idea of “worldships” (or generation ships) have been around for many years; basically vast self-sustaining spaceships that allow their passengers to live out their lives and pass on their knowledge (and mission) to the next generation. These ships would have to be massive and contain everything that each generation needs. It’s hard to comprehend what that starship would look like, though DSTART’s concept of hollowing out an asteroid to convert it into an interstellar vehicle doesn’t sound so outlandish. To hollow out an asteroid and bootstrap a self-sustaining society inside, however, is a headache. Granted, DSTART isn’t saying that they are actually going to build this thing (their project website even states: “DSTART is not developing hardware, nor is it building an actual spacecraft”), but they do assume some magic is going to have to happen before it’s even a remote possibility — such as transformative developments in nanotechnology, for example. The life-support system, however, would need to be inspired by nature, so ESA and DSTART scientists are going to continue to help develop this technology for self-sustaining, long-duration missions, though not necessarily for a massive interstellar spaceship.
Hyperbolic Space Rocks, Batman!
Though interesting, my reservation about the whole thing is simple: even if we did build an asteroid spaceship, how the heck would we accelerate the thing? This asteroid would have to be big and probably picked out of the asteroid belt. The energy required to move it would be extreme; to propel it clear of the sun’s gravity (potentially via a series of gravitational assists of other planets) could rip it apart.
So, back to ʻOumuamua.
The reason why astronomers knew ʻOumuamua wasn’t from ’round these parts was that it was moving really, really fast and on a hyperbolic trajectory. It basically barreled into our inner star system, swung off our sun’s gravitational field and slingshotted itself back toward the interstellar abyss. So, could these interstellar asteroids, which astronomers estimate are not uncommon occurrences, be used in the future as vehicles to escape our sun’s gravitational domain?
Assuming a little more science fiction magic, we could have extremely advanced survey telescopes tasked with finding and characterizing hyperbolic asteroids that could spot them coming with years of notice. Then, we could send our wannabe interstellar explorers via rendezvous spacecraft capable of accelerating to great speeds to these asteroids with all the technology they’d need to land on and convert the asteroid into an interstellar spaceship. The momentum that these asteroids would have, because they’re not gravitationally bound to the sun, could be used as the oomph to achieve escape velocity and, once setting up home on the rock, propulsion equipment would be constructed to further accelerate and, perhaps, steer it to a distant target.
If anything, it’s a fun idea for a sci-fi story.
I get really excited about projects like DSTART; they push the limits of human ingenuity and force us to find answers to seemingly insurmountable challenges. Inevitably, these answers can fuel new ideas and inspire younger generations to be bolder and braver. And when these projects start partnering with space agencies to develop existing tech, who knows where they will lead.
Having a bad day? Well, spare a thought for any hypothetical aliens living on Proxima b.
Proxima Centauri is a small, dim M dwarf—commonly known as a red dwarf—located approximately 4.2 light-years away. Over the last couple of years, this diminutive star has spent a lot of time in the headlines after the discovery of a small rocky world, called Proxima b, inside the star’s habitable zone.
With the knowledge that there’s a potentially temperate world on our cosmic doorstep, speculation started to fly that this exoplanet could become a future interstellar destination for humanity or that it’s not just a “habitable” world, perhaps it’s inhabited, too.
Putting aside the fact that we have no idea whether this interesting exoplanet possesses water of any kind, let alone if it even has an atmosphere (two pretty important ingredients for life as we know it), it is certainly an incredible find. But there are some caveats to Proxima b’s habitability and the main one is the unpredictability of its star.
The problem with red dwarfs is that they are angry little stars. In fact, they have long been known as “flare stars” as, well, they produce flares. What they lack in energy output they certainly make up for in explosions. Really, really big explosions.
“March 24, 2017, was no ordinary day for Proxima Cen,” said astronomer Meredith MacGregor, of the Carnegie Institution for Science in Washington D.C., in a statement.
Over just ten seconds on that special day, a powerful flare boosted Proxima Centauri’s brightness by over 1,000 times greater than normal. This mega-flare event was preceded by a smaller flare event and both flares occurred over a two minute period.
Although astronomers have little idea where Proxima b was in relation to the flaring site, it would have undoubtedly received one hell of a radiation dose from the eruption.
“It’s likely that Proxima b was blasted by high energy radiation during this flare,” said MacGregor. “Over the billions of years since Proxima b formed, flares like this one could have evaporated any atmosphere or ocean and sterilized the surface, suggesting that habitability may involve more than just being the right distance from the host star to have liquid water.”
The habitable zone around any star is the distance at which a world must orbit to receive just the right amount of energy to maintain water in a liquid state. Liquid water, as we all know, is necessary for life (as we know it) to evolve. Whereas the Earth orbits the Sun at an average distance of nearly 100 million miles (a distance that unsurprisingly puts us inside our star’s habitable zone), for a star as cool as Proxima Centauri, its habitable zone is closer. Much, much closer. This means Proxima b, with an orbital distance of approximately 4.6 million miles, is nearly 22 times closer to its star than the Earth is to the Sun. Orbiting so close to a star pumping out a flare ten times more powerful than the largest flare our Sun can generate is the space weather equivalent of sitting inside the blast zone of a nuclear weapon.
As MacGregor argues, Proxima Centauri is known to generate these kinds of flares, and Proxima b has been bathed in its radiation for eons. It doesn’t seem likely that the exoplanet would be able to form an atmosphere, let alone hold onto one.
So, what of Proxima b’s hypothetical aliens? Well, unless they’ve found a niche deep under layers of ice and/or rock, it seems that this “habitable” world is anything but.
If you thought detecting small planets orbiting stars dozens of light-years distant was impressive, imagine trying to “see” individual comets zoom around their star. Well, astronomers have done just that after poring over 201,250 targets in the Kepler dataset.
NASA’s Kepler mission has been taking observational data since 2009, staring unblinkingly at a small area of sky in the direction of the constellation Cygnus until it transitioned into the K2 mission in 2013. In total, the space telescope has discovered over 2,500 confirmed exoplanets (and over 5,000 candidate exoplanets), transforming our understanding of the incredible menagerie of alien worlds in our galaxy. After including discoveries by other observatories, we know of over 3,500 exoplanets that are out there.
Kepler detects exoplanets by watching out for periodic dips in the brightness of stars in its field of view. Should a slight dip in brightness be detected, it could mean that there’s an exoplanet orbiting in front of its host star—an event known as a “transit.” While these transits can help astronomers learn about the physical size of exoplanets and the period of their orbits, for example, there’s much more information in the transit data than initially meets the eye.
In a new study to be published in the journal Monthly Notices of the Royal Astronomical Society on Feb. 21, a team of researchers are reporting that they have found evidence for individual comets transiting in front of two stars. They detected six individual transits at the star KIC 3542116, which is located approximately 800 light-years from Earth, and one transit at KIC 11084727. Both stars of a similar type (F2V) and are quite bright.
Though other observations have revealed dusty evidence of cometary activity in other star systems before, this is the first time individual comets have been found leaving their own transit signal in Kepler data. And it turns out that their transit fingerprint is a little bit special:
“The transits have a distinct asymmetric shape with a steeper ingress and slower egress that can be ascribed to objects with a trailing dust tail passing over the stellar disk,” the astronomers write in their paper (arXiv preprint). “There are three deeper transits with depths of ≃ 0.1 percent that last for about a day, and three that are several times more shallow and of shorter duration.”
In other words, when compared with the transit of an exoplanet, comet transits appear wonky (or asymmetric). This is because comets possess tails of gas and dust that trail the nucleus; as the comet passes in front of its star, starlight is quickly blocked, but as it drifts by in its orbit, the dusty tail will act as a starlight dimmer, gradually allowing more starlight to be seen by Kepler. An exoplanet—or, indeed, any spherical object without a dusty tail—will create a symmetrical dip in the transit signal. Other possible causes of this unique transit signal (such as starspots and instrumental error) were systematically ruled out. (Interestingly, in a 1999 Astronomy & Astrophysics paper, this asymmetric comet transit signal was predicted by another team of researchers, giving this current work some extra certainty.)
But just because there was evidence of six comet transits at KIC 3542116, it doesn’t mean there were six comets. Some of those transits could have been caused by the same comet, so the researchers have hedged their bets, writing: “We have tentatively postulated that these are due to between 2 and 6 distinct comet-like bodies in the system.”
Using these transit data, the study also takes a stab at how big these comets are and even estimates their orbital velocities. The researchers calculate that these comets have masses that are comparable to Halley’s Comet, the famous short-period comet that orbits the sun every 74-79 years and was last visible from Earth in 1986. For the deeper transits (for KIC 3542116 and the single transit at KIC 11084727), they estimate that the comets causing those transits are travelling at speeds of between 35 to 50 kilometers per second (22 to 31 miles per second). For the shallow, narrow transits at KIC 3542116, the inferred speeds are between 75 to 90 kilometers per second (47 to 56 miles per second).
“From these speeds we can surmise that the corresponding orbital periods are ⪆ 90 days (and most probably, much longer) for the deeper transits, and ⪆ 50 days for the shorter events,” they write.
But the fact that comets were detected at two similar F2V-type stars gives the researchers pause. Is there something special about these stars that means there’s more likelihood of possessing comets? Or is it just chance? Also, the fact that these comet transits were identified by visually analyzing the Kepler datasets suggests that there are likely many more transits hiding in the archived Kepler observations.
One thing’s for sure: this is a mind-blowing discovery that underscores just how valuable exoplanet-hunting missions are for probing the environment around other stars and not just for discovering strange new worlds. I’m excited for what other discoveries are waiting in Kepler transit data and for future exoplanet-hunting missions such as NASA’s Transiting Exoplanet Survey Satellite (TESS) that is scheduled for launch this year.
Like the infamous “Crasher Squirrel” that launched one of the most prolific memes in online history, “crasher asteroids” have photobombed the Hubble Space Telescope’s otherwise uninterrupted view of the ancient universe.
While carrying out its Frontier Fields survey of a random postage stamp-sized part of the sky in the direction of the galaxy cluster Abell 370, Hubble imaged many galaxies located at different distances over different epochs in time.
Visible in the observation are elliptical galaxies and spiral galaxies. Many are bright and bluish, but the vast majority are dim and reddish. The reddest blobs are the most distant galaxies in our observable universe; their light has been stretched (red-shifted) after traveling for billions of years through an expanding cosmos. These galaxies are the most ancient galaxies that formed within a billion years after the Big Bang.
But mixed in with this Hubble view of ancient light are bright arcs and dashes — tracks carved out by the rocky junk in our own solar system that is drifting in Hubble’s field of view, located a mere 160 million miles from Earth (on average). It’s sobering to think that the light from the reddest galaxies is nearly three times older than these asteroids.*
Abel 370 is located along the solar system’s ecliptic plane, around which the planets orbit the sun and the majority of asteroids in the asteroid belt between Mars and Jupiter are located. So, like looking through a swarm of bees, Hubble has captured the trails of asteroids in the foreground.
The trails themselves are created not by the motion of the asteroids, however, but by the motion of Hubble. While fixing its gaze on distant galaxies for hours at a time as it orbits Earth, Hubble’s position changes and, through an observational effect known as parallax, the positions of those asteroids appear to trace an arc when compared with the stationary background of galaxies billions of light-years distant.
As Hubble scanned its field of view, it revealed 20 asteroid trails, seven of which are unique objects (some of the asteroid trails were repeated observations of the same object, just captured at different times in Hubble’s orbit). Only two of these asteroids were previously discovered, the other five are newly discovered objects that were too faint for other observatories to detect.
So it goes to show that photobombing asteroids are useful for science and, though Hubble was observing the most distant objects in the cosmos, it was able to see a few of the rocks in our cosmic backyard.
*NOTE: Asteroids formed around the time our solar system first started creating planets, some 4.6 billion years ago. The most ancient galaxies are located over 13 billion light-years away, meaning the ancient light from those galaxies was produced 13 billion years ago.
Update: At original time of writing, C/2017 U1 was assumed to be a comet. But Followup observations by the Very Large Telescope in Chile on Oct. 25 found no trace of cometary activity. The object’s name has now been officially changed to A/2017 U1 as it is more likely an interstellar asteroid, not a comet.
Comets and asteroids usually originate from the outermost reaches of the solar system — they’re the ancient rocky, icy debris left over from the formation of the planets 4.6 billion years ago.
However, astronomers have long speculated that comets and asteroids originating from other stars might escape their stars, traverse interstellar distances and occasionally pay our solar system a visit. And looking at C/2017 U1’s extreme hyperbolic trajectory, it looks very likely it’s not from around these parts.
“If further observations confirm the unusual nature of this orbit this object may be the first clear case of an interstellar comet,” said Gareth Williams, associate director of the International Astronomical Union’s Minor Planet Center (MPC). A preliminary study of C/2017 U1 was published earlier today. (Since this statement, followup observations have indicated that the object might be an asteroid and not a comet.)
According to Sky & Telescope, the object entered the solar system at the extreme speed of 16 miles (26 kilometers) per second, meaning that it is capable of traveling a distance of 850 light-years over 10 million years, a comparatively short period in cosmic timescales.
Spotted on Oct. 18 as a very dim 20th magnitude object, astronomers calculated its trajectory and realized that it was departing the solar system after surviving a close encounter with the sun on Sept. 9, coming within 23.4 million miles (0.25 AU). Comets would vaporize at that distance from the sun, but as C/2017 U1’s speed is so extreme, it didn’t have time to heat up.
“It went past the sun really fast and may not have had time to heat up enough to break apart,” said dynamicist Bill Gray. Gray estimates that the comet is approximately 160 meters wide with a surface reflectivity of 10 percent.
But probably the coolest factor about this discovery is the possible origin of C/2017 U1. After calculating the direction at which the comet entered the solar system, it appears to have come from the constellation of Lyra and not so far from the star Vega. For science fiction fans this holds special meaning — that’s the star system where the SETI transmission originated in the Jodie Foster movie Contact.
Although comets are static lumps of ancient ice for most of their lives, their personalities can rapidly change with a little heat from the sun. Now, astronomers have witnessed just how dynamic comets can be, seeing one dramatically slow its rate of rotation to the point where it may even reverse its spin.
Comets are the leftover detritus of planetary formation that were sprinkled around our sun 4.6 billion years ago. These primordial icy remains collected in the outermost reaches of the solar system and that’s where they stay until they get knocked off their gravitational perches to begin an interplanetary roller coaster ride. Some are unlucky and end up diving straight to a fiery, solar death. But others set up in stable orbits, making regular passes through the inner solar system, dazzling observers with their beautiful tails formed through heating by the sun.
One mile-wide short-period comet is called 41P/Tuttle-Giacobini-Kresak and it’s a slippery celestial object. First discovered in 1858 by U.S. astronomer Horace Parnell Tuttle, it disappeared soon after. But in 1907, French astronomer Michael Giacobini “rediscovered” the comet, only for it to disappear once again. Then, in 1951, Slovak astronomer Ľubor Kresák made the final “discovery” and now astronomers know exactly where to find it and when it will turn up in our night skies.
Its name, Tuttle-Giacobini-Kresak, reflects the wonderful 100-year discovery and rediscovery history of astronomy’s quest to keep tabs on the comet’s whereabouts.
Now, 41P is the focus of an interesting cometary discovery. Taking 5.4 years to complete an orbit around the sun, 41P came within 13-million miles to Earth earlier this year, the closest it has come to our planet since it was first discovered by Tuttle. So, astronomers at Lowell Observatory, near Flagstaff, Ariz., used the 4.3-meter Discovery Channel Telescope near Happy Jack, the 1.1-meter Hall telescope and the 0.9-meter Robotic telescope on Anderson Mesa, to zoom-in on the interplanetary vagabond to measure its rotational speed.
Comets can be unpredictable beasts. Composed of rock and icy volatiles, when they are slowly heated by the sun as they approach perihelion (the closest point in their orbit to the sun), these ices sublimate (i.e. turn from ice to vapor without melting into a liquid), blasting gas and dust into space.
Over time, these jets are known to have a gradual effect the comet’s trajectory and rotation, but, over an astonishing observation run, Lowell astronomers saw a dramatic change in this comet’s spin. Over a short six-week period, the comet’s rate of rotation slowed from one rotation every 24 hours to once every 48 hours — its rate of rotation had halved. This is the most dramatic change in comet rotation speed ever recorded — and erupting jets from the comet’s surface are what slammed on the brakes.
This was confirmed by observing cyanogen gas, a common molecule found on comets that is composed of one carbon atom and one nitrogen atom, being ejected into space as the comet was being heated by sunlight.
“While we expected to observe cyanogen jets and be able to determine the rotation period, we did not anticipate detecting a change in the rotation period in such a short time interval,” said Lowell astronomer David Schleicher, who led the project, in a statement. “It turned out to be the largest change in the rotational period ever measured, more than a factor of ten greater than found in any other comet.”
For this rapid slowdown to occur, the researchers think that 41P must have a very elongated shape and be of very low density. In this scenario, if the jets are located near the end of its length, enough torque could be applied to cause the slowdown. If this continues, the researchers predict that the direction of rotation may even reverse.
“If future observations can accurately measure the dimensions of the nucleus, then the observed rotation period change would set limits on the comet’s density and internal strength,” added collaborator Matthew Knight. “Such detailed knowledge of a comet is usually only obtained by a dedicated spacecraft mission like the recently completed Rosetta mission to comet 67P/Churyumov-Gerasimenko.”
The day before Cassini plunged into Saturn’s atmosphere, dramatically ending 13 years of Saturn exploration (and nearly two decades in space), I was sitting on a bench outside the Von Karman Visitor Center on the NASA Jet Propulsion Laboratory campus in La Cañada Flintridge with Linda Spilker, who served as the mission’s project scientist since before Cassini was launched.
“I feel very fortunate to be involved with Cassini since the very beginning … and just to be there, to be one of the first to see SOI [Saturn Orbital Insertion] with those first incredible ring pictures,” she told me. “I love being an explorer. I worked on the Voyager mission during the flybys of Jupiter, Saturn, Uranus and Neptune; that sort of whet my appetite and made me want more, to become an explorer to go to the Saturn system.”
Spilker especially loved studying Saturn’s rings, not only from a scientific perspective, but also because they are so beautiful, she continued. “It’s been a heartwarming experience,” she said.
But Cassini’s “legacy discovery,” said Spilker, was the revelation that the tiny icy moon of Enceladus is active, venting water vapor into space from powerful geysers emerging from the moon’s “tiger stripes” — four long fissures in the moon’s south pole. After multiple observations of these geysers and direct sampling of the water particles during flybys, Cassini deduced that the icy space marble hides a warm, salty ocean.
“What Cassini will be remembered for — its legacy discovery — will be the geysers coming from Enceladus with the ocean with the potential for life. It’s a paradigm shift.” — Linda J. Spilker, Cassini project scientist, NASA Jet Propulsion Laboratory (JPL), Sept. 14, 2017.
Alongside Jupiter’s moon Europa, Enceladus has become a prime destination for future explorations of life beyond Earth. Its subsurface ocean contains all the ingredients for life as we know it and Cassini was the mission that inadvertently discovered its biological potential. So now we know about this potential, Spilker is keen to see a dedicated life-hunting mission that could go to Enceladus, perhaps even landing on the surface to return samples to Earth.
As Enceladus is much smaller and less massive than Europa, its gravity is lower, meaning that landing on the surface is an easier task. Also, the radiation surrounding Saturn is much less aggressive than Jupiter’s radiation belts, meaning less radiation shielding is needed for spacecraft going to Saturn’s moons.
But if we ever send a surface mission to Enceladus (or any of the icy moons in the outer solar system), the planetary protection requirements will be extreme.
“If any life were found on these moons, it would be microbial,” said Larry Soderblom, an interdisciplinary scientist on the Cassini mission. “Some [terrestrial] bacteria are very resilient and can survive in hot acid-reducing environments. They can be tenacious. We have to make sure we don’t leave any of these kinds of Earthly bacteria on these promising moons.”
Soderblom has a unique perspective on solar system exploration. His career spans a huge number of NASA missions since the 1960’s, including Mariner 6, 7, 9, Viking, Voyager, Galileo, Magellan, Mars Pathfinder, the Mars Exploration Rovers, Deep Space 1, to name a few. While chatting to me under the shade of a tree on the JPL campus, he pointed out that the outer solar system was seen as a very different place over half a century ago.
“When I started to explore the solar system as a young guy just out of graduate school, our minds-eye view of the outer solar system was pretty bleak,” he remembered. “We expected lifeless, dead, battered moons with no geologic activity.”
After being involved with many outer solar system missions, this view has radically changed. Not only have we discovered entire oceans on Enceladus and Europa, there’s active volcanoes on Jupiter’s tortured moon Io, an atmosphere on Titan sporting its own methane cycle and surface lakes of methane and ethane. Other moons show hints of extensive subsurface oceans too, including distant Triton, a moon of Neptune. When NASA’s New Horizons flew past Pluto in 2015, the robotic spacecraft didn’t see a barren, dull rock as all the artistic impressions that came before seemed to suggest. The dwarf planet is a surprisingly dynamic place with a rich geologic history.
Sending our robotic emissaries to these distant and unforgiving places has revolutionized our understanding of the solar system and our place in it. Rather than the gas and ice giant moons being dull, barren and static, our exploration has revealed a rich bounty of geologic variety. Not only that, we’re almost spoilt for choices for our next giant leap of scientific discovery.
Missions like Cassini are essential for science. Before that spacecraft entered Saturn orbit 13 years ago, we had a very limited understanding of what the Saturnian system was all about. Now we can confidently say that there’s a tiny moon there with incredible biological potential — Enceladus truly is Cassini’s legacy discovery that will keep our imaginations alive until we land on the ice to explore its alien ocean.
For more on my trip to JPL, read my two HowStuffWorks articles:
This morning, the sun erupted with the most powerful solar flare in a decade, blasting the Earth’s upper atmosphere with energetic X-ray and extreme ultraviolet (EUV) radiation.
The flare was triggered by intense magnetic activity over an active region called AR2673 that has been roiling with sunspot activity for days, threatening an uptick in space weather activity. As promised, that space weather brought an explosive event at 1202 UTC (8:02 a.m. PT) that ionized the Earth’s upper atmosphere and causing a shortwave radio blackout over Europe, Africa and the Atlantic Ocean, reports Spaceweather.com.
The powerful X9.3-class flare came after an earlier X2.2 blast from the same active region, a significant flare in itself. X-class flares are the most powerful type of solar flares.
The electromagnetic radiation emitted by flaring events affect the Earth’s ionosphere immediately, but now space weather forecasters are on the lookout for a more delayed impact of this eruption.
Solar flares can create magnetic instabilities that may launch coronal mass ejections (CMEs) — basically vast magnetized bubbles of energetic solar plasma — into interplanetary space. Depending on the conditions, these CMEs may take hours or days to reach Earth (if they are Earth-directed) and can generate geomagnetic storms should they collide and interact with our planet’s global magnetic field.