MORE: The Wow! Signal: Intercepted Alien Transmission?

While pointed in the direction of 3 star systems named Chi Sagittarii, in the constellation of Sagittarius, Big Ear detected a 72 second radio wave burst, a signal far stronger than background noise. On the observatory’s computer printout, Ehman circled the burst with the infamous annotation "Wow!"

This excitement wasn't an overstatement, it was this kind of signal he was looking for, the kind of signal astronomers thought a technologically-capable alien civilization would produce.

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.

However, since that day in 1977, a detection of a signal of that strength has not been replicated. Even after the SETI Institute was founded in 1984, and countless efforts have been made to find another radio burst like the "Wow!" signal, astronomers have been faced with silence in the cosmos; a problem that has only served to intensify the Fermi Paradox unease.

13 Ways to Hunt Intelligent Aliens

Now, Antonio Paris of St Petersburg College, Fla., an ex-analyst of the US Department of Defense, hopes to solve the mystery and he suspects that an entirely different cosmic phenomenon is to blame.

In an interview with TheGuardian.com, Paris says that his investigative background sent him on a mission to find another possible explanation for the "Wow!" signal and he tracked down two "suspicious" comets that may have been in the vicinity of Chi Sagittarii on Aug. 15, 1977. Interestingly, these comets, called 266P/Christensen and 335P/Gibbs, were only discovered in 2006 and 2008, so weren't considered as possible reasons for the signal in 1977 as no one knew of their existence.

But what have comets got to do with errant radio bursts?

The "Wow!" signal was recorded in the 1420MHz radio frequency band. It just so happens that cosmic neutral hydrogen naturally radiates at this frequency — it is therefore an abundant signal that is commonly used in astronomy. This is no coincidence; through alien-hunting logic, should there be an extraterrestrial species wanting to make contact, what frequency would they use? Firstly, as we only have ourselves to use as an alien template, we have to assume that hypothetical aliens will likely use radio waves. Secondly, if they are using radio waves to communicate with us, they would likely use a frequency that other intelligent aliens would be naturally tuned into. 1420MHz is the "universal water cooler," where intelligent life could check into and potentially chat.

ANALYSIS: Seeking the Aliens Who Are Looking Right At Us

The bummer is, however, that comets contain copious amounts of hydrogen in their atmospheres. Say if the "Wow!" signal was actually caused by the chance passage of a comet through the radio telescope's field of view, packing a powerful radio surge?

In 2017, Comet 266P will once again orbit in front of Chi Sagittarii and Comet 335P will do so the following year and Paris wants to test this hypothesis. Unfortunately, existing radio telescopes are already booked, so he has to buy or build his own radio antennae in time for the cosmic encounters. He has a crowdfunding campaign set up to raise the $20,000 he needs and is most of the way there.

It may be a long shot, but as is the way with many astronomical studies, all possible phenomena need to be ruled out before a discovery is made and, should Paris' experiment prove the "Wow!" signal was in fact caused by interference by an undiscovered comet, the universe will get quieter once again, making the Fermi Paradox even more bewildering.

Source: The Guardian

Originally published by Discovery News.

"This implies that any group of animals that is under prolonged periods of high extinction rate can undergo mass extinction should there be a catastrophic event," said study lead researcher Manabu Sakamoto, a postdoctoral research assistant of biological sciences at the University of Reading in the United Kingdom.

The study isn't the first to suggest that dinosaurs were in a major decline before the asteroid event. In previous studies, scientists have recorded the number of species in each geological age and compared those levels to the subsequent ages (each age lasts for millions of years) to get a sense of how diverse the dinosaurs were, Sakamoto said.

But that method focuses on snapshots in time and doesn't take into account the extinction and speciation rate within each branch of thedinosaur family tree. So the researchers of the new study looked at the dinosaur fossil record and the family tree to get a robust picture of when new dinosaur species came onto the scene, Sakamoto said.

"Our study is the first to incorporate such phylogenetic [family tree] information when studying speciation and extinction in dinosaurs," Sakamoto told Live Science. "This is what has allowed us to build a more nuanced and certain picture of dinosaur speciation than has ever before been possible."

Dinosaur detectives

The researchers separately analyzed the three major groups of dinosaurs: the ornithischians (such as Stegosaurus), sauropodomorphs (the long-necked, long-tailed herbivores) and theropods (bipedal, mostly carnivorous dinosaurs, such as T. rex and Albertosaurus).

The sauropodomorphs had the most prominent downturn, the scientists found. The research showed spikes in new species of this type of dinosaur emerging during the Triassic and early Jurassic periods, until about 195 million years ago, when that speciation rate began to slow down. At 114 million years ago, during the early Cretaceous period, species of sauropodomorphs were going extinct faster than new species were emerging, the researchers found.

"The subsequent originations of [the] titanosaurian [group] were not nearly enough to compensate for the continuous loss of sauropods throughout the remainder of the Cretaceous," the scientists wrote in the study.

Duck-billed dinosaurs were one of the few dinosaur groups to thrive during the late Mesozoic period.
Credit: Catmando |Shutterstock.com

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Theropods had an "early burst" of speciation followed by a speciation slowdown from the late Triassic to the early Cretaceous (about 215 million years ago to about 120 million years ago), when extinction rate exceeded speciation rate, the researchers found.

Likewise, ornithischians show an early increase followed by a speciation slowdown at about 114 million years ago, when extinction rate surpassed speciation rate. But there were a few success stories within this group. The hadrosauriforms (duck-billed dinosaurs) and ceratopsids (the horned dinosaurs, such asTriceratops) did well, likely because they had developed jaws that helped them munch on new food, possibly flowering plants, the researchers said. [Dinosaur Detective: Find Out What You Really Know]

When the researchers considered the three dinosaur groups separately, "We found unequivocal evidence that dinosaurs were in decline up to 50 million years prior to the mass extinction event 66 million years ago," Sakamoto said.

Extinction lessons

It's unclear why the dinosaurs started going extinct so early, but there are clues as to why speciation increased during certain periods, the scientists said. One idea is that rising sea levels cut into the land, fragmenting dinosaur habitats and nudging the beasts to evolve separately into new species in different areas, the researchers said.

However, after dinosaur extinction rates began to rise, another group of animals started thriving: mammals.

"The decline of the dinosaurs would have left plenty of room for mammals, the group of species which humans are a member of, to flourish before the impact, priming them to replace dinosaurs as the dominant animals on Earth [after the impact]," study co-author Chris Venditti, an evolutionary biologist at the University of Reading, said in a statement.

The new findings may help scientists understand the possible consequences of today's extinctions, the researchers added.

"We live in a time when species are undergoing unprecedented levels of extinctions," Sakamoto told Live Science. "This means that if some major catastrophe hits, then it is highly possible that whole groups of animals [will] be completely wiped out off the face of the Earth."

The study is an interesting one, said Alan Turner, an associate professor of anatomical sciences at Stony Brook School of Medicine in New York, who was not involved in the research.

"Through modeling of speciation dynamics, it appears that dinosaur diversity was declining well in advance of the end-Cretaceous extinction event that killed off all nonavian dinosaurs, as well as numerous other vertebrate groups," Turner told Live Science in an email.

The study was published online April 18 in the journal Proceedings of the National Academy of Sciences.

Follow Laura Geggel on Twitter @LauraGeggel. Follow Live Science@livescience, Facebook & Google+. Original article on Live Science.

Auroras are produced when solar particles that are ejected from the sun and carried to Earth by solar winds collide with electrically charged particles in Earth's magnetic field, triggering reactions in the upper atmosphere that release light.

They are most commonly glimpsed on Earth at high latitudes, in the Northern and Southern hemispheres. While auroras are typically green, they can also appear violet, red, blue, while or pink, according to NASA.

To produce the auroras video, NASA partnered with media infrastructure experts at Harmonic, with whom they also launched a new UHD channel featuring 4K content — the first noncommercial UHD channel in North America — the agency said in a statement.

And the auroras are just part of the dynamic activity captured in NASA's videos. The agency has also released 4K UHD footage of lightning flashes, the setting moon, expanses of clouds spread over the oceans, and the sprawl of city lights at night.

This is one video you're going to want to watch as large as possible — trust us, it'll be worth it.

Follow Mindy Weisberger on Twitter and Google+. Follow us@livescience, Facebook & Google+. Original article on Live Science.

Backtracking sound waves

Lord Rayleigh — the brilliant British physicist who discovered the noble gas argon and explained why the sky is blue — also made a bizarre prediction about sound waves nearly a century ago. Rayleigh reasoned that, because the speed of sound is fixed, an object traveling faster than that while spewing out sound would result in sound waves that would seem to travel in the opposite direction of the object and thus seem to be reversed in time orientation. For instance, a phonograph on a plane traveling at Mach 2, or twice the speed of sound, would seem to play the music backward.

No scientists really doubted this notion, but there was no easy way to test it.

"Using sound, it's something that's really hard to verify and actually hear," said study co-author Daniele Faccio, a physicist at Heriot-Watt University in Scotland.

Sound travels at 761.2 mph (1,225 km/h), but that means that, to hear a 3-second clip of music going backward, a supersonic jet traveling at Mach 2 (or twice the speed of sound) would start replaying the music more than a mile from the listener's location. The scattering and absorption of the sound waves in the air would make the music completely inaudible by that time, Faccio said. 

Light reversal

But Faccio and his colleagues realized that if Rayleigh's predictions held true, the same effect would occur in other types of waves, such as light waves. Light travels much, much faster than sound, at 670 million mph (1.1 billion km/h). And the wavelengths themselves are tiny, meaning the time reversal can be demonstrated in a normal-size room.

The researchers were also interested in studying this idea because they were developing ultra-high-speed cameras that could peer around corners, and the phenomenon could affect their algorithms.

There was just one problem with testing Rayleigh's prediction with light: Nothing can travel faster than the speed of light.

To create a faster-than-light source, the team used a strange phenomenon called illumination fronts, which had previously been described in a series of fascinating thought experiments.

The trick behind illumination fronts is that, while an image may be traveling faster than light, the photons themselves never exceed light speed.

Here's how Illumination fronts work. Imagine taking a laser pointer and flicking the point across a vast and distant wall. While the photons traveling from the laser pointer to the wall are moving at their ordinary speed, because the light hits the wall at an angle, the dot on the wall (the illumination front) always moves faster than that. [Science Fiction or Fact? The Plausibility of 10 Sci-Fi Concepts]

Freezing photons in midair

Next, however, the team had to find some way to capture the speedy paths of images as they zoomed across a wall.

"The key piece of equipment was the camera that allows us to essentially freeze light in motion," Faccio told Live Science. [Video: How to Freeze Light]

To catch time reversal in the act, the team created an illumination front by projecting a single line of light on a screen and moving that line across the screen faster than the speed of light. At the same time, they captured the reflected light in motion using a super-high-speed camera. The camera snapped photos in a few picoseconds, or trillionths of a second, during which time photons travel just a few feet.

Sure enough, the camera captured the line on the wall moving in the opposite direction from the way they moved the line, as if it had traveled backward in time.

Self-annihilating twins

In a second experiment, the team verified an even more bizarre effect, called pair creation and annihilation. (Robert Nemiroff, a physicist at Michigan Technological University, predicted this effect for astronomical objects in a study posted online in May 2015 in the preprint journal arXiv.)

Faccio and his colleagues had an illumination front travel across a curved screen. As the speed of the projected lines exceeded light speed, a pair of lines was created, and the two lines moved away from each other. Using a different curvature, the pair of lines moved toward each other, merged and then annihilated each other, the researchers reported Friday (April 15) in the journal Science Advances.

The findings may have implications for the researchers' corner-peering cameras. This kind of "supersight" requires scientists to analyze the paths that light particles take as they bounce and scatter off various objects. Normally, light travels so fast that, to the human eye, the light coming from many different locations seems to appear instantaneously, making it impossible for the eye to resolve these different light paths and "see" behind corners.

But because high-speed cameras can capture the light in motion, researchers can reconstruct the shape of objects that might not be in the immediate line of sight. However, the mathematical calculation of these paths would need to account for the possibility that some of the light rays they see are time-reversed, because they are coming from an illumination front, Faccio said.

The new findings apply to any type of wave, Faccio said. For instance, there may be certain instances when a seismic wave bounces off a slanted piece of rock deep below Earth's surface, pointing to earthquake activity in one direction, when, in fact, the temblor occurred in the opposite direction, Faccio said.

The new paper also has some other interesting implications, said Nemiroff, who was not involved in the current study.  

"I am not sure that either Lord Rayleigh nor [the paper's authors] were aware that sonic booms are the sound equivalent of illumination-front pair-creation events," Nemiroff told Live Science in an email. "With light, you first see a flash when a pair event is created, but with sound, you hear a boom."

Follow Tia Ghose on Twitter and Google+. Follow Live Science@livescience, Facebook & Google+. Original article on Live Science.