This 3-D image shows the entire nucleus of Hartley 2 with jets and an icy particle cloud. Circles have been added to highlight the location of individual particles. Image Credit: NASA/JPL-Caltech/UMD/Brown
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As Jessica Sunshine said, Comet Hartley 2 might be the smallest of the five comets that our spacecraft have visited, but no doubt it is the most interesting, and for its size, the most active. Sunshine is the EPOXI mission deputy principal investigator, and she and her team have had the chance to analyze images from the Nov. 4 flyby of the comet. Closeup views yielded some big surprises: Hartley 2 is throwing snowballs.
“When we first saw all the specks surrounding the nucleus, our mouths dropped,” said Pete Schultz, EPOXI mission co-investigator at Brown University. “Stereo images reveal there are snowballs in front and behind the nucleus, making it look like a scene in one of those crystal snow globes.”
Estimates of the size of the largest particles ranges from a golf ball to a basketball.
Another surprise, which was noted almost immediately from the flyby images, were that the very active jets on the comet were powered by carbon dioxide. “This is the first time we’ve ever seen individual chunks of ice in the cloud around a comet or jets definitively powered by carbon dioxide gas,” said Michael A’Hearn, principal investigator for the spacecraft. “We looked for, but didn’t see, such ice particles around comet Tempel 1,” the comet that the Deep Impact spacecraft flew by in 2005.
Here are highlights from the press conference last week, along with some of the fantastic imagery of Comet Hartley 2.
Hartley 2 CO2 jet up close. Credit: NASA/JPL-Caltech/UMD/Brown Comet Hartley 2 can be seen in glorious detail in this image from NASA's EPOXI mission. It was taken as the spacecraft flew by around 6:59 a.m. PDT (9:59 a.m. EDT), from a distance of about 700 kilometers (435 miles). The comet's nucleus, or main body, is approximately 2 kilometers (1.2 miles) long and .4 kilometers (.25 miles) at the 'neck' or most narrow portion. Jets can be seen streaming out of the nucleus. Image credit: NASA/JPL-Caltech/UMDThis image from the High-Resolution Instrument on NASA's EPOXI mission spacecraft shows part of the nucleus of comet Hartley 2. The sun is illuminating the nucleus from the right. A distinct cloud of individual particles is visible. This image was obtained on Nov. 4, 2010, the day the EPOXI mission spacecraft made its closest approach to the comet. Image Credit: NASA/JPL-Caltech/UMD Infrared scans of comet Hartley 2 by NASA's EPOXI mission spacecraft show carbon dioxide, dust, and ice being distributed in a similar way and emanating from apparently the same locations on the nucleus. Water vapor, however, has a different distribution implying a different source region and process. Image Credit: NASA/JPL-Caltech/UMDThis zoomed-in image from the High-Resolution Instrument on NASA's EPOXI mission spacecraft shows the particles swirling in a 'snow storm' around the nucleus of comet Hartley 2. Scientists estimate the size of the largest particles ranges from a golf ball to a basketball. They have determined these are icy particles rather than dust. The particles are believed to be very porous and fluffy. Image Credit: NASA/JPL-Caltech/UMDThe motion of some icy particles in the cloud around Hartley 2, as seen by NASA's EPOXI mission spacecraft. A star moving through the background is marked with red and moves in a particular direction and with a particular speed, while the icy particles move in random directions. The icy particles are marked in green, blue and light blue. Image Credit: NASA/JPL-Caltech/UMD/Brown This image shows the nuclei of comets Tempel 1 and Hartley 2, as imaged by NASA's Deep Impact spacecraft, which continued as an extended mission known as EPOXI. Tempel 1 is five times larger than Hartley 2. Visible jets are easily seen in images of Hartley 2, but required extensive processing to be seen in images of Tempel 1. Tempel 1 is 7.6 kilometers (4.7 miles) in the longest dimension. Hartley 2 is 2.2 km (1.4 miles) long. The Tempel 1 image was built up from more than 25 images captured by the impactor targeting sensor on July 4, 2005. The Hartley 2 image was obtained by the Medium- Resolution Imager on Nov. 4, 2010.
NASA successfully launched its first 'FASTSAT' on Nov. 17, 2010. Image Credit: NASA
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While the U.S. Air Force unsuccessfully tried to get a Delta IV off the ground in Florida – things worked out far better for NASA at the Kodiak Launch Complex located in Kodiak, Alaska. Friday’s Minotaur 4 rocket launch successfully accomplished its mission of placing not one – but six satellites into orbit some 400 miles above the Earth.
The mission took off just before sunset from Launch Pad 1. After launch the $170 million flight turned southeast from its launch site going out over the Pacific Ocean. The launch took place under a clear sky with the moon lighting its way.
The payload for this flight was a rather mixed bag of NASA, military and university experiments. All six of the launch vehicle’s payloads were released right on time about 30 minutes after launch. The so-called ‘FASTSAT’ for Fast, Affordable, Science and Technology Satellite automatically switched itself on upon deployment. The project is a demonstration of ways to deploy experiments and other payloads cheaply and effectively to orbit.
Four of the satellites that were onboard the STP-S26 mission included the “ESPA-class:” STPSat-2, FalconSAT-5, FASTSAT-HSV01 and FASTRAC.
The FASTSAT program is NASA’s first microsatellite designed to provide multiple customers with access to orbit – at a lower cost. The main goal of the FASTSAT flight is to prove the viability of this capability to various government, academic and industry customers. The intent is to show that you do not have to invest millions of dollars into a single, large-scale satellite to conduct experiments on orbit.
The launch vehicle itself is also rather cheap as it is comprised of spare Peacekeeper missile tech. The STP-S26 mission was powered to orbit by a Minotaur IV launch vehicle, which was provided by the Rocket Systems Launch Program. The Minotaur IV is produced by Orbital Sciences Corporation.
One of the ‘firsts’ on this flight was the utilization of the Hydrazine Auxiliary Propulsion System (HAPS) to allow for dual-orbit capabilities. It is hoped, that in future flights this could be used to allow satellites to other orbits to give them far greater flexibility.
Another first employed on this mission was the first to use the Multi-Mission Satellite Operations Center Ground System Architecture. This center is capable of operating various satellites at the same time at a minimal cost. Indeed, the overriding theme of this launch would appear to be providing access to orbit – for less.
The Delta IV rocket now scheduled for launch on Nov. 21, 2010. Credit: Alan Walters (awaltersphoto.com) for Universe Today
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Those waiting for a launch from Florida’s Space Coast will have to wait a little more. The liftoff of a United Launch Alliance (ULA) Delta IV Heavy rocket has been pushed back yet again, and is now scheduled for Sunday, Nov. 21 at 5:58 p.m. EST (2258 GMT) from Space Launch Complex 37 (SLC 37) at Cape Canaveral Air Force Station. The rocket will carry a National Reconnaissance Office payload.
Launch Complex 37 at Cape Canaveral Air Force Station. Credit: Alan Walters (awaltersphoto.com) for Universe Today.
Delayed from the 18th, the next countdown started on Friday, but this too was not to be. As technicians started to fuel up the rocket’s twin strap on boosters encountered temperature anomalies. Engineers did not want to give an estimate as to when the rocket will be ready for launch – until they had a chance to unload the fuel and give the vehicle a closer look.
The Delta IV with a NRO payload. Photo Credit: Universe Today/Alan Walters - awaltersphoto.com
The payload for this mission is a classified spy satellite. In media advisories released by the 45th Space Wing it is described only as a ‘Galaxy 3.’ The 45th is stationed out of Patrick Air Force Base. The Delta IV Heavy is the largest rocket in the Delta 4 family, with three booster cores combined to form what is essentially a triple-bodied rocket.
As far as space shuttle Discovery, NASA managers are still keeping all their options open. Inspectors this week found a fourth crack in support beams on the external fuel tanks of the space shuttle. The work to repair the cracks is ongoing, but the teams will need to complete an engineering review and develop the necessary flight rationale in order to launch with a damaged tank. On Thursday, NASA announced that the flight will launch no earlier than Dec. 3, four days after the opening of a short end-of-year launch window.
The window closes Dec. 6. If NASA cannot get Discovery off the ground in the next available launch window, there is only one other planned launch at KSC/CCAFS for this year. This is the Dec. 7 launch of SpaceX’s Falcon-9 with its Dragon spacecraft payload. If this launch happens before the end of this year, it will mark the first demonstration flight of the $1.6 billion Commercial Orbital Transportation Services contract that the private space firm has with the space agency.
Well, not only may up to 25% of Sun-like stars have Earth-like planets – but if they are in the right temperature zone, apparently they are almost certain to have oceans. Current thinking is that Earth’s oceans formed from the accreted material that built the planet, rather than being delivered by comets at a later time. From this understanding, we can start to model the likelihood of a similar outcome occurring on rocky exoplanets around other stars.
Assuming terrestrial-like planets are indeed common – with a silicate mantle surrounding a metallic core – then we can expect that water may be exuded onto their surface during the final stages of magma cooling – or otherwise out-gassed as steam which then cools to fall back to the surface as rain. From there, if the planet is big enough to gravitationally retain a thick atmosphere and is in the temperature zone where water can remain fluid, then you’ve got yourself an exo-ocean.
We can assume that the dust cloud that became the Solar System had lots of water in it, given how much persists in the left-over ingredients of comets, asteroids and the like. When the Sun ignited some of this water may have been photodissociated – or otherwise blown out of the inner solar system. However, cool rocky materials seem to have a strong propensity to hold water – and in this manner, could have kept water available for planet formation.
Meteorites from differentiated objects (i.e. planets or smaller bodies that have differentiated such that, while in a molten state, their heavy elements have sunk to a core displacing lighter elements upwards) have around 3% water content – while some undifferentiated objects (like carbonaceous asteroids) may have more than 20% water content.
Mush these materials together in a planet formation scenario and materials compressed at the centre become hot, causing outgassing of volatiles like carbon dioxide and water. In the early stages of planet formation much of this outgassing may have been lost to space – but as the object approaches planet size, its gravity can hold the outgassed material in place as an atmosphere. And despite the outgassing, hot magma can still retain water content – only exuding it in the final stages of cooling and solidification to form a planet’s crust.
Mathematical modelling suggests that if planets accrete from materials with 1 to 3% water content, liquid water probably exudes onto their surface in the final stages of planet formation – having progressively moved upwards as the planet’s crust solidified from the bottom up.
Otherwise, and even starting with a water content as low as 0.01%, Earth-like planets would still generate an outgassed steam atmosphere that would later rain down as fluid water upon cooling.
As the Earth formed, water contained in rocky materials either 'outgassed' or just exuded onto the surface - as magma solidified, from the bottom up, to form the Earth's crust. And OK, this is just a nice image of a deep sea volcanic vent - but you get the idea. Credit: Woods Hole Oceanographic Institution.
If this ocean formation model is correct, it can be expected that rocky exoplanets from 0.5 to 5 Earth masses, which form from a roughly equivalent set of ingredients, would be likely to form oceans within 100 millions years of primary accretion.
This model fits well with the finding of zircon crystals in Western Australia – which are dated at 4.4 billion years and are suggestive that liquid water was present that long ago – although this preceded the Late Heavy Bombardment (4.1 to 3.8 billion years ago) which may have sent all that water back into a steam atmosphere again.
Currently it’s not thought that ices from the outer solar system – that might have been transported to Earth as comets – could have contributed more than around 10% of Earth’s current water content – as measurements to date suggest that ices in the outer solar system have significantly higher levels of deuterium (i.e. heavy water) than we see on Earth.
A landform on Mars that looks like a naturally occuring bridge across a chasm. Credit: NASA/JPL/U of Arizona/ colorization by Stu Atkinson.
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The HiRISE camera on the Mars Reconnaissance Orbiter took an image of a thin channel, and a portion of it contains a naturally occurring bridge over the chasm. Kelly Kolb from the HiRISE team says it is probably a remnant of the original surface, the rest of which has collapsed downward. It isn’t likely there’s a opening underneath the formation, but if there were, it would look very similar to a rock bridge formation found in Jordan in the Wadi Rum, the Valley of the Moon. See an image below.
Kolb also said this is unlikely to be a channel formed by a running water, as there are no obvious source or deposit regions. The channel is probably a just a collapse feature.
And see the full HiRISE image of the thin channel, found in Mars northern hemisphere between some “knobs” called Tartarus Colles, below.
Any chance the Mars rockbridge could look like this one in Wadi Rum, Jordan -- also known as the Valley of the Moon?Small Winding Channel in Tartarus Colles. Credit: NASA/JPL/University of Arizona
Ever wonder what it would be like to be a particle of light starting out at some distant astronomical object and then zoom (at light speed, of course) towards Earth and wind up being seen by hoards of Earthlings out looking at the stars at night? This video from ESA is an animation (and artist’s impression) showing just that. Enjoy the ride! Continue reading “Light Speed Animation”
‘Twinkle twinkle little star, how I wonder what you are?’ This nursery rhyme is one of the best loved around the World. For astronomers though, stars can be a bit more of a nightmare, not only in understanding their complex evolutionary processes but also and perhaps more simply, figuring out how many there are. Until now there has been a gross mismatch between the number of stars that are found within our galaxy, the Milky Way and the amount that astronomer think should be there. In short, where are the missing stars?
The Milky Way is joined by about 30 other galaxies that make up our local group of galaxies, including the Andromeda Galaxy and according to current theories there should be about 100 billion stars in each. The calculations are based on the rate of star birth in the Milky Way, about 10 new stars per year. But according to Dr Jan Pflamm-Altenburg of the Argelander Institute for Astronomy at the University of Bonn “Actually, it would give many more stars than we actually see” and therein lies the problem.
The recent study by Dr Pflamm-Altenburg and Dr. Carsten Weidner of the Scottish St. Andrews University suggests that perhaps the estimated rate of star birth being used to calculate the number of stars could simply be too high. With galaxies in our Local Group its relatively easy to just count the number of new stars that can be seen but for more distant galaxies, they are too far away for individual stars to be seen.
By studying the nearby galaxies, Pflamm-Altenburg and Weidner discovered that for every 300 young small stars, there seems to be one large massive new star and fortunately this seems to be universal. Due to the unique nature of the massive young stars, they leave a tell tail sign in the light of distant galaxies so even though they cannot be individually identified they can still be detected and the strength of the signal determines the number of massive stars. Multiply by the number of massive stars by this ratio of 300 and the actual rate of stellar birth can be calculated.
It seems though that this rate has varied over the history of the Universe and dependent on the amount of ‘space’ available in the vicinity of the star formation. If there is a baby boom in star formation then a higher number of heavies seem to form in a theory called ‘stellar crowding’. When stars form, they form as clusters rather than individual stars but it seems that the overall mass of the group is the same, regardless of how many star embryo’s there really are. When star birth is at a high rate, space can be limited so larger more massive stars tend to form compared to smaller stars.
Massive galaxies like this where star birth is booming are called “ultra-compact dwarf galaxies” (UCDs). Sometimes its possible in these galaxies that young stars can even fuse together to form larger stars so the large to small ratio can be around 1:50 instead of 1:300. This means we have been using the wrong figure and estimating far too high.
Using this new found figure, Pflamm-Altenburg and Weidner have recalculated the number of stars that ‘should’ be in a galaxy and compared to those that we can see and rather pleasantly, the numbers match! It seems that the conundrum of the missing stars that has been perplexing astronomers for decades has finally been resolved.
A recent aurora as seen by astronaut Doug Wheelock on the International Space Station. Credit: NASA
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With the Sun’s activity increasing just a bit, sky watchers have witnessed an uptick in aurorae, especially northern observers. This top image is from an *extreme* northern observer, as in way up; about 320 km (220 miles) up above the Earth. Astronaut Doug Wheelock took this image from the International Space Station, and the beautiful sight made him wax poetic:
“Aurora Borealis as I will forever paint it in my dreams,” he wrote on Twitter. “Almost time to return home… no regrets… but mixed emotions. Leonardo da Vinci was right… ‘For once you have tasted flight, you will forever walk the Earth with your eyes turned skyward, for there you have been… and there you will long to return.'”
See other stunning recent aurora images from a more Earthly viewpoint:
Colorful Clouds, taken on Nov. 14, 2010 by Ole C. Salomonsen in Tromsø, Norway. Used by permission.
Describing this picture, Salomonsen said on Flickr: “With a CME expected to hit earth on Nov.14th we could still see only a faint aurora. We got frustrated and then decided to drive back towards the city where it now was reported to clear up. After 5 minutes in the car suddenly we could see a strong aurora bursting out behind the partially cloudy sky.”
Aurora over Tromsø, Norway, November 14, 2010. Credit: Ole C. Salomonsen. Used by permission
This is another gorgeous shot by Salomonsen, and on his Flickr site, he points out Ursa Major is visible in the top left, said it was just amazing how there were two rays of white and purple aurora, one moving faster than the other.
Aurora Activity near Dettah, in the Northwest Territories. Credit: Credit: Sean Davies; used by permission.
Photographer Sean Davies took this image on Nov. 13, 2010 near Dettah in the Northwest Territories, Canada, and said, “The aurora put on a great show just outside Yellowknife. The show lasted a good hour.” There’s another from Sean, below, on the same night. You can see more of Sean’s images at his Flickr site.
More aurora activity near Dettah, NWT. Credit: Sean Davies; used by permission.
The photo below was taken on November 13, 2010 in Auster-Skaftafellssysla, Iceland by Skarphéðinn Þráinsson. See more of his images at Flickr.
Aurora Borealis at Jökulsárlón (Glacier Lagoon) south coast Iceland. Credit: Skarphéðinn Þráinsson. Used by permission
This timelapse video was taken by Tor Even Mathisen, also from Tromsø, Norway.
What is the smallest unit of time you can conceive? A second? A millisecond? Hard to say seeing as how time is relative. Under the right circumstances, hours can fly by and seconds can feel like a lifetime. But unfortunately for physicists, time is not something that can be dealt with so philosophically. And since they deal with cosmological forces both infinitesimally large and small, they need units that can objectively measure them. When it comes to dealing with the small, Planck Time is the measurement of choice. Named after German physicist Max Planck, the founder of quantum theory, a unit of Planck time is the time it takes for light to travel, in a vacuum, a single unit of Planck length. Taken together, they part of the larger system of natural units known as Planck units.
Originally proposed in 1899 by German physicist Max Planck, Planck units are physical units of measurement defined exclusively in terms of five universal physical constants. These are the Gravitational constant (G), the Reduced Planck constant (h), the speed of light in a vacuum (c), the Coulomb constant 1/4??0 (ke or k), and Boltzmann’s constant (kB, sometimes k). Each of these constants can be associated with at least one fundamental physical theory: c with special relativity, G with general relativity and Newtonian gravity, ? with quantum mechanics, ?0 with electrostatics, and kB with statistical mechanics and thermodynamics. They were invented as a means of simplifying the particular algebraic expressions appearing in theoretical physics, especially in quantum mechanics.
Ultimately, Planck time is derived from the field of mathematical physics known as dimensional analysis, which studies units of measurement and physical constants. The Planck time is the unique combination of the gravitational constant G, the relativity constant c, and the quantum constant h, to produce a constant with units of time. They are often semi-humorously referred to by physicists as “God’s units” because eliminate anthropocentric arbitrariness from the system of units, unlike the meter and second, which exist for purely historical reasons and are not derived from nature. Some challenges to Planck’s Time have been mounted. For example, in 2003 during the analysis of the Hubble Space Telescope Deep Field images, some scientists speculated that where there are space-time fluctuations on the Planck scale, images of extremely distant objects should be blurry. The Hubble images, they claimed, were too sharp for this to be the case. Other scientists disagreed with this assumption however, with some saying the fluctuations would be too small to be observable, others saying that the speculated blurring effect that was expected was off by a very large magnitude.
A unit of Planck Time can be expressed as follows:
Planck Time
We have written many articles about Planck Time for Universe Today. Here’s an article about the Big Bang Theory, and here’s an article about astronomical units.
Oftentimes when we think of the Earth, we tend to think of stable landmasses that are surrounded by vast oceans. It’s easy for us to forget that the Earth is still very much a work in a progress, that its foundations are mobile slabs of rock, known as plates, which are constantly on the move and shuffling back and forth. In our next of the woods, aka. North American, we inhabit what is appropriately named the North American Plate, the tectonic boundary that covers most of North America, Greenland, Cuba, Bahamas, and parts of Siberia and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. It is composed of two types of lithosphere: the upper crust (where the continental land masses reside) and the thinner oceanic crust.
As one of the Earth’s original continents, the North American Plate started forming some three billion years ago when the planet was much hotter and mantle convection much more vigorous. Roughly two billions years ago, the Earth cooled and these old floating pieces of the lithosphere, called cratons, stopped growing. Since that time, the plates have been moving back and forth across the globe, their cratons colliding to form the continents that we know and recognize today. Beginning in the Cambrian period, over five hundred million years ago, the cratons of Laurentia and Siberia broke off from the main landmass of Pangaea, which thereafter would be known as Gondwana. By the late Mezosoic era (circa two hundred million years ago) the Laurentian and Eurasian cratons combined to form the supercontinent of Laurasia. Since that time, the separation of the North American and Eurasian plates has led to the separation of the North America from Asia. As the North American plate drifted west, the landmasses of Iceland and Greenland broke off in the east while in the west, it collided with the Eurasian plate again, adding the landmass of Siberia to East Asia.
In terms of what makes the plates move across the Earth, a number of theories coexist. One theory is what is known as the “conveyor belt” principle, where the Earth’s lithosphere has a higher strength and lower density than the underlying asthenosphere and lateral density variations in the mantle result in the slow drifting motion of the plates, resulting in collisions and subduction zones. One of the main points of the theory is that the amount of surface of the plates that disappear through subduction along the boundaries where they collide is more or less equal to the new crust that is formed along the margins where they are drifting apart. In this way, the total surface of the Globe remains the same. A different explanation lies in different forces generated by the rotation of the Globe and tidal forces of the Sun and the Moon. A final theory which predates the Plate Tectonics “paradigm”, has it that a gradual shrinking (contraction) or gradual expansion of the Globe is responsible.
We have written many articles about the North American Plate for Universe Today. Here’s an article about the continental plate, and here’s an article about the plate tectonics theory.
