Here’s a round-up of recent science headlines we didn’t want you to miss!

Ancient Rivers

Without a smart phone or GPS device, how did early humans find their way out of Africa? A study published last week in PLoS One determines that ancient rivers, now covered by the Sahara Desert, provided habitable routes to follow.

Simulating paleoclimates in the region, the researchers found evidence of three major river systems that likely existed in North Africa 130,000–100,000 years ago, but are now largely buried by dune systems in the desert. When flowing, these rivers likely provided fertile habitats for animals and vegetation, creating “green corridors” across the region.

“It’s exciting to think that 100,000 years ago there were three huge rivers forcing their way across 1000-km of the Sahara desert to the Mediterranean—and that our ancestors could have walked alongside them,” says lead author Tom Coulthard of the University of Hull, UK.

Cosmic Beginnings?

Did life on Earth hail from Mars, as one researcher proposed last month, or comet collisions? Apparently, in both cases, it all has to do with the chemistry. Carl Zimmer, one of our favorite science writers, has a recent New York Times article about the chemistry needed to produce DNA from RNA. And while it doesn’t look like early Earth had those compounds, Mars might have.

Then, earlier this week, a study published in Nature Geoscience finds that the collision of icy comets with planetary bodies could result in the formation of complex amino acids, the building blocks of proteins (and life).

The researchers suggest that this process provides another piece to the puzzle of how life was kick-started on Earth, after a period of time between 4.5 and 3.8 billion years ago when the planet was being bombarded by comets and meteorites.

The team made their discovery by recreating the impact of a comet by firing projectiles through a large high-speed gun. This gun, located at the University of Kent, uses compressed gas to propel projectiles at speeds of 7.15 kilometers per second into targets of ice mixtures, which have a similar composition to comets. The resulting impact created amino acids such as glycine and D- and L-alanine. Sounds like a fun method of discovery…

Speaking of fun collisions, if you want more of them, the Morrison Planetarium at the Academy is featuring Cosmic Collisions in its current show rotation. From the our website:

Creative and destructive, dynamic and dazzling, collisions are a key mechanism in the evolution of the Universe.

Missing Mars Methane

One chemical Mars seems to be missing? Methane. The gas was sought as a possible sign of microbial life currently living on the seemingly barren world. However, despite earlier reports that NASA’s Mars rover, Curiosity, discovered methane on the red planet, NASA reports today in Science that none has been found.

Curiosity’s earlier evidence of methane detection turned out to be within leftover air from Earth. And previous reports of localized methane concentrations up to 45 parts per billion on Mars were based on observations from Earth and from orbit around Mars.

“It would have been exciting to find methane, but we have high confidence in our measurements,” says the report’s lead author, Chris Webster. “We measured repeatedly from Martian spring to late summer, but with no detection of methane.”

But don’t give up on microbial Martians just yet… “This important result will help direct our efforts to examine the possibility of life on Mars,” says NASA’s Michael Meyer. “It reduces the probability of current methane-producing Martian microbes, but this addresses only one type of microbial metabolism. As we know, there are many types of terrestrial microbes that don’t generate methane.”

Looking for extraterrestrial life? Next month’s Brilliant!Science festival can deliver it to you. Visit this page for more information.

Image: the Tunable Laser Spectrometer on-board Curiosity: NASA/JPL-Caltech

This Sunday and Monday, Earth will be passing through the path of Comet Swift-Tuttle. This periodic comet approaches the Sun every 133 years and isn’t expected to come around again for more than a century, but Earth will encounter particles of dust lingering in the comet’s path.

When the comet’s frozen nucleus approaches the Sun, it heats up, and its outer layers of ice evaporate. This process releases dirt and dust embedded in the ice, and when this cosmic debris collides with Earth’s atmosphere at high speeds (up to 45 miles per second), it burns up, This causes the streak of light in the night sky that people sometimes refer to as a “shooting star.”

Shooting stars are properly called meteors, and meteor showers are named after the constellation from which the meteors seem to radiate.  From an Earthly point of view, the current display appears to emanate from the constellation Perseus the Hero, so we call these meteors the Perseids.

Although the meteors are actually falling in parallel paths, their trajectories, if traced backward, appear to converge in the distance—in this case pointing backward to the stars of Perseus.  This does not mean to look only toward that constellation, since the meteors can appear anywhere in the sky, so use your unaided eye to see the widest possible field of view. No telescope required!

The perfect time for this warm summer activity is the night of Sunday, August 11^th, to the morning of Monday the 12th, and the night of Monday the 12th to the morning of Tuesday the 13th. Ideally, head out after midnight, because then you will be facing the direction Earth is moving, directly into the trail of comet dust. And this year, the sky will also be darker because the moon will have set. Finally, if possible, get away from light pollution.

Andrew Fraknoi, Academy Fellow and astronomy professor at Foothill College in Los Altos, California, offers professional viewing advice: “It’s more important to decide WHERE to watch them, than WHEN to watch them. The crucial issue is that meteors are faint, so you need a location where the sky is DARK. That means getting away from city and car lights as much as possible. The darker your site, the more you will see.”

If you’re an amateur astronomer, this shower will be one of the most rewarding of the year. While casual observers might see 4–6 meteors per hour on any given night, the Perseids can produce approximately 60–80 meteors per hour at their peak and generate the most fireballs (bright meteors) of any shower! To keep count of the meteors you see, and to be a part of NASA meteor research, download an app called Meteor Counter.

Fraknoi offers even more incentive. “Since comets are ‘left-overs’ from the early days of our solar system, you can tell yourself that each flash you see is the ‘last gasp’ of cosmic material that formed about five billion years ago.”

Earth is estimated to accumulate between 37,000–78,000 tons of this cosmic material, so head out with warm clothes, a blanket, or sleeping bag to check out nature’s fireworks in the sky.

For more info, check out these top 10 facts on the Perseids, read more about their history, peruse this blog post from our friends at Zerve, or watch Tom Hanks being hit by a meteor while talking about the Perseids on the Tonight Show a few years ago (about 10:53 in, with Turkish subtitles).

Image: Andreas Möller/Wikipedia

Cause for celebration! The 10,000th near-Earth object (NEO) has been discovered.

Asteroid 2013 MZ5 joined the ranks of asteroids and comets whose orbits pass near Earth. On an astronomical scale, “near” means within 28 million miles…

The Near-Earth Object Program looks for all NEOs, especially large ones with the potential to harm Earth (called a Potentially Hazardous Asteroid). This type of candidate would need to be at least about 100 feet (about 30 meters) across to do significant damage a populated area—and about 3,200 feet (nearly a kilometer) in diameter to cause global devastation.

As you might expect, large asteroids are easier to find than small ones. NASA estimates that we have discovered all but a few dozen of the largest asteroids, those 460 feet (140 meters) in diameter or larger. (Whew!) Therefore, NASA is shifting its attention to medium-sized threats. If 90% of these were found, the threat of an unexpected impact would be greatly reduced, perhaps even to one percent!

“Finding 10,000 near-Earth objects is a significant milestone,” said Lindley Johnson, program executive for NASA’s Near-Earth Object Observations Program. “But there are at least 10 times that many more to be found before we can be assured we will have found any and all that could impact and do significant harm to the citizens of Earth.”

Discovered by the Pan-STARRS-1 telescope in Hawaii, this new asteroid is about 1,000 feet in diameter. That would put it in a pretty dangerous category if it were headed toward Earth, but its orbit does not pass close enough to us to be a significant threat.

“The first near-Earth object was discovered in 1898,” said Don Yeomans, manager of the Near-Earth Object Program Office at NASA’s Jet Propulsion Laboratory. “Over the next hundred years, only about 500 had been found. But then, with the advent of NASA’s NEO Observations program in 1998, we’ve been racking them up ever since. And with new, more capable systems coming on line, we are learning even more about where the NEOs are currently in our solar system, and where they will be in the future.”

A privately-funded mission called Sentinel might extend the search with a space-based telescope that will likely identify hundreds of thousands of NEOs. You can watch Science Today story on Sentinel or watch an animation narrated by former astronaut Ed Lu describing the mission.

10,000 down, how many to go…?

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: PS-1/UH

Discovered in June 2011, Comet C/2011 L4 Pan-STARRS (yeah, quite a mouthful) is one of two comets that astronomershope will flare to spectacular brightness this year, becoming easily visible to the naked eye. While the December appearance of Comet C/2012 S1 ISON is still too far away to predict its brightness accurately, Comet Pan-STARRS has been putting on a good show for Southern Hemisphere observers for the past few weeks, swinging up through the plane of the solar system from below.

Now past perihelion (its closest approach to the Sun), the cometcontinues to drift northward, and Northern Hemisphere observers can now take a gander. However, it isn’t quite as bright as astronomers originally hoped it would be. While photos taken from Southern Hemisphere locations have been quite striking, the comet is now starting to fade as it retreats from the Sun, gradually climbing out of the evening twilight for northern viewers.

Skywatchers will need binoculars to see it low in the west about 30-45 minutes after sunset, after the twilight glow has dimmedenough to not wash it from view, but before the comet sets. Still, any comet that can be seen at all is a beautiful, ethereal sight, and Pan-STARRS has been noted for its bright head anddelicate, fan-shaped tail.

The next few nights offer the waxing Moon as a reference to help locate the comet. On the evening of Tuesday the 12th, look for it just to the left of the razor-thin, day-old crescent, and on Wednesday the 13th, with the Moon slightly higher in the sky, the comet will lie below it.

Where did that mouthful of a name come from, anyway? Following the tradition of naming comets after their discoverers,Comet Pan-STARRS got its moniker from the telescope array used to discover it, the Panoramic Survey Telescope and Rapid Response System in Hawaii.

If geochronology is “the science of determining the ages of earth materials” (according to the center’s website), then Renne must know his gnat’s eyebrow. For those of us lay-folk, it’s about 5,000 years.

Renne and his colleagues have a new paper in Science pinpointing the dates of both the impact and the dinosaur extinction, placing them within the same time of each other—providing evidence, once again, for an asteroid or comet impact being the cause of extinction.

The 110 mile-wide Chicxulub (cheek’-she-loob) crater, off the Yucatan coast of Mexico, is likely the result of a six-mile in diameter asteroid or comet. Using and refining a technique called argon-argon dating, the scientists determined that the impact occurred 66,038,000 years ago, plus or minus 11,000 years.

The same argon-argon dating put the dinosaur extinction at 66,043,000 years ago, with the same margin of error.

The first link between the impact event and dinosaur extinction was published in 1980 by UC Berkeley’s Luis and Walter Alvarez. Since then, many other scientists have supported or refuted the theory, sometimes putting the extinction several hundred thousand years before the impact.

“When I got started in the field, the error bars on these events were plus or minus a million years,” says UC Berkeley paleontologist William Clemens. “It’s an exciting time right now, a lot of which we can attribute to the work that Paul and his colleagues are doing in refining the precision of the time scale with which we work.”

Despite the synchronous impact and extinction, Renne cautions that the impact was not the sole cause of extinction. Dramatic climate variation over the previous million years, including long cold snaps amidst a general Cretaceous hothouse environment, probably brought many creatures to the brink of extinction, and the impact kicked them over the edge.

“These precursory phenomena made the global ecosystem much more sensitive to even relatively small triggers, so that what otherwise might have been a fairly minor effect shifted the ecosystem into a new state,” Renne says. “The impact was the coup de grace.”

The third Thursday of every month, the Morrison Planetarium hosts “Universe Update” at the 6:30 planetarium show during NightLife. I select my favorite astronomy stories from the past month, and I give a brief run-down of current discoveries while taking audiences on a guided tour of the Universe. As you may or may not know, the planetarium sports a three-dimensional atlas of the Universe, so we can take you places virtually while talking about the latest astronomy news.

I always start at Earth and work my way out to cosmological distances, so I’ll list the news stories in the same order—from closest to farthest from home.

Fourth graders from the Emily Dickinson Elementary School in Bozeman, Montana, proved themselves more creative than NASA engineers! Crazy rocket scientists named their two lunar-orbiting spacecraft “GRAIL-A” and “GRAIL-B” (where, of course, “GRAIL” is an acronym, which stands for “Gravity Recovery and Interior Laboratory”). The elementary school students selected the names “Ebb” and “Flow,” which NASA selected as the winning contribution in a nationwide contest. The GRAIL mission measures the ebb and flow of gravity, in a sense, as the two spacecraft orbit the Moon and measure variations in its gravitational pull. From the GRAIL website:

As they fly over areas of greater and lesser gravity, caused both by visible features such as mountains and craters and by masses hidden beneath the lunar surface, they will move slightly toward and away from each other. An instrument aboard each spacecraft will measure the changes in their relative velocity very precisely, and scientists will translate this information into a high-resolution map of the Moon’s gravitational field.

A little farther from home, new reports from a comet impact on the Sun that took place last July. We like to describe comets as “dirty snowballs,” and as you might imagine, a comet getting too close to the Sun stands a snow ball’s chance in… Well, a million-degree plasma irradiated by incident solar flux. The comet evaporated over a period of about 20 minutes, and as described in a paper that appears in today’s Science magazine, it probably measured between 150 and 300 feet across and had a mass equivalent to an aircraft carrier. According to Karel Schrijver, a solar scientist at Lockheed Martin in Palo Alto, the comet moved speedily to its demise: “It was moving along at almost 400 miles per second through the intense heat of the Sun—and was literally being evaporated away.”

A fair bit farther from the scorching heat of the Sun, the Dawn spacecraft is sending back gorgeous images of the asteroid Vesta, including this gorgeous snapshot of a crater on the asteroid’s surface. Dawn has entered a low-altitude orbit that gives it a close look at the potato-shaped planetoid. Learning more about such objects should help us better understand the formation of the solar system, and after its stay at Vesta, Dawn will move on to Ceres, the dwarf planet (like Pluto) that resides between the orbits of Mars and Jupiter.

Beyond our own solar system, of course, we are rapidly discovering planets in orbit around other stars: these extrasolar planets (or exoplanets) now number in excess of 700, and astronomers find more all the time.

As I described in one of my updates from the American Astronomical Society meeting last week, astronomers have announced the discovery of the most compact extrasolar planetary system yet detected. Looking at the KOI 961 system side-by-side with Jupiter and its major satellites strikes me as a particularly illuminating comparison: only 70% larger than Jupiter, the host star (the smallest known to have planets) has at least three planets (the smallest yet found) in orbit around it, the smallest of which is about the size of Mars. John Johnson, an astronomer at Caltech, announced the superlative system last week, and on April 2nd, he will give a talk in the Morrison Planetarium as part of our Benjamin Dean Lecture Series, “The Quest for Habitable Planets Orbiting Red Dwarfs.”

And astronomers have help in their search. Just this week, we had a glimpse into the democratization of astronomy… Viewers of a British television program(me) may have discovered a new exoplanet! Evidence from the Kepler mission suggests the existence of a Neptune-sized planet around the star SPH10066540, orbiting every 90 days at a distance equivalent to Mercury from our Sun. The discovery awaits confirmation, but you don’t have to watch telly in the U.K. to join in the search for such objects. You can go to the PlanetHunters website and start sifting through Kepler data in hopes of finding a planet of your own…

In another of my posts last week, I mentioned the spectacular new Spitzer image of Cygnus X, a massive star-forming region in the constellation (you guessed it) Cygnus. Ten times the size of the Orion Molecular Cloud Complex, Cygnus X appears to host some 26,000 possible young stellar objects, according to an announcement last week.

Moving farther from home, I talked a bit about the new dark matter map that I previously described in a post from Austin. It turns out that analyzing the light from 10 million galaxies call tell you a lot about where dark matter resides, and since dark matter drives the formation of much of the structure in the Universe, that knowledge helps us understand more about the evolution of the cosmos…

The dark matter maps tell one part of the story, but we also rely on studies of the cosmic microwave background to tease out how the Universe has evolved over time. Since 2003, the gold standard of such measurements have come from the Wilkinson Microwave Anisotropy Probe (WMAP). But ESA’s Planck mission recently completed its survey of the cosmic microwave background: the sensor used to make the observations ran out of its coolant a little less than a week ago. It had collected more than two years’ worth of data, however, and the first new high-resolution maps will be released early next year. (Hey! It takes a while to process all that data.)

That’s all for now. Check back for next month’s update! Or come to NightLife on Thursday, 15 February, and check out “Universe Update” live in the Morrison Planetarium.

Ryan Wyatt is the director of the Morrison Planetarium and Science Visualization at the California Academy of Sciences.

Image: SOHO (ESA & NASA)

Now, new evidence, published last week in Nature, supports the theory that comets delivered a significant portion of Earth’s oceans, which scientists believe formed about 8 million years after the planet itself.

“Life would not exist on Earth without liquid water, and so the questions of how and when the oceans got here is a fundamental one,” says University of Michigan astronomer Ted Bergin. “It’s a big puzzle and these new findings are an important piece.”

Bergin is a co-investigator on HiFi, the Heterodyne Instrument for the Infrared on the Hershel Space Observatory. With measurements from HiFi, the researchers found that the ice on a comet called Hartley 2 has the same chemical composition as our oceans. Both have similar D/H ratios. The D/H ratio is the proportion of deuterium, or heavy hydrogen, in the water. A deuterium atom is a hydrogen with an extra neutron in its nucleus.

This was the first time ocean-like water was detected in a comet. “We were all surprised,” admits Bergin.

Six other comets HiFi measured in recent years had a much different D/H ratio than our oceans, meaning similar comets could not have been responsible for more than 10 percent of Earth’s water.

The astronomers hypothesize that Hartley 2 was born in a different part of the solar system than the other six. Hartley most likely formed in the Kuiper belt, which starts near Pluto at about 30 times farther from the sun than Earth is. The other six hail from the Oort Cloud more than 5,000 times farther out.

“The results show that the amount of material out there that could have contributed to Earth’s oceans is perhaps larger than we thought,” speculates Bergin.

Image courtesy of NASA

The scientists used data from NASA’s Cassini, Galileo and New Horizons missions (dating from 1996 to 2009) to search the ring systems of Jupiter and Saturn for patterns of cometary disruptions.

In the case of Jupiter, the ripple-producing culprit was the well-known comet Shoemaker-Levy 9, whose debris cloud hurtled through the thin Jupiter ring system during a kamikaze course into the planet in July 1994. Scientists attribute Saturn’s ripples to a similar object—likely another cloud of comet debris—plunging through the inner rings in the second half of 1983. The researchers believe this comet passed through when Saturn was on the other side of the Sun from Earth.

“We now know that collisions into the rings are very common—a few times per decade for Jupiter and a few times per century for Saturn,” said Mark Showalter of SETI and lead author of the paper on Jupiter. “Now scientists know that the rings record these impacts like grooves in a vinyl record, and we can play back their history later.”

The tightness of the rings’ “grooves” gives clues to when the comet debris came hurling through, according to Nature News:

As time passed, this tilt has become a progressively tighter spiral, meaning that the shorter the ripple’s wavelength, the longer ago it was formed.

(Discover has a great NASA video of the rings becoming tighter with age on their site.)

The ripples also give scientists a measurement of the size of the clouds of cometary debris that hit the rings. In each of these cases, the nuclei of the comets were a few kilometers wide before they likely broke apart.

“Finding these fingerprints still in the rings is amazing and helps us better understand impact processes in our solar system,” said Linda Spilker, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Cassini’s long sojourn around Saturn has helped us tease out subtle clues that tell us about the history of our origins.”

“What’s cool is we’re finding evidence that a planet’s rings can be affected by specific, traceable events that happened in the last 30 years, rather than a hundred million years ago,” said Matthew Hedman, of Cornell and lead author of the Saturn paper. “The solar system is a much more dynamic place than we gave it credit for.”

Image credit: NASA/JPL-Caltech/SETI

Observed annually for about 2,000 years, the Perseid shower qualifies as one of the most spectacular of the many meteor showers occurring during the year, with an average rate of 50-60 meteors per hour, compared to 5-15 per hour for many other showers.  Because the shower takes place during the summertime, when more people are inclined to be out late at night, the Perseids are one of the best-known displays of celestial fireworks.  This year, the peak of the shower coincides with a very young crescent Moon that sets early in the evening. Skywatchers observing during the recommended early morning hours won’t have to worry about interference from moonlight, making viewing conditions ideal.

To best observe the shower (weather-permitting), skywatchers should plan for the midnight-to-predawn hours of both August 12th & 13th.  Select a viewing site away from bright lights and with as much of a view of the sky as possible—atop a high hill with no obstructions (such as trees or buildings) along the horizon works best.  Meteor-watching isn’t a quick activity that one can do in just a few minutes—it takes time and patience (a lawn-chair, sleeping bag, or even a blanket on the ground make for comfortable viewing).  Allow at least 20 minutes for your eyes to adapt to dark conditions so that you can spot fainter meteors (getting away from bright lights helps considerably).

Although Perseids are often described as being fast and bright with some glowing trails, don’t expect a regular, evenly-spaced stream of fireballs to streak predictably across the sky.  Meteors may occur at irregular intervals or in bursts, and many will appear quite faint – often, seeing them is simply a matter of looking in the right direction at the right time.  That’s why you should seek out a wide-angle view of the sky.  In addition, although meteor showers are named for the constellations from which meteors appear to radiate,  meteors can appear anywhere in the sky. It’s simply the effect of perspective that makes meteor paths seem to converge at a point within a single star pattern.

Estimates of the number of dust particles that strike Earth vary, but some astronomers calculate that our planet sweeps up between 37,000-78,000 tons of space debris every day, although most debris takes the form of dust-sized particles too small to survive the fiery journey to our planet’s surface.

For more info, check out these top 10 facts on the Perseids, read more about their history or watch Tom Hanks being hit by a meteor while talking about the Perseids on the Tonight Show last year (about 10:53 in, with Turkish subtitles).

We know it’s 153 light years away, that it has water in its atmosphere, and that it orbits its star in three and a half days at a distance 100 times closer than Jupiter is to the sun.

And, last week, University of Colorado scientists using the Hubble Space Telescope confirmed another remarkable fact about the gas giant: the heat of its star and the stellar winds are whipping its atmosphere into a comet-like tail coming off of the planet. The study was published in The Astrophysical Journal.

Hubble’s Cosmic Origins Spectrograph (COS) detected the heavy elements carbon and silicon in the planet’s super-hot, 2,000-degree-Fahrenheit atmosphere. This detection revealed the parent star is heating the entire atmosphere, dredging up the heavier elements and allowing them to escape the planet in the form of gas.

Some of that gas is coming off the planet at pretty fast speeds, heading in the direction toward Earth. Lead author and astronomer Jeffrey Linsky, PhD, said that:

We found gas escaping at high velocities, with a large amount of this gas flowing toward us at 22,000 miles per hour. This large gas flow is likely gas swept up by the stellar wind to form the comet-like tail trailing the planet.

Although this extreme planet is being roasted away by its star, it won’t be destroyed anytime soon. At almost the same mass as Jupiter, “It will take about a trillion years for the planet to evaporate,” according to Linsky.

Image credit: NASA, ESA, and G. Bacon (STScI)