ESA Rosetta’s navigation camera obtained the four images in this mosaic on Dec. 7, 2014, from a distance of 12.2 miles (19.7 km) from the center of Comet 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
Asteroids, not comets, may have delivered most of Earth's water to the planet when the solar system was young, new data from the ESA Rosetta probe orbiting comet 67/P suggests.
Comets are some of the solar system's most primitive building blocks, with many dating to soon after its formation.
Scientists think that these dirty snowballs probably helped seed Earth with key ingredients for life, such as organic compounds.
The European Space Agency's (ESA) Rosetta spacecraft is helping scientists learn more about the role these icy nomads have played in the evolution of the solar system and life on Earth by analyzing the composition of Comet 67P/Churyumov–Gerasimenko.
In August, Rosetta became the first spacecraft to orbit a comet, and in November, its Philae lander became the first probe to make a soft touchdown on a comet's surface.
Rosetta is also the first mission to escort a comet as it travels around the sun.
Now, Rosetta has helped solve a mystery about how Earth became the watery world it is today.
Scientists focused on data from the instrument regarding water to help uncover whether asteroids or comets delivered the water in Earth's oceans.
Rosetta has provided data from Comet 67P/C-G, another Kuiper Belt comet.
However, Rosetta has discovered that this comet possesses an even higher deuterium-to-hydrogen ratio than seen in Oort Cloud comets, three times the amount of heavy water compared to normal water as Earth has.
If Earth's water had come from Kuiper Belt objects, even if most of them were like comet 103P/Hartley 2, and if only a small fraction were like Comet 67P/C-G, Earth's deuterium-to-hydrogen ratio would be significantly higher than it is today.
"This probably rules out Kuiper Belt comets from bringing water to Earth," Altwegg said. Instead, most of Earth's water was probably delivered by asteroids, Altwegg said.
"Today's asteroids have very little water, that's clear," Altwegg added. "But that was probably not always the case. During the Late Heavy Bombardment 3.8 billion years ago, at that time, asteroids could have had much more water than they could now."
The asteroids seen now "have stayed in the vicinity of the sun for 4.6 billion years," Altwegg said.
"They've lost water due to the sun, due to heat. But to start with, they might have had much more water than they have now."
Future analysis of ice-rich bodies in the asteroid belt could shed light on whether Earth's water really did come from there, Altwegg said.
An illustration of the early solar system shows proto-Earth, proto-Mars, Vesta within the asteroid belt, and proto-Jupiter. The dashed white line represents the "snow line" boundary for water ice in the solar system. Credit: Jack Cook, Woods Hole Oceanographic Institution
The water that supports life on Earth may have been on the planet much earlier than scientists previously thought, new research suggests.
While the environmental conditions in Earth's early years made it impossible for water to remain on the planet's surface, scientists have found evidence that the ingredients for water were protectively stored inside rocky bodies near our planet, and maybe inside Earth itself.
The new findings suggest that there was water in the inner solar system 135 million years earlier than previous evidence had shown.
"Our findings show the earliest evidence of water in the inner solar system," said Adam Sarafian, a Ph.D. student at the Woods Hole Research Center in Massachusetts and lead author of the new study.
This image of the giant asteroid Vesta was captured by NASA's Dawn spacecraft on Sept. 5, 2012. Credit: NASA
Meteorites from an asteroid
The smoking gun appears inside meteorites that once belonged to the asteroid Vesta, one of the largest members of the asteroid belt that sits between Jupiter and Mars. Meteorites from Vesta, dark chunks of cooled magma often as big as grapefruits, continue to be found in Antarctica.
Previous analysis found no water or water-forming ingredients in those meteorites, but Sarafian and his colleagues zoomed in on the molecular contents of the meteorites, and found trace amounts of hydrogen-oxygen molecules.
More than 4.5 billion years ago, or about 15 million years after solid bodies began to form around the young sun, water existed in the outer, cooler parts of the solar system, previous studies have shown.
But in the inner solar system, where Vesta and a young Earth resided, temperatures were far too hot and solar winds would send any water vapor to the outer regions of the solar system.
While the Earth grew and changed over the next 4 billion years or so, Vesta remained frozen in time, according to Sarafian.
"Vesta gives us a snapshot of what Earth maybe looked like when it was first forming," Sarafian said.
This artist's impression shows exocomets orbiting the star Beta Pictoris. Astronomers analysing observations of nearly 500 individual comets made with the HARPS instrument at ESO's La Silla Observatory have discovered two families of exocomets around this nearby young star. The first consists of old exocomets that have made multiple passages near the star. The second family, shown in this illustration, consists of younger exocomets on the same orbit, which probably came from the recent breakup of one or more larger objects. Credit: ESO/L. Calçada
Beta Pictoris is a young star located about 63 light-years from the Sun. It is only about 20 million years old and is surrounded by a huge disc of material, a very active young planetary system where gas and dust are produced by the evaporation of comets and the collisions of asteroids.
Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study sets the scene: "Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system."
For almost 30 years astronomers have seen subtle changes in the light from Beta Pictoris that were thought to be caused by the passage of comets in front of the star itself.
Comets are small bodies of a few kilometres in size, but they are rich in ices, which evaporate when they approach their star, producing gigantic tails of gas and dust that can absorb some of the light passing through them.
The dim light from the exocomets is swamped by the light of the brilliant star so they cannot be imaged directly from Earth.
The researchers selected a sample of 493 different exocomets. Some exocomets were observed several times and for a few hours.
Careful analysis provided measurements of the speed and the size of the gas clouds.
Some of the orbital properties of each of these exocomets, such as the shape and the orientation of the orbit and the distance to the star, could also be deduced.
This analysis of several hundreds of exocomets in a single exo-planetary system is unique. It revealed the presence of two distinct families of exocomets: a) one family of old exocomets whose orbits are controlled by a massive planet, and b) another family, probably arising from the recent breakdown of one or a few bigger objects. Different families of comets also exist in the Solar System.
The exocomets of the first family have a variety of orbits and show a rather weak activity with low production rates of gas and dust.
This suggests that these comets have exhausted their supplies of ices during their multiple passages close to Beta Pictoris.
The exocomets of the second family are much more active and are also on nearly identical orbits.
This suggests that the members of the second family all arise from the same origin: probably the breakdown of a larger object whose fragments are on an orbit grazing the star Beta Pictoris.
Flavien Kiefer concludes: "For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago."
More information: "Two families of exocomets in the Beta Pictoris system" Nature, 23 October 2014. dx.doi.org/10.1038/nature13849
This rotating 3-D map shows how HNC molecules (made of hydrogen, carbon and nitrogen) are released from the nucleus of comet Lemmon and then spread evenly throughout the atmosphere, or coma. Similar maps revealed that HNC and formaldehyde are produced in the coma, rather than the comet's nucleus. Image courtesy Brian Kent /NRAO /AUI /NSF.
A NASA-led team of scientists has created detailed 3-D maps of the atmospheres surrounding comets, identifying several gases and mapping their spread at the highest resolution ever achieved.
"We achieved truly first-of-a-kind mapping of important molecules that help us understand the nature of comets," said Martin Cordiner, a researcher working in the Goddard Center for Astrobiology at NASA's Goddard Space Flight Center in Greenbelt, Maryland. Cordiner led the international team of researchers.
Almost unheard of for comet studies, the 3-D perspective provides deeper insight into which materials are shed from the nucleus of the comet and which are produced within the atmosphere, or coma.
This helped the team nail down the sources of two key organic, or carbon-containing, molecules.
The observations were conducted in 2013 on comets Lemmon and ISON using the Atacama Large Millimeter/submillimeter Array (ALMA), a network of high-precision antennas in Chile. These comets are the first to be studied with ALMA.
The ALMA observations combine a high-resolution 2-D image of a comet's gases with a detailed spectrum at each point.
From these spectra, researchers can identify the molecules present at every point and determine their velocities (speed plus direction) along the line-of-sight; this information provides the third dimension - the depth of the coma.
"So, not only does ALMA let us identify individual molecular species in the coma, it also gives us the ability to map their locations with great sensitivity," said Anthony Remijan, a scientist with the National Radio Astronomy Observatory, one of the organizations that operates ALMA, and a co-author of the study.
The researchers reported results for three molecular species, focusing primarily on two whose sources have been difficult to discern (except in comet Halley).
The 3-D maps indicated whether each molecule was flowing outward evenly in all directions or coming off in jets or in clumps.
In each comet, the team found that two species - formaldehyde and HNC (made of one hydrogen, one nitrogen and one carbon) - were produced in the coma.
For formaldehyde, this confirmed what researchers already suspected, but the new maps contained enough detail to resolve clumps of the material moving into different regions of the coma day-by-day and even hour-by-hour.
For HNC, the maps settled a long-standing question about the material's source. Initially, HNC was thought to be pristine interstellar material coming from the nucleus of a comet, whereas later work suggested other possible sources.
The new study provided the first proof that HNC is produced during the breakdown of large molecules or organic dust in the coma.
"Understanding organic dust is important, because such materials are more resistant to destruction during atmospheric entry, and some could have been delivered intact to early Earth, thereby fueling the emergence of life," said Michael Mumma, Director of the Goddard Center for Astrobiology, and a co-author on the study.
"These observations open a new window on this poorly known component of cometary organics."
Asteroids and comets that repeatedly smashed into the early Earth covered the planet's surface with molten rock during its earliest days, but still may have left oases of water that could have supported the evolution of life, scientists say.
The new study reveals that during the planet's infancy, the surface of the Earth was a hellish environment, but perhaps not as hellish as often thought, scientists added.
Earth formed about 4.5 billion years ago. The first 500 million years of its life are known as the Hadean Eon.
Although this time amounts to more than 10 percent of Earth's history, little is known about it, since few rocks are known that are older than 3.8 billion years old.
An artistic conception of the early Earth-moon system showing the Earth's surface after being bombarded with large impacts, causing magma extrusion on the surface, though some liquid water was retained. Image released on July 30, 2014. Credit: Simone Marchi
Earth's violent youth
For much of the Hadean, Earth and its sister worlds in the inner solar system were pummeled with an extraordinary number of cosmic impacts.
"It was thought that because of these asteroids and comets flying around colliding with Earth, conditions on early Earth may have been hellish," said lead study author Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado.
This imagined hellishness gave the eon its name, Hadean comes from the word Hades, the lord of the underworld in Greek mythology.
However, in the past dozen years or so, a radically different picture of the Hadean began to emerge.
Analysis of minerals trapped within microscopic zircon crystals dating from this eon "suggested there was liquid water on the surface of the Earth back then, clashing with the previous picture that the Hadean was hellish," Marchi said.
This could explain why the evidence of the earliest life on Earth appears during the Hadean, maybe the planet was less inhospitable during that eon than previously thought.
This artist's illustration shows a close-up of the early Earth, revealing magma extrusion on the surface and the scars from severe cosmic bombardment. Image released on July 30, 2014. Credit: Simone Marchi
Cosmic bombardment history
The exact timing and magnitude of the impacts that smashed Earth during the Hadean are unknown.
To get an idea of the effects of this bombardment, Marchi and his colleagues looked at the moon, whose heavily cratered surface helped model the battering that its close neighbour Earth must have experienced back then.
"We also looked at highly siderophile elements (elements that bind tightly to iron), such as gold, delivered to Earth as a result of these early collisions, and the amounts of these elements tells us the total mass accreted by Earth as the result of these collisions," Marchi said.
Prior research suggests these impacts probably contributed less than 0.5 percent of the Earth's present-day mass.
The researchers discovered that "the surface of the Earth during the Hadean was heavily affected by very large collisions, by impactors larger than 100 kilometers (60 miles) or so, really, really big impactors," Marchi said.
"When Earth has a collision with an object that big, that melts a large volume of the Earth's crust and mantle, covering a large fraction of the surface," Marchi added.
These findings suggest that Earth's surface was buried over and over again by large volumes of molten rock, enough to cover the surface of the Earth several times. This helps explain why so few rocks survive from the Hadean, the researchers said.
However, although these findings might suggest that the Hadean was a hellish eon, the researchers found that "there were time gaps between these large collisions," Marchi said.
"Generally speaking, there may have been something on the order of 20 or 30 impactors larger than 200 km (120 miles) across during the 500 million years of the Hadean, so the time between such impactors was relatively long," Marchi said.
Any water vapourised near these impacts "would rain down again," Marchi said, and "there may have been quiet tranquil times between collisions, there could have been liquid water on the surface."
The researchers suggested that life emerging during the Hadean was probably resistant to the high temperatures of the time.
Marchi and his colleagues detailed their findings in the July 31 issue of the journal Nature.
More Information: Widespread mixing and burial of Earth’s Hadean crust by asteroid impacts. - Authors: S. Marchi, W. F. Bottke, L. T. Elkins-Tanton, M. Bierhaus, K. Wuennemann, A. Morbidelli & D. A. Kring - doi:10.1038/nature13539
The scorching heat produced by asteroid or comet impacts can melt tons of soil and rock, some of which forms glass as it cools. Some of that glass preserves bits of ancient plant material. Credit: Brown University
Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth.
Scientists exploring large fields of impact glass in Argentina suggest that what happened on Earth might well have happened on Mars millions of years ago. Martian impact glass could hold traces of organic compounds.
Asteroid and comet impacts can cause widespread ecological havoc, killing off plants and animals on regional or even global scales.
But new research from Brown University shows that impacts can also preserve the signatures of ancient life at the time of an impact.
A research team led by Brown geologist Pete Schultz has found fragments of leaves and preserved organic compounds lodged inside glass created by a several ancient impacts in Argentina.
The material could provide a snapshot of environmental conditions at the time of those impacts. The find also suggests that impact glasses could be a good place to look for signs of ancient life on Mars.
The scorching heat produced by asteroid or comet impacts can melt tons of soil and rock, some of which forms glass as it cools.
The soil of eastern Argentina, south of Buenos Aires, is rife with impact glass created by at least seven different impacts that occurred between 6,000 and 9 million years ago, according to Schultz.
One of those impacts, dated to around 3 million years ago, coincides with the disappearance of 35 animal genera, as reported in the journal Science a few years back.
"We know these were major impacts because of how far the glass is distributed and how big the chunks are," Schultz said.
"These glasses are present in different layers of sediment throughout an area about the size of Texas."
Within glass associated with two of those impacts—one from 3 million years ago and one from 9 million years ago, Schultz and his colleagues found exquisitely preserved plant matter.
"These glasses preserve plant morphology from macro features all the way down to the micron scale," Schultz said. "It's really remarkable."
The glass samples contain centimeter-size leaf fragments, including intact structures like papillae, tiny bumps that line leaf surfaces.
Bundles of vein-like structures found in several samples are very similar to modern pampas grass, a species common to that region of Argentina.
Chemical analysis of the samples also revealed the presence of organic hydrocarbons, the chemical signatures of living matter.
"Impact glass may be where the 4 billion-year-old signs of life are hiding," Schultz said. "On Mars they're probably not going to come out screaming in the form of a plant, but we may find traces of organic compounds, which would be really exciting."
These illustrations show the asteroid belt in the present day and in the early Solar System, located between the Sun (at centre) and four terrestrial planets (near the Sun) and Jupiter (at bottom left). The top image shows the conventional model for the asteroid belt; largely composed of rocky material. The middle image shows the proposed model, with a small number of active comets and a dormant cometary population. The lower diagram shows how the asteroid belt might have looked in the early Solar System, with vigorous cometary activity. Credit: Ignacio Ferrin / University of Anitoquia
A team of astronomers from the University of Anitoquia, Medellin, Colombia, have discovered a graveyard of comets.
The researchers, led by Anitoquia astronomer Prof. Ignacio Ferrin, describe how some of these objects, inactive for millions of years, have returned to life leading them to name the group the 'Lazarus comets'.
The team publish their results in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.
Comets are among the smallest objects in the Solar System, typically a few km across and composed of a mixture of rock and ices.
If they come close to the Sun, then some of the ices turn to gas, before being swept back by the light of the Sun and the solar wind to form a characteristic tail of gas and dust.
Most observed comets have highly elliptical orbits, meaning that they only rarely approach the Sun. Some of these so-called long period comets take thousands of years to complete each orbit around our nearest star.
There is also a population of about 500 short period comets, created when long period comets pass near Jupiter and are deflected in orbits that last anything between 3 and 200 years.
Although uncommon events, comets also collide with Earth from time to time and may have helped bring water to our planet.
The new work looked at a third and distinct region of the Solar System, the main belt of asteroids between the orbits of Mars and Jupiter.
This volume of space contains more than 1 million objects ranging in size from 1 m to 800 km.
The traditional explanation for asteroids is that they are the building blocks of a planet that never formed, as the movement of the pieces was disrupted by the strong gravitational field of Jupiter.
In the last decade 12 active comets have been discovered in the asteroid main belt region. This was something of a surprise and the Medellin team set out to investigate their origin.
The team, made up of Prof. Ferrin and his colleagues Profs. Jorge Zuluaga and Pablo Cuartas, now think they have an explanation.
"We found a graveyard of comets," exclaims Professor Ferrín. He adds: "Imagine all these asteroids going around the Sun for aeons, with no hint of activity. We have found that some of these are not dead rocks after all, but are dormant comets that may yet come back to life if the energy that they receive from the Sun increases by a few per cent."
Surprisingly, this can happy fairly easily, as the orbits of many objects in the asteroid belt are nudged by the gravity of Jupiter. The shape of their orbits can then change, leading to a decrease in the minimum distance between the object and the Sun (perihelion) and a slight increase in average temperature.
According to this interpretation, millions of years ago the main belt was populated by thousands of active comets.
This population aged and the activity subsided. What we see today is the residual activity of that glorious past.
Twelve of those rocks are true comets that were rejuvenated after their minimum distance from the Sun was reduced a little.
The little extra energy they received from the Sun was then sufficient to revive them from the graveyard.
Prof. Ferrin describes the 12 active comets. "These objects are the 'Lazarus comets', returning to life after being dormant for thousands or even millions of years. Potentially any one of the many thousands of their quiet neighbours could do the same thing."
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