How did life arise on Earth? How did it survive the Hadean eon, a time when repeated massive impacts excavated craters thousands of kilometres in diameter into the Earth’s surface? Those impacts turned the Earth into a hellish place, where the oceans turned to steam, and the atmosphere was filled with rock vapour. How could any living thing have survived?
Ironically, those same devastating impacts may have created a vast subterranean haven for Earth’s early life. Down amongst all those chambers and pathways, pumped full of mineral-rich water, primitive life found the shelter and the energy needed to keep life on Earth going. And the evidence comes from the most well-known extinction event on Earth: the Chicxulub impact event.
Plate tectonics have played a vital role in the geological evolution of our planet. In addition, many scientists believe that Earth’s geologically activity may have played an important role in the evolution of life – and could even be essential for a planet’s habitability. For this reason, scientists have long sought to determine how and when Earth’s surface changed from molten, viscous rock to a solid crust that is constantly resurfacing.
When an extraterrestrial object slams into the Earth, it sends molten rock high into the atmosphere. That debris cools and re-crystallizes and falls back down to Earth. Tiny glass beads that form in this process are called microtektites, and researchers in Florida have found microtektites inside fossilized clams.
Ever wonder what your refrigerator’s impacting at the speed of a tank artillery shell would do to the Moon? The Lunar Reconnaissance Orbiter’s (LRO) primary camera has provided an image of just such an event when it located the impact site of another NASA spacecraft, the Lunar Atmosphere and Dust Environment Explorer (LADEE). The fridge-sized LADEE spacecraft completed its final Lunar orbit on April 18, 2014, and then crashed into the far side of the Moon. LADEE ground controllers were pretty certain where it crashed but no orbiter had found it until now. With billions of craters across the lunar surface, finding a fresh crater is a daunting task, but a new method of searching for fresh craters is what found LADEE.
The primary purpose of the LADEE mission was to search for lunar dust in the exceedingly thin atmosphere of the Moon. NASA Apollo astronauts had taken notes and drawings of incredible spires and rays of apparent dust above the horizon of the Moon as they were in orbit. To this day it remains a mystery although LADEE researchers are still working their data to find out more.
The LRO spacecraft has been in lunar orbit since 2007. With the LROC Narrow Angle Camera, LRO has the ability to resolve objects less than 2 feet across, and it was likely just a matter of finding time to snap and to search photos for a tiny impact crater.
However, the LROC team recently developed a new algorithm in software to search for fresh craters. Having a good idea where to begin the search, they decided to search for LADEE and quickly found it. The LROC team said the impact site is “about half a mile (780 meters) from the Sundman V crater rim with an altitude of about 8,497 feet (2,590 meters) and was only about two tenths of a mile (300 meters) north of the location mission controllers predicted based on tracking data.” Sundman Crater is about 200 km (125 miles) from a larger crater named Einstein.
The LADEE impact site is within 300 meters of the location estimated by the LADEE team. The ground control team at Ames Research Center knew the location very well within just hours after the time of the planned impact. They had to know LADEE’s location in orbit with split-second accuracy and also know very accurately the altitude of the terrain LADEE was skimming over. LADEE was traveling at 1699 meters per second (3,800 mph, 5,574 feet/sec) upon impact.
But still, finding something as small as this crater can be difficult.
Looking at these images, the scale of lunar morphology is very deceiving. Craters that are 10 meters in diameter can be mistaken for 100 meter or even 1000 meters. The first image and third images (below) in this article are showing only a small portion of the external slope of the eastern rim of Sundman V, the satellite crater to the southeast of crater Sundman. Sundman V is 19,000 meters in diameter (19 km, 11.8 miles) whereas the first image is only 223 meters across.
The following image, which is the ratioing of “before” and “after” impact images by LROC, clearly reveals the impact scar from LADEE. LADEE’s crater is only approximately 10 feet in diameter (3 m) with the ejecta fanning out 200 meters to the west by northwest. LADEE was traveling westward across the face of the Moon that we see from Earth, reached the western limb and finally encountered Sundman.
In the third image of this article (above), only a 1000 meter square view of the outer slope of Sundman V’s eastern rim is seen. Rather than take the difference between the two images, which is essentially what your eye-brain does with an image pair, LROC engineers take the ratio which effectively raises the contrast dramatically. Sundman V crater is on the far side of the Moon but very near the limb. At times, due to lunar libration, this site can be seen from the Earth. In the Lunar Orbiter image, below, Sundman and satellites J & V are marked. The red circle in the image below is the area in which LROC’s high resolution images reside. Furthermore, the famous Arizona meteor crater east of Flagstaff would also easily fit inside the circle.
The discovery so close to the predicted impact site confirmed how accurately the LADEE team could model the chaotic orbits around the Moon – at least during short intervals of time. Gravitationally, the Moon is truly like Swiss cheese. The effects of upwelling magma during its creation, the effects of the Earth’s tidal forces, and all the billions of asteroid impacts created a very chaotic gravitational field. Where the lunar surface is higher or more dense, gravity is stronger and vice-versa. LADEE struggled to maintain an orbit that would not run into the Moon. Without a constant vigil by Ames engineers, LADEE’s orbit would be shifted and rotated relative to the Moon’s surface until it eventually would intersect the Lunar surface – run into the Moon. Eventually, this had to happen as LADEE ran out of propulsion fuel.
The method used by the LROC team in its basic approach is by no means new. Clyde Tombaugh used a blink comparator to search for Planet X for several months and many frame pairs of the night sky. The comparator would essentially show one image and then a second of the same view taken a few nights apart to Clyde’s eye. Tombaugh’s eye and brain could process the two images and identify slight shifts of an object from one frame to the other. Stars are essentially fixed, don’t move but objects in our solar system do move in the night sky over hours or days. In the same way, the new software employed by LROC engineers takes two images and compares them mathematically. A human is replaced by a computer and software to weed out the slightest changes between a pair of images; images of the same area but spaced in time. Finding changes on the surface of a body such as the Moon or Mars is made especially difficult because of the slightest changes in lighting and location of the observer (the spacecraft). The new LROC software marks a new step forward in sophistication and thus has returned LADEE back to us.
The following Lunar Orbiter image from the 1960s is high contrast and reveals surface relief in much more detail. Einstein crater is clearly seen, as is Sundman with J and V satellite craters on its rim.
It was 20 years ago this past July when images of Jupiter being pummeled by a comet caught the world’s attention. Comet Shoemaker-Levy 9 had flown too close to Jupiter. It was captured by the giant planet’s gravity and torn into a string of beads. One by one the comet fragments impacted Jupiter — leaving blemishes on its atmosphere, each several times larger than Earth in size.
Until that event, no one had seen a comet impact a planet. Now, Mars will see a very close passage of the comet Siding Spring on October 19th. When the comet was first discovered, astronomers quickly realized that it was heading straight at Mars. In fact, it appeared it was going to be a bulls-eye hit — except for the margin of error in calculating a comet’s trajectory from 1 billion kilometers (620 million miles, 7 AU) away.
It took several months of analysis for a cataclysmic impact on Mars to be ruled out. So now today, Mars faces just a cosmic close shave. But this comet packs enough energy that an impact would have globally altered Mars’ surface and atmosphere.
So what should we Earthlings gather from this and other events like it? Are we next? Why or why not should we be prepared for impacts from these mile wide objects?
For one, ask any dinosaur and you will have your answer.
Initially the margin of error in the trajectory was large, but a series of observations gradually reduced the error. By late summer 2014, Mars was in the clear and astronomers could confidently say the comet would pass close but not impact. Furthermore, as observations accumulated — including estimates of the outpouring of gases and dust — comet Siding Spring shrunk in size, i.e. the estimates of potentially tens of kilometers were down to now 700 meters (4/10th of a mile) in diameter. Estimates of the gas and dust production are low and the size of the tail and coma — the spherical gas cloud surrounding the solid body — are small and only the outer edge of both will interact with Mars’ atmosphere.
Yet, this is a close call for Mars. We could not rule out a collision for over six months. While this comet is small, it is moving relative to Mars at a speed of 200,000 kilometers/hour (125,000 mph, 56 km/sec). This small body packs a wallop. From high school science or intro college Physics, many of us know that the kinetic energy of an object increases by the square of the velocity. Double the velocity and the energy of the object goes up by 4, increase by 3 – energy increases by 9.
So the close shave for Mars is yet another wake up call for the “intelligent” space faring beings of the planet Earth. A wake up call because the close passage of a comet could have just as easily involved Earth. Astronomers would have warned the world of a comet heading straight for us, one that could wipe out 70% of all life as happened 65 million years ago to the dinosaurs. Replace dinosaur with humans and you have the full picture.
Time would have been of the essence. The space faring nations of the world — those of the EU, and Russia, the USA, Japan and others — would have gathered and attempted to conceive some spacecrafts with likely nuclear weapons that could be built and launched within a few months. Probably several vehicles with weapons would be launched at once, leaving Earth as soon as possible. Intercepting a comet or asteroid further out would give the impulse from the explosions more time to push the incoming body away from the Earth.
There is no way that humanity could sit on their collective hands and wait for astronomers to observe and measure for months until they could claim that it would just be a close call for Earth. We could imagine the panic it would cause. Recall the scenes from Carl Sagan’s movie Contact with people of every persuasion expressing at 120 decibels their hopes and fears. Even a small comet or asteroid, only a half kilometer – a third of a mile in diameter would be a cataclysmic event for Mars or Earth.
But yet, in the time that has since transpired from discovery of the comet Siding Spring (1/3/2013), the Chelyabinsk asteroid (~20 m/65 ft) exploded in an air burst that injured 1500 people in Russia. The telescope that discovered Comet Siding Spring was decommissioned in late 2013 and the Southern Near-Earth Object Survey was shutdown. This has left the southern skies without a dedicated telescope for finding near-Earth asteroids. And proposals such as the Sentinel project by the B612 Foundation remain underfunded.
We know of the dangers from small celestial bodies such as comets or asteroids. Government organizations in the United States and groups at the United Nations are discussing plans. There is plenty of time to find and protect the Earth but not necessarily time to waste.
In case you need a reminder that the solar system was a harsh place to grow up, the early Earth looks like it was in the middle of a shooting gallery in this model. The map that you see above shows a scenario for where researchers believe asteroids struck our planet about four billion to 4.5 billion years ago, which is very early in the Earth’s five-billion-year history.
The research reveals the surface of the Earth repeatedly being churned by these impacts as the young solar system came together, with small rocks gradually coalescing into planetesimals. Much of the leftover debris peppered the planets, including our own.
“Prior to approximately four billion years ago, no large region of Earth’s surface could have survived untouched by impacts and their effects,” stated Simone Marchi, who led the research and works at the Southwest Research Institute in Colorado.
“The new picture of the Hadean Earth emerging from this work has important implications for its habitability,” added Marchi, who is also senior researcher at NASA’s Solar System Exploration Research Virtual Institute.
In this dangerous early period, the researchers estimate the Earth was smacked by 1-4 asteroids or comets that were more than 600 miles (966 kilometers) wide — enough to wipe out life across the planet. They also believe that between 3-7 impactors were more than 300 miles (482 kilometers) wide, which would evaporate oceans across the world.
“During that time, the lag between major collisions was long enough to allow intervals of more clement conditions, at least on a local scale,” added Marchi. “Any life emerging during the Hadean eon likely needed to be resistant to high temperatures, and could have survived such a violent period in Earth’s history by thriving in niches deep underground or in the ocean’s crust.”
To produce the model, the researchers took a recent model of lunar impacts and applied it to Earth. The moon’s scarred surface helps them estimate what happened on our own planet, they said, because the craters provide an “absolute impactor flux” separate from any models that talk about how the Earth came together. Recall that erosion on the moon is very slow, providing accessible records of things that happened millions or billions of years ago.
On the morning of February 15, 2013, people in western Russia were dazzled by an incredibly bright meteor blazing a fiery contrail across the sky. A few minutes later a shockwave struck, shaking the buildings and blowing out windows. 1,500 people went to the hospital with injuries from shattered glass. This was the Chelyabinsk meteor, a chunk of rock that struck the atmosphere going almost 19 kilometers per second. Astronomers estimate that it was 15-20 meters across and weighed around 12,000 metric tonnes.
Here’s the crazy part. It was the largest known object to strike the atmosphere since the Tunguska explosion in 1908. Catastrophic impacts have shaped the evolution of life on Earth. Once every 65 million years or so, there’s an impact so destructive, it wipes out almost all life on Earth. The bad news is the Chelyabinsk event was a surprise. The asteroid came out of nowhere. We need to find all the potential killer asteroids, and understand what risks we face.
“I’m Ned Wright…”
That’s Dr. Ned Wright. He’s a professor of physics and astronomy at UCLA, and the Primary Investigator for the Wide-field Infrared Survey Explorer mission; a space telescope that looks for low temperature objects in the infrared spectrum.
“I think the best way to protect the Earth from asteroids is to get out and look very assiduously to find all the hazardous asteroids. Although astronomers have been finding and cataloging asteroids for decades, we still only have a fraction of the dangerous asteroids tracked. The large continent destroyers have mostly been found, but there’s a whole class of smaller, city killers out there, and they’re almost entirely unknown. There are… these dark asteroids that may not be the most dominant part of the population but they certainly can be a very hazardous subset, it’s important to do the observations in the infrared. So you actually, instead of looking for the ones that reflect the most light, you look for the ones that have the biggest area and therefore the ones that are the heaviest and can do the most damage. And so, I think that an infrared survey is the way to go.”
“In the infrared wavelengths, we can find these objects because they’re large, not because they’re bright. And to really do this right, we need a space-based infrared observatory capable of surveying vast areas of the sky, searching for anything moving.”
The WISE mission has been offline for a few years, but WISE is actually being reactivated right now to look for more Near Earth Objects, so we’re currently cooled down to 93 K, and when we get to 73 K, which is where we were when we turned off in 2011 we’ll probably be able to go out and find more Near Earth Objects.
Note: this interview was recorded in November, 2013. WISE resumed operations in December 23, 2013
But to really find the vast majority of dangerous asteroids, you need a specialized mission. One proposal is the Near Earth Asteroid Camera, or NEOCam because it’d be much better to have a telescope that was slightly colder than the 73 K WISE is with coolant, and you can do that by getting away from the Earth. and so the NEOcam telescope is designed to go a million and a half kilometers from the Earth and therefore it would be quite cold, about 35 K and at that temperature, it can operate longer into the infrared and do a very sensitive survey for asteroids.
NEOCam is just one idea. There’s also the Sentinel proposal from B612 Foundation. It’s also an infrared survey and it would go into an orbit like Venus’ orbit, so it would be hundreds of millions of km away from Earth, but not orbiting around Venus, because that would be too hot as well and then with an infrared telescope, it would survey for asteroids.
NEOCam and Sentinel would operate for years, scanning the sky in the infrared to find all of the really hazardous asteroids. You wouldn’t be able to necessarily find the ones the size of the one that hit Chelyabinsk, and so that broke some windows, but it didn’t kill people, didn’t knock buildings down. So that’s definitely a hazard, but not the city destroying hazard that a 100 meter diameter asteroid would be.
We live in a cosmic shooting gallery. Rocks from space impact the Earth all the time, our next dangerous asteroid is out there, somewhere. Let’s build a space-based infrared survey mission so we can find it, before it finds us.
If you were looking up at the Moon on March 17, 2013 at 03:50:55 UTC, you might have seen one of the brightest “lunar flashes” ever witnessed. And it would have been visible with just the naked eye.
“On March 17, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium,” says Bill Cooke of NASA’s Meteoroid Environment Office. “It exploded in a flash nearly 10 times as bright as anything we’ve ever seen before.”
The scientists estimate that the flash came from a 40 kg meteoroid measuring 0.3 to 0.4 meters wide hitting the Moon, likely traveling about 90,000 km/hr (56,000 mph.) The resulting explosion packed as much punch as 5 tons of TNT.
(FYI, lunar meteors hit the ground with so much kinetic energy that they don’t require an oxygen atmosphere to create a visible explosion. The flash of light comes not from combustion but rather from the thermal glow of molten rock and hot vapors at the impact site.)
The crater could be as wide as 20 meters. The scientists for the Lunar Reconnaissance Orbiter are hoping to image the impact site the next time the spacecraft passes over the area. It should be relatively easy to spot, and lunar scientists are always on the lookout for recent impacts. Additionally, comparing the size of the crater to the brightness of the flash would give researchers a valuable “ground truth” measurement to validate lunar impact models.
Were you observing the Moon that night? Universe Today’s David Dickinson pointed out to me that it is quite possible an amateur could have caught it; however no amateur images have surfaced yet. The Moon would’ve been a waxing crescent and visible to the Pacific region and US West Coast at the time. If you have archived images or video, it might be worth a look. And we’d love to hear from you if you happened to catch anything! NASA said the impact site would have glowed like a 4th magnitude star for about one second.
During the past 8 years, Cooke and a team of NASA astronomers have been monitoring the Moon for signs of explosions caused by meteoroids hitting the lunar surface.
Ron Suggs, an analyst at the Marshall Space Flight Center, was the first to notice the March 17th impact in a digital video recorded by one of the monitoring program’s 14-inch telescopes. “It jumped right out at me, it was so bright,” he said.
During the 8 years of observations, the team has found that the flashes on the Moon are more common than anyone expected, with hundreds of detectable impacts occurring every year.
Since the monitoring program began in 2005, NASA’s lunar impact team has detected more than 300 strikes, most orders of magnitude fainter than the March 17th event. Statistically speaking, more than half of all lunar meteors come from known meteoroid streams such as the Perseids and Leonids. The rest are sporadic meteors–random bits of comet and asteroid debris of unknown parentage.
Cooke believes the lunar impact might have been part of a much larger event.
“On the night of March 17, NASA and University of Western Ontario all-sky cameras picked up an unusual number of deep-penetrating meteors right here on Earth,” he said. “These fireballs were traveling along nearly identical orbits between Earth and the asteroid belt.”
This means Earth and the Moon were pelted by meteoroids at about the same time.
“My working hypothesis is that the two events are related, and that this constitutes a short duration cluster of material encountered by the Earth-Moon system,” said Cooke.
One of the goals of the lunar monitoring program is to identify new streams of space debris that pose a potential threat to the Earth-Moon system. The March 17th event seems to be a good candidate.
A 20-km asteroid has just been predicted to hit Earth and you want to know if a. You should run for it, b. You should call Bruce Willis, or c. You can rest easy because your part of the world won’t be affected. All you have to do is input the parameters of the asteroid on the recently updated “Impact Earth” website, and you’ll find out everything about what an impactor will do to Earth, including an estimate of the size of the crater, how far away you’ll need to be in order to avoid being affected by the impact (and if that is possible), tsunami wave height, and other details of the subsequent disaster. The fun part is, you can simulate the destruction of Earth multiple times, without hurting anyone.
The original Impact Earth website was created in 2002 for use by NASA and homeland security. The new version, built in a collaboration between Purdue University and Imperial College London, is more user-friendly for the general public, as well as providing more visual details of an impact. Besides being rather fun to play around with, the website is highly educational about what a various sized impacts would do Earth, depending on if it hit ground or water.
Ever since our recent encounter with asteroid 2008 TC3 — the first asteroid that was correctly predicted to hit our planet — I’ve had impact craters on the brain. Earth has about 175 known impact craters, but surely our planet has endured more bashing than that in its history. All the other terrestrial planets and moons in our solar system are covered by impact craters. Just look at our Moon through a telescope or binoculars, or check out the recent images of Mercury sent back by the MESSENGER spacecraft, or pictures of Mars from the armada of spacecraft orbiting the Red Planet, and you’ll see that impact craters are the most common landforms in our solar system.
Here’s my list of Earth’s Ten Most Impressive Impact Craters, starting with #1. the largest and oldest known impact crater, Vredefort Crater, shown above, located in South Africa. It is approximately 250 kilometers in diameter and is thought to to be about two billion years old. The Vredefort Dome can be seen in this satellite image as a roughly circular pattern. What an impact that must have been!
2. Manicouagan Crater: fifth largest known impact crater. This crater is located in Quebec, Canada. It was created about 212 million years ago. Now, it is an ice-covered lake about 70 km across. This image, taken by space shuttle astronauts, shows an outer ring of rock. Close up, the rock reveals clear signs of having been melted and altered by a violent collision. The original rim of the crater, though now eroded away, is thought to have had a diameter of about 100 km.
3. Chicxulub Crater, third largest and possible dinosaur killer. The third largest impact crater lies mostly underwater and buried underneath the Yucatán Peninsula in Mexico. At 170km (105 miles) in diameter, the impact is believed to have occurred roughly 65 million years ago when a comet or asteroid the size of a small city crashed, unleashing the equivalent to 100 teratons of TNT. Likely, it caused destructive tsunamis, earthquakes and volcanic eruptions around the world, and is widely believed to have led to the extinction of dinosaurs, because the impact probably created a global firestorm and/or a widespread greenhouse effect that caused long-term environmental changes.
4. Aorounga Crater: possible triple crater. The main Aorounga Crater in Chad, Africa, visible in this radar image from space, shows a concentric ring structure that is about 17 kilometers wide. But, this crater might have been formed as the result of a multiple impact event. A second crater, similar in size to the main crater, appears as a circular trough in the center of the image. And a third structure, also about the same size, is seen as a dark, partial circular trough on the right side of the image. The proposed crater “chain” could have formed when a 1 km to 2 km (0.5 mile to 1 mile) diameter object broke apart before impact. Ouch!
5. Clearwater Craters: two for the price of one. Twin, lake-filled impact craters in Quebec, Canada were probably formed simultaneously, about 290 million years ago, by two separate but probably related meteorite impacts. The larger crater, Clearwater Lake West has a diameter of 32 km, and Clearwater Lake East is 22 km wide.
6. Barringer Crater: well preserved. While this crater isn’t all that big, what’s most impressive about Barringer Crater in Arizona (USA) is how well preserved it is. Measuring 1.2 km across and 175 m deep, Barringer Crater was formed about 50,000 years ago by the impact of an iron meteorite, probably about 50 m across and weighing several hundred thousand tons. Most of the meteorite was vaporized or melted, leaving only numerous, mostly small fragments with in the crater and scattered up to 7 km from the impact site. Only about 30 tons, including a 693-kg sample, are known to have been recovered.
7. Wolfe Creek Crater, well preserved, too. Another relatively well-preserved meteorite crater is found in the desert plains of north-central Australia. Wolfe Creek crater is thought to be about 300,000 years old and is 880 meters across and and about 60 meters deep. It’s partially buried under the wind-blown sand of the region, and although the unusual landform was well-known to the locals, scientists didn’t find the crater until 1947.
8. Deep Bay Crater: deep and cold. Deep Bay crater is located in Saskatchewan, Canada. The bay is a strikingly circular 13 km wide impact crater and is also very deep (220 m). It is part of an otherwise irregular and shallow lake. The age of the crater is estimated to be 99 million years old.
9. Kara-Kul Crater: high altitude crater. This crater was formed about 10 million years ago, and is located in Tajikistan, near the Afghan border. In total, the crater is about 45 km in diameter and is partially filled with a 25 km-wide lake. This might be the “highest” impact crater, almost 6,000 m above sea-level in the Pamir Mountain Range. It was found only recently from satellite images.
10. Bosumtwi Crater: built of bedrock. The last crater on our tour of impressive impact craters is this located in Ghana, Africa. It is about 10.5 km in diameter and about 1.3 million years old. The crater is filled almost entirely by water, creating Lake Bosumtwi. The lakebed is made of crystalline bedrocks.