This graphic depicts the passage of asteroid 2014 RC past Earth on September 7, 2014. At time of closest approach, the space rock will be about one-tenth the distance from Earth to the moon. Times indicated on the graphic are Universal Time. Subtract 4 hours for Eastern Daylight Time. Credit: NASA/JPL-Caltech
Guess who’s dropping by for a quick visit this weekend? On Sunday, a 60-foot-wide (20-meters) asteroid named 2014 RC will skim just 25,000 miles (40,000 km) from Earth. That’s within spitting distance of all those geosynchronous communication and weather satellites orbiting at 22,300 miles.
Size-wise, this one’s similar to the Chelyabinsk meteorite that exploded over Russia’s Ural Mountains region in February 2013. But it’s a lot less scary. 2014 RC will cleanly miss Earth this time around, and although it’s expected back in the future, no threatening passes have been identified. Whew!
2014 RC will pass along the outer edge of the geosynchronous satellite belt, home to many weather and communications satellites. The chance of a hit is close to infinitesimal. Click for more information and detailed finder charts. Credit: SatFlare
NEOs or Near Earth Asteroids are defined as space rocks that come within about 28 million miles of Earth’s orbit. Nearly once a month astronomers discover an Earth-crossing asteroid that passes within the moon’s orbit. In spite of hype and hoopla, none has threatened the planet. As of February 2014, we know of 10,619 near-Earth asteroids. It’s estimated that 93% of all NEOs larger than 1 km have been discovered but 99% of the estimated 1 million NEOs 100 feet (30-meters) still remain at large.
No surprise then that new ones pop up routinely in sky surveys. Take this past Sunday night for example, when the Catalina Sky Survey nabbed 2014 RA, a 20-foot (6-meter) space rock that whistled past Earth that evening at 33,500 miles (54,000 km). It’s now long gone.
Artist view of an asteroid (with companion) passing near Earth. Credit: P. Carril / ESA
2014 RC was picked up on or about September 1-2 by both the Catalina Sky Survey and Pan-STARRS 1 survey telescope atop Mt. Haleakala in Maui. The details are still being worked out as to which group will take final discovery credit. Based on current calculations, 2014 RC will pass closest to Earth around 2:15 p.m. EDT (18:15 UT) on Sunday, September 7th. When nearest, the asteroid is expected to brighten to magnitude +11.5 – too dim for naked eye observing but visible with a good map in 6-inch and larger telescopes.
Seeing it will take careful planning. Unlike a star or planet, this space rock will be faint and barreling across the sky at a high rate of speed. Discovered at magnitude +19, 2014 RC will brighten to magnitude +14 during the early morning hours of September 7th. Even experienced amateurs with beefy telescopes will find it a challenging object in southern Aquarius both because of low altitude and the unwelcome presence of a nearly full moon.
64-frame movie showing Toutatis tumbling through space only 4.3 million miles from Earth on Dec. 12-13. Credit: NASA/Goldstone radar
Closest approach happens in daylight for North and South America , but southern hemisphere observers might spot it with a 6-inch scope as a magnitude +11.5 “star” zipping across the constellations Pictor and Puppis. 2014 RC fades rapidly after its swing by Earth and will quickly become impossible to see in all amateur telescopes, though time exposure photography will keep the interloper in view for a few additional hours.
2014 RC accelerates across the sky between 4 a.m. to 4 p.m EDT September 7 in this path created by Gianluca Masi using SkyX Pro software and the latest positions from JPL.
Most of us won’t have the opportunity to run outside and see the asteroid, but Gianluca Masi and his Virtual Telescope Project site will cover it live starting at 6 p.m. EDT (22:00 UT). Lance Benner, who researches radar imaging of near-Earth and main-belt asteroids, hopes to image 2014 RC with 230-foot (70-m) radar dish at the Goldstone complexon September 5-7 and possibly the big 1,000-foot (305-m) radar dish at Arecibo. Both provide images based on radar echoes that show asteroids up close with shapes, craters, ridges and all.
NASA is planning to launch a time capsule aboard the Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer (OSIRIS-REx) spacecraft, which is expected to head to an asteroid in 2016. Credit: Heather Roper/University of Arizona/OSIRIS-REx
What’s your vision for solar system exploration? And how cool would it be to send it literally into the solar system?
NASA is offering its fans the chance to compose a tweet or send a picture showing how we can step out into the cosmos. The best ones among these will be placed aboard a spacecraft that will zoom to an asteroid in 2016.
The “time capsule” will be placed aboard the Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer (OSIRIS-REx). If all goes to plan, it will meet with the asteroid Bennu in 2019, pick up a sample and then return it to Earth in 2023.
And by the way, you can also send your name to Bennu via this form (a joint initiative of NASA and the Planetary Society.) Seems a good chance to get your name off of Earth, until the time when space travel becomes affordable to ordinary citizens.
For more details about the tweets and images time capsule, visit this NASA website. Make sure to submit your message before Sept. 30.
What if Earth had multiple moons? Our world has one large natural satellite, just over a quarter the diameter, 1/50th the volume, and less than 1/80th the mass of our fair world. In fact, the Earth-Moon system has sometimes been referred to as a “binary planet,” and our Moon stands as the largest natural satellite of any planet — that is, if you subscribe to bouncing Pluto and Charon out of “the club” — in contrast to its primary of any moon in our solar system.
But what if we had two or more moons? And are there any tiny “moonlet” candidates lurking out there, awaiting discovery and perhaps exploration?
While historical searches for tiny secondary moons of the Earth — and even “moons of our Moon” — have turned up naught, the Earth does indeed capture asteroids as temporary moons and eject them back into solar orbit from time to time.
Now, a recent paper out of the University of Hawaii written in partnership with the SETI Institute and the Department of Physics at the University of Helsinki has looked at the possible prospects for the population of captured Near-Earth asteroids, and the feasibility of detecting these with existing and future systems about to come online.
The hunt for spurious moons of the Earth has a fascinating and largely untold history. Arthur Upgren’s outstanding book Many Skies devotes an entire chapter to the possible ramifications of an Earth with multiple moons… sure, more moons would be a bane for astrophotographers, but hey, eclipses and transits of the Sun would be more common, a definite plus.
In 1846, astronomer Frederic Petit announced the discovery of a tiny Earth-orbiting moon from Toulouse observatory. “Petit’s Moon” was said to orbit the Earth once every 2 hours and 44 minutes and reach an apogee of 3,570 kilometres and a perigee of just 11.4 (!) kilometres, placing it well inside the Earth’s atmosphere on closest approach.
The announcement (in German) of the discovery of Waltemath’s Moon. “Ein zweiter Mond der Erde” translates into “a second Earth moon.” Credit: Wikimedia Commons image in the public domain.
A slightly more believable claim came from astronomer Georg Waltemath in 1898 for a moon 700 kilometres in size — he claimed it was, of course, a very dark body and not very easily visible — orbiting the Earth at about 2.5 times the distance of the Moon. Waltemath even made an announcement of his discovery, and claimed to have found a third moon of the Earth for good measure.
And a much more dubious claim came from the astrologer Walter Gornold in 1918 of a secondary moon, dubbed Lilith. Apparently, then (as now) astrologers never actually bothered to look at the skies…
Turns out, our large Moon makes a pretty good goaltender, ejecting —and sometimes taking a beating from — any tiny second moon hopeful. Of course, you can’t blame those astronomers of yore entirely. Though none of these spurious moons survived the test of observational verification, these discoveries often stemmed from early efforts to accurately predict the precise motion of the Moon. Astronomers therefore felt they were on the right track, looking for an unseen perturbing body.
Fast forward to the 21st century. Quasi-moons of the Earth, such as 3753 Cruithne, have horseshoe-shaped orbits and seem to approach and recede from our planet as both orbit the Sun. Similar quasi-moons of Venus have also been discovered.
And even returning space junk can masquerade as a moon of Earth, as was the case of J002E3 and 2010 QW1, which turned out to be boosters from Apollo 12 and the Chinese Chang’e-2 missions, respectively.
What modern researchers are looking for are termed Temporarily Captured Orbiters, or TCOs. The study notes that perhaps an average of a few dozen asteroids up to 1 to 2 metres in size are in a “steady state” population that may be orbiting the Earth at any given time on an enter, orbit, and eject sort of conveyor belt. Estimates suggest that a large 5 to 10 metre asteroid is captured every decade so, and a 100 metre or larger TCO is temporarily captured by the Earth every 100,000 years. The study also estimates that about 1% occasionally hit the Earth. And though it wasn’t a TCO, the ability to detect an Earthbound asteroid before impact was demonstrated in 2008 with the discovery of 2008 TC3, less than 24 hours prior to striking in the Sudanese desert.
“There are currently no projects that are solely looking for minimoons at this time,” lead researcher Bryce Bolin of the University of Hawaii told Universe Today. “There are several surveys, such as PanSTARRS, the Catalina Sky Survey and the Palomar Transit Factory that are currently in operation that have the capability of discovering minimoons.”
The convoluted orbit of 2006 RH120 around the Earth-Moon system, to date the only confirmed TCO. Credit: Wikimedia Commons/Ohms law.
We’re getting better at this hazardous asteroid detection business, that’s for sure. The researchers modeled paths and orbits for TCOs in the study, and also noted that collections may “clump” at the anti-sunward L2 opposition point, and the L1 sunward point, with smaller distributions located at the east and west quadrature points located 90 degrees on either side of the Earth. The L2 point in particular might make a good place to start the search.
Ironically, systems such as LINEAR and PanSTARRS may have already captured a TCO in their data and disregarded them in their quest for traditional Near Earth Objects.
“Surveys such as PanSTARRS/LINEAR utilize a filtration process to remove artifacts and false positives in the data as it gets processed through the data pipeline,” Researcher Bryce Bolin told Universe Today. “A common method is to apply a rate of motion cut… this is effective in eliminating many artifacts (which) tend to have a rate of motion as measured by the pipeline which is very high.”
Such systems aren’t always looking for fast movers near Earth orbit that can produce a trail or streak which may reassemble space junk or become lost in the gaps over multiple detection devices. And speaking of which, researchers note that Arecibo and the U.S. Air Force’s Space Surveillance System may be recruited in this effort as well. To date, one definite TCO, named 2006 RH120 has been documented orbiting and departing from the vicinity of the Earth, and such worldlets might make enticing targets for future manned missions due to their relatively low Delta-V for arrival and departure.
An artist’s concept of a possible future asteroid mission near Earth. Credit: NASA.
PanSTARRS-2 saw first light last year in 2013, and is slated to go online for full science operations by the end of 2014. Eventually, the PanSTARRS system will employ four telescopes, and may find a bevy of TCOs. The researchers estimate in the study that a telescope such as Subaru stands a 90% chance of nabbing a TCO after only five nights of dedicated sweeps of the sky.
Finally, the study also notes that evidence miniature moonlets orbiting Earth may lurk in the all sky data gathered by automated cameras and amateur observers during meteor showers. Of course, we’re talking tiny, dust-to-pebble sized evidence, but there’s no lower limit as to what constitutes a moon…
And so, although moons such a “Lilith” and “Petit’s Moon” belong to the annuals of astronomical history, temporary “minimoons” of Earth are modern realities. And as events such as Chelyabinsk remind us, it’s always worthwhile to hunt for hazardous NEOs (and TCOs) that may be headed our way. Hey, to paraphrase science fiction author Larry Niven: unlike the dinosaurs, we have a space program!
Read more about the fascinating history of moons that never were and more in the classic book The Haunted Observatory.
The crescent moon, Saturn and Mars will form a compact triangle in the southwestern sky in this evening August 31st. 3.5º separate the moon and Saturn; Mars and Saturn will be 5º apart. Stellarium
Check it out. Look southwest at dusk tonight and you’ll see three of the solar system’s coolest personalities gathering for a late dinner. Saturn, Mars and the waxing crescent moon will sup in Libra ahead of the fiery red star Antares in Scorpius. All together, a wonderful display of out-of-this-world worlds.
Four dark lunar seas, also called ‘maria’ (MAH-ree-uh), pop out in binoculars. Four featured craters are also highlighted – the triplet of Theophilus, Cyrillus and Catharina and Maurolycus, named after Francesco Maurolico, a 16th century Italian scientist. Credit: Virtual Moon Atlas / Christian LeGrande, Patrick Chevalley
If you have binoculars, take a closer look at the thick lunar crescent. Several prominent lunar seas, visible to the naked eye as dark patches, show up more clearly and have distinctly different outlines even at minimal magnification. Each is a plain of once-molten lava that oozed from cracks in the moon’s crust after major asteroid strikes 3-3.5 billion years ago.
Larger craters also come into view at 10x including the remarkable trio of Theophilus, Cyrillus and Catharina, each of which spans about 60 miles (96 km) across. Even in 3-inch telescope, you’ll see that Theophilus partly overlaps Cyrillus, a clear indicator that the impact that excavated the crater happened after Cyrillus formed.
Close-up of our featured trio of craters. Sharpness indicates freshness. Comparing the three, the Theophilus impact clearly happened after the others. Craters gradually become eroded over time from micrometeorite impacts, solar wind bombardment, moonquakes and extreme day-to-night temperature changes. Credit: Damian Peach
Notice that the rim Theophilus crater is still relatively crisp and fresh compared to the older, more battered outlines of its neighbors. Yet another sign of its relative youth.
Astronomers count craters on moons and planets to arrive at relative ages of their surfaces. Few craters indicate a youthful landscape, while many overlapping ones point to an ancient terrain little changed since the days when asteroids bombarded all the newly forming planets and moons. Once samples of the moon were returned from the Apollo missions and age-dated, scientists could then assign absolute ages to particular landforms. When it comes to planets like Mars, crater counts are combined with estimates of a landscape’s age along with information about the rate of impact cratering over the history of the solar system. Although we have a number of Martian meteorites with well-determined ages, we don’t know from where on Mars they originated.
At least three different impact sequences are illustrated in this photo. Maurolycus appears to lie atop an older crater, while younger, sharp-rimmed craters pock its center and southern rim. Even a 3-inch telescope will show signs of all three ages. Credit: Damian Peach
Another crater visible in 10x binoculars tonight is Maurolycus (more-oh-LYE-kus), a great depression 71 miles (114 km) across located in the moon’s southern hemisphere in a region rich with overlapping craters. Low-angled sunlight highlighting the crater’s rim will make it pop near the moon’s terminator, the dividing line between lunar day and night.
Like Theophilus, Maurolycus overlaps a more ancient, unnamed crater best seen in a small telescope. Notice that Maurolycus is no spring chicken either; its floor bears the scares of more recent impacts.
Putting it all into context, despite their varying relative ages, most of the moon’s craters are ancient, punched out by asteroid and comet bombardment more than 3.8 billion years ago. To look at the moon is to see a fossil record of a time when the solar system was a terrifyingly untidy place. Asteroids beat down incessantly on the young planets and moons.
Despite the occasional asteroid scare and meteorite fall, we live in relative peace now. Think what early life had to endure to survive to the present. Deep inside, our DNA still connects us to the terror of that time.
End of flight fragmentation of the Nov. 18, 2012, fireball over the San Francisco Bay Area (shown in a horizontally mirrored image to depict the time series from left to right). The photographs were taken from a distance of about 40 miles (65 km). Image Credit: Robert P. Moreno Jr., Jim Albers and Peter Jenniskens
What’s the chance of that thump you just heard in your house was a meteorite hitting your roof? That was the case for one family in Novato, California during a fireball event that took place in the north bay area near San Francisco on October 17, 2012.
Researchers have now released new results from analysis of the meteor that fell to Earth, revealing that the “Novato meteorite” was part of numerous collisions over a span of 4 billion years.
There is nothing ordinary about a meteorite whether it just spent 4.4 billion years all alone or spent such time in a game of cosmic pinball, interacting with other small or large bodies of our Solar System. On any given night one can watch at least a couple of meteors overhead burning up, lighting up the sky but never reaching the Earth below. However, in less than two years, Dr. Peter Jenniskens, SETI Institute’s renowned meteor expert was effectively host to two meteorites within a couple hours drive from his office in Mountain View, California.
The first was the Sutter Mill meteorite, a fantastic carbonaceous chondrite full of organic compounds. The second was the Novato meteorite, identified as a L6 chondrite fragmental breccia. which is the focus of new analysis, to be released in a paper in the August issue of Meteoritics and Planetary Science. Early on, it was clear that this meteorite had been a part of a larger asteroidal parent body that had undergone impact shocks.
Analysis of the meteorite was spearheaded by Jenniskens who initially determined the trajectory and orbit of the meteoroid from the Cameras for Allsky Meteor Surveillance (CAMS) which he helped establish in the greater San Francisco bay area. Jenniskens immediately released information about the fireball to local news agencies to ask for the public’s help with the hopes of finding pieces of the meteorite. One resident recalled hearing something hit her roof, and with the help of neighbors, they investigated and soon found the first fragment in their backyard.
Finding fragments was the first step, and over a two year period, the analysis of the Novato meteorite was spread across several laboratories around the world with specific specialties.
Novato N04, found by Bob Verish. The fourth of six fragments of the Novato fireball recovered. Fusion crust from entry into the Earth’s atmosphere is clearly evident. A 1 centimeter cube is shown for size comparison. (Image Credit, B. Verish, cams.seti.org)
Dr. Jenniskens, along with 50 co-authors, have concluded that the Novato meteorite had been involved in more impacts than previously thought. Dr. Qingzhu Yin, professor in the Department of Earth and Planetary Sciences at the University of California, Davis stated, “We determined that the meteorite likely got its black appearance from massive impact shocks causing a collisional resetting event 4.472 billion years ago, roughly 64-126 million years after the formation of the solar system.”
The predominant theory of the Moon’s formation involves an impact of the Earth by a Mars-sized body. The event resulted in the formation of the Moon but also the dispersal of many fragments throughout the inner Solar System. Dr. Qingzhu Yin continued, “We now suspect that the moon-forming impact may have scattered debris all over the inner solar system and hit the parent body of the Novato meteorite.”
Additionally, the researcher discovered that the parent body of the Novato meteorite experienced a massive impact event approximately 470 million years ago. This event dispersed many asteroidal fragments throughout the Asteroid Belt including a fragment from which resulted the Novato meteorite.
The Novato meteorite strewn field determined by Dr. Jenniskens team’s analysis of CAMS allsky images. (Illustration Credit, P. Jenniskens, NASA, SETI – cams.seti.org)
The trajectory analysis completed earlier by Dr. Jenniskens pointed the Novato meteorite back to the Gefion asteroid family. Dr. Kees Welten, cosmochemist at UC Berkeley, was able to further pinpoint the time, drawing the conclusion, “Novato broke from one of the Gefion family asteroids nine million years ago.” His colleague at Berkeley, cosmochemist Dr. Kunihiko Nishiizumialso added, “but may have been buried in a larger object until about one million years ago.”
There was more that could be revealed about history of the Novato meteorite. Dr. Derek Sears a meteoriticist working for the Bay Area Environmental Research Institute in Sonoma, California and stationed at NASA Ames Reserach Center applied his expertise in thermoluminescence. Dr. Sears was involved in the analysis of Lunar regolith returned by the Apollo astronauts using this analysis method.
“We can tell the rock was heated, but the cause of the heating is unclear,” said Dr. Sears, “It seems that Novato was hit again.” As stated in the NASA press release, “Scientists at Ames measured the meteorites’ thermoluminescence – the light re-emitted when heating of the material and releasing the stored energy of past electromagnetic and ionizing radiation exposure – to determine that Novato may have had another collision less than 100,000 years ago.”
From this apparent final collision one hundred thousand years ago, the Novato meteoroid completed over 10,000 orbits of the Sun and with its final Solar orbit, intercepted the Earth, entering our atmosphere and mostly burning up over California. The meteoroid is estimated to have measured 14 inches across (35 cm) and have weighed 176 pounds (80 kg). What reached the ground likely amounted to less than 5 lbs. (~ 2 kg). Only six fragments were recovered and many more remain buried or hidden in Sonoma and Napa counties.
Besides the analysis that revealed the series of likely impact events in the meteoroids history, a team led by Dr. Dan Glavin from NASA Goddard Space Flight Center undertook analysis in search of amino acids, the building blocks of life. They detected non-protein amino acids in the meteorite that are very rare on Earth. Dr. Jenniskens emphasized that the quick recovery of the fragments by scores of individuals that searched provided pristine samples for analysis.
The impact dent on the rooftop of the Webber home in Novato. Luis Rivera points to the dent. (Image Credit, P.Jenniskens, L.Rivera, cams.seti.org)
Robert P. Moreno, Jr. in Santa Rosa, CA photographed the fireball in greatest detail with a high resolution camera. Several other photos were brought forward from other vantage points. Dr. Jenniskens stated, “These photographs show that this meteorite – now one of the best studied meteorites of its kind – broke in spurts, each time creating a flash of light as it entered Earth’s atmosphere.”
An animated gif of the series of photographs taken by Robert Moreno Jr. Click on the image to animate in full resolution. (Credit, R. Moreno Jr., NASA, SETI)
Numerous individuals and groups undertook the search for the Novato meteorite. Dr. Jenniskens trajectory analysis included a likely impact zone or strewn field. People from all walks of life roamed the streets, open fields and hillsides of the north bay in search of fragments. Despite organized searches by Dr. Jenniskens, it was the footwork from other individuals that led to finding six fragments and was the first step which led to these studies that add to the understanding of the early Solar System’s development.
For Dr. Jenniskens, Novato was part of a trifecta – the April 22, 2012, Sutter Mill meteorite in the nearby foothills of the Sierras, the Novato meteorite and the massive Chelyabinsk airburst event in Russia on February 15, 2013. Throughout this period, Dr. Jenniskens all-sky camera network continued to expand and record “falling stars” – meteors. The number of meteors recorded with calculated trajectories is now over 175,000. The SETI Institute researcher has been supported by NASA and personnel at the institute and ordinary citizens including amateur astronomers that have refined the methods for meteor orbital determination and estimating their size and mass. Several websites have compiled images and results for the Novato meteorite with Dr. Jenniskens’ – CAMS.SETI.ORG being most prominent.
Rubble piles are common among asteroids, as illustrated by this artist's conception of 2011 MD. Credit: NASA/JPL-Caltech
How do asteroids hold their rubble piles together? Previously, scientists said it was a combination of friction and gravity. But new observations of asteroid 1950 DA reveals something else is at work. The asteroid is rotating too quickly for gravity to keep it together, so what’s going on?
“We found that 1950 DA is rotating faster than the breakup limit for its density,” stated Ben Rozitis, a postdoctoral researcher at the University of Tennessee, Knoxville who led the research. “So if just gravity were holding this rubble pile together, as is generally assumed, it would fly apart. Therefore, interparticle cohesive forces must be holding it together.”
Image of asteroid 1950 DA. Credit: NASA
Cohesive forces refer to the act of individual molecules or particles sticking together. It’s the first time scientists have found this in action on an asteroid. Better yet, if confirmed in other asteroids this has implications for protecting Earth from a killer asteroid should one come our way.
If the threat turns out to be a loosely held together asteroid, an impact in just the right spot would break the single asteroid into many. (Of course, you’d want to make sure that the problem doesn’t end up turning into multiple smaller asteroids hitting Earth instead of a single large one.)
Now the researchers are interested in knowing if cohesive forces are also in action on Comet 67P/Churyumov–Gerasimenko — the comet being examined by Rosetta right now and in November, by the lander Philae.
Artist's concept of OSIRIS-REx at Bennu. (Credit: NASA/GSFC)
I love anything that attempts to provide a sense of scale about the Solar System (see here and here for even more examples) and this one brings us down past the Sun, planets, and moons all the way to asteroid size — specifically asteroid 101955 Bennu, the target of the upcoming OSIRIS-REx mission.
Created by the OSIRIS-REx “321Science!” team, consisting of communicators, film and graphic arts students, teens, scientists, and engineers, the video shows some relative scales of our planet compared to the Sun, and also the actual size of asteroid Bennu in relation to some familiar human-made structures that we’re familiar with. (My personal take-away from this: Bennu — one of those “half grains of sand” — is a rather small target!)
A NASA New Frontiers mission, OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) will launch in Sept. 2016 on a two-year journey to the asteroid 101955 Bennu. Upon arrival OSIRIS-REx will map Bennu’s surface and also measure the Yarkovsky effect, by which asteroids’ trajectories can change over time due to the small force exerted by radiant heat.
Artist's conception of early Earth after several large asteroid impacts, moving magma on to the surface. Credit: Simone Marchi/SwRI
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.
Artist’s conception of early Earth after several large asteroid impacts, moving magma on to the surface. Credit: Simone Marchi/SwRI
“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.
But once the stuff is extracted, who does it belong to? A bill being considered by the U.S. House of Representatives says it would belong to “the property of the entity that obtained such resources.”
In a blog on Space Politics, aerospace analyst Jeff Foust outlined a discussion on the bill at the NewSpace 2014 conference last week. There are still a few wrinkles to be worked out, with one of the most pressing being to define what the definition of an asteroid is. Also, the backers of the bill are talking with the U.S. State Department to see if it would conflict with any international treaty obligations. (Here’s a copy of the bill on the Space Politics website.)
A single radar image frame close-up view of 2014 HQ124. Credit: NASA
The panel also noticed there is precedent for keeping and even selling samples: the visits to the Moon. Both Apollo astronauts (with the United States) and the Luna robotic missions (from the Soviet Union) returned samples of the Moon to the Earth. Some of the Apollo rocks, for example, are on display in museums. Others are stored in the NASA Lunar Sample Laboratory Facility at the Johnson Space Center in Houston.
That said, extraterrestrial property rights are difficult to define. For example, the United Nations Moon Treaty (more properly known as Agreement Governing the Activities of States on the Moon and Other Celestial Bodies) allows samples to be removed and stored for “scientific purposes”, and during these investigations they may “also use mineral and other substances of the moon in quantities appropriate for the support of their missions.” But it also adds that “the moon and its natural resources are the common heritage of mankind.”
Comet 67P/C-G photographed on July 14, 2014 from a distance of approximately 12 000 km.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
I thought the photos earlier this week were amazing. This little movie, made of 36 ‘smoothed’ or interpolated images of Comet 67P/Churyumov-Gerasimenko, takes it to the next level, showing the comet’s complex shape even more clearly as Rosetta nudges ever closer to its target. Some have likened it to a duck, a boot and even a baby’s foot. The original photos used for the animation were more pixelated, but a technique known as “sub-sampling by interpolation” was used to smooth out the pixels for a more natural look. Be aware that because of processing, 67P C-G appears smoother than it might be. While the surface looks textured, including what appears to be a small crater atop the duck’s head, we have to be careful at this stage not to over-interpret – some of the details are artifacts.
Raw pixelated image of the comet (left) and after smoothing. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
No one knows yet how such an unusual shape formed in the first place. Possibly the comet is a ‘contact binary’ made of two separate comets or two parts of larger, shattered comet that stuck together during a low-velocity collision. This may have happened more 4 billion years ago when the icy building blocks of the planets and comets were numerous and collisions far more frequent than they are today. Contact binaries aren’t uncommon; we see them in asteroids and comets alike.
* The comet may have once been a more spherical object but after many trips around the sun developed an asymmetrical shape from ice vaporization and outgassing.
* A near-catastrophic impact blasted away a huge chunk of comet ice.
* The strong gravitational pull experienced during a close pass of a large planet like Jupiter or Saturn may have pulled it into an irregular shape.
* A large outburst could have weakened a region on the comet’s surface that later crumbled away.
Detailed view of the likely contact binary asteroid 25143 Itokawa visited by the Japanese spacecraft Hayabusa in 2005. Credit: JAXA
“We will need to perform detailed analyses and modelling of the shape of the comet to determine how best we can fly around such a uniquely shaped body, taking into account flight control and astrodynamics, the science requirements of the mission, and the landing-related elements like landing site analysis and lander-to-orbiter visibility,” said Rosetta Mission Manager Fred Jansen. ” But with fewer than 10,000 km to go before the August 6th rendezvous, our open questions will soon be answered.”
In the meantime, keep the photos and movies coming. We can’t get enough.
