Smithsonian.com

After waiting patiently, sky gazers around the planet were rewarded yesterday with one of the rarest astronomical phenomena this side of Halley’s comet: the Transit of Venus. During the evening, viewers in the United States were treated to the spectacle as Venus crossed between the earth and the sun, appearing as a small, perfectly round black dot that moved gradually across our star until sunset. As we wrote last week, the transit has historically been a valuable event for scientists seeking to understand our solar system. It’s also simply one of the coolest sights you’ll see in the sky.

If the skies were cloudy in your area—or if you simply forgot to check it out—you have to wait until 2117 to see the event again. As an alternative, take a look at this remarkable NASA video of the transit, produced using the Solar Dynamic Observatory telescope, an orbiting spacecraft charged with the mission of closely observing the sun.

NASA's Voyager probes are now exploring the outer reaches of the solar system

In 1977, the twin Voyager probes were launched by NASA with a radical mission in mind: after studying Jupiter and Saturn, scientists and engineers hoped the probes would become the first-ever human-made objects to exit the solar system.

Nearly 35 years later, data coming back from one of the probes indicates that they’re close but haven’t made it out of the solar system just yet.

According to a study published this month in Geophysical Research Letters, Voyager One is now approximately 111 astronomical units from the sun—meaning that it is 111 times farther from the sun than is the Earth. However, even drifting at this great distance, the probes continue to transmit back fascinating information about this previously uncharted area of the solar system, known as the heliosheath, where the outgoing particles of solar wind emanating from the sun are slowed by the pressure of interstellar gas.

The Voyagers are still within the heliosheath, the outer layer of the solar system

Most recently, Voyager One detected increases in the intensity of low-energy cosmic ray electrons. As a result, scientists have concluded that the probe is has not yet passed the heliopause—generally considered the outer boundary of the solar system, where the solar wind is stopped by the interstellar medium—because outside the solar system, this electron intensity is assumed to be constant. These unexpected spikes in electron intensity may be evidence of different regions in the outer heliosheath, helping us better understand the heliospheric “bubble” where the solar system butts up against interstellar space.

In the years since their launches, the Voyagers have made a number of stunning discoveries. They’ve photographed the active volcanoes on Jupiter’s moon Io, helped us better understand the intricacies of Saturn’s rings and were the only spacecraft to visit Neptune and Uranus. Scientists back on Earth hope that the probes will gather as much information as possible before their plutonium power sources fail and they stop transmitting data forever, projected to occur sometime between 2020 and 2025.

Even after that, though, the Voyagers might have an even more significant role to play: They may serve humanity’s time capsules for future alien civilizations. Each probe carries a ”Golden Record,” Carl Sagan’s brainchild, which was designed to communicate the essence of human civilization to any forms of life they may encounter. The records contain everything from photographs of the structure of DNA to the sound of human brainwaves to greetings in 55 different languages to popular music from a wide range of different cultures, including Chuck Berry’s “Johnny B. Goode.”

In this month’s issue of Smithsonian, Timothy Ferris, who helped design the records, reflects upon the remarkable journey they have already undertaken and the amazing possibilities of what they may encounter in years to come. Ferris writes:

The Voyagers will wander forever among the stars, mute as ghost ships but with stories to tell. Each carries a time capsule, the “Golden Record,” containing information about where, when and by what sort of species they were dispatched. Whether they will ever be found, or by whom, is utterly unknown. In that sense, the probes’ exploratory mission is just beginning.

The distinct plumes of water and other organic compounds on Saturn's moon Enceladus. Image courtesy of NASA/JPL/Space Science Institute.

NASA’s Cassini spacecraft has revealed that Enceladus, a tiny moon orbiting beyond Saturn’s rings, may be capable of hosting some of the life forms found on Earth, NASA Science News reported today.

Planetary scientists using Cassini’s spectrometers found that more than 90 jets near the moon’s south pole are spurting water vapor, organic material, salt and icy particles through fissures. Essentially, it is snowing on Enceladus, and the snow’s composition is microbe-friendly, making this moon a prime candidate for gathering samples in the search for life.

“We can fly through the plume and sample it. Or we can land on the surface, look up and stick our tongues out. And voilà…we have what we came for,” Carolyn Porco, a planetary scientist and leader of the Imaging Science team for the Cassini spacecraft, said in the NASA report.

More critical reading and viewing to understand what we’ve learned about Saturn’s moons:

- An image of four distinct plums plumes at the south pole of Enceladus, from Cassini’s mission news earlier this week.

- Astrobiology.com’s explanation with an image of the “tiger stripes,” or fissures where water and ice sprays near the south pole of Enceladus.

- Scientific American‘s coverage last year of the discovery of water beneath Saturn’s icy moon Enceladus.

- Smithsonian’s story on Saturn’s two types of moons: those like Enceladus are similar to moons around other giant planets, such as Jupiter; the others are tiny, icy moonlets that reside on the outer edges of Saturn’s rings. They weren’t discovered until about 8 years ago when the Cassini spacecraft began imaging the Saturn system, and they were an unexpected find.

- A study published in Nature in 2010 found that Saturn’s moons formed from the accretion of material in the planet’s rings. When ring material moves beyond a certain distance from the planet—called the Roche limit—it becomes gravitationally unstable and clumps up to form the tiny moons.

- And Smithsonian’s story that year about the mystery of Saturn’s walnut-shaped moon, Iapetus.

What else have you read that’s great about Saturn’s moons? Let us know in the comments.

Last summer, on July 6, solar scientist Karel Schrijver spotted something unusual. Looking at a coronagraph—an image created by blocking out the center of the sun, revealing only the corona, the area near its surface—he saw a bright comet, identified as C/2011 N3, descending into the solar atmoshpere. When he searched for the comet on images produced by the Solar Dynamic Observatory (SDO), a solar observation satellite that orbits the earth, he realized he was seeing something unprecedented. For the very first time, the death of a comet crashing into the sun had been caught on camera.

A new paper, published by Schrivjer and a team of scientists today in Science, details the find and what it means for astronomy. Comets dive into the sun frequently, but previous ones had been too small and dim to be seen against the glaring backdrop of the sun. But this comet, an ultra-bright one from a group known as the Kreutz comets, was caught by SDO imaging equipment plunging to its death. Over the course of 20 minutes, it clearly appears descending across the sun before disappearing into its surface. Space.com notes:

“It was very surprising to see this comet at all,” Karel Schrijver, an astrophysicist at Lockheed Martin Advanced Technology Center in Palo Alto, Calif., told SPACE.com. “We may think that an object of some 60,000 metric tons and some 50 meters [164 feet] across is large and heavy, but if you compare it to the sun, which can easily hold a million Earths, it is astonishing that such a small object glows brightly enough to be seen.”

The find, it turns out, is more than merely interesting: It has helped the scientists develop a new method for calculating the size of comets from afar. Using two figures—the amount of time it took the comet to evaporate and the distance over the sun it traveled while doing so—the team figured out its size and speed.

The C/2011 N3 comet is caught on a coronagraph, an image that blocks out the sun to reveal its corona. Image courtesy of NASA Solar and Heliospheric Observatory

“It was moving along at almost 400 miles per second through the intense heat of the sun—and was literally being evaporated away,” said Schrijver, the lead author of the paper. As the Bad Astronomy blog points out, that speed means it would have crossed the width of the United States in about 8 seconds.

The researchers also estimate that the comet came within 62,000 miles of the sun’s surface before evaporating, and was 70,000 tons in size (about the weight of an aircraft carrier), trailed by a tail 10,000 miles in length.

Some aspects of the discovery, though, are still confusing for the scientists. Most surprising is the fact that we could see the comet at all. Because objects passing in front of the sun absorb light, the comet should have appeared as a dim spot rather than a bright one. Solving this mystery, along with others, might help reveal information about the composition of comets, the sun’s corona and perhaps even the origins of the solar system. Scientists will continue to look to the sun—and scrutinize the data—for answers.

The best place to find "aliens" might be Comic-Con (2008, credit; Jim Merithew/Wired.com, via Wired Photostream on flickr)

A 2010 poll found that one in four Americans (and one in five people worldwide) believe that aliens have visited our planet. And many of these people believe that the evidence of these visits has been covered up by the government. Area 51, Roswell, mutilated cows in Colorado—there’s got to be some truth in that, right? And so two petitions were created on the White House We The People site, one calling “for the President to disclose to the American people the long withheld knowledge of government interactions with extraterrestrial beings” and the other asking the President “to formally acknowledge an extraterrestrial presence engaging the human race.”

The petitions easily reached the threshold of 5,000 signatures needed to get a response from the White House. But the signers are likely to be disappointed. Phil Larson, who works on space policy and communications at the White House Office of Science & Technology Policy, wrote in the response:

The U.S. government has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race. In addition, there is no credible information to suggest that any evidence is being hidden from the public’s eye.

He gives a few examples of ongoing and planned research—SETI, Kepler, the Mars Science Laboratory—that may lead to the discovery of alien life and then reminds us that the odds of finding alien life are probably pretty slim:

Many scientists and mathematicians have looked with a statistical mindset at the question of whether life likely exists beyond Earth and have come to the conclusion that the odds are pretty high that somewhere among the trillions and trillions of stars in the universe there is a planet other than ours that is home to life.

Many have also noted, however, that the odds of us making contact with any of them—especially any intelligent ones—are extremely small, given the distances involved.

While reading this, I was reminded of a conversation I had with Cassie Conley last year when I was reported a story about what will happen should we actually find alien life. Conley is NASA’s Planetary Protection Officer; she’s the one who makes certain that NASA missions don’t contaminate other planets and that any sample return missions don’t harm us here on Earth. She told me that after she took the NASA job, some people befriended her in the hopes of ferreting out NASA’s secrets about aliens. “I was dropped as an acquaintance immediately upon their realizing that, in fact, I didn’t have any secrets,” she said. “They were disappointed when they found out there weren’t any.” (But at least she had a good attitude about it all: “It was rather entertaining,” she said.)

I will admit that it is possible that some grand conspiracy exists, that a government or corporation could be hiding this information from us all. (I can’t disprove a negative.) But keep in mind what Conley says: “If you think the U.S. government is that good at keeping secrets, you’ve got a lot higher opinion of them than I do.”

In addition, such a conspiracy would necessitate excluding the scientists most interested and most qualified in this area, and all of them have committed to making a discovery of alien life public. “I think there’s a big misconception in the public that somehow this is all a cloak-and-dagger operation,” says Arizona State University astrobiologist Paul Davies. “It’s not. People are quite open about what they are doing.”

Even the White House.