Posted on by Nancy Atkinson

Best Evidence Yet That Comets Delivered Water for Earth’s Oceans

New measurements from the Herschel Space Observatory have discovered water with the same chemical signature as our oceans in a comet called Hartley 2 (pictured at right). Image credit: NASA/JPL-Caltech

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The idea isn’t new that Earth’s oceans originated from comets bombarding our planet back in its early days. But astronomers have now found the best evidence yet for this scenario. The Herschel infrared space observatory detected that comet Hartley 2, which originates from the distant Kuiper Belt, contains water with the same chemical signature as Earth’s oceans.

“Our results with Herschel suggest that comets could have played a major role in bringing vast amounts of water to an early Earth,” said Dariusz Lis, senior research associate in physics at the California Institute of Technology in Pasadena and co-author of a new paper in the journal Nature, published online on Oct. 5. “This finding substantially expands the reservoir of Earth ocean-like water in the solar system to now include icy bodies originating in the Kuiper Belt.”

Previous looks at various other comets showed water content different from Earth, with deuterium levels around twice that of Earth’s oceans, but those comets came from the Oort Cloud. Scientists theorized that if comets of this kind had collided with Earth, they could not have contributed more than a few percent of Earth’s water.

The Deep Impact spacecraft successfully flew past Comet Hartley 2 in November 2010 and is an example of the type of comet that the UCLA scientists describe in their research. Image: UPI/NASA/JPL-Caltech/UMD.

But Herschel’s observations of Hartley 2 are the first in-depth look at water in a comet from the Kuiper Belt — home of icy, rocky bodies that includes dwarf planets and innumerable comets — and it showed a surprising difference.

Using HIFI, a highly sensitive infrared spectrometer, Herschel peered into the comet’s coma, or thin, gaseous atmosphere, and found that Hartley 2 possessed half as much “heavy water” as other comets analyzed to date. In heavy water, one of the two normal hydrogen atoms has been replaced by the heavy hydrogen isotope known as deuterium. The ratio between heavy water and light, or regular, water in Hartley 2 is the same as the water on Earth’s surface.

“Comet Hartley’s deuterium-to-hydrogen ratio is almost exactly the same as the water in Earth’s oceans,” says Paul Hartogh, Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany, who led the international team of astronomers in this study.

The amount of heavy water in a comet is related to the environment where the comet formed, and by comparing the deuterium to hydrogen ratio found in the water in Earth’s oceans with that in extraterrestrial objects, astronomers were hoping to identify the origin of our water.

Astronomers know Hartley 2 comes from the Kuiper Belt, since they can track its path as it swoops into Earth’s neighborhood in the inner solar system every six-and-a-`half years. The five comets besides Hartley 2 whose heavy-water-to-regular-water ratios have been obtained all came from the Oort Cloud, an even more distant region in the solar system. This region is 10,000 times farther away than the Kuiper Belt, and is home to the most documented comets.

The team is now using Herschel to look at other Kuiper Belt comets to see whether they, too, carry the same type of water.

“Thanks to this detection made possible by Herschel, an old, very interesting discussion will be revived and invigorated,” said Göran Pilbratt, ESA Herschel Project Scientist. “It will be exciting to see where this discovery will take us.”

Paper: “Ocean-like Water in the Jupiter-family Comet 103P Hartley”

Sources: JPL, ESA

Posted on by Nancy Atkinson

An Alien’s View of Our Solar System

We have just begun to try and image distant solar systems around other stars, and hopefully our techniques and technology will improve in the near future so that we can one day find — and take pictures of — planets as small as Earth. But what if another civilization from a distant star was looking at us? What would they see? A new supercomputer simulation tracking the interactions of thousands of dust grains show what our solar system might look like to alien astronomers searching for planets. It also provides a look back to how our planetary system may have changed and matured over time.

Continue reading “An Alien’s View of Our Solar System”

Posted on by Steve Nerlich

Astronomy Without A Telescope – Coloring In The Oort Cloud

A very distant and very red Sedna. Credit: NASA, JPL, Caltech.

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It’s possible that if we do eventually observe the hypothetical objects that make up the hypothetical Oort cloud, they will all be a deep red color. This red coloring will probably be a mix of ices, richly laced with organic compounds – and may represent remnants of the primordial material from which the solar system was formed.

Furthermore, the wide range of colors found across different classes of trans-Neptunian objects may help to determine their origins.

The current observable classes of trans-Neptunian objects includes Pluto and similar objects called plutinos, which are caught in a 2:3 orbital resonance with Neptune towards the inner edge of the Kuiper belt. There are other Kuiper belt objects caught in a range of different resonant orbital ratios, including two-tinos – which are caught in a 1:2 resonance with Neptune – and which are found towards the outer edge of the Kuiper belt.

Otherwise, the majority of Kuiper belt objects (KBOs) are cubewanos (named after the first one discovered called QB1), which are also known as ‘classical’ KBOs. These are not obviously in orbital resonance with Neptune and their solar orbits are relatively circular and well outside Neptune’s orbit. There are two fairly distinct populations of cubewanos – those which have little inclination and those which are tilted more than 12 degrees away from the mean orbital plane of the solar system.

Beyond the Kuiper belt is the scattered disk – which contains objects with very eccentric elliptical orbits. So, although it may take hundreds of years for them to get there, the perihelions of many of these objects’ orbits are much closer to the Sun – suggesting this region is the main source of short period comets.

The trans-Neptunian landscape. Classical Kuiper belt objects have relatively circular orbits that never stray within the orbit of Neptune (yellow circle) - while plutinos and scattered disk objects have eccentric orbits that may. Classical objects with low inclinations (see ecliptic view) tend to have the deepest red coloration. Objects with higher inclination - and those with eccentric solar orbits which take them closer to the Sun - appear faded.

Now, there are an awful lot of trans-Neptunian objects out there and not all of them have been observed in detail, but surveys to date suggest the following trends:

  • Cubewanos with little inclination or eccentricity are a deep red color; and
  • Plutinos, scattered disk objects and highly inclined cubewanos are much less red.

Beyond the scattered disk are detached objects, that are clearly detached from the influence of the major planets. The best known example is Sedna – which is… yep, deep red (or ultra-red as the boffins prefer to say).

Sedna and other extreme outer trans-Neptunian objects are sometimes speculatively referred to as inner Oort cloud objects. So if we are willingly to assume that a few meager data points are representative of a wider (and hypothetical) population of Oort cloud objects – then maybe, like Sedna, they are all a deep red color.

And, looking back the other way, the ‘much less red’ color of highly inclined and highly eccentric trans-Neptunian objects is consistent with the color of comets, Centaurs (comets yet to be) and damocloids (comets that once were).

On this basis, it’s tempting to suggest that deep red is the color of primordial solar system material, but it’s a color that fades when exposed to moderate sunlight – something that seems to happen to objects that stray further inward than Neptune’s orbit. So maybe all those faded objects with inclined orbits used to exist much nearer to the Sun, but were flung outward during the early planetary migration maneuvers of the gas giants.

And the primordial red stuff? Maybe it’s frozen tholins – nitrogen-rich organic compounds produced by the irradiation of nitrogen and methane. And if this primordial red stuff has never been irradiated by our Sun, maybe it’s a remnant of the glowing dust cloud that was once our Sun’s stellar nursery.

Ah, what stories we can weave with scant data.

Further reading: Sheppard, S.S. The colors of extreme outer solar system objects.

Posted on by Nancy Atkinson

New Horizons Spacecraft Now Closer to Pluto Than Earth

Fastest Spacecraft
Artist concept of the New Horizons spacecraft. Credit: NASA/JPL

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The New Horizons spacecraft crossed a milestone boundary today: it is now closer to its primary destination, Pluto, than to Earth. But New Horizons –the fastest man-made object — is not yet halfway to the dwarf planet. That won’t happen until February 25, 2010. New Horizons is now 1,440 days into its 9.5-year journey and well past 15 AU (astronomical units) from the Sun. But there is a long haul yet to go: there are still 1,928 days until operations begin for the close encounter, and 2022 days until the spacecraft reaches the closest point to Pluto in the summer of 2015. It is exciting to think what we will learn about Pluto and the Kuiper Belt in five and a half years. Will our perspectives change? Hard to believe they won’t.

New Horizons is currently traveling at about 50,000 kph (31,000 mph) (relative to the Sun) and is located about 2.4 billion kilometers (1.527 billion miles) from Earth.

The spacecraft launched in January 2006.

New Horizons will be taken out of hibernation in early January to repoint the communications dish antenna to keep up with the changing position of the Earth around the Sun. It was last awoken in November to download several months of stored science data from the Venetia Burney Student Dust Counter, to correct a recently discovered bug in the fault protection system software, (last thing anyone wants is to have the spacecraft go into safe mode at closest approach), and to upload instructions to run the spacecraft through early January. Telemetry shows that New Horizons is in very good health and almost exactly on its planned course.

Principal Investigator Alan Stern wrote in his last PI’s Perspective notes that the science team will meet in January to discuss which Kuiper Belt Objects they hope to “fly by and reconnoiter after Pluto. Those searches will begin next summer and continue through 2011 and 2012. Hopefully, they’ll net us four to 10 potential targets.”

Posted on by Jerry Coffey

Where Do Asteroids Come From?

An artists impression of an asteroid belt. Credit: NASA

[/caption]Where do asteroids come from? Most of them are grouped in the main belt, but that is not the only asteroid field in the solar system. There are actually four sets of asteroids grouped into different fields: the main belt, Trojans, scattered disc, and the Kuiper belt. To understand where do asteroids come from, you need to know the theory on how they were formed.

Most scientists agree that all of the asteroids are the result of the the big bang. After the initial turmoil, large asteroids collided together and through the process known as accretion planets and dwarf planets were formed. The planets and dwarfs grew large enough to develop gravity and became rounded and able to sustain their own gravity. Asteroids continued to collide and destroy each other until we have the elliptical and other odd shaped, pock-marked solar objects that we have today. Here is a little information to help you understand where do asteroids come from today.

The asteroid field known as the main belt is a large collection of objects that are in orbit between Jupiter and Mars. The largest known asteroid in the belt is Ceres which accounts for 27% of the belts’ total mass. Ceres is also the only asteroid in the belt that is classified as a dwarf planet. Vesta, Hygeia, and Pallas are the other of the four largest bodies in the asteroid field. There have been several space missions that have crossed the field. The asteroids are far enough apart that traversing it is easily done. The Dawn space mission to the next to visit the main belt and will visit two of the largest bodies, hopefully it will be able to help reclassify Vesta as a dwarf planet.

The Kuiper belt is populated with thousands of icy bodies. The only one that is currently designated as a dwarf planet is the former planet Pluto. That may change in the near future since there are at least two bodies in the belt that are larger than Pluto. Our ability to send spacecraft that far out is what is holding us back right now.

The Trojans asteroid field, originally referred to the Trojan asteroids, orbits around Jupiter’s 4th and 5th Lagrangian points. Subsequently objects have been found orbiting the same Lagrangian points of Neptune and Mars. The word Trojan, in astronomy, refers to a natural satellite that shares an orbit with a larger planet or moon, but does not collide with it because it orbits around one of the two Lagrangian points of stability.

The scattered disc asteroid field is a subset of the Kuiper belt. Because their orbits take them well beyond 100AU from the Sun they are the coldest objects in the Solar System. Due to its unstable nature, astronomers now consider the scattered disc to be the place of origin for most periodic comets. Many of the objects in the Oort cloud are thought to have originated in the scattered disc.

Answering the question: ”Where do asteroids come from?” is pretty easy, but it is ambiguous at the same time. What we have are mostly theories and few definite facts. Things get even more blurry as you study different asteroids and find that some from different belts have somehow inter-mixed. Ah, the beauty of astronomy!

There is some good info on the asteroid belt here. NASA has a good piece on KBO’s. Here on Universe Today there is an article on the possibility of an alien asteroid belt and the Milky Ways’ own asteroid belts.

Reference:
Wikipedia