Alien vs. Comet: Is the SETI “Wow!” Signal Dead? (Astroengine Video)

There’s a new hypothesis about what happened on August 15, 1977, and, sadly, it doesn’t involve aliens — just a photobombing comet. I was surprised about the controversy surrounding Antonio Paris’ research into the possibility of comets generating radio signals at 1420MHz and mimicking the famous “Wow!” signal nearly 40 years ago, so I decided to record Astroengine’s second YouTube video on the topic. Enjoy! And remember to subscribe and like, there’s a lot more to come!

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SETI “Wow!” Signal Wasn’t Chatty Aliens After All — It Was a Fizzing Comet

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Big Ear Radio Observatory

On Aug. 15, 1977 at 10:16 p.m. ET Ohio State University’s Big Ear radio telescope detected a curious signal from deep space. Nearly 40 years later, we finally know what caused it and, sadly, it’s not aliens.

For decades, the signal has been the strongest piece of “go-to” evidence that intelligent extraterrestrials are out there in our galaxy. When found by astronomer Jerry Ehman on that fateful night, the 72-second signal — that had been recorded on a computer printout — certainly stood out.

While pointing at three star systems called Chi Sagittarii in the constellation of Sagittarius, Big Ear had picked up a powerful burst of radio waves. To the untrained eye, the assortment of printed digits might not mean much, but as I wrote in 2016, those letters and numbers could hold the answer to the biggest question we’re currently asking of the universe: Are we alone?

The Big Ear printout contains a bunch of apparently random numbers and letters, but Ehman’s red pen circles a cluster of digits “6EQUJ5” with other circles around a “6” and “7” on separate columns. This particular code first uses the numbers 1-9 and then the alphabet A-Z to denote signal strength. As the burst suggests, the signal strength hit “6” and then blasted through the letters reaching a peak of “U” before subsiding back into the numerical scale at “5.” There was then a slight wave trailing the main signal (hence the circled “6″ and “7″). The wave profile of the “Wow!” signal is graphically envisaged here. (Discovery News, April 18, 2016)

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Maksim Rossomakhin

The maddening thing about the Wow! signal has always been a lack of replication. To science, one random signal in the dark proves nothing. It would be like trying to plot a trend line on a graph with one data point. More data is obviously needed and yet, since 1977, there’s been no other radio signal quite like it.

Curious, yes. Definite proof of chatty aliens? A solid nope.

So, when researching other possible causes of the Wow! signal that were also rare occurrences (but not aliens), Antonio Paris of St Petersburg College, Fla. (and an ex-analyst of the US Department of Defense), suggested that the signal might have been generated by one of two comets that serendipitously drifted into the line of sight of the Big Ear radio telescope.

In 1977, neither 266P/Christensen and 335P/Gibbs were known of (they were discovered in 2006 and 2008 respectively) and Paris calculated that both comets would have been in the right place in the sky when the Wow! signal was recorded.

What’s more, the Wow! signal has a frequency of 1420MHz — the same frequency that neutral hydrogen radiates at. Hydrogen is abundant in our universe, so this frequency is commonly observed in astronomy.

At first blush, observing in this frequency to look for alien transmissions might seem like a fool’s errand; if the universe is humming in hydrogen noise, why would aliens bother using that frequency to ping their extraterrestrial neighbors?

Through SETI logic, the frequency of neutral hydrogen might be used by advanced civilizations as a kind of interstellar water cooler. It is the most abundant signal in the universe, every intelligent life-form would know this. So why not use 1420MHz as THE frequency to communicate across the light-years in hopes that other civilizations might already be tuned in?

But a SETI signal would need to stand out from the crowd — it would need to be powerful and possess other qualities that hint at its artificial nature. But should a comet quickly pass through the observing window of a radio telescope, Paris predicted that the received 1420MHz signal might mimic that of an artificial source.

And this year, an opportunity presented itself. Comet 266P/Christensen would pass through the sky in a similar orbital position as it did in 1977. During an observing campaign from November 2016 to February 2017, Paris studied the radio frequencies coming from the region and from the comet itself. He also compared these observations with other known comets.

The upshot: 266P is indeed producing a strong 1420MHz signal, as are other comets.

“The results of this investigation, therefore, conclude that cometary spectra are detectable at 1420 MHz and, more importantly, that the 1977 “Wow!” Signal was a natural phenomenon from a solar system body,” he writes in a study published in the Journal of the Washington Academy of Sciences

It appears that, in this case, the signal wasn’t aliens trying to make contact with us; it was a chance comet that just happened to be in the right place at the right time.

So, back to that alien megastructure

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Fox

This Super-Hot, Super-Weird Space Doughnut Could Be a New “Planetary Object”

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The structure of a planet, a planet with a disk and a synestia, all of the same mass (Simon Lock and Sarah Stewart)

Pluto is going to be pissed.

After studying computer simulations of planetary collisions, scientists have discovered a possible phase of planetary formation that has, so far, been overlooked by astronomy. And they think this phase is so significant that it deserves its own planetary definition.

After two planetary objects collide, researchers from the University of California Davis and Harvard University in Cambridge, Mass., realized that a bloated, spinning mass of molten rock can form. It looks a bit like a ring doughnut with the hole filled in. What’s more, it is thought that Earth (and other planets in the solar system) probably went through this violent period before becoming the solid spinning globes we know and love today.

They call this partly vaporized rock “synestia” — “syn-” for “together” and “Estia” after the Greek goddess of architecture and structures.

Over a range of masses and collision speeds, planetary scientist Sarah Stewart (Davis) and graduate student Simon Lock (Harvard) simulated planetary collisions and focused on how the angular momentum of colliding bodies might influence the system. Their study has been published in the Journal of Geophysical Research: Planets. Basically, when two bodies — with their own angular momentum — collide and merge, the sum of their momenta must be conserved and this can have a dramatic effect on the size and structure of the merged mass.

“We looked at the statistics of giant impacts, and we found that they can form a completely new structure,” said Stewart.

After colliding, the energetic event causes both planets to melt and partially vaporize, expanding with a connected ring-like structure. And this structure — a synestia — would eventually cool, contract and solidify. It could also form moons; post-collision molten debris in the synestia doughnut ring may emerge in a stable orbit around the planet.

The synestia phase would be a fleeting event in any planet’s life, however. For an Earth-sized mass, the post-collision synestia would likely last only 100 years or so. But the larger the mass, the longer the phase, the researchers theorize.

So, giving this theoretical “planetary object” a classification might be a little generous — a move that would raise recently “demoted” Pluto’s eyebrow — but as telescopes become more advanced, we might one day be lucky enough to spy a synestia in a young star system where dynamic instabilities are causing planets to careen into one another.

Cassini Finds ‘Nothing’ in Saturn’s Ring Gap

NASA/JPL-Caltech

It’s official, there’s a whole lot of nothing in Saturn’s innermost ring gap.

This blunt — and slightly mysterious — conclusion was reached when scientists studied Cassini data after the spacecraft’s first dive through the gas giant’s ring plane. At first blush, this might not sound so surprising; the 1,200-mile-wide gap between Saturn’s upper atmosphere and the innermost edge of its rings does appear like an empty place. But as the NASA spacecraft barreled through the gap on April 26, mission scientists expected Cassini to hit a few stray particles on its way through.

Instead, it hit nothing. Or, at least, far fewer particles than they predicted.

“The region between the rings and Saturn is ‘the big empty,’ apparently,” said Earl Maize, Cassini’s project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”

Using Cassini’s Radio and Plasma Wave Science (RPWS), the scientists expected to detect multiple “cracks and pops” as the spacecraft shot through the gap. Instead, it picked up mainly signals from energetic charged particles buzzing in the planet’s magnetic field. When converted into an audio file, these signals make a whistling noise and this background whistle was expected to be drowned out by the ruckus of dust particles bouncing off the spacecraft’s body. But, as the following audio recording proves, very few pops and cracks of colliding debris were detected — it sounds more like an off-signal radio tuner:

Compare that with the commotion Cassini heard as it passed through the ring plane outside of Saturn’s rings on Dec. 18, 2016:

Now that is what it sounds like to get smacked by a blizzard of tiny particles at high speed.

“It was a bit disorienting — we weren’t hearing what we expected to hear,” said William Kurth, RPWS team lead at the University of Iowa, Iowa City. “I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear.”

From this first ring gap dive, NASA says Cassini likely only hit a handful of minute, 1 micron particles — particles no larger than those found in smoke. And that’s a bit weird.

As weird as it may be, the fact that the region of Cassini’s first ring dive is emptier than expected now allows mission scientists to carry out optimized science operations with the spacecraft’s instruments. On the first pass, Cassini’s dish-shaped high-gain antenna was used as a shield to protect the spacecraft as it made the dive. On its next ring dive, which is scheduled for Tuesday at 12:38 p.m. PT (3:38 p.m. ET), this precaution is evidently not needed and the spacecraft will be oriented to better view the rings as it flies through.

So there we have it, the first mysterious result of Cassini’s awesome Grand Finale! 21 ring dives to go…

KCRW ‘To The Point’ Interview: Cassini’s Grand Finale

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Artist’s impression of Cassini passing through the gap between Saturn and the planet’s rings (NASA/JPL-Caltech)

After all the excitement of last night’s Cassini mission checking in and transmitting data to NASA’s Deep Space Network, I joined Warren Olney on his NPR-syndicated show “To The Point” this morning to chat about the mission and why the “Grand Finale” is an awesome, yet bittersweet, part of Saturn exploration. Listen to the 10 minute segment here. It was great as always to chat with Warren, thanks for having me on the show!

Cassini Sees Earth and Moon Through Saturn’s Rings

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NASA/JPL-Caltech/Space Science Institute

NASA’s Cassini mission sure has a knack for putting stuff into perspective — and this most recent view from Saturn orbit is no different. That dot in the center of the image isn’t a dud pixel in Cassini’s camera CCD. That’s us. All of us. Everyone.

To quote Carl Sagan:

“Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives…”

Sagan wrote that passage in his book “Pale Blue Dot: A Vision of the Human Future in Space” when reflecting on the famous “Pale Blue Dot” image that was beamed back to Earth by NASA’s Voyager 1 spacecraft in 1990. That’s when the mission returned a profound view of our planet from a distance of 3.7 billion miles (or 40.5AU) as it was traveling through the solar system’s hinterlands, on its way to interstellar space. Since then, there’s been many versions of pale blue dots snapped by the armada of robotic missions around the solar system and Cassini has looked back at us on several occasions from its orbital perch.

Now, just before Cassini begins the final leg of its Saturnian odyssey, it has again spied Earth through a gap between the gas giant’s A ring (top) and F ring (bottom). In a cropped and enhanced version, our moon is even visible! The image is composed of many observations captured on April 12, stitched together as a mosaic when Saturn was 870 million miles (roughly 9.4AU) from Earth.

On April 20 (Friday), Cassini will make its final flyby of Titan, Saturn’s largest moon, using its gravity to fling itself through Saturn’s ring plane (on April 26) between the innermost ring and the planet’s cloudy upper atmosphere, revealing a view that we’ve never before seen. For 22 orbits, Cassini will dive into this uncharted region, possibly revealing new things about Saturn’s evolution, what material its rings contain and incredibly intimate views of its atmosphere.

This daring maneuver will signal the beginning of the end for this historic mission, however. On Sept. 15, Cassini will be intentionally steered into Saturn’s atmosphere to burn up as a human-made meteor. It is low in fuel, so NASA wants to avoid the spacecraft from crashing into and contaminating one of Saturn’s potentially life-giving moons — Titan or Enceladus.

So, appreciate every image that is captured by Cassini over the coming weeks. The pictures will be like nothing we’ve seen before of the ringed gas giant, creating a very bittersweet phase of the spacecraft’s profound mission to Saturn.

NASA Uses Gravitational Wave Detector Prototype to Detect ‘Space Mosquito’ Splats

Artist impression of ESA LISA Pathfinder in interplanetary space (ESA)

Imagine speeding down the highway and plowing into an unfortunate swarm of mosquitoes. Now imagine that you had the ability to precisely measure the mass of each mosquito, the speed at which it was traveling and the direction it was going before it exploded over your windscreen.

Granted, the technology to accomplish that probably isn’t feasible in such an uncontrolled environment. Factors such as vibration from the car’s motor and tires on the road, plus wind and air turbulence will completely drown out any “splat” from a minuscule insect’s body, rendering any signal difficult to decipher from noise.

But move your hypothetical “car and mosquitoes” into space — as silly as that may sound — and things become a lot less noisy. And now NASA is measuring its own special kind of “mosquito splat” signal by using a rather unlikely space experiment.

The European LISA Pathfinder spacecraft is a proof of concept mission that’s currently in space, orbiting a region of gravitational stability between the Earth and the sun — called the L1 point located a million miles away. The spacecraft was launched there in late 2015 to carry out precision tests of instruments that will eventually be used in the space-based gravitational wave detector eLISA. Inside the payload is a miniaturized laser interferometer system that measures the distance between two test masses.

When launched in 2034, eLISA (which stands for Evolved Laser Interferometer Space Antenna) will see three spacecraft, orbiting the sun at the L1 point, firing ultra-precise lasers at one another as part of a space-based gravitational wave detector. Now we actually know gravitational waves exist — after the US-based Laser Interferometer Gravitational-wave Observatory (or LIGO) detected the space-time ripples created after the collisions of black holes — excitement is building that we might, one day, be able to measure other phenomena, such as the ultra-low frequency gravitational waves that were created during the Big Bang.

But the only way we can do this is to send stunningly precise interferometers into space, away from our vibration-filled atmosphere to stand a chance of detecting some of the faintest space-time rumbles in our cosmos that would otherwise be drowned out by a passing delivery truck or windy day. And LISA Pathfinder is currently out there, testing a tiny laser interferometer in a near-perfect gravitational free-fall, making the slightest of slight adjustments with its “ultra-precise micro-propulsion system.”

Although LISA Pathfinder is a test (albeit a history-making test of incredible engineering ingenuity), NASA thinks that it could actually be used as an observatory in its own right; not for hunting gravitational waves, but for detecting comet dust.

Like our mosquito-windscreen analogy, spacecraft get hit by tiny particles all the time, and LISA Pathfinder is no exception. These micrometeoroides come from eons of evaporating comets and colliding asteroids. Although measuring less than the size of a grain of sand, these tiny particles zip around interplanetary space at astonishing speeds — well over 22,000 miles per hour (that’s 22 times faster than a hyper-velocity rifle round) — and can damage spacecraft over time, slowly eroding unprotected hardware.

Therefore, it would be nice if we could create a map of regions in the solar system that contain lots of these particles so we can be better prepared to face the risk. Although models of solar system evolution help and we can estimate the distribution of these particles, they’ve only ever been measured near Earth, so it would be advantageous to find the “ground truth” and measure them directly from another, unexplored region of the solar system.

This is where LISA Pathfinder comes in.

As the spacecraft gets hit by these minuscule particles, although they are tiny, their high speed ensures they pack a measurable punch. As scientists want the test weights inside the spacecraft to be completely shielded from any external force — whether that’s radiation pressure from the sun or marauding micro-space rocks — the spacecraft has been engineered to be an ultra-precise container that carefully adjusts its orientation an exact amount to directly counter these external forces (hence the “ultra-precise micro-propulsion system”).

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When LISA Pathfinder is struck by space dust, it compensates with its ultra-precise micro-thrusters (ESA/NASA)

This bit is pretty awesome: Whenever these tiny space particles hit the spacecraft, it compensates for the impact and that compensation is registered as a “blip” in the telemetry being beamed back to Earth. After careful analysis of the various data streams, researchers are learning a surprising amount of information about these micrometeoroides — such as their mass, speed, direction of travel and even their possible origin! — all for the ultimate goal of getting to know the tiny pieces of junk that whiz around space.

“Every time microscopic dust strikes LISA Pathfinder, its thrusters null out the small amount of momentum transferred to the spacecraft,” said Diego Janches, of NASA’s Goddard Space Flight Center in Greenbelt, Md. “We can turn that around and use the thruster firings to learn more about the impacting particles. One team’s noise becomes another team’s data.”

So, it turns out that you can precisely measure a mosquito impact on your car’s windshield — so long as that “mosquito” is a particle of space dust and your “car” is a spacecraft a million miles from Earth.

NASA put together a great video, watch it:

Aside: So it turned out that I inadvertently tested the “car-mosquito” hypothesis when driving home from Las Vegas — though some of these were a lot bigger than mosquitoes…

Enceladus Could Be a Cosmic Shaker for the Cocktail of Life

NASA/JPL-Caltech/Space Science Institute

A little frozen Saturn moon, with a diameter that could easily fit inside the state of New Mexico, holds some big promises for the possibility of finding basic alien life in our solar system.

Enceladus is often overshadowed by its larger distant cousin, Europa, which orbits Jupiter and the Jovian moon’s awesome potential has been widely publicized. But Enceladus has one thing Europa doesn’t — it has been visited very closely by a robotic space probe that could take a sniff of its famous water vapor plumes. And this week, there was much excitement about another facet of the moon’s complex subsurface chemistry, thanks to analysis carried out on data gathered by NASA’s Cassini mission.

But before we get into why this new discovery is so cool, let’s take a very quick look at the other signs of Enceladus’ life-giving potential.

The Cocktail Of Life

Being living, breathing creatures on a habitable planet, it may not come as a surprise to you that for biology to evolve, it needs a few basic ingredients. Liquid water is a definite requirement, of course. Heat also helps. Throw some organic chemistry into the mix and we have a party.

Enceladus, however, is a tiny icy globe, there’s no sign of liquid water on its surface. But when Cassini arrived at Saturn in 2004, Enceladus revealed some of its best-kept secrets. Firstly, it may be a smooth ice ball, but the moon has a large quantity of water under its surface. This water even escapes as geysers, through fissures in its icy crust, producing stunning plumes that eject material hundreds of miles high and into Saturn’s rings.

Before Cassini was launched to Saturn, we had little clue about Enceladus’ watery potential — though this finding explained why Enceladus appeared so bright and how it contributes material to Saturn’s E-ring. Fortunately, the spacecraft has an instrument on board — a mass spectrometer — that could be used to “taste” the watery goodness of these plumes. During its Enceladus flybys, Cassini was able to fly through the plumes, revealing a surprisingly rich chemical cocktail — including a high concentration of organic chemistry.

It’s as if all the building blocks of life have been thrown into a small icy cocoon, shaken up and gently heated from within.

Now, another fascinating discovery has been made. Further analysis of Cassini data from its last 2015 plume fly-through, molecular hydrogen has been detected and planetary scientists are more than a little excited to add this to Enceladus’ habitable repertoire.

Deep In The Enceladus Abyss

“Hydrogen is a source of chemical energy for microbes that live in the Earth’s oceans near hydrothermal vents,” said Hunter Waite, principal investigator of Cassini’s Ion Neutral Mass Spectrometer (INMS) at the Southwest Research Institute (SwRI), in a statement on Thursday (April 13). “Our results indicate the same chemical energy source is present in the ocean of Enceladus.”

This hydrogen could be a byproduct of chemical reactions going on between the moon’s rocky core and the warm water surrounding it. And there’s a lot of hydrogen gas being vented, probably enough to sustain basic lifeforms deep in the Enceladus abyss.

“The amount of molecular hydrogen we detected is high enough to support microbes similar to those that live near hydrothermal vents on Earth,” added co-author Christopher Glein, who specializes in extraterrestrial chemical oceanography, also of SwRI. “If similar organisms are present in Enceladus, they could ‘burn’ the hydrogen to obtain energy for chemosynthesis, which could conceivably serve as a foundation for a larger ecosystem.”

Yes, we’re talking alien microbes. (Also, “extraterrestrial chemical oceanography” — oceans on other worlds! — is one hell of a mind-blowing topic to specialize in, just sayin’.) And did he mention “larger ecosystem”? Why yes! Yes he did.

So, in short, we know Enceladus has a liquid water ocean. We know that it has an internal heat source (hence the liquid oceans). We also know there’s organic chemistry. And now there’s solid hints that there’s water-rock interactions going on that terrestrial microbes living at Earth’s ocean vents like to munch on. If that’s not a huge, blinking neon sign pointing at Enceladus, saying: “We need a surface mission here!” I don’t know what is.

Although the researchers are keen to emphasize that alien microbes have not been found (because Cassini isn’t capable of looking for life), the universe has given us a moon-sized Petri dish where an “ecosystem” may have taken hold. All the ingredients are there, wouldn’t it be cool to find out if Enceladus could be another place in the solar system where life may be hanging out?

There was also some great news about Europa’s habitable potential this week, but you can go here for that piece of cosmic awesomeness.

Want to know more about Cassini’s final months at Saturn, check out my recent Space.com article on the commencement of the veteran mission’s Grand Finale.

Vast Magnetic Canyon Opens up on the Sun — Choppy Space Weather Incoming?

A “live” view of our sun’s corona (NASA/SDO)

As the sun dips into extremely low levels of activity before the current cycle’s “solar minimum”, a vast coronal hole has opened up in the sun’s lower atmosphere, sending a stream of fast-moving plasma our way.

To the untrained eye, this observation of the lower corona — the sun’s magnetically-dominated multi-million degree atmosphere — may look pretty dramatic. Like a vast rip in the sun’s disk, this particular coronal hole represents a huge region of “open” magnetic field lines reaching out into the solar system. Like a firehose, this open region is blasting the so-called fast solar wind in our direction and it could mean some choppy space weather is on the way.

As imaged by NASA’s Solar Dynamics Observatory today, this particular observation is sensitive to extreme ultraviolet radiation at a wavelength of 193 (19.3 nanometers) — the typical emission from a very ionized form of iron (iron-12, or FeXII) at a temperature of a million degrees Kelvin. In coronal holes, it looks as if there is little to no plasma at that temperature present, but that’s not the case; it’s just very rarefied as it’s traveling at tremendous speed and escaping into space.

The brighter regions represent closed field lines, basically big loops of magnetism that traps plasma at high density. Regions of close fieldlines cover the sun and coronal loops are known to contain hot plasma being energized by coronal heating processes.

When a coronal hole such as this rotates into view, we know that a stream of high-speed plasma is on the way and, in a few days, could have some interesting effects on Earth’s geomagnetic field. This same coronal hole made an appearance when it last rotated around the sun, generating some nice high-latitude auroras. Spaceweather.com predicts that the next stream will reach our planet on March 28th or 29th, potentially culminating in a “moderately strong” G2-class geomagnetic storm. The onset of geomagnetic storms can generate impressive auroral displays at high latitudes. Although not as dramatic as an Earth-directed coronal mass ejection or solar flare, the radiation environment in Earth orbit will no doubt increase.

The sun as seen right now by the SDO’s HMI instrument (NASA/SDO)

The sun is currently in a downward trend in activity and is expected to reach “solar minimum” by around 2019. As expected, sunspot numbers are decreasing steadily, meaning the internal magnetic dynamo of our nearest star is starting to ebb, reducing the likelihood of explosive events like flares and CMEs. This is all part of the natural 11-year cycle of our sun and, though activity is slowly ratcheting down its levels of activity, there’s still plenty of space weather action going on.

Cassini Says “Ciao!” to Pan, Saturn’s Ravioli Moon

Never before has a space probe come so close to the pint-sized moon embedded in Saturn’s rings — and when NASA’s Cassini buzzed Pan, the spacecraft revealed what a strange moon it really is.

NASA/JPL-Caltech/Space Science Institute

This is Pan, a 22 mile-wide moon that scoots through Saturn’s rings, orbiting the gas giant once every 13.8 hours. And it’s weird.

Resembling a giant ravioli or some kind of “flying saucer” from a classic alien invasion sci-fi comic, Pan is known as a “shepherd moon” occupying the so-called Encke Gap inside Saturn’s A Ring. This gap is largely free of particles and it has become Pan’s job to hoover up any stray material — the moon’s slight gravity pulls particles onto its surface and scatters others back out into the ring system. This gravitational disturbance creates waves that ripple through the ring material, propagating for hundreds of miles.

On March 7, NASA’s Cassini mission came within 15,268 miles of Pan, revealing incredible detail in the moon’s strange surface. It’s thought that its characteristic equatorial ridge (a trait it shares with another Saturn moon Atlas) is caused by the gradual accumulation of ring material throughout the moon’s formation and with these new observations, scientists will be able to better understand how Pan came to be.

NASA/JPL-Caltech/Space Science Institute

As Cassini rapidly approaches the end of its mission, eventually orbiting through Saturn’s ring plane as a part of its “Grand Finale,” we can expect more of these striking views from orbit before the veteran probe is steered into Saturn’s atmosphere in September, bringing its historic mission to an end.