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►  Spectacular Cassini photo puts Earth in perspective

For a moment four years ago, the spacecraft Cassini watched Earth from 900 million miles away. The probe had ducked behind Saturn. There, shielded from the sun’s rays, the robot turned its delicate lenses toward home. On July 19, 2013, Earthlings in the know waved and smiled for the paparazzo in the sky. Everyone else went about their day. Cassini, a gracious photographer, caught the entire Earth on camera anyway.

Cassini will end its 20-year mission on September 15, burned up in Saturn’s atmosphere. The mission has been a major success. Cassini landed the Huygens probe on Saturn’s moon Titan and sensed hydrogen in the icy plumes of Enceladus. The spacecraft took half a million photos while orbiting the sixth planet, capturing Saturn’s rings and superstorms in unprecedented detail.

But perhaps no other Cassini photograph carries the emotional heft of the Day the Earth Smiled.

The greatest space photos are named. Apollo 17 gave us Earth as the Blue Marble. Voyager 1’s portrait of our planet from beyond Neptune is the Pale Blue Dot. The Pillars of Creation show the hydrogen spires of the Eagle Nebula. Astronomer Carolyn Porco, the leader of the Cassini imaging team who conceived of the July 2013 photo shoot, decided to name the view from Saturn after the beaming residents of Earth.

Porco and her colleagues organized a campaign to smile into the void at 21:27 Coordinated Universal Time (accounting, of course, for light’s 15-minute dash from Earth to Saturn). It would be only the third time that Earth had been photographed from such a distance, after an earlier Cassini image and the Voyager portrait. It also marked the first time that Earth inhabitants knew they were being photographed from the outer solar system, beyond the asteroid belt.

“This could be a day, I thought, when all the inhabitants of Earth, in unison, could issue a full-throated, cosmic shout-out and smile a big one for the cameras from far, far away,“ Porco wrote in June 2013.

“The experience itself was both exciting because so many people were interested in the event, but also a bit scary because we wouldn’t know until afterward whether the images worked,“ said Matthew Hedman, a physicist at the University of Idaho who was involved with the project but spoke only on behalf of himself.

Zooming in on the Day the Earth Smiled, you can see sunlight scattering through Saturn’s E ring, pointed out Italian astronomer Gianrico Filacchione in a recent article in Nature Astronomy. (NASA’s Jet Propulsion Laboratory notes this is a composite of images taken with green, red and blue filters, which when combined offers a view in natural color.) Brighter are the F and G rings, which contrast against the darkness of Saturn’s night.

It was a view of Saturn impossible to get from Earth. Cassini photographed what was, essentially, an eclipse of the sun by Saturn, Hedman said. Our planet shines beneath those massive rings. Earth is a pinprick - at that distance, the image scale is 53,820 miles per pixel, and the Earth’s diameter is just under 8,000 miles.

“Among the numerous images returned by Cassini,“ Filacchione wrote, “this is the one that for me best collects the richness of Saturn’s system.“

The images came back in to Earth in pieces. “We were seeing glimpses of the entire system, one image showing Tethys, another showing some of the main rings, another showing Enceladus in the E ring, and of course a few showing Earth near the rings,“ Hedman said. As the scientists assembled the images into a mosaic, Hedman could see light through the broad sweep of the E ring, made of microscopic particles expelled from Enceladus. “I guess it was kind of like putting [together] a jigsaw puzzle,“ he said.

The picture of Earth wasn’t the only image taken that day. The Cassini team ultimately stitched together 141 photos into a sweeping view of Saturn, a mosaic 404,880 miles across. Shot from the back, Saturn is a black ball suspended in ink, enclosed in the coffee-colored circles of its rings.

“On the one hand, it is a beautiful image that will serve as a reminder of all the great data Cassini obtained,“ Hedman said. “And on the other, it contains a lot of information about the properties of the rings that we will be trying to understand for many years to come.“

►  How to steer a spacecraft into Saturn

A billion-dollar spacecraft named Cassini is about to burn up as it plunges into the atmosphere of Saturn this month. That’s the plan, exquisitely crafted. Cassini will transmit data to Earth to the very end, squeezing out the last drips of science as a valediction for one of NASA’s greatest missions.

Dreamed up when Ronald Reagan was president, and launched during the tenure of Bill Clinton, Cassini arrived at Saturn in the first term of George W. Bush. So it’s old, as space hardware goes. It has fulfilled its mission goals and then some. It has sent back stunning images and troves of scientific data. It has discovered moons, and geysers spewing from the weird Saturn satellite Enceladus. It landed a probe on the moon Titan.

It has also run out of gas, basically, though precisely how much fuel is left is unknown. Program manager Earl Maize says, “One of our lessons learned, and it’s a lesson learned by many missions, is to attach a gas gauge.“

The spacecraft is tracked in the Charles Elachi Mission Control Center of the Jet Propulsion Laboratory in Pasadena, California. Mission Control is a darkened chamber with no external windows. The room (named after a retired JPL director) is dominated by glowing screens and people peering into consoles. Someone wandering into the place by accident would think: This looks like the kind of place where they fly spaceships.

On the far wall is a screen showing the operations of the three huge radio antennae – in the California desert; near Madrid; and in Canberra, Australia – that together make up NASA’s Deep Space Network. As Earth turns, there’s always a big dish looking out for Cassini and for JPL’s other spacecraft roaming the solar system.

The navigators have a computer model that tells them where the spacecraft probably is and probably will be.

“We need to be able to point instruments to objects. Nothing is static. Everything is moving. The timing is critical,“ said navigation team leader Duane Roth. “We don’t know exactly where Titan is at any given moment, or where Saturn is, or where Cassini is. When you want to propagate that out to some future time, all our errors grow.“

But they’re getting it done.

Cassini’s final orbits have taken it, amazingly, inside the rings of Saturn, where the spacecraft practically skims the tops of the planet’s clouds. These orbits can plausibly be compared to Luke Skywalker flying into that narrow trench on the Death Star.

The navigators here at NASA’s Jet Propulsion Laboratory do not boast of their prowess, however. For them, it’s just . . . math.

“The key is to calculate this change in velocity,“ said navigation team member Mar Vaquero as she explained a complex set of equations on a whiteboard in her workspace at the lab. “So you use math. You have matrices. And you have partials. Those are changes in your trajectories with respect to each parameter. So you use your matrices, your vectors, position and velocity and your partials to come up with this delta V that you see here.“

So they’ve done the calculations, and they’ve plotted the trajectory. If the atmosphere is thicker than expected, they might have to send a slight course correction using small hydrazine thrusters. But, really, there’s not much to do other than let gravity handle everything, and watch the data come in, and clap, and maybe shed a few tears.

“We’re kind of going through the mourning cycle,“ said Julie Webster, head of spacecraft operations.

“You form a family,“ said Linda Spilker, the Cassini project scientist, speaking of the team. “Your kids grow up together.“

Cassini closes out an era in NASA space science. This is hardly the end of solar system exploration, but it’s essentially the end of the first, heroic phase – the initial reconnaissance of the planets.

Sixty years ago, the Soviet Union put the first satellite, Sputnik, into orbit. Within a few years, there were spacecraft flying by the moon, crashing into the moon, even landing softly on the moon. More would go winging by Mars to see for the first time the craters and canyons and volcanoes of that desert planet.

Forty-one years ago, NASA soft-landed the two Viking probes on Mars and scratched the surface looking for signs of life (the results are disputed, but the smart money says the surface is sterile).

This year, NASA marked the 40th anniversary of the astonishing Voyager program – two robotic spacecraft that explored the outer solar system, the first Voyager flying by Jupiter and Saturn, the second flying by Jupiter, Saturn, Uranus and Neptune – a solar system superfecta, to borrow a term from the horse track. The two Voyagers are now out in the exurbs of the solar system, far beyond the orbit of even the dwarf planet Pluto.

The colossal scale of Cassini is a legacy of the go-big mentality of the early days of space exploration. The United States put men on the moon with a jumbo rocket, and NASA for a long time skewed toward muscle-bound spacecraft even when humans weren’t along for the ride.

No single event changed everything, but what happened to a spacecraft called Mars Observer in 1993 certainly had an impact. It was large and fully adorned with instruments. And then, one day shortly before it was to go into Mars orbit, it simply went silent.

Webster was part of the Mars Observer team and remembers how, for many days, JPL staffers tried to reconnect with the spacecraft. But Mars Observer was never heard from again. Webster said that the fuel tanks were being pressurized with helium in advance of the Mars orbital insertion. “Probably the pressurization system had a leak somewhere and it essentially blew up.“

Space is hard. Space will break your heart.

“It’s like a loss of a family member,“ Webster said.

By that point, Cassini had already been conceived, the instruments already coming online, and so it was essentially grandfathered in to the old-fashioned go-big protocol. NASA Administrator Dan Goldin wasn’t a fan. He had a name for Cassini: “Battlestar Galactica.“

Actually, it wasn’t simply the “Cassini” mission. It was the “Cassini-Huygens” mission. The Europeans designed the Huygens probe, a separate vehicle that detached from Cassini when it passed close to Titan.

After Cassini, launched in 1997, arrived at Saturn in 2004, Huygens disengaged from the main spacecraft and dropped through Titan’s thick clouds. It sent back details of an alien world that possesses a stew of complex organic molecules, including liquid methane. Hydrocarbons rain from the sky. There are lakes and rivers.

It’s the only place in the solar system other than Earth known to have rain and open bodies of liquid on the surface.

Cassini also discovered something amazing about Saturn’s moon Enceladus: It has geysers spewing from its south pole. Almost certainly it has an interior ocean, sealed beneath ice, that contains great volumes of water and possibly hydrothermal vents.

Someday NASA or some other space agency is likely to send a probe to Enceladus to sample those geysers and test them for indications of life.

“The legacy for which Cassini will be remembered will be Enceladus,“ said project scientist Spilker.

Exploration begets more exploration. Every mission drops a rope ladder in its wake.

Cassini has slowed down slightly in its final few orbits as it has passed through the outermost layers of Saturn’s atmosphere. The drag on the spacecraft hastens the final plunge slightly.

At about 1:37 a.m. Friday, the spacecraft will roll into position to enable one of its instruments to sample Saturn’s atmosphere as it gets closer and closer to the planet. It will stream data back to the Deep Space Network.

In the final minute of its life, Cassini will fire its thrusters in an attempt to keep its high-gain antenna pointing to Earth. But that is a battle Cassini is destined to lose.

The navigators at the Jet Propulsion Laboratory are still calculating precisely when the spacecraft will send its final signal on September 15. At last report, it will be 4:55 a.m. Pacific Daylight Time, about 13 minutes earlier than the time calculated a couple of months ago.

But it will be already gone, in a sense. It will have been destroyed 83 minutes earlier. That’s how long it takes at the speed of light for news to travel from Saturn to Pasadena.

Cassini won’t exactly “crash” into Saturn, because it’s a gaseous planet and there’s no surface to hit. In the last moments, the spacecraft will go into a tumble and lose contact with Earth. Then it will burn up as it plunges through Saturn’s atmosphere. It will disintegrate.

And then nothing will be left.

“It’ll just be vaporized and completely disassociated,“ Maize said.

“It will become part of Saturn.“

►  New elements spread scientific knowledge, fear

I’m no scientist, although I played one in the 1966 horror movie “Mothra’s Excellent Adventure.“ In fact, my science knowledge stops at the freezing temperature for water (cold) and what’s in table salt (salt).

But news that scientists added have items to the periodic chart was an eye-opener for me.

The International Union of Pure and Applied Chemistry (IUPAC) last winter approved the name and symbols of four elements – elements 113, 115, 117 and 118. They are called, in order, Nihonium, Moscovium, Tennessine and Oganesson.

According to an announcement by IUPAC, the newly discovered elements were named after a location or a scientist, following the early naming convention that honored Frank Oxygen and Harriet Nitrogen, both whom lived in the Hydrogen neighborhood of Baltimore.

I wouldn’t give a nickel for that gag. Get it? Nickel is an element!

I just hope that the person who came up with Oganesson, which is abbreviated as Og, now calls himself “the Wizard of Og.“ Seriously.

But let’s commemorate the use of the word Tennessine, which I have always used as the past tense for the word Tennessee. Now I know differently.

The periodic chart is interesting, although I missed most of the instruction about it during high school science due to the fact that I was surreptitiously listening to the Giants on a transistor radio. But I was apparently misinformed: I thought that like the number of planets in the solar system (eight after Pluto’s unfair demotion), faces on Mount Rushmore (four), members of the pop group Hanson (three) and turtle doves (two), the number of elements on the periodic table was settled.

Apparently not. It never was.

Sneaky scientists have been adding to the chart since it was introduced in 1869 – bringing criticism that they’re just doing it to force amateur chemists to keep buying new charts, like those pesky college textbook authors.

The four new elements last winter were the first to be added to the table since Flevorium and Livermorium were accepted in June 2011.

Livermorium! It’s from Livermore . . . and it also gives cachet to my plan to buy a crematorium in Livermore and name it “The Livermorium.“ Cool, right?

That the periodic table of the elements continues to expand should be seen as good news. Knowledge keeps expanding. People keep discovering new things. The borders of science keep growing.

Except . . .

The first 94 elements exist naturally and the subsequent 24 have been synthesized in labs or nuclear reactors.

There’s no reason to fear.

I’m sure scientists creating new elements in a lab or a nuclear reactor is purely harmless. The fact that every time that’s happened in a movie has led to disaster shouldn’t make us fear. Right?


I guess we’ll just have to trust the scientists. And hope that nothing goes wrong with the new, synthesized elements.

If it goes bad, I guess we should have Tennessine it coming, right?

Dumb puns are a key element in jokes. Get it? Element?

--> Tuesday, September 12, 2017
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