Tagged: Comets Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 10:02 am on September 11, 2019 Permalink | Reply
    Tags: "All comets in the solar system might come from the same place", , , , Comets, , ,   

    From Universiteit Leiden via phys.org: “All comets in the solar system might come from the same place” 


    From Universiteit Leiden

    via


    phys.org

    September 9, 2019
    Bryce Benda

    1
    (NASA/W. Liller)

    2
    This single frame Rosetta navigation camera image of Comet 67P/Churyumov-Gerasimenko was taken on 7 July 2015 from a distance of 154 km from the comet centre. Credit: ESA/Rosetta/NAVCAM

    A team of American and European scientists found that 14 different comets originated at the same time and place: a protoplanetary disk orbiting near our newly-formed Sun.

    All comets might share their place of birth, new research says. For the first time ever, astronomer Christian Eistrup applied chemical models to fourteen well-known comets, surprisingly finding a clear pattern. His publication has been accepted in the journal Astronomy & Astrophysics.

    Given that comet impacts are thought to be a potential source of organic materials on Earth, exploring this new cosmic origin story could lead to a better understanding of the origin of life.

    This particular survey of 14 comets is too small in scale to use as evidence that all comets came from the same time and place in the early Solar System.

    But it is an interesting starting point for future research, given that the researchers didn’t expect to find so much in common among their samples in the first place.

    Comets: balls of ice or more?

    Comets travel through our solar system and are composed of ice, dust, and small rock-like particles. Their nuclei can be as large as tens of kilometers across. “Comets are everywhere, and sometimes with very funky orbits around the Sun. In the past, comets even have hit the Earth,” Christian Eistrup says. “We know what comets consist of and which molecules are present in them. They vary in composition, but are normally seen as just one group of icy balls. Therefore, I wanted to know whether comets are indeed one group, or whether different subsets can be made.”

    A new take on comets

    “What if I apply our existing chemical models to comets?”, Eistrup thought during his Ph.D. at Leiden University. In the research team at Leiden Observatory, which included Kavli Prize winner Ewine van Dishoeck, he developed models to predict the chemical composition of protoplanetary discs—flat discs of gas and dust encompassing young stars. Understanding these discs can give insight into how stars and planets form. Conveniently, these Leiden models turned out to be of help in learning about comets and their origins.

    “I thought it would be interesting to compare our chemical models with published data on comets,” says the astronomer. “Luckily, I had the help of Ewine. We did some statistics to pin down if there was a special time or place in our young solar system, where our chemical models meet the data on comets.” This happened to be the case, and to a surprising extent. Where the researchers hoped for a number of comets sharing similarities, it turned out that all fourteen comets showed the same trend. “There was a single model that fitted each comet best, thereby indicating that they share their origin.”


    Credit: Leiden University

    Ice-cold

    And that origin is somewhere close to our young Sun, when it was still encircled by a protoplanetary disc and our planets were still forming. The model suggests a zone around the Sun, inside the range where carbon monoxide becomes ice—relatively far away from the nucleus of the young Sun. “At these locations, the temperature varies from 21 to 28 Kelvin, which is around minus 250 degrees Celsius. That’s very cold, so cold that almost all the molecules we know are ice.

    “From our models, we know that there are some reactions taking place in the ice phase—although very slowly, in a time-frame of 100,000 to 1 million years. But that could explain why there are different comets with different compositions.”

    But if comets come from the same place, how do they end up in different places and orbits in our solar system? “Although we now think they formed in similar locations around the young Sun, the orbits of some of these comets could be disturbed—for instance by Jupiter—which explains the different orbits.”

    Comet data hunter

    As befits a scientist, Eistrup places some side-notes to his publication. “With only fourteen comets, the sample is quite small. That’s why I’m currently hunting for data on many more comets, to run them through our models and further test our hypothesis.” Eistrup also hopes that astronomers that study the origin of our solar system and its evolution can use his results. “Our research suggests that comets have formed during the period they’re studying, so this new information might give them new insights.”

    He is also keen to get in touch with other comet researchers. “Because we show a new trend, I would like to discuss what other astronomers think of our research.”

    The seeds of life

    Comets and life on Earth, they go hand in hand. “We still don’t know how life on Earth began. But the chemistry on comets could lead to the production of organic molecules, including some building blocks for life. And if the right comet hits the right planet, with the right environment, life could start growing,” Eistrup concludes. So, interestingly, understanding the birth of comets potentially could help us understand the birth of life on Earth.

    See the full article here.

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Universiteit Leiden Heijmans onderhoudt

    Universiteit Leiden was founded in 1575 and is one of Europe’s leading international research universities. It has seven faculties in the arts, sciences and social sciences, spread over locations in Leiden and The Hague. The University has over 6,500 staff members and 26,900 students. The motto of the University is ‘Praesidium Libertatis’ – Bastion of Freedom.

     
  • richardmitnick 9:57 am on April 22, 2019 Permalink | Reply
    Tags: , By simulating conditions in the early solar system researchers can calculate the ratio of heavy water to ordinary water when the planets were forming., Comets, From Astronomy Magazine: "Where did Earth's water come from?", Reservoirs with a high quantity of heavy water have a high D/H ratio while deuterium-poor reservoirs show a lower ratio., What do the samples suggest is the source of Earth’s water? Hallis suspects it came from the solar nebula., When hydrogen-rich and oxygen-rich minerals melt because of the mantle’s heat the resulting water can spew from the planet’s crust., When the European Giotto spacecraft visited Halley’s Comet in 1986 researchers noticed its heavy water content was higher than the gas in Earth’s part of the early solar system.   

    From Astronomy Magazine: “Where did Earth’s water come from?” 

    Astronomy magazine

    From Astronomy Magazine

    April 01, 2019
    Nola Taylor Redd

    Most astronomers believe asteroids carried water to early Earth. But new research suggests it may have come from even closer to home.

    1
    Asteroids could have carried water, locked away in their minerals, to a young Earth, depositing it through impacts during our planet’s early years. But this isn’t the only possible explanation for our watery world. Ron Miller for Astronomy.

    Karen Meech doesn’t spend a lot of time digging through Earth’s rocks. An astronomer by trade, she is usually behind the telescope, investigating comets and looking for hints about how Earth got its water. But a field trip to Iceland in 2004 ultimately sent her scrambling through the craters of Hawaii nearly a decade later in search of clues about the liquid that helped birth life on this planet.

    On that fateful Icelandic tour, Meech saw geothermal areas with gas billowing out of the ground. The guide told the group not to worry — it was only water. “Then she said, ‘This is probably primordial water,’ and it set a lightbulb off,” Meech says.

    The flavors of water

    The source of Earth’s water has been a long-standing mystery; Meech herself has been trying to solve it for at least 20 years. Most of that search has focused on sorting out the various isotopes of hydrogen that go into making the water — or “the flavor of water,” as Lydia Hallis of the University of Glasgow calls it. One of those “flavors” is heavy water, a form of water that incorporates deuterium, an isotope of hydrogen whose nucleus contains one proton and one neutron. Normal hydrogen lacks a neutron, so water with deuterium weighs more than ordinary water.

    By simulating conditions in the early solar system, researchers can calculate the ratio of heavy water to ordinary water when the planets were forming. On Earth, the observed ratio is higher than it would have been in the young solar system, leading many astronomers to suspect that the water was imported because the ratio should remain constant over time. Today, most scientists believe asteroids carried water to the young, dry Earth.

    Meech was suspicious of this idea because measurements of Earth’s deuterium-to-hydrogen (D/H) ratio, which is connected to the ratio of heavy water to normal, is generally based on the composition of today’s oceans. Reservoirs with a high quantity of heavy water have a high D/H ratio, while deuterium-poor reservoirs show a lower ratio.

    2
    Earth formed from the dust and gas of the nebula that surrounded our infant Sun. This artist’s concept shows the protoplanetary disk of material around a young star. The disk contains the individual components of water — hydrogen and oxygen — and water in both ice and vapor forms. NASA/JPL-Caltech.

    But Earth’s ratio should have changed over time. Like most planets, Earth probably lost some of its atmosphere to space, and the lighter hydrogen would be easier to strip from the planet than its heavier counterpart. Geological processes, such as the evaporation of water from reservoirs such as lakes and oceans, can also change the ratio, as can biological reactions, because lighter isotopes are used differently than heavier ones in metabolic processes. All of these processes would give the modern Earth a higher D/H ratio compared with when the planet was newly formed.

    When Meech heard that primordial water could be spouting from the surface in Iceland, she grew excited at the chance to study the earliest flavor of water. But after chatting with a geologist, she learned that the plumes actually came from more recent activity — they weren’t primordial after all. However, the geologist revealed that some rocky material brought up from Earth’s mantle does contain small traces of water. That material may never have mixed with the stuff on the surface and could represent Earth’s early water. No one had investigated the D/H ratio in those samples because the technology to do so was new. But the University of Hawaii, where Meech is based, had just purchased a new ion microprobe that might be able to do the job.

    U Hawaii Ion microprobe

    UH Researchers Shed New Light on the Origins of Earth’s Water 12 November 2015

    “I thought, wow, here’s a way we can actually measure the original fingerprints,” Meech says. “At that point, I got very excited.”

    In search of the culprit

    Earth and the rest of the planets formed inside a nest of gas left over from the birth of the Sun. This material, known as the solar nebula, contained all the elements that built the planets, and the compositions varied with distance from the Sun. The region near the star was too warm for some material to coalesce as ices, which instead formed in the outer part of the solar system. Around Earth, hydrogen and other elements could stick around only as a gas. Because the nebula was short-lived, most scientists suspect that Earth didn’t have enough time to collect these gases before they escaped into space. That idea, along with the planet’s high D/H ratio, led many to believe that Earth’s water must have arrived after Earth had cooled.

    When the European Giotto spacecraft visited Halley’s Comet in 1986, researchers noticed its heavy water content was higher than the gas in Earth’s part of the early solar system.

    3
    ESA Giotto spacecraft

    A new theory emerged: Comets could have carried water to early Earth. After the planets formed, the enormous bodies would continue to stir things up, with giant planets like Jupiter hurling some material toward the inner solar system. Icy objects that formed in the outer solar system could have been tossed at Earth to rain down as giant water-laden impacts.

    4
    Heavy water, or D2O, contains deuterium in place of hydrogen. Deuterium is an isotope of hydrogen whose nucleus contains one proton and one neutron, whereas normal hydrogen contains only a proton. The ratio of heavy water to normal water in a sample gives scientists information about how it formed — information researchers are now using to try to unravel the origin of Earth’s water. Astronomy: Roen Kelly.

    But as other missions probed more comets, it became clear that the amount of heavy water wasn’t consistent among them. In fact, most of the comets’ heavy water ratios were far too high to be responsible for dropping water on Earth. Another culprit must be responsible.

    Comets weren’t the only thing that the gas giants tossed around. As Jupiter plowed through the asteroid belt early in our solar system’s history, it scattered the rocky debris in all directions. Like comets, some of the material rained down on Earth. Unlike comets, asteroids don’t lock up water as ice. Instead, they trap its components — hydrogen and oxygen — inside minerals. Also, the heavy water content in asteroids falls much closer to Earth’s current ratio. That’s why asteroids are the leading suspect for the source of our planet’s water.

    “Really, we’re not talking about water; we’re talking about hydrogen,” says Anne Peslier, a geochemist at NASA’s Johnson Space Center. Peslier studies the geochemistry of Earth’s mantle and the other terrestrial planets, including the hydrogen trapped within minerals.

    When Earth formed, the hydrogen surrounding the growing planet was captured in its rocks and minerals. When hydrogen-rich and oxygen-rich minerals melt because of the mantle’s heat, the resulting water can spew from the planet’s crust.

    Most of the mantle is rocky, and enormous quantities of hydrogen and oxygen could be trapped inside. Researchers estimate that as much as 10 oceans of water may exist within the mantle.

    Erupting volcanoes usually bring up magma from the upper part of Earth’s mantle, the region closer to the surface. This material is more likely to be polluted by hydrogen from the crust, which contains the same higher D/H ratios measured in the oceans today. More pristine samples lie much farther down in the mantle. Although it’s hot there, less than 20 percent of the mantle rock has melted, Peslier says. When the melted material erupts, it can have a violent effect on the solid rock.

    “If [the lavas] go fast enough and brutally enough, they sometimes break off pieces of what they are traversing along the way,” Peslier says. She describes the result — called mantle xenolith, after the Greek word for “foreign rock” — as crystals of bright green olivine and black pyroxene embedded in the black lava.

    If the hydrogen-rich olivine crystals were captured early enough during Earth’s formation and remained undisturbed for the planet’s 4.5 billion-year lifetime, they could reveal how much the ancient ratios of heavy and normal water shifted, if they changed at all. The tiny time capsules could provide answers to the long-standing questions regarding the source of Earth’s water.

    But first, they had to be found.

    Hunting primordial water

    While Meech knows a great deal about water in the solar system, she wasn’t as familiar with rocks on Earth. She pulled in Hallis, then a postdoctoral student, to lead geological excavations in a hunt for those early fingerprints of normal and heavy water. Hallis was intrigued by the chance to scramble across craters in Hawaii and along the shores of Baffin Island in Canada in search of clues. Baffin is one of the few places where Earth’s deep mantle is accessible. The chain of eruptions that formed the island also created Greenland and Iceland. “The Baffin Island samples are the most pristine examples that we have of the deep mantle,” Hallis says.

    Hallis also received samples collected by Don Francis, now an emeritus professor at McGill University in Montreal, from a tiny uninhabited island called Padloping, off the eastern coast of Canada and northwest of Baffin Island. According to Hallis, Francis collected the first of his samples in 1985. The isolation of Padloping Island meant that researchers had to travel there by boat and set up camp. The sheer cliffs made falling rocks plentiful, and Francis picked up the best-looking minerals from the beach. A return trip in 2004 netted even more samples. “Something I would really like to do is go back [to Padloping Island],” Hallis says. The imposing cliffs make it challenging to collect samples, but if she could obtain some from the steep overhangs, she would be able to pinpoint where and when the material rose to the surface.

    5
    Green olivine crystals in lava can contain and protect hydrogen collected during Earth’s formation, allowing researchers to determine its ratio of deuterium to hydrogen.
    S. Rae/Flickr.

    With the well-preserved samples in hand, Hallis and her colleagues began to systematically destroy them. The rocks were ground up into sandlike powder. Using the microprobe, the scientists sorted the enclosed crystals by color.

    Meech helped to categorize the crystals. “I found it hard to manipulate the tiny little bits of sand without spilling them on the floor,” she admits ruefully.

    Part of the process involved ensuring the samples were stripped from the mantle rather than the crust as the volcanic plume burst upward. Previous studies of the Baffin Island minerals suggested that they came from the mantle’s depths, and mineralogical evidence revealed that the samples Hallis had in the lab were most likely pristine. The tiny glass beads were protected in part by olivine crystals, which act as a barrier to prevent weathering once the rocks are on the surface. Even so, they weren’t entirely perfect.

    “Even with the most pristine samples that we have, it’s not 100 percent exactly deep mantle,” Hallis says. “It’s always going to have some incorporation of the [upper] mantle in there, just because it has to travel through so much of the mantle to get to the surface.”

    While the Baffin Island samples were free of crust pollution, the team wasn’t so fortunate with the rocks gathered near their university. The Hawaiian minerals had suffered from weathering and had been heavily affected by surface water, most likely rain. The pollution kept these samples from revealing the flavors of pristine water.

    With the first fingerprints of Earth’s water finally taken, Meech and Hallis began to compare them with other samples. Hallis expected to observe a heavy water content closer to the meteorites thought to have delivered water to the young planet. Instead, the samples weighed in with about 25 percent less heavy water compared with normal water — far less than expected.

    “That was a bit of a surprise,” Hallis says. “It suggests that carbonaceous chondrites [a class of meteorites] are not a good fit for the source of Earth’s water.” While meteorites may have provided some of Earth’s water, she doesn’t think that they delivered all of it.

    The source of Earth’s water

    What do the samples suggest is the source of Earth’s water? Hallis suspects it came from the solar nebula. While many scientists argue that the nebula would have dissipated within 6 million years — long before our planet could have grown large enough to capture it — she points out that several young stars have been found with gas around them for as long as 10 million years. That would give the tiny rocks that ultimately built Earth enough time to incorporate elements like hydrogen and nitrogen into their structure. Hallis says nitrogen and hydrogen in the solar system tend to follow one another — “If you have a certain flavor of hydrogen, you have a certain flavor of nitrogen,” she says.

    “Perhaps you still have pockets in the Earth that have preserved this initial hydrogen source,” says Zachary Sharp, a researcher at the University of New Mexico who also suspects that Earth’s D/H ratio has shifted over time.

    7
    Geysers such as Strokkur in Iceland inspired Karen Meech to hunt for Earth’s primordial water. Although such geysers do not spew the unaltered early water needed to pursue this line of study, other geological processes, such as volcanic plumes, do. Ivan Sabljak/Wikimedia Commons.

    Hallis’ results aren’t the only ones to suggest that Earth may have picked up the bulk of its water from the start. While the Moon was once thought to be completely dry, recent re-examinations of Apollo Moon rocks have revealed traces of water. The leading theory for the Moon’s formation is that it was created when a Mars-sized object slammed into the young Earth. Liquid water on the surface would have been vaporized, leading many to conclude that Earth had to pick up more water from elsewhere. But the low D/H ratios from the lunar samples suggest that the Moon could have collected the water in minerals locked in its interior, a region neither comets nor asteroids could have polluted. Later volcanic eruptions hurled that material to the surface, to be returned to Earth by astronauts.

    Why is this important? The high temperatures post-collision would have been similar to those found in the solar nebula, Hallis says. That helps to make the case that even in the hot early solar system, volatiles and water could be accreted.

    But hydrogen comes in heavy and light flavors, so doesn’t that mean the ratio could change in either direction? Not really, according to Sharp, who has revisited the idea that most of Earth’s water may have been collected from the nebula rather than later collisions. “It’s easy to increase the isotopic ratio of the samples, but it’s difficult to lower them,” he says. That’s because the lighter hydrogen is easier to remove. For instance, hydrogen rises more easily to the top of the atmosphere, where the solar wind can strip it away. The heavier deuterium tends to stay closer to the ground.

    Asteroids are also providing hints that Earth’s water may have come from the gas that birthed the planets. Studies of meteorites from the large asteroid Vesta have revealed ratios of heavy water similar to the Baffin Island estimates.

    “Now that we are finding low values in Earth, the Moon, and Vesta, and also in the water reservoir of the asteroids, now maybe the [nebula] story is possible,” says Alice Stephant of Arizona State University, who studies Vesta. “It seems like they all share a common reservoir that is lower [in deuterium] than what we thought.”

    8
    Padloping Island is isolated, uninhabited, and home to what may be some of Earth’s oldest rock. Future expeditions to this island in Canada may confirm preliminary findings that our Sun’s protoplanetary nebula may have stuck around long enough for a forming Earth to capture hydrogen — a building block of water. Doc Searls/Flickr.

    The smoking gun

    The lower D/H ratios revealed by Hallis, Meech, and their colleagues are not yet widely accepted. Conel Alexander, a cosmo-chemist at the Carnegie Institution of Washington, says there are two reasons why other researchers didn’t immediately change their minds about the source of Earth’s water.

    One argument against the results stems from how Hallis extrapolated the isotopes and elemental abundances in her measurements; Alexander says some scientists disagree with how the final numbers play out using her method. The other issue is how Hallis explained her results. “Lydia’s interpretation was unique,” Alexander says. “There may be other ways of getting hydrogen into the melt inclusions that she was measuring.”

    Alexander’s chief concern stems from the fact that only a single source of rocks — the Baffin Island samples — was used to estimate the entire planet’s ancient ratios. “The bulk of Earth may have a completely different composition, and there may be something weird about ocean islands’ basalts,” he says. He hopes that other scientists will follow Hallis’ lead and measure the D/H ratio from a variety of deep-mantle plumes.

    Hallis is ready to take her own trip to Padloping Island to collect more samples. One thing she would like to do is investigate not just the hydrogen involved, but also the nitrogen. But analyzing the nitrogen in samples is more difficult than hunting down hydrogen, partly because there is even less nitrogen in these samples than hydrogen. Measuring nitrogen also requires instruments capable of very high precision. Hallis says it’s pushing the limit of what current technology can do.

    Alexander says that Hallis’ goal of hunting down nitrogen from future samples will also help firm up any doubts about the primordial nature of the Baffin Island samples. “If she can show that there is both light hydrogen and light nitrogen in these inclusions, I think that would be a smoking gun,” he says.
    “If the nitrogen follows the hydrogen, then we proved our theory that [the samples] are primitive,” Hallis says.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • richardmitnick 2:34 pm on October 20, 2017 Permalink | Reply
    Tags: , , , Comets, , ,   

    From Universe today: “Where Do Comets Come From? Exploring the Oort Cloud” 

    universe-today

    Universe Today

    19 Oct , 2017
    Fraser Cain

    Oort cloud Image by TypePad, http://goo.gl/NWlQz6


    Oort Cloud NASA

    Oort Cloud, The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA, Universe Today

    Before I get into this article, I want to remind everyone that it’s been several decades since I’ve been able to enjoy a bright comet in the night sky. I’ve seen mind blowing auroras, witnessed a total solar eclipse with my own eyeballs, and seen a rocket launch. The Universe needs to deliver this bright comet for me, and it needs to do it soon.

    By writing this article now, I will summon it. I will create an article that’ll be hilariously out of date in a few months, when that bright comet shows up.

    Like that time we totally discovered a supernova in the Virtual Star Party, by saying there wasn’t a supernova in that galaxy, but there was, and we didn’t get to make the discovery.

    Anyway, on to the article. Let’s talk about comets.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 8:53 am on August 31, 2017 Permalink | Reply
    Tags: , , , Comets, , deflected comets and a closer look at the triggers of cosmic disaster, , Heavy stellar traffic, , TRAPPIST–South national telescope at ESO's La Silla Observatory   

    From Max Planck Institute for Astronomy: “Heavy stellar traffic, deflected comets, and a closer look at the triggers of cosmic disaster” 

    Max Planck Institute for Astronomy

    Max Planck Institute for Astronomy

    August 31, 2017

    Science Contact
    Bailer-Jones, Coryn
    Coryn Bailer-Jones
    Phone: (+49|0) 6221 528-224
    calj@mpia.de

    Public Information Officer
    Markus Pössel
    Public Information Officer
    Phone:(+49|0) 6221 528-261
    poessel@hda-hd.de

    4
    Image of the Week
    Close stellar encounters from the first Gaia data release
    Figure 1: The open circles show the time (horizontal axis) and distance (vertical axis) of the closest approach of stars to the Sun. Negative times indicate times in the past from today. Each point has been calculated as the median of the distribution of a swarm of surrogate particles which have been integrated through a Galactic potential. The “error” bars show the limits of the 5% and 95% percentiles of these distributions (which together form an asymmetric 90% confidence interval). That is, the swarm is used to propagate the uncertainties in the TGAS measurements to uncertainties in the perihelion parameters. The background colour (scale on the right) indicates the estimated completeness of the TGAS survey. That is, if all TGAS stars had radial velocities (and most do not), this gives the probability that a star with any particular perihelion parameters would be present in TGAS. Image credit: Coryn Bailer-Jones

    1
    Image of the Comet C/2012 S1 (ISON), taken with the TRAPPIST–South national telescope at ESO’s La Silla Observatory on the morning of Friday 15 November 2013, whose likely origin is the Oort cloud. This comet is definitely not colliding with Earth, but it shows the typical appearance of comets entering the inner solar system, including the typical tail made of gas and dust. Image: TRAPPIST/E. Jehin/ESO


    ESO Belgian robotic Trappist-South National Telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    As stars pass close by our solar system, they can nudge comets from the distant Oort cloud into the inner regions around the Sun. Thus, stellar encounters are an important factor in determining the risk of large cosmic impacts on Earth. Now, Coryn Bailer-Jones from the Max Planck Institute for Astronomy has used data from the ESA satellite Gaia to give the first systematic estimate of the rate of such close stellar encounters. Every million years, up to two dozen stars pass within a few light-years of the Sun, making for a near-constant state of perturbation. The results have been published in the journal Astronomy & Astrophysics.

    Oort Cloud NASA

    ESA/GAIA satellite

    Comets colliding with Earth are among the more violent and extensive cosmic catastrophes that can befall our home planet. The best known such impact is the one which, 66 million years ago, caused or at least hastened the demise of the dinosaurs (although it is not known whether the blame in this case falls on a comet or an asteroid).

    It must be said that, to the best of current knowledge, impacts with regional or even global consequences are exceedingly rare, and occur at a rate of no more than one per million years. Also, monitoring systems give us a fairly complete inventory of larger asteroids and comets, none of which is currently on a collision course with Earth.

    Still, the consequences are serious enough that studies of the causes of comet impacts are not purely academic. The prime culprits are stellar encounters: stars passing through our Sun’s cosmic neighborhood. The outskirts of our solar system are believed to host a reservoir of cold and icy objects – potential comets – known as the Oort cloud. The gravitational influence of passing stars can nudge these comets inwards, and some will begin a journey all the way to the inner solar system, possibly on a collision course with Earth. That is why knowledge of these stellar encounters and their properties has a direct impact on risk assessment for comet impacts.

    Now, Bailer-Jones has published the first systematic estimate of the rate of such stellar encounters. The new result uses data from the first data release (DR1) of the Gaia mission that combines new Gaia measurements with older measurements by ESA’s Hipparcos satellite. Crucially, Bailer-Jones modeled each candidate for a close encounter as a swarm of virtual stars, showing how uncertainties in the orbital data will influence the derived rate of encounters.

    Bailer-Jones found that within a typical million years, between 490 and 600 stars will pass the Sun within a distance of 16.3 light-years (5 parsecs, to use a unit more common in professional astronomy) or less. Between 19 and 24 stars will pass at 3.26 light-years (1 parsec) or less. All these hundreds of stars would be sufficiently close to nudge comets from the Oort cloud into the solar system. The new results are in the same ballpark as earlier, less systematic estimates that show that when it comes to stellar encounters, traffic in our cosmic neighborhood is rather heavy.

    The current results are valid for a period of time that reaches about 5 million years into the past and into the future. With Gaia’s next data release, DR2 slated for April 2018, this could be extended to 25 million years each way. However, astronomers intending to go even further and search for the stars that might be responsible for hurling a comet towards the dinosaurs will need to know our home galaxy and its mass distribution in much more detail than we currently do – a long-term goal of the researchers involved in Gaia and related projects.
    Background information

    The research described here is published as C. A. L. Bailer Jones, The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release in the journal Astronomy & Astrophysics.

    E-print on arXiv
    ESA picture of the week
    ESA press release

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 2:06 pm on July 25, 2017 Permalink | Reply
    Tags: , , , Comets, , , , ,   

    From JPL: “Large, Distant Comets More Common Than Previously Thought” 

    NASA JPL Banner

    JPL-Caltech

    July 25, 2017
    Elizabeth Landau
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-6425
    elizabeth.landau@jpl.nasa.gov

    1
    This illustration shows how scientists used data from NASA’s WISE spacecraft to determine the nucleus sizes of comets. They subtracted a model of how dust and gas behave in comets in order to obtain the core size. Credit: NASA/JPL-Caltech.

    2
    An animation of a comet. Credit: NASA/JPL-Caltech.

    Comets that take more than 200 years to make one revolution around the Sun are notoriously difficult to study. Because they spend most of their time far from our area of the solar system, many “long-period comets” will never approach the Sun in a person’s lifetime. In fact, those that travel inward from the Oort Cloud — a group of icy bodies beginning roughly 186 billion miles (300 billion kilometers) away from the Sun — can have periods of thousands or even millions of years.

    Oort Cloud NASA

    NASA’s WISE spacecraft, scanning the entire sky at infrared wavelengths, has delivered new insights about these distant wanderers.

    NASA/WISE Telescope

    Scientists found that there are about seven times more long-period comets measuring at least 0.6 miles (1 kilometer) across than had been predicted previously. They also found that long-period comets are on average up to twice as large as “Jupiter family comets,” whose orbits are shaped by Jupiter’s gravity and have periods of less than 20 years.

    Researchers also observed that in eight months, three to five times as many long-period comets passed by the Sun than had been predicted. The findings are published in The Astronomical Journal.

    “The number of comets speaks to the amount of material left over from the solar system’s formation,” said James Bauer, lead author of the study and now a research professor at the University of Maryland, College Park. “We now know that there are more relatively large chunks of ancient material coming from the Oort Cloud than we thought.”

    The Oort Cloud is too distant to be seen by current telescopes, but is thought to be a spherical distribution of small icy bodies at the outermost edge of the solar system. The density of comets within it is low, so the odds of comets colliding within it are rare. Long-period comets that WISE observed probably got kicked out of the Oort Cloud millions of years ago. The observations were carried out during the spacecraft’s primary mission before it was renamed NEOWISE and reactivated to target near-Earth objects (NEOs).

    “Our study is a rare look at objects perturbed out of the Oort Cloud,” said Amy Mainzer, study co-author based at NASA’s Jet Propulsion Laboratory, Pasadena, California, and principal investigator of the NEOWISE mission. “They are the most pristine examples of what the solar system was like when it formed.”

    Astronomers already had broader estimates of how many long-period and Jupiter family comets are in our solar system, but had no good way of measuring the sizes of long-period comets. That is because a comet has a “coma,” a cloud of gas and dust that appears hazy in images and obscures the cometary nucleus. But by using the WISE data showing the infrared glow of this coma, scientists were able to “subtract” the coma from the overall comet and estimate the nucleus sizes of these comets. The data came from 2010 WISE observations of 95 Jupiter family comets and 56 long-period comets.

    The results reinforce the idea that comets that pass by the Sun more often tend to be smaller than those spending much more time away from the Sun. That is because Jupiter family comets get more heat exposure, which causes volatile substances like water to sublimate and drag away other material from the comet’s surface as well.

    “Our results mean there’s an evolutionary difference between Jupiter family and long-period comets,” Bauer said.

    The existence of so many more long-period comets than predicted suggests that more of them have likely impacted planets, delivering icy materials from the outer reaches of the solar system.

    Researchers also found clustering in the orbits of the long-period comets they studied, suggesting there could have been larger bodies that broke apart to form these groups.

    The results will be important for assessing the likelihood of comets impacting our solar system’s planets, including Earth.

    “Comets travel much faster than asteroids, and some of them are very big,” Mainzer said. “Studies like this will help us define what kind of hazard long-period comets may pose.”

    NASA’s Jet Propulsion Laboratory in Pasadena, California, managed and operated WISE for NASA’s Science Mission Directorate in Washington. The NEOWISE project is funded by the Near Earth Object Observation Program, now part of NASA’s Planetary Defense Coordination Office. The spacecraft was put into hibernation mode in 2011 after twice scanned the entire sky, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA’s efforts to identify potentially hazardous near-Earth objects.

    For more information on WISE, visit:

    https://www.nasa.gov/wise

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

    Caltech Logo

    NASA image

     
  • richardmitnick 9:02 am on April 4, 2017 Permalink | Reply
    Tags: , , , Comets,   

    From Astronomy Now: “See a trio of comets in the April sky” 

    Astronomy Now bloc

    Astronomy Now

    2 April 2017
    Ade Ashford

    1
    Comet 41P/Tuttle–Giacobini–Kresák in the constellation of Draco was about magnitude +6.5 on the night of 1-2 April when captured in this three-minute integration with a colour Starlight Xpress Ultrastar camera at the f/2 HyperStar focus of the author’s Celestron C11 Schmidt-Cassegrain telescope. AN image by Ade Ashford.

    Despite the glow of a waxing Moon, early April is a good time to catch a glimpse of two interesting comets that are currently circumpolar from the British Isles, meaning that they are sufficiently close to the North Celestial Pole such that they neither rise or set, visible throughout the hours of darkness.

    Comet 41P/Tuttle–Giacobini–Kresák, a periodic comet that orbits the Sun every 5.4 years, is predicted to fade from magnitude +6.7 to +7.6 during the month. Comet 41P passes just 0.6 degrees north of Thuban, otherwise known as alpha (α) Draconis, at 2am BST on 3 April. By 11 April, 41P lies between eta (η) and theta (θ) Draconis; then the comet passes just 0.6 degrees from beta (β) Draconis – the magnitude +2.8 star known as Rastaban in the head of the celestial dragon – eight days later.

    4
    Comets 41P/Tuttle–Giacobini–Kresák in Draco and C/2015 V2 (Johnson) in Hercules are very well placed for Northern Hemisphere observers during April — particularly in the dark of the Moon. Click on the graphic for a detailed PDF finder chart suitable for printing and use outside at the telescope. AN graphic and finder chart by Ade Ashford.

    Comet 41P crosses the border into neighbouring Hercules on 20 April, a constellation where another bright comet resides this month. C/2015 V2 (Johnson) is a hyperbolic comet destined to leave the Solar System but predicted to brighten a full magnitude to +7.4 by the end of April. C/2015 V2 lies between naked-eye stars tau (τ) and upsilon (υ) Herculis at 12am BST on 22 April, and between the latter and phi (φ) Herculis on 25 April.

    5
    Displaying more of a tail than Comet 41P, C/2015 V2 (Johnson) in the constellation of Hercules was about magnitude +8 on the night of 1-2 April when captured in this seven-minute integration with a colour Starlight Xpress Ultrastar camera at the f/2 HyperStar focus of the author’s Celestron C11 Schmidt-Cassegrain telescope. AN image by Ade Ashford.

    There’s also a bright comet in the morning sky. C/2017 E4 (Lovejoy) was discovered by Australian comet hunter Terry Lovejoy last month and is currently a seventh-magnitude object in eastern Pegasus, currently some 7 degrees northeast of magnitude +2.4 star epsilon (ε) Pegasi, otherwise known as Enif. C/2017 E4 (Lovejoy) presently rises in the east-northeast around 3am BST from the British Isles.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 12:32 pm on December 30, 2016 Permalink | Reply
    Tags: , , , Comets, , ,   

    From JPL-Caltech: “NASA’s NEOWISE Mission Spies One Comet, Maybe Two” 

    NASA JPL Banner

    JPL-Caltech

    December 29, 2016
    DC Agle
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-5011
    agle@jpl.nasa.gov

    Laurie Cantillo /
    NASA Headquarters, Washington
    202-358-1077
    laura.l.cantillo@nasa.gov

    Dwayne Brown
    NASA Headquarters, Washington
    202-358-1726
    dwayne.c.brown@nasa.gov

    1
    An artist’s rendition of 2016 WF9 as it passes Jupiter’s orbit inbound toward the sun. Image credit: NASA/JPL-Caltech.

    NASA’s NEOWISE mission has recently discovered some celestial objects traveling through our neighborhood, including one on the blurry line between asteroid and comet. Another–definitely a comet–might be seen with binoculars through next week.

    NASA/WISE Telescope
    NASA/WISE Telescope

    An object called 2016 WF9 was detected by the NEOWISE project on Nov. 27, 2016. It’s in an orbit that takes it on a scenic tour of our solar system. At its farthest distance from the sun, it approaches Jupiter’s orbit. Over the course of 4.9 Earth-years, it travels inward, passing under the main asteroid belt and the orbit of Mars until it swings just inside Earth’s own orbit. After that, it heads back toward the outer solar system. Objects in these types of orbits have multiple possible origins; it might once have been a comet, or it could have strayed from a population of dark objects in the main asteroid belt.

    2016 WF9 will approach Earth’s orbit on Feb. 25, 2017. At a distance of nearly 32 million miles (51 million kilometers) from Earth, this pass will not bring it particularly close. The trajectory of 2016 WF9 is well understood, and the object is not a threat to Earth for the foreseeable future.

    A different object, discovered by NEOWISE a month earlier, is more clearly a comet, releasing dust as it nears the sun. This comet, C/2016 U1 NEOWISE, “has a good chance of becoming visible through a good pair of binoculars, although we can’t be sure because a comet’s brightness is notoriously unpredictable,” said Paul Chodas, manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California.

    As seen from the northern hemisphere during the first week of 2017, comet C/2016 U1 NEOWISE will be in the southeastern sky shortly before dawn. It is moving farther south each day and it will reach its closest point to the sun, inside the orbit of Mercury, on Jan. 14, before heading back out to the outer reaches of the solar system for an orbit lasting thousands of years. While it will be visible to skywatchers at Earth, it is not considered a threat to our planet either.

    NEOWISE is the asteroid-and-comet-hunting portion of the Wide-Field Infrared Survey Explorer (WISE) mission. After discovering more than 34,000 asteroids during its original mission, NEOWISE was brought out of hibernation in December of 2013 to find and learn more about asteroids and comets that could pose an impact hazard to Earth. If 2016 WF9 turns out to be a comet, it would be the 10th discovered since reactivation. If it turns out to be an asteroid, it would be the 100th discovered since reactivation.

    What NEOWISE scientists do know is that 2016 WF9 is relatively large: roughly 0.3 to 0.6 mile (0.5 to 1 kilometer) across.

    It is also rather dark, reflecting only a few percent of the light that falls on its surface. This body resembles a comet in its reflectivity and orbit, but appears to lack the characteristic dust and gas cloud that defines a comet.

    “2016 WF9 could have cometary origins,” said Deputy Principal Investigator James “Gerbs” Bauer at JPL. “This object illustrates that the boundary between asteroids and comets is a blurry one; perhaps over time this object has lost the majority of the volatiles that linger on or just under its surface.”

    Near-Earth objects (NEOs) absorb most of the light that falls on them and re-emit that energy at infrared wavelengths. This enables NEOWISE’s infrared detectors to study both dark and light-colored NEOs with nearly equal clarity and sensitivity.

    “These are quite dark objects,” said NEOWISE team member Joseph Masiero, “Think of new asphalt on streets; these objects would look like charcoal, or in some cases are even darker than that.”

    NEOWISE data have been used to measure the size of each near-Earth object it observes. Thirty-one asteroids that NEOWISE has discovered pass within about 20 lunar distances from Earth’s orbit, and 19 are more than 460 feet (140 meters) in size but reflect less than 10 percent of the sunlight that falls on them.

    The Wide-field Infrared Survey Explorer (WISE) has completed its seventh year in space after being launched on Dec. 14, 2009.

    JPL manages NEOWISE for NASA’s Science Mission Directorate at the agency’s headquarters in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colorado, built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

    Data from the NEOWISE mission are available on a website for the public and scientific community to use. A guide to the NEOWISE data release, data access instructions and supporting documentation are available at:

    http://wise2.ipac.caltech.edu/docs/release/neowise/

    Access to the NEOWISE data products is available via the on-line and API services of the NASA/IPAC Infrared Science Archive.

    A list of peer-reviewed papers using the NEOWISE data is available at:

    http://neowise.ipac.caltech.edu/publications.html

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

    Caltech Logo

    NASA image

     
  • richardmitnick 7:56 am on September 26, 2016 Permalink | Reply
    Tags: , , Comets,   

    From phys.org: “Astronomers image newly discovered comet” 

    physdotorg
    phys.org

    September 26, 2016
    Tricia Ennis

    1
    Credit: Slooh

    Earlier this week, Slooh member Bernd Lütkenhöner and Slooh astronomer Paul Cox were able to image the newly discovered Comet C/2016 R3 (Borisov) under extraordinary conditions. The comet had been close to the Sun since its discovery on September 11, 2016, by Gennady Borisov, making it extremely difficult to observe.

    It had already fallen out of reach of other telescopes around the world by September 16th, but Lütkenhöner and Cox managed to image it on September 20th using Slooh’s robotic Half Metre telescope at their flagship observatory at the Institute of Astrophysics of the Canary Islands.

    iac-telescopes-campus
    IAC

    Cox said, “We usually observe objects when they’re high in the sky, so we’re peering through as little of our atmosphere as possible. But in this case, the comet was only observable in the last 30-minutes before dawn, when it was only 5° above the horizon in a rapidly brightening sky. Given the factors stacked against us, we were amazed when we managed to pinpoint the faint and diffuse fuzz ball in our images.”

    “We may have obtained the last observations of this comet for the next 100 or even 100,000 years,” said Lütkenhöner. The reason for that huge timespan is that the orbit of this comet hasn’t been fixed with any certainty. Added Cox, “Our latest observations will help determine the orbit of the comet with greater certainty.”

    The comet is set to make its closest approach to the Sun (perihelion) on October 12, 2016. Says Cox, “We don’t even know if the comet will survive its journey around the Sun, but if it does, it will remain an extremely difficult object to image because of its proximity to the Sun from Earth’s perspective—but we’ll still give it a try!”

    Astronomers require further observations of the comet to confirm whether this is a new discovery or a recovery of a comet discovered in 1915, Comet C/1915 R1 (Mellish).

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 6:45 am on April 29, 2016 Permalink | Reply
    Tags: , , Comets, Earth Has Mystery Gas Delivered from Space,   

    From SA: “Earth Has Mystery Gas Delivered from Space” 

    Scientific American

    Scientific American

    April 28, 2016
    Anthony King, ChemistryWorld

    1
    Credit: Wikimedia Commons/NASA/JPL-Caltech

    Xenon from deep within the Earth’s mantle has shone a light on the planet’s formation and early evolution. The isotopic signature of this earthly xenon has been shown to resemble that of primitive meteorites and differs markedly from the profile of the gas found in the atmosphere, which is mysteriously missing most of its xenon.

    The origin of Earth’s volatile elements such as water, carbon and nitrogen remains a puzzle. It is difficult to determine if these elements originated from solar gas after the solar system formed or were delivered by asteroids or comets.

    A new study, which sampled xenon from carbon dioxide-rich mineral spring gas from the volcanic Eifel province in Germany, points to an asteroidal origin for part of the volatile elements trapped in Earth’s mantle—planetary bodies whose remnants now lie between Mars and Jupiter. The mysterious xenon in the atmosphere came from elsewhere, possibly comets.

    ‘We conclude that this [mantle] component was contributed by asteroids when the proto-Earth was still building up,’ notes senior author Bernard Marty at the University of Lorraine, France. ‘The ancestor atmosphere xenon was contributed later on at the Earth’s surface, by late bombardments, and never mixed up with mantle xenon.’ This late bombardment occurred around 800 million years after Earth’s formation and might have involved cometary bodies. The isotopic signature of xenon on comets is unknown, however.

    The extraterrestrial chondritic xenon found in the mantle has been isolated for 4.45 billion years. It also proves that volcanism in Eifel relates to upwelling from the deep mantle, likely to be over 700 km deep.

    ‘It’s a small step forward to show that mantle xenon came from meteorites, but the big step forward is showing that this component is not related to the atmosphere,’ says Christopher Ballentine, a geochemist at the University of Oxford, UK, who was not involved with this work.

    Atmospheric xenon’s origin was not just from outgassing of the mantle and is more complex, Ballentine explains. ‘Nobody has measured xenon composition in comets yet, so maybe that is the source,’ he adds. Around 90% of the xenon expected to be in Earth’s atmosphere is missing, with various theories posited. The enigma of the ‘missing xenon’ and where it went is one of the big unsolved puzzles in geochemistry.

    ‘Understanding xenon really is a lynchpin for understanding the early formation of volatiles. And resolving how volatiles arrived at the planet tells us something fundamental about the way in which the planets formed,’ Ballentine says.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

     
  • richardmitnick 12:12 pm on December 22, 2015 Permalink | Reply
    Tags: , , Comets,   

    From RAS: “Giant comets could pose danger to life on Earth” 

    Royal Astronomical Society

    Royal Astronomical Society

    22 December 2015
    Media contacts
    Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)7802 877 699
    rm@ras.org.uk

    Diana Blamires
    University of Buckingham
    diana.blamires@buckingham.ac.uk

    Science contacts
    Dr David Asher
    dja@arm.ac.uk
    Professor Mark Bailey
    meb@arm.ac.uk
    Armagh Observatory
    Northern Ireland
    Tel: +44 (0)28 3752 2928
    http://star.arm.ac.uk

    Professor Bill Napier
    University of Buckingham
    Tel (Ireland): +353 87361 8376
    bill_napier121@hotmail.com

    Professor Duncan Steel
    University of Buckingham
    Tel (New Zealand): +64 4889 0241
    tma1@duncansteel.com

    1
    Because they are so distant from the Earth, Centaurs appear as pinpricks of light in even the largest telescopes. Saturn’s 200-km moon Phoebe, depicted in this image, seems likely to be a Centaur that was captured by that planet’s gravity at some time in the past. Until spacecraft are sent to visit other Centaurs, our best idea of what they look like comes from images like this one, obtained by the Cassini space probe orbiting Saturn. NASA’s New Horizons spacecraft, having flown past Pluto six months ago, has been targeted to conduct an approach to a 45-km wide trans-Neptunian object at the end of 2018. Credit: NASA/JPL-Caltech/Space Science Institute.

    NASA Cassini Spacecraft
    NASA/Cassini

    2
    The outer solar system as we now recognise it. At the centre of the map is the Sun, and close to it the tiny orbits of the terrestrial planets (Mercury, Venus, Earth and Mars). Moving outwards and shown in bright blue are the near-circular paths of the giant planets: Jupiter, Saturn, Uranus and Neptune. The orbit of Pluto is shown in white. Staying perpetually beyond Neptune are the trans-Neptunian objects (TNOs), in yellow: seventeen TNO orbits are shown here, with the total discovered population at present being over 1,500. Shown in red are the orbits of 22 Centaurs (out of about 400 known objects), and these are essentially giant comets (most are 50-100 km in size, but some are several hundred km in diameter). Because the Centaurs cross the paths of the major planets, their orbits are unstable: some will eventually be ejected from the solar system, but others will be thrown onto trajectories bringing them inwards, therefore posing a danger to civilisation and life on Earth. Credit: Duncan Steel.

    A team of astronomers from Armagh Observatory and the University of Buckingham report that the discovery of hundreds of giant comets in the outer planetary system over the last two decades means that these objects pose a much greater hazard to life than asteroids. The team, made up of Professors Bill Napier and Duncan Steel of the University of Buckingham, Professor Mark Bailey of Armagh Observatory, and Dr David Asher, also at Armagh, publish their review of recent research in the December issue of Astronomy & Geophysics (A&G), the journal of the Royal Astronomical Society.

    The giant comets, termed centaurs, move on unstable orbits crossing the paths of the massive outer planets Jupiter, Saturn, Uranus and Neptune. The planetary gravitational fields can occasionally deflect these objects in towards the Earth.

    Centaurs are typically 50 to 100 kilometres across, or larger, and a single such body contains more mass than the entire population of Earth-crossing asteroids found to date. Calculations of the rate at which centaurs enter the inner solar system indicate that one will be deflected onto a path crossing the Earth’s orbit about once every 40,000 to 100,000 years. Whilst in near-Earth space they are expected to disintegrate into dust and larger fragments, flooding the inner solar system with cometary debris and making impacts on our planet inevitable.

    Known severe upsets of the terrestrial environment and interruptions in the progress of ancient civilisations, together with our growing knowledge of interplanetary matter in near-Earth space, indicate the arrival of a centaur around 30,000 years ago. This giant comet would have strewn the inner planetary system with debris ranging in size from dust all the way up to lumps several kilometres across.

    Specific episodes of environmental upheaval around 10,800 BCE and 2,300 BCE, identified by geologists and palaeontologists, are also consistent with this new understanding of cometary populations. Some of the greatest mass extinctions in the distant past, for example the death of the dinosaurs 65 million years ago, may similarly be associated with this giant comet hypothesis.

    Professor Napier comments: “In the last three decades we have invested a lot of effort in tracking and analysing the risk of a collision between the Earth and an asteroid. Our work suggests we need to look beyond our immediate neighbourhood too, and look out beyond the orbit of Jupiter to find centaurs. If we are right, then these distant comets could be a serious hazard, and it’s time to understand them better.”

    The researchers have also uncovered evidence from disparate fields of science in support of their model. For example, the ages of the sub-millimetre craters identified in lunar rocks returned in the Apollo program are almost all younger than 30,000 years, indicating a vast enhancement in the amount of dust in the inner Solar system since then.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: