Salt Piles on Shoreline, Senegal
Salt piles line the shoreline of Lake Retba, Senegal. The high salinity content of the lake provides a livelihood for salt collectors.
Biplane Over Monomoy Shoals, Massachusetts
A biplane flies above Monomoy Island, Massachusetts.
Sand Dunes, Rub al Khali
The borders of four nations—Saudi Arabia, Oman, Yemen, and the United Arab Emirates—blur beneath the shifting sands of the Rub al Khali, or Empty Quarter, desert.
Drying Fronds, Kenya
Fronds dry in neat lines around a tree in Kenya.
Cave Dwellings, Turkey
Cavelike dwellings built into soft rock dot the Cappadocia region of Turkey.
Fairy Circles, Namib Desert
Fairy circles, or grassless patches, spot the Namib Desert in Namibia, seen here from an airplane.
Bacteria, New Zealand
Photosynthesizing bacteria in a New Zealand thermal pool absorb carbon dioxide and release oxygen.
Beads of dew cling to the florets that spiral inside a sunflower head.
Lichens grow on a granite gravestone in Lake Champlain, New York.
The characteristic spikes of a banksia flower are common across Australia. This one was photographed on a farm in Mount Barker.
Water Reflection, Utah
Reflecting off water, light paints peacock-feather patterns onto a rock wall in Glen Canyon National Recreation Area, Utah.
Giant Clam Mantle
Iridescent spots surround the mantle of a giant clam in Palau, Micronesia. The mantle is a fleshy outer layer that secretes the clam’s shell.
Cactus, Manzanillo, Mexico
Bursts of yellow punctuate a cactus in Manzanillo, Mexico.
Exhibiting its main defense mechanism, a millipede curls into a tight spiral. In this fashion it protects its legs—on average between 100 and 300, not the thousand its name suggests—inside its body.
The scales of an Atlantic salmon, such as these on a fish in Quebec, Canada, can help biologists determine the fish’s age.
Seen here 400 times their true size, diatoms are a type of algae found in oceans, fresh water, and soil.
Basket Sea Star, Cuba
The complexly branched arms of the basket sea star, or starfish, catch plankton for the echinoderm.
Sunlight radiates through the Xpacay cenote in the Mexican Yucatán. Cenotes are freshwater sinkholes usually found on the Yucatán peninsula.
Snapping Turtle Shell
The bony plates of a snapping turtle’s carapace protect it from predators. Snappers are freshwater turtles found in much of North America.
Mammatus clouds roil in the Nebraska sky, identifiable by their sagging, pouch-like shape. The name comes from the Latin word for “breast.”
The next regularly scheduled meteor shower wil be the Draconids in early evening on October 7 and 8. Then try the Orionids before dawn on October 21.
In October 2012, there will be two scheduled chances to see meteor showers. First, try the Draconids around nightfall and early evening on October 7 and 8. Then try the Orionids before dawn on October 21.
October 7, 2012 Draconids
The radiant point for the Draconid meteor shower almost coincides with the head of the constellation Draco the Dragon in the northern sky. That’s why the Draconids are best viewed from the Northern Hemisphere. The Draconid shower is a real oddity, in that the radiant point stands highest in the sky as darkness falls. Unlike many meteor showers, the Draconids are more likely to fly in the evening hours than in the morning hours after midnight. This shower is usually a sleeper, producing only a handful of languid meteors per hour in most years. But watch out if the Dragon awakes! In rare instances, fiery Draco has been known to spew forth many hundreds of meteors in a single hour. With no moon to interfere during the evening hours, try watching at nightfall and early evening on October 7 and 8.
October 21, 2012, before dawn. Orionids
With the waxing crescent moon setting before midnight (on October 20), that means a dark sky between midnight and dawn, or during the best viewing hours for the Orionid meteors. On a dark, moonless night, the Orionids exhibit a maximum of about 15 meteors per hour. These fast-moving meteors occasionally leave persistent trains and bright fireballs. If you trace these meteors backward, they seem to come from the Club of the famous constellation Orion the Hunter. You might know Orion’s bright, ruddy star Betelgeuse. The radiant is north of Betelgeuse. The Orionids have a broad and irregular peak that isn’t easy to predict. More meteors tend to fly after midnight, and the Orionids are typically at their best in the wee hours before dawn. The best viewing for the Orionids in 2012 will probably be before dawn on October 21..
November 4/5, 2012, late night November 4 until dawn November 5 South Taurids
The South (and North) Taurids are perhaps best suited to die-hard meteor aficionados. The meteoroid stream that feeds the Taurids is very spread out and dissipated. That means the Taurids are extremely long lasting (September 25 to November 25) but usually don’t offer more than about 7 meteors per hour. That’ll be true even on the South Taurids’ expected peak night of November 4 (before dawn November 5). The waxing crescent moon sets at early evening, leaving a dark sky for the South Taurid meteors, which are expected to produce the most meteors in the wee hours just after midnight on November 5.
November 11/12, 2012, late night November 11 until dawn November 12 North Taurids
This shower is long-lasting (October 12 – December 2) but modest, and the peak number is forecast at about 7 meteors per hour. Typically, you see the maximum numbers at around midnight to 1 a.m., when Taurus the Bull moves nearly overhead. This year, the thin waning crescent moon won’t rise till close to dawn, leaving a long dark night for these rather slow-moving but sometimes bright North Taurid meteors. you might even see some Taurid fireballs. The greatest numbers of North Taurid meteors come just after midnight on November 12..
November 16/17, 2012, late night November 16 until dawn November 17 Leonids
Radiating from the constellation Leo the Lion, the Leonid meteor shower is famous. Historically, this shower has produced some of the greatest meteor storms in history – at least one in living memory, 1966 – with rates as high as many thousands of meteors per hour. Indeed, on that beautiful night in 1966, the meteors did fall like rain. Some who watched the shower said they felt as if they needed to grip the ground, so strong was the impression of Earth plowing along through space, fording the meteoroid stream. The meteors, after all, were all streaming from a single point in the sky – the radiant point – in this case in the constellation Leo the Lion. Leonid meteor storms sometimes recur in cycles of 33 to 34 years, but the Leonids around the turn of the century – while wonderful for many observers – did not match the shower of 1966. And, in most years, the Lion whimpers rather than roars, producing a maximum of perhaps 10-15 meteors per hour. Like most meteor showers, the Leonids ordinarily pick up steam after midnight and display the greatest meteor numbers just before dawn. In 2012, however, the waxing crescent moon will setting at early evening, leaving a dark night for Leonid meteor shower.
December 13/14, 2012, late night December 13 until dawn December 14 Geminids
The final major meteor shower of every year (unless one surprises us!) is always the December Geminid shower, often producing 50 or more meteors per hour. It is a beloved shower, because, as a general rule, it’s either the August Perseids or the December Geminids that give us the most prolific display of the year. Best of all, the new moon guarantees a dark sky on the peak night of the Geminid shower (mid-evening December 13 until dawn December 14). But the nights on either side of the peak date should be good as well. Unlike many meteor showers, you can start watching the Geminids by 9 or 10 p.m. local time. The peak might be around 2 a.m. local time on these nights, because that’s when the shower’s radiant point is highest in the sky as seen around the world. With no moon to ruin the show, 2012 presents a most favorable year for watching the grand finale of the meteor showers. Best viewing of the Geminids will probably be from about 1 a.m. to 3 a.m. on December 14.
Most important: a dark sky. Here’s the first thing – the main thing – you need to know to become as proficient as the experts at watching meteors. That is, to watch meteors, you need a dark sky.
Know your dates and times. You also need to be looking on the right date, at the right time of night. Meteor showers occur over a range of dates, because they stem from Earth’s own movement through space. As we orbit the sun, we cross “meteor streams.” These streams of icy particles in space come from comets moving in orbit around the sun. Comets are fragile icy bodies that litter their orbits with debris. When this cometary debris enters our atmosphere, it vaporizes due to friction with the air. If moonlight or city lights don’t obscure the view, we on Earth see the falling, vaporizing particles as meteors.
What to bring. You can comfortably watch meteors from many places, assuming you have a dark sky: your back yard or deck, the hood of your car, the side of a road. If you want to bring along equipment to make yourself more comfortable, consider a blanket or reclining lawn chair, a thermos with a hot drink, binoculars for gazing along the pathway of the summer Milky Way. Be sure to dress warmly enough. Even the summer nights can be chilly, especially in the hours before dawn when the most meteors should be flying.
Are the predictions reliable? Although astronomers have tried to publish exact predictions in recent years, meteor showers remain notoriously unpredictable. Your best bet is to go outside at the times we suggest, and plan to spend at least an hour reclining comfortably while looking up at the sky.
In 2012, the full moon gets in the way of the May Eta Aquarids. Moon-free nights greet the April Lyrids, the November North Taurids and the December Geminids. Moonlight should not pose much of a problem for the October Draconids, October Orionids, November South Taurids and November Leonids. Some moon-free viewing time is in store for the January Quadrantids and July Delta Aquarids. Our almanac page provides links for access to the moonrise and moonset times in your sky.
Peak dates are derived from data published in the Observer’s Handbook by the Royal Astronomical Society of Canada and Guy Ottewell’s Astronomical Calendar.
January 4, 2012 in the wee hours before dawnQuadrantids
When we say January 4, we mean in the wee hours before dawn, not that night. Although thewaxing gibbous moon lights up most of the night and doesn’t set until roughly 3 a.m. local time, this is about the best time of night to watch for these meteors. Click here to know when the moon sets in your sky. Although the Quadrantids can produce over 100 meteors per hour, the sharp peak only lasts for a few hours, and doesn’t always come at an opportune time. In other words, you have to be in the right spot on Earth to view this meteor shower in all its splendor. If this year’s forecast proves correct, eastern North America, the North Atlantic Ocean and possibly western Europe will be in a fine position to watch this shower. However, meteor showers are notorious for defying predictions. This shower is worth a try at northerly latitudes all around the globe. Face the general direction of north-northeast, but take in as wide an expanse of sky as possible. Watch from about 2 a.m. until dawn.
April 22, 2012 Lyrids
The Lyrid meteors – April’s “shooting stars” – tend to be bright and often leave trails. About 10-20 meteors per hour at peak can be expected. Plus, the Lyrids are known for uncommon surges that can sometimes bring the rate up to 100 per hour. Those rare outbursts are not easy to predict, but they’re one of the reasons the tantalizing Lyrids are worth checking out. The radiant for this shower is in the constellation Lyra, which rises in the northeast at about 10 p.m. Fortunately, in 2012, the new moon guarantees a dark sky in the late night and morning hours, the best time to watch the Lyrid shower. As a general rule, the greatest number of Lyrid meteors fall in the dark hours before dawn.
May 5 and 6, 2012 Eta Aquarids
This shower has a relatively broad maximum but is expected to show the greatest number of meteors before dawn on May 5 or 6. Unfortunately, the closest and largest full moon of 2012 will be out all night long, leaving no dark sky for this year’s Eta Aquarid show. But die-hard meteor enthusiasts will be watching anyway, to see how many Eta Aquarids can be seen in a moonlit sky. At northerly latitudes – for example, in the northern U.S. and Canada, or northern Europe – the meteor numbers are few and far between. In the southern half of the U.S., 10 to 20 meteors per hour might be visible in a dark sky. Farther south – for example, in the Southern Hemisphere – the meteor numbers increase dramatically, perhaps two to three times more Eta Aquarid meteors streaking the southern skies. For the most part, this is a predawn shower. The radiant for this shower appears in the east-southeast at about 4 a.m. local time (the time at all locations) and the hour or two before dawn offers the most meteors. The broad peak to this shower means that some meteors may fly in the dark hour before dawn for a few days before and after the predicted optimal date. Although the most meteors will probably rain down on May 5 or 6 before dawn, the full moon is sure to wash away all but the brightest Eta Aquarid meteors.
July 28 and 29, 2012 Delta Aquarids
Like the Eta Aquarids, this shower favors the Southern Hemisphere, and the tropical latitudes in the Northern Hemisphere. Although the waxing gibbous moon won’t set till after midnight, the hours between moonset and dawn will probably offer the most Delta Aquarid meteors. (Click here to know when the moon sets in your sky.) The meteors appear to radiate from the southern part of the sky. From northern temperate latitudes, the maximum hourly rate may reach 15-20 meteors in a dark sky. Unlike many meteor showers, this one doesn’t have a very definite peak, despite the dates given above. Instead, these medium-speed meteors ramble along fairly steadily throughout late July and early August. An hour or two before dawn usually presents the most favorable view of the Delta Aquarids. Try watching in late July, in the hours between moonset and dawn.
August 10/11, 11/12, and 12/13, 2012 Perseids
Meteors are typically best after midnight, but in 2012, with the moon rising into the predawn sky, you might want to watch for Perseid meteors in late evening as well. You can get moonrise times via this custom sunset calendar. As seen from around the world, the waning crescent moon will rise later on August 12 than on August 11, and, on the morning of August 13, although you’re slightly past the peak, the moon will rise later still. On any of those mornings, moonlight shouldn’t be so overwhelming as to ruin the show. Plus the moon on those mornings will be near the bright planets Venus and Jupiter in the eastern predawn sky. It’ll be a beautiful early morning scene. The Perseids are typically fast and bright meteors. They radiate from a point in the constellation Perseus the Hero. You don’t need to know Perseus to watch the shower because the meteors appear in all parts of the sky. The Perseids are considered by many people to be the year’s best shower, and often peak at 50 or more meteors per hour in a dark sky. The Perseids tend to strengthen in number as late night deepens into midnight, and typically produce the most meteors in the wee hours before dawn. These meteors are often bright and frequently leave persistent trains. Starting in late evening on the nights of August 10/11, 11/12 and 12/13. The Perseid meteors will streak across these short summer nights from late night until dawn, with only a little interference from the waning crescent moon. Plus the moon will be near the bright planets Venus and Jupiter in the eastern predawn sky.
EarthSky Facebook friend Dave Walker caught this 2012 Perseid meteor on the morning of August 12, 2012.
A bright Perseid meteor seen by astrophotographer Stefano De Rosa this morning (August 12) on the island of Isola D’Elba in Italy.
An Eta Aquarid meteor streaks over northern Georgia on April 29, 2012. Image credit: NASA/MSFC/B. Cooke
Remember, meteor showers are like fishing. You go, you enjoy nature … and sometimes you catch something.
Bottom line: The Delta Aquarid and Perseid meteor showers combine in late July and August to create what most consider the best and most reliable meteor display for Northern Hemisphere observers. In 2012, watch for the Delta Aquarids from midnight to dawn around late July, when the moon is absent from that part of the sky. Then watch for the Perseids at their peak on the mornings of August 11, 12 and 13. On those August mornings, as an added treat, the moon will be sweeping past the brightest planets – Venus and Jupiter – in the eastern predawn sky. You can’t ask for more!
A night view of Kuwait City, the coastal city which serves as Kuwait’s political and economic capital. The metropolitan area has a population approaching 2.5 million
The Black Sea looks crazy right now, as you can see in this photo taken by the MODIS instrument onboard NASA’s Aqua satellite on July 15. These intense swirls are the work of a microorganism called coccolithophore, a “calcite-shedding phytoplankton [that] can color much of the Black Sea cyan.”
It’s an impressive feat for such a tiny organism, as the Black Sea has a surface a 168,500 square miles (436,400 square kilometers). The Black Sea—which should be called Cyan Sea—is located between Eastern Europe and Western Asia, and it is connected to the Atlantic Ocean through the Aegean and Mediterranean seas.
Austrian skydiver Felix Baumgartner plans to attempt a record-breaking freefall jump from 120,000 feet (23 miles) sometime this summer. This would beat the previous record – set in 1960 by Joe Kittinger – by 3.5 miles. The jump has the commercial backing of sponsor Red Bull. The mission has been named Red Bull Statos.
Baumgartner will be carried to his jump position in a capsule carried by a high-altitude balloon. By doing so he hopes to also set the altitude record for the highest manned balloon flight. You can read more about the pressurized capsule he will be riding in here. The image above shows Baumgartner about to jump from the edge of the capsule from a test from 71,581 feet on March 15, 2012.
In addition to the freefall distance jump and manned balloon records, Baumgartner also plans to become the first human to break the speed of sound while wearing only a spacesuit. The suit he will be wearing is pictured above. A Universe Today story notes that the human body is not designed for supersonic speeds.
Red Bull Stratos medical director Dr. Jonathan Clark, who was the crew surgeon for six Space Shuttle flights, wants to explore the effects of acceleration to supersonic velocity on humans. He says, “We’ll be setting new standards for aviation. Never before has anyone reached the speed of sound without being in an aircraft. Red Bull Stratos is testing new equipment and developing the procedures for inhabiting such high altitudes as well as enduring such extreme acceleration. The aim is to improve the safety for space professionals as well as potential space tourists.”
Red Bull plans a live webcast of the Baumgartner’s jump. Here is a video about the jump from Red Bull. Take a look:
Photos: Red Bull Stratos
Hot enough to boil oceans and vaporize rock. The highest terrestrial temperatures occurred more than four billion years ago, when a Mars-size proto-planet smashed into the Earth. (The debris from this collision formed our moon.) Within a millennium, the surface air temperature had dropped from a high of about 3,700°F down to 3,000°. Then the planet went into a period of slower cooling that lasted a few tens of millions of years. As the atmosphere thickened with heat-trapping water clouds and carbon dioxide and a shell of solid rock formed around the Earth’s core, conditions stabilized at 440°.
The warmest weather we’ve had in recent times—since mammals diverged from the tree of life—came about 55 million years ago, during a period known as the Paleocene-Eocene Thermal Maximum. In just a few thousand years, global surface temperatures increased by 5° to 10°, with parts of North America experiencing a tropical climate and spring-like average temperatures in the Arctic.
The star at the center of our solar system is one giant ball of nuclear fusion that’s perpetually blasting out dangerous solar winds. Closer planets like Venus take a real beating, but Earth is protected by a magnetosphere, and instead harnesses the sun’s energy to power our planet’s climate.
This NASA video is actually a clip from a longer documentary playing at the Smithsonian called Dynamic Earth: Exploring Earth’s Climate Engine, and its visualizations of wind and ocean currents were created using the agency’s powerful climate simulators. The Earth’s spinning molten core actually produces a strong magnetic field that deflects most of the sun’s harmful ejections, and what energy that isn’t blocked or reflected by clouds and ice serves to heat the planet and generate the weather systems that let us grow food. So in a way, the sun’s our biggest enemy and our biggest ally at the same time. Even if today it feels like it’s doing more harm than good. [Universe Today viaGeekosystem]
Earth is changing. It’s changing so fast that images like this one, which show our planet’s Arctic polar ice cap in unprecedented detail, could be impossible to capture, as soon as twenty years from now.
If you’re going to use a picture of the Earthto talk about climate change, it might as well be one of the highest resolution photos of the planet ever taken. This composite image, stitched together from fifteen photographs captured by NASA’s recently launched Suomi NPP satellite, is exactly that.
Released yesterday on the NASA Goddard Photo Stream, the image is the latest in a series of incredibly detailed views of our planet’s surface. This particular vantage point captures the planet’s northernmost latitudes in greater detail than any image in history.
But as Smithsonian Magazine’s Colin Schultzpoints out, that’s hardly the most significant thing about this photo:
The most intriguing aspect of the new Arctic image, though, is that this could be one of the last times we’ll be able to get a picture like this.
Sea ice in the Arctic is disappearing blazingly fast, and by June the summer melt season is usually well underway.
Schultz includes the two images shown hereto illustrate how perennial sea ice (that portion of the Arctic ice cap which survives through summer) has declined from 1980 to 2012. It’s a dramatic picture, but it does little to portray the cap’s steady deterioration over the last several decades.
That’s why I’ve thrown in the video featured here, which I think does a better job of depicting what Nicola Jones characterizes as a decades-long march “towards an ice-free Arctic” in this 2011 issue of Nature Climate Change:
The trend for summer sea-ice extent since 1970 has been downwards, with the past five years (2007–2011) being the lowest of the bunch. The Northwest Passage that links the Pacific Ocean to the Atlantic Ocean through the islands of northern Canada is now clear of ice and open to ships for weeks to months, as is the Northeast Passage that links northern Russia to the eastern side of Greenland.
The rate of ice disappearance is faster than models predicted: the last round of models from the Intergovernmental Panel on Climate Change predicted that the Arctic Ocean would be free of floating summer ice by 2070–2100, but in reality it looks likely to happen between 2030 and 2050. “2030 may be more realistic,” says Walter Meier of the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.
This is a very special version of the Blue Marble: Earth captured on its entirety from an altitude of 512 miles (824 kilometers) over the North Pole. Humanity has never had an image so detailed of our home planet from this unique perspective.
Here you can clearly see Britain, the whole of Europe, with Spain kissing Northern Africa, the entire Mediterranean Sea, the Red Sea, and almost all of Asia, plus Greenland and North America on the top.
The Arctic view of the Blue Marble is not a single photo. Like the other Blue Marbles—except for the original, which was a photo taken by the Apollo 17 crew on December 7, 1972, at a distance of about 45,000 kilometres—it took 15 orbits to “gather the pixels for this synthesized view of Earth,” according to NASA.
Those pixels were captured by the Visible Infrared Imaging Radiometer Suite (VIIRS)on board the Suomi National Polar-orbiting Partnership satellite. The VIIRS is a 22-band radiometer designed to take photographs on infrared and visible light. It also takes “radiometric measurements of the land, atmosphere, cryosphere, and oceans” and it’s capable of measuring “cloud and aerosol properties, ocean color, sea and land surface temperature, ice motion and temperature, fires, and Earth’s albedo,” our home planet’s sunlight reflection coefficient.
The Suomi NPP—named after American meteorologist Verner E. Suomi—was launched on top of a Delta II rocket from Vandenberg Air Force Base in California on October 28, 2011. It’s being operated by the US National Oceanic and Atmospheric Administration. [Flickr]
We know a lot about the history of life on Earth, but how it began is still one of our greatest scientific mysteries. One hypothesis is that life actually originated on another planet, and many scientists today take the idea quite seriously. Though it sounds like the plot from recent scifi movie Prometheus, it’s an old idea that even the celebrated nineteenth century physicist Lord Kelvin and Nobel winning geneticist Francis Crick have advocated. That’s right — the evolution of life might have its beginnings on another planet.
Over 120 years ago, Kelvin shocked the British scientific community in a speech about what he called “panspermia,” where he suggested that life might have come from planets smashing into each other and sending bits of life hurtling through space. He and a few colleagues had hit upon this notion after observing the massive 1880 eruption of a volcano on Krakatoa. To be more precise, they observed the aftermath of the volcano, which completely sterilized the island. No life was left at all. But then, within months, seedlings began to sprout and life took hold again.
Where had that life come from? To naturalists of the nineteenth century, it was obvious that it had drifted there from nearby islands. Seeds and insects blown on the wind, or floating on the tides, had begun the process of re-greening the stricken landscape. This got Kelvin thinking about the origin of life on Earth. Couldn’t the same thing happen to barren planets drifting in space? Perhaps life had drifted to Earth on the stellar winds.
Aliens Seeded the Planet with Life
Today, we know that most life wouldn’t survive the trip through space. It would be bombarded by radiation and subjected to hard vacuum. But Francis Crick, who was one of the first biologists to identify the structure of DNA, suggested a way around this problem. In a 1972 paper he co-authored with biologist Leslie Orgel called “Directed Panspermia,” Crick suggested that perhaps extraterrestrials had seeded the Earth with microbes sent in specialized spaceships that would protect the microbes. This is an idea we see a lot in science fiction, including Prometheus. Still, Crick and Orgel didn’t imagine aliens dribbling DNA into our water supply — they suggested it might have been sent out in automated probes, perhaps with a kind of “missionary zeal.”
The problem, which Crick and Orgel discuss in the paper, is that it’s incredibly hard to prove this hypothesis, or even to gather evidence one way or the other. That’s why most scientists who study panspermia don’t have much to say about the directed panspermia scenario. “It’s not completely ridiculous,” Purdue geophysicist Jay Melosh told io9. “It’s fun to speculate about, but it’s not the subject of really respectable scientific research because there’s no evidence.”
That said, Melosh and many other scientists do think panspermia might be part of the solution to the mystery of how life began.
We Come from Mars (or Europa)
Directed panspermia is simply the most unlikely version of a story that is actually quite plausible. Take out the aliens and the spaceships, and you still have many possible ways that microbes from other worlds might have made it to Earth. And if those microbes came from nearby, the panspermia scenario becomes even more plausible.
Cal Tech geologist Joe Kirschvink has suggested that Mars is a likely origin for life in the solar system because it would have been habitable long before Earth was. 4 billion years ago, when Earth was still a roiling cauldron of methane and magma, Mars was a stable, cool planet covered in vast oceans. It would have been the perfect place for microbial life to take hold. But how did that life make it all the way from the seas of Mars to the seas of Earth? Most likely, meteorites crashing into Mars would send fragments of the planet’s surface back into space — packed with millions of microbes. In fact, around the time that Mars might have been developing life, the solar system was undergoing what astronomers call the “late heavy bombardment,” a time of countless intense meteorite strikes.
Purdue geologist Melosh, who has spent most of his career studying meteorite impacts, has actually done experiments where he and a team recreated what might have happened when meteorites slammed into Mars billions of years ago, sending ejecta out of the atmosphere and eventually all the way to Earth. This process is sometimes called “ballistic panspermia,” or “lithopanspermia,” because it depends on rocks being ejected into space. To recreate one part of this process in their experiments, Melosh and his team shot a bacteria-covered rock with an aluminum projectile moving at 5.4 km per second, and the shattered chunks flew over a kilometer. The bacteria survived the trauma of what Melosh and his team called “extremes of compressional shock, heating, and acceleration.”
After several of these tests, Melosh and his colleagues were certain that microbes could survive one of the most destructive parts of the ballistic panspermia journey:
A lot [of the microbes] would die, but a lot would survive in a dormant state. Their journey would take possibly millions of years. But it’s as if atmospheres are almost designed for this transfer of life. The meteorite comes from Mars, full of microbes protected from radiation by the rock. It enters Earth’s atmosphere, and as it comes in at high speed the outside melts because of friction and gets hot, but the inside is protected just like a spacecraft capsule. The microbes inside are protected. Then the aerodynamic forces in the lower atmosphere fracture the meteorite, exposing the interior.
The rock fragments rain over the land, and the surviving microbes can take hold.
Most scientists who subscribe to this idea suggest that Mars is the likely source for a ballistic panspermia event, though Melosh isn’t ruling out Jupiter’s moon Europa either. Astronomers believe Europa harbors vast oceans beneath a thick layer of ice, and it’s very possible that a meteorite could have crashed there, sending microbe-laced chunks of rocky ice into the inner solar system. Still other scientists suggest that life could even jump from one star system to another, and a recent paper on the topic explores how this could happen in star clusters. Still, it’s not likely that Earth was seeded from beyond the system — unless aliens were behind it.
A Valid Scientific Hypothesis
A big question is why scientists are entertaining this idea at all. Doesn’t it seem outlandish? Perhaps, but then again so is the sudden appearance of life on Earth over 3.5 billion years ago. How did we go from lifeless puddles of chemicals to strings of self-reproducing DNA on a planet that was at the time so inhospitable?
Panspermia doesn’t answer this question — we still aren’t sure how the life switch got flipped — but it could help explain the conditions where that life evolved.
NASA planetary scientist Chris McKayoffered io9 a terrific, point-by-point explanation of why panspermia is, as he put it, “a valid scientific hypothesis” worth taking seriously:
1. The geological evidence for the earliest life on Earth is very early, soon after the end of the late bombardment. There is good evidence for life on Earth at 3.5 billion years ago, indirect evidence at 3.8 billion. The end of the late heavy bombardment is 3.8 billion years ago.
2. The genetic evidence indicates that the last universal common ancestor (LUCA) of life could have been roughly 3.5 billion years ago (but with large uncertainties) and that LUCA was a fairly sophisticated life form in terms of metabolic and genetic capabilities.
1 and 2 together give the impression that life appeared on Earth soon after the formation of suitable environments and it appears to have come in being remarkably developed – like Athena born fully formed from the head of Zeus.
3. Rocks from Mars have traveled to Earth and the internal temperatures experienced in these rocks during this trip would not have sterilized the interiors. Thus in principle life can be carried from Mars to Earth.
4. Mars did not suffer the large Moon-forming impact that would have been detrimental to the early development of life on Earth.
3 and 4 have lead to the suggestion that Mars would have been a better place for life to start in the early Solar System and it could have then been carried to Earth via meteorites.
5. Organic molecules are widespread in comets, asteroids, and the interstellar medium.
6. Comets could have supported subsurface liquid water environments soon after their formation due to internal heating by decay of radioactive aluminum.
7. As comets move past the Earth they shed dust which settles into Earth’s atmosphere.
5, 6 and 7 have lead to the suggestion that life could have started in the interstellar medium or in small bodies such as comets and then been carried to the Earth by comet dust.
So, yes panspermia is a valid scientific hypotheses and warrants further investigation.
We Are Not Alone
And as we engage in that investigation, maybe we’ll discover more than we bargained for. After all, if we owe our existence to life on other planets in our solar system, that makes a strong case for life outside it too. SETI astronomer Jill Tarter told io9 via email:
I think that intelligent life here on Earth is a proof of concept that it could exist elsewhere, but we will not know unless we search systematically and exhaustively enough to accumulate sufficient information to justify significant null result. Remember the last sentence of the 1959 Cocconi and Morrison paper [published in Nature]: “The probability of success is difficult to estimate, but if we never search, the chance of success is zero.”
The search for life’s origins on Earth could ultimately lead to the discovery of extraterrestrial life, too.
References linked in the text.
Top illustration by 1@Eraxion/Pond5
Probes landing via NASA
Tree egg by Shutterstock