Posted on by Nancy Atkinson

Apophis’ Odds of Earth Impact Downgraded

Apophis proposed trajectory in 2029

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NASA scientists have recalculated the path of the large asteroid Apophis, significantly downgrading the odds of it hitting Earth. Using new information, the refined path indicates a 1 in 250,000 chance of impact in 2036, reduced from the 1 in 45,000 odds calculated earlier. The asteroid is expected to make a record-setting — but harmless — close approach to Earth on Friday, April 13, 2029, when it comes no closer than 18,300 miles above Earth’s surface.

The new information provided a more accurate glimpse of 2036 Apophis’ orbit well into the latter part of this century. Among the findings is another close encounter by the asteroid with Earth in 2068 with chance of impact currently at approximately 1 in 333,000. As with earlier orbital estimates where Earth impacts in 2029 and 2036 could not initially be ruled out due to the need for additional data, it is expected that the 2068 encounter will diminish in probability as more information about 2029 Apophis is acquired.

Initially, Apophis was thought to have a 2.7 percent chance of impacting Earth in 2029. Additional observations of the asteriod ruled out any possibility of an impact in 2029.

The Apophis asteroid is approximately the size of two-and-a-half football fields.

“The refined orbital determination further reinforces that Apophis is an asteroid we can look to as an opportunity for exciting science and not something that should be feared,” said Don Yeomans, manager of the Near-Earth Object Program Office at JPL. “The public can follow along as we continue to study Apophis and other near-Earth objects by visiting us on our AsteroidWatch Web site and by following us on the @AsteroidWatch Twitter feed.”

The new data were documented by near-Earth object scientists Steve Chesley and Paul Chodas at NASA’s Jet Propulsion Laboratory. A majority of the data that enabled the updated orbit of Apophis came from observations made by Dave Tholen and collaborators at the University of Hawaii’s Institute for Astronomy in Manoa. Tholen pored over hundreds of previously unreleased images of the night sky made with the University of Hawaii’s 88-inch telescope, located near the summit of Mauna Kea.

Tholen made improved measurements of the asteroid’s position in the images, enabling him to provide Chesley and Chodas with new data sets more precise than previous measures for Apophis. Measurements from the Steward Observatory’s 90-inch Bok telescope on Kitt Peak in Arizona and the Arecibo Observatory on the island of Puerto Rico also were used in Chesley’s calculations.

“Apophis has been one of those celestial bodies that has captured the public’s interest since it was discovered in 2004,” said Chesley. “Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about four-in-a million.”

The science of predicting asteroid orbits is based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids.

NASA detects and tracks asteroids and comets passing close to Earth using both ground and space-based telescopes. The Near Earth-Object Observations Program, commonly called “Spaceguard,” discovers these objects, characterizes a subset of them and plots their orbits to determine if any could be potentially hazardous to our planet.

Source: NASA

Posted on by Nancy Atkinson

Understanding 2008 TC3 a Year After Impact

Discovery images of asteroid 2008 TC3, as it was seen on October 6, 2008, by the Catalina Sky Survey at Mount Lemmon in Arizona (Richard Kowalski).

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The first asteroid to have been spotted before hitting Earth, 2008 TC3, crashed in northern Sudan one year ago on October 6. Several astronomers have been trying to piece together a profile of this asteroid, pulling together information from meteorites found at the impact site and the images captured of the object in the hours before it crashed to Earth.

“We have a gigantic jigsaw puzzle on our hands, from which we try to create a picture of the asteroid and its origins,” said SETI Institute astronomer Peter Jenniskens, who worked at the crash site, “and now we have with a composite sketch of the culprit, cleverly using the eyewitness accounts of astronomers that saw the asteroid sneak up on us.” Their description? 2008 TC3 looked like a loaf of walnut-raisin bread.

“The asteroid now has a face,” said Jenniskens, chair of the special session at the fall meeting for the Division for Planetary Sciences of the American Astronomical Society. Last December, Jenniskens and Sudan astronomer Muawia Shaddad went to the crash site and recovered 300 fragments in the Nubian Desert. Like detectives, students from the University of Khartoum helped sweep the desert to look for remains of the asteroid. They found many different-looking meteorites close to, but a little south, of the calculated impact trajectory.

The team has also been able to recreate the shape of the asteroid from looking at images captured by Astronomers Marek Kozubal and Ron Dantowitz of the Clay Center Observatory in Brookline, Massachusetts, who tracked the asteroid with a telescope and captured the flicker of light during a two hour period just before impact.

An irregular shape and rapid tumbling caused asteroid 2008 TC3 to flicker when it reflected sunlight on approach to Earth.

Peter Scheirich and colleagues at Ondrejov Observatory and Charles University in the Czech Republic combined all the various observations to work out the shape and orientation of the asteroid.

Watch a video recreation of 2008 TC3 tumbling in space.

Larger version. (1.32 MB Mpeg 4 file)

Video of 2008 TC3 as seen through a telescope (large file, 7.63 MB)

Other forensic evidence based on analysis of the recovered meteorites at the Almahata Sitta site showed the asteroid was an unusual “polymict ureilite” type. Jason S. Herrin of NASA’s Johnson Space Center confirmed that the meteorites still carry traces of being heated to 1150-1300 degrees C, before rapidly cooling down at a rate of tens of degrees C per hour, during which carbon in the asteroid turned part of the olivine mineral iron into metallic iron. Hence, asteroid 2008 TC3 is the remains of a minor planet that endured massive collisions billions of years ago, melting some of the minerals, but not all, before a final collision shattered the planet into asteroids.

Mike Zolensky of NASA’s Johnson Space Center first pointed out that, as far as ureilites are concerned, his meteorite is unusually rich in pores, with pore walls coated by crystals of the mineral olivine. He now reports, from X-ray tomography work with Jon Friedrich of Fordham University in New York, that those pores appear to outline grains that have been incompletely welded together and that the pore linings appear to be vapor phase deposits. According to Zolensky, “Almahata Sitta may represent an agglomeration of coarse- to fine-grained, incompletely reduced pellets formed during impact, and subsequently welded together at high temperature.”

The carbon in the recovered meteorites is among the most cooked of all known meteorites. Carbon crystals of graphite and nanodiamonds have been detected. Still, it turns out that some of the organic matter in the original material survived the heating. Amy Morrow, Hassan Sabbah, and Richard Zare of Stanford University have found polycyclic aromatic hydrocarbons in high abundances. Amazingly, Michael Callahan and colleagues of NASA’s Goddard Space Flight Center now report that even some amino acids have survived.

Jenniskens and Shaddad plan to revisit the scene of the crash in the Nubian Desert. They reported their findings at the Division for Planetary Sciences of the American Astronomical Society meeting in Puerto Rico.

Listen to Oct. 6th’s 365 Days of Astronomy podcast by Emily Lakdawalla about 2008 TC3.

Source: AAS Planetary Science Division

Posted on by Nancy Atkinson

NASA Tests New Robotic Lander for Future Moon, Asteroid Missions

NASA’s Marshall Space Flight Center is testing a new robotic lunar lander test bed that will aid in the development of a new generation of multi-use landers for future robotic space exploration. Image Credit: NASA/MSFC/David Higginbotham

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The best way to study the new-found water on the Moon would be with in-situ instruments. Since humans won’t be making any lunar landings for at least a decade, the next best option is robotic spacecraft. NASA’s Marshall Space Flight Center is developing and testing a new robotic lander to explore not only the Moon, but also asteroids and Mars. This design is definitely next generation: it’s bigger than any lander yet and MSFC is currently testing the all-important final of reaching the destination: landing.

“Specifically, what we are doing at Marshall is identifying the terminal – or the final – phase of landing, and designing a robotic lander to meet those needs,” said Brian Mulac, a test engineer at Marshall, quoted in an article in the Huntsville Times. “That last part is the highest risk of setting down on the moon.”

Of course, parachutes can’t be used for landing on the Moon or asteroids, since neither destination has an atmosphere, so thrusters are key for landing.

Large, oval-shaped tanks on the craft are used to store fuel for thrusters. Thrusters guide the lander, controlling the vehicle’s altitude and speed for landing. An additional thruster on this test vehicle, above, offsets the effect of Earth’s gravity so that the other thrusters can operate as they would in a lunar environment.

Just in case the tests don’t go as planned, a huge net is place under the lander to catch the vehicle and avoid damaging it.

As the saying goes, it’s not the fall that’s dangerous, but the sudden stop.

Landing on Mars requires a different architecture, such as the Mars Science Laboratory’s sky-crane, because of the pesky, thin atmosphere on the Red Planet. Read our previous article with Rob Manning of JPL about the issues of landing large payloads on Mars.

Sources: Huntsville Times, Gizmodo

Posted on by Nancy Atkinson

Craters on Vesta and Ceres Could Show Jupiter’s Age

Images of Ceres and Vesta from the Hubble Space Telescope. Credit: NASA

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Scientists use crater distributions to tell the ages of planetary surfaces on rocky bodies. But how can the ages of gas planets be determined? Believe it or not, possibly from craters. Scientists from the National Institute of Astrophysics in Rome say that crater patterns on the two largest asteroids in the asteroid belt, Vesta and Ceres, could help pinpoint when Jupiter began to form during the evolution of the early Solar System. Their study modeling the cratering history of the two asteroids – which are believed to be among the oldest in the Solar System — indicates that the type and distribution of craters would show marked changes at different stages of Jupiter’s development.

The study explored the hypothesis that one of the asteroids, or perhaps both objects, formed at the same time as Jupiter, and that studying their cratering histories could provide information about the birth of the giant planet.

The team’s simulation described Jupiter’s formation in three stages: an initial accretion of its core followed by a stage of rapid gas accretion. This is, in turn, followed by a phase where the gas accretion slows down while the giant planet reaches its final mass. During the last two phases Jupiter’s gravitational pull starts to affect more and more distant objects. For each of these phases, the team simulated how Jupiter affected the orbits of asteroids and comets from the inner and outer Solar System, and the likelihood of them being moved onto a collision path with Vesta or Ceres.

“We found that the stage of Jupiter’s development made a big difference on the speed of impacts and the origin of potential impactors,” said Dr. Diego Turrini, from the research team. “When Jupiter’s core approaches its critical mass, it causes a sharp increase in low-velocity impacts from small, rocky bodies orbiting nearby to Vesta and Ceres which lead to intense and uniform crater distribution patterns. These low-speed collisions may have helped Vesta and Ceres gather mass. Once Jupiter’s core has formed and the planet starts to rapidly accrete gas, it deflects more distant objects onto a collision course with Ceres and Vesta and the impacts become more energetic. Although rocky objects from the inner Solar System are the dominant impactors at this stage, the higher energies of collisions with icy bodies from the outer Solar System make the biggest mark.”

The third stage of Jupiter’s formation is complicated by a period known as the Late Heavy Bombardment, which occurred around 3.8 – 4.1 billion years ago. During this time a significant number of objects, rich in organic compounds, from the outer Solar System were injected on planet-crossing orbits with the giant planets and may have reached the Asteroid Belt. In addition, Jupiter is thought to have migrated in its orbit around this time, which would have caused an addition flux of impactors on Vesta and Ceres.

Artist's concept of the Dawn spacecraft with Ceres and Vesta. Credit: JPL
Artist's concept of the Dawn spacecraft with Ceres and Vesta. Credit: JPL

The team will have an opportunity to confirm their results when NASA’s Dawn space mission reaches Vesta in 2011 and then flies on for a further rendezvous with Ceres in 2015. Dawn will gather information on the structure and the surface morphology of the two asteroids and send back high-resolution images of crater patterns. Although the two asteroids are thought to have formed close to each other, they are quite different. Vesta is a rocky body, while Ceres is believed to contain large quantities of ice.

“If we can see evidence of an underlying intense, uniform crater pattern, it will support the theory that one or both of these minor planets formed during the final phases of Jupiter accretion, provided that they aren’t obliterated by the later heavy bombardment,” said Turrini. “Dawn will also measure concentrations of organic material, which may give us further information about the collisional history with organic-rich objects from the outer Solar System.”

The science team discussed their results at the European Planetary Science Congress in Potsdam, Germany.

Source: Europlanet

Posted on by Nancy Atkinson

NASA Doesn’t Receive Enough Money for Mandated Asteroid Search

Planet Killer
Artist's conception of an asteroid hitting Earth.

In 2005, the US Congress mandated that NASA discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020. But they forgot one minor detail: Congress or the administration did not request or appropriate any new funds to meet this objective, and with NASA’s existing budget, there is no way NASA can meet the mandated goal.

Does anyone else see a pattern here?

“For the first time, humanity has the capacity and the audacity to avoid a natural disaster,” says Irwin Shapiro of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who headed a National Research Council panel to asses NASA’s progress in reaching the asteroid detection goal . “It really is a question of how much to invest in an insurance policy for the planet.”

NASA was also directed by the Bush administration to build spacecraft to return to the Moon, and perhaps go on to Mars, but do the job (as well as complete the space station and make sure the shuttles can fly safely) with no real increase in budget.

From the report:

Currently, the U.S. government spends a relatively small amount of money funding a search and survey program to discover and track near-Earth objects, and virtually no money on studying methods of mitigating the hazards posed by such objects. Although Congress has mandated that NASA conduct this survey program and has established goals for the program, neither Congress nor the administration has sought to fund it with new appropriations. As a result, NASA has supported this activity by taking funds from other programs, while still leaving a substantial gap between the goals established by Congress and the funds needed to achieve them.

The report is available here (download the free pdf version)

But in summary, the report says that since only limited facilities are currently involved in the asteroid survey/discovery effort, NASA cannot meet the goals of the Congressional mandate on the existing budget. Instead, the three current survey efforts dedicated to the problem, supported at current levels, will likely find only about 15%.

The report also says that Harvard-Smithsonian’s Minor Planet Center is more than capable of handling the observations of the congressionally mandated survey, but there isn’t enough funds for adequate staffing.

If this is true, the facilities to do the job appear to be in place, and no new observatories need to be built or spacecraft need to be launched. How much more money would it take to hire enough people?

However, only three surveys are currently involved in the search (Catalina Sky Survey, Spacewatch and Lincoln Near Earth Asteroid Research), and the panel suggests that more telescopes and spacecraft would be beneficial to the search. Several ground-based telescopes have been proposed or are currently under development that could contribute substantially to meeting the goal established by Congress. However, none has yet been fully funded, nor principally dedicated to the NEO discovery goal.

Right now, the US is the only country that currently has an operating survey/detection program for discovering near-Earth objects. Canada and Germany are both building spacecraft that may contribute to the discovery of near-Earth objects, but neither mission will detect fainter or smaller objects than ground-based telescopes.

But the US isn’t alone in the non-funding of asteroid searches. “Virtually no international funds are spent supporting ground-based NEO surveys, and international NEO discovery efforts are largely conducted on an ad hoc, voluntary, or amateur basis. NASA is the agency that has funded more than 97 percent of the discoveries of NEOs in the last decade,” says the report.

Sources: USA Today, National Acadamies Press

Posted on by Nancy Atkinson

Near-Earth Object Has Two Moons

Radar imaging at NASA's Goldstone Solar System Radar on June 12 and 14, 2009, revealed that near-Earth asteroid 1994 CC is a triple system. Image Credit: NASA/JPL/GSSR

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Radar images have shown that a near-Earth object is actually a triple system; an asteroid with two small moons. NASA’s Goldstone Solar System Radar on June 12 and 14, 2009, revealed the new informaton about Asteroid 1994 CC. It came within 2.52 million kilometers (1.56 million miles) on June 10. Prior to the flyby, very little was known about this celestial body. 1994 CC is only the second triple system known in the near-Earth population. A team led by Marina Brozovic and Lance Benner, both scientists at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., made the discovery.

Asteroid 1994 CC encountered Earth within 2.52 million kilometers (1.56 million miles) on June 10. Prior to the flyby, very little was known about this celestial body. Image Credit: NASA/JPL/GSSR
Asteroid 1994 CC encountered Earth within 2.52 million kilometers (1.56 million miles) on June 10. Prior to the flyby, very little was known about this celestial body. Image Credit: NASA/JPL/GSSR

1994 CC consists of a central object about 700 meters (2,300 feet) in diameter that has two smaller moons revolving around it. Preliminary analysis suggests that the two small satellites are at least 50 meters (164 feet) in diameter. Radar observations at Arecibo Observatory in Puerto Rico, led by the center’s director Mike Nolan, also detected all three objects, and the combined observations from Goldstone and Arecibo will be utilized by JPL scientists and their colleagues to study 1994 CC’s orbital and physical properties.

The next comparable Earth flyby for asteroid 1994 CC will occur in the year 2074 when the space rock trio flies past Earth at a distance of two-and-a-half million kilometers (1.6 million miles).

Of the hundreds of near-Earth asteroids observed by radar, only about 1 percent are triple systems.

Source: JPL

Posted on by Nancy Atkinson

Half Comet-Half Asteroid a Fluke? Nope

Images of known MBCs from UH 2.2-meter telescope data. Credit: Henry Hsieh

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Back in 1996, astronomers discovered a strange object in the asteroid belt. They decided it was either a “lost” comet or an icy asteroid, as it ejected dust like a comet but had an orbit like an asteroid. No one had ever seen anything like the object, called 133P. Ever since it was found, astronomers have wondered if it was just an oddity — one of a kind. We now know it is not, and the discovery of more of these half asteroids/half comets means there is a new class of objects in our solar system.

One of these new objecst, 176P/LINEAR is also emitting dust as it orbits in the asteroid belt. It was found by Henry Hsieh at Queen’s University, Belfast in Northern Ireland. Hsieh has been working to figure out the unusual behavior of 133P. He hypothesized that either one of two things could explain the existence of the comet-asteroid: “(1.) 133P is a classical comet from the outer solar system that has evolved onto a main-belt orbit, or (2.) 133P is a dynamically ordinary main-belt asteroid on which subsurface ice has recently been exposed,” Hsieh wrote in his paper. “If (1) is correct, the expected rarity of a dynamical transition onto an asteroidal orbit implies that 133P could be alone in the main belt. In contrast, if (2) is correct, other icy main-belt objects should exist and could also exhibit cometary activity.”

Hsieh thought it was unlikely a comet could have been kicked around enough to end up in orbit in the asteroid belt, so he followed the assumption that 133P was a dynamically ordinary, yet icy main-belt asteroid. He set out to prove the hypothesis that 133P-like objects should be common and could be found by an well-designed observational survey.

Hsieh made 657 observations of 599 asteroids in the asteroid belt and found 176P/LINEAR. He also determined the asteroid is partially made of ice, which is being ejected following a collision with another object, thus the comet-like attributes.

Additionally, since there is evidence for past and even present water in main-belt asteroids, Hsieh says statistically there should be around 100 currently active Main Belt Comets (MBCs) as these objects are called, among the kilometer-scale, low-inclination, outer belt asteroid population.

The Technology Review blog offered suggestions for what to name these new objects that are half comet and half asteroid: “Comsteroids? Asteromets? Hsiehroids?”

Hseih’s paper,
 Hseih’s website on MBCs
Sources: Technology Review Blog, arXiv

Posted on by Nancy Atkinson

Keep Track of NEOs with New “Asteroid Watch” Website

With the recent impact on Jupiter, a lot of people out there have asteroids on their mind and wonder if one could possibly hit Earth. Now, NASA and JPL have a new website called “Asteroid Watch” which will keep everyone updated if any object approaches Earth. They’ve also created an Asteroid Watch Twitter account that Tweet updates on NEOs, plus there’s a downloadable widget as well.

“The goal of our Web site is to provide the public with the most up-to-date and accurate information on these intriguing objects,” said Don Yeomans, manager of NASA’s Near-Earth Object Program Office at JPL.

“This innovative new Web application gives the public an unprecedented look at what’s going on in near-Earth space,” said Lindley Johnson, program executive for the Near-Earth Objects Observation program at NASA Headquarters in Washington.

Information is garnered from surveys and missions that detect and track asteroids and comets passing close to Earth. The Near-Earth Object Observation Program, commonly called “Spaceguard,” also plots the orbits of these objects to determine if any could be potentially hazardous to our planet.

There’s also another non-NASA Twitter feed called lowflyingrocks that lets you know about every Near Earth Object that passes within 0.2AU of Earth.

Source: JPL

Posted on by Anne Minard

Heat-Shocked Diamonds Provide New Clue of Horse-Killing Impact

California's Channel Islands, where heat-shocked soot and diamonds are suggesting a killing comsic impact. Courtesy NOAA and UC Santa Barbara

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Archeologists have been divided about whether an extraterrestiral impact blasted North America about 12,900 years ago, wreaking havoc on Earth’s surface and sending scores of species — including a pygmy mammoth and the horse — into oblivion.

New clues from California’s Channel Islands should put any doubt to rest, says an international team of researchers.

This transmission electron microscopy close-up shows a single lonsdaleite crystal, left, and associated diffraction pattern. Credit: University of Oregon
This transmission electron microscopy close-up shows a single lonsdaleite crystal, left, and associated diffraction pattern. Credit: University of Oregon

The 17-member team, led by University of Oregon archaeologist Douglas J. Kennett, has found what may be the smoking gun.

The team has found shock-synthesized hexagonal diamonds in 12,900-year-old sediments on the Northern Channel Islands off the southern California coast.

The tiny diamonds and diamond clusters were buried deeply below four meters (13 feet) of sediment. They date to the end of Clovis — a Paleoindian culture long thought to be North America’s first human inhabitants. The nano-sized diamonds were pulled from Arlington Canyon on the island of Santa Rosa, which had once been joined with three other Northern Channel Islands in a landmass known as Santarosae.

The diamonds were found in association with soot that forms in extremely hot fires, and they suggest associated regional wildfires, based on nearby environmental records.

Such soot and diamonds are rare in the geological record. They were found in sediment dating to massive asteroid impacts 65 million years ago in a layer widely known as the K-T Boundary. The thin layer of iridium-and-quartz-rich sediment dates to the transition of the Cretaceous and Tertiary periods, which mark the end of the Mesozoic Era and the beginning of the Cenozoic Era.

“The type of diamond we have found — Lonsdaleite — is a shock-synthesized mineral defined by its hexagonal crystalline structure. It forms under very high temperatures and pressures consistent with a cosmic impact,” Kennett said. “These diamonds have only been found thus far in meteorites and impact craters on Earth and appear to be the strongest indicator yet of a significant cosmic impact [during Clovis].”

The age of this event also matches the extinction of the pygmy mammoth on the Northern Channel Islands, as well as numerous other North American mammals, including the horse, which Europeans later reintroduced. In all, an estimated 35 mammal and 19 bird genera became extinct near the end of the Pleistocene with some of them occurring very close in time to the proposed cosmic impact, first reported in October 2007 in PNAS.

Source: University of Oregon, via Eurekalert. The results appear in a paper online ahead of print in the Proceedings of the National Academy of Sciences.

Posted on by Anne Minard

A Benevolent Sort of Asteroid Bombardment?

Celestial impacts can bring life as well as wipe it out, say the authors of a new study out of the University of Colorado at Boulder.

A case in point: the bombardment of Earth nearly 4 billion years ago by asteroids as large as Kansas would not have had the firepower to extinguish potential early life on the planet and may even have given it a boost.

In a new paper in the journal Nature, Oleg Abramov and Stephen Mojzsis report on their study of impact evidence from lunar samples, meteorites and the pockmarked surfaces of the inner planets. The evidence paints a picture of a violent environment in the solar system during the Hadean Eon 4.5 to 3.8 billion years ago, particularly through a cataclysmic event known as the Late Heavy Bombardment about 3.9 billion years ago.

Although many believe the bombardment would have sterilized Earth, the new study shows it would have melted only a fraction of Earth’s crust, and that microbes could well have survived in subsurface habitats, insulated from the destruction.

“These new results push back the possible beginnings of life on Earth to well before the bombardment period 3.9 billion years ago,” Abramov said. “It opens up the possibility that life emerged as far back as 4.4 billion years ago, about the time the first oceans are thought to have formed.”

Because physical evidence of Earth’s early bombardment has been erased by weathering and plate tectonics over the eons, the researchers used data from Apollo moon rocks, impact records from the moon, Mars and Mercury, and previous theoretical studies to build three-dimensional computer models that replicate the bombardment. Abramov and Mojzsis plugged in asteroid size, frequency and distribution estimates into their simulations to chart the damage to the Earth during the Late Heavy Bombardment, which is thought to have lasted for 20 million to 200 million years.

The 3-D models allowed Abramov and Mojzsis to monitor temperatures beneath individual craters to assess heating and cooling of the crust following large impacts in order to evaluate habitability. The study indicated that less than 25 percent of Earth’s crust would have melted during such a bombardment.

The CU-Boulder researchers even cranked up the intensity of the asteroid barrage in their simulations by 10-fold — an event that could have vaporized Earth’s oceans. “Even under the most extreme conditions we imposed, Earth would not have been completely sterilized by the bombardment,” said Abramov.

Instead, hydrothermal vents may have provided sanctuaries for extreme, heat-loving microbes known as “hyperthermophilic bacteria” following bombardments, said Mojzsis. Even if life had not emerged by 3.9 billion years ago, such underground havens could still have provided a “crucible” for life’s origin on Earth, Mojzsis said.

Geologic evidence suggests that life on Earth was present at least 3.83 billion years ago, said Mojzsis. “So it is not unreasonable to suggest there was life on Earth before 3.9 billion years ago. We know from the geochemical record that our planet was eminently habitable by that time, and this new study sews up a major problem in origins of life studies by sweeping away the necessity for multiple origins of life on Earth.”

The results also support the potential for microbial life on other planets like Mars and perhaps even rocky, Earth-like planets in other solar systems that may have been resurfaced by impacts, said Abramov.

Source: Eurekalert